crystal ball issue 21 vol june 2012

CRYSTAL BALL | CRYSTAL BALL | Periodical of the New ZealaNd avalaNche commuNity

DISCOVERMORE, SAFELY

vOLU

ME

21W

intE

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012

www.avalanche.net.nzwww.mountainsafety.org.nzwww.adventuresmart.org.nzwww.incidentreport.org.nz

NEW ZEALAND MOUNTAIN SAFETY COUNCIL

PERIODICAL OF THE NEW ZEALAND AVALANCHE COMMUNITY


CONTENTS01 welcome

02 Sharpen your tools

02 Snow and avalanche committee

03 News Bites

04 avalanche.net forecaster summaries

12 developing a new avalanche management programme

15 cooling and avalanches

21 Slim pickings in utah’s wasatch

22 So you dig a pit and then what?

26 2010 Saddle Peak avalanche

29 Burn, baby, burn

31 accurately assessing avalanche size

33 in the deep end

35 avalanches, powder and curry...

36 winter - time to rime

WELCOMEhi and welcome to the first issue of the 2012 crystal Ball. it has been a busy summer working on a wide range of things including the redevelopment of the info-ex, education resources, brochures and avalanche.net.nz website.

as many of you are aware, the introduction of Powdercloud (Pc) last year, as the 2011 info-ex was not as smooth as we hoped and after much feedback from the industry, the ski areas, hoG representatives and the Snow and avalanche committee, we decided to end our relationship with Pc and undertook a complete new design and build for a New Zealand info-ex site.

many of you asked for a far simpler system with the primary goal of sharing information. we have taken the information from the industry survey and developed a base level information sharing tool. it is similar to the old New Zealand programme but with all the annoying bits fixed. we believe that this will satisfy the documenting and sharing needs of the snow-sports operators without drifting into a complicated operational tool. the concept is that this will be a cooperative project, managed by the mSc and direction and feedback from the users will drive the development from now on. Now that we once again own and control the programme, we are in a position to make changes and enhancements as required.

the Professional avalanche Safety Stage 1 course has had a good deal of work done on it and this will ensure that it is still the baseline for entering a ski patrol or guiding pathway. there has been redevelopment and updating of most areas with some pre-field course online content to ensure that the participants are arriving with a good general understanding of the nature of avalanches.

a new plastic decision making card has been developed for the public courses and an Avalanche Safety and Avalanche Rescue brochure have been created and printed to further support people to get into the mountains and come home again.

after much debate we decided to publish this periodical electronically. the printing costs were unsustainable and we hope that this medium will reach a wider audience. i welcome your feedback on this new format and hope that it still gets printed off and left around the office/staff room for all to read.

See you out in the hills.

hobbie

- Andrew Hobman Avalanche and Alpine programme manager New Zealand Mountain Safety Council

01

the crystal Ballissue 21, July 2012

Editor: Gordon Smith

Managing Editor: andrea corrigan

Designer: dani millar

Cover Photo: andrew hobman

thank you to the contributors for giving permission to reproduce their material.

copyright © New Zealand mountain Safety council 2012.all rights reserved.All opinions expressed in this magazine are not necessarily those of New Zealand Mountain Safety.

Editorial and Advertising enquiries

do you have something to say or show? we would like articles relating to the professional avalanche industry, public avalanche safety, teaching tips, research papers, accounts of avalanche events, book and gear reviews, event listings, interviews, letters to the editor, and humorous stories related to avalanches. we are also looking for winter mountain photography of avalanches, touring, terrain, skiing, snowboarding, active control work, backcountry recreation or avalanche awareness activities.

for more information please contact:

andrew hobmanTel: +64 3 371 3724Fax: +64 4 385 7366Email: [email protected]

to have your voice heard at the Sac committee, contact your industry representative, or email: [email protected]

CRYSTAL BALL | CRYSTAL BALL | Periodical of the New ZealaNd avalaNche commuNity 02

at the time of writing this, most of the mountainous regions in New Zealand had just received their first significant snowfall of the 2012 winter season. as ever, this encourages the first thoughts of the avalanche community to take hold, generally drifting onto past experiences. it sends a subconscious signal to start getting your head back in the game; ‘where did i put my transceiver?’ and ‘hmm... i meant to get my head around that article that don wrote on ateS over summer’.

it’s the time of year when we start looking at what is in our ‘avalanche tool Box’ and assessing if we need to upgrade/add to it for the imminent winter. it could be some form of continued professional development such as completing the next step in formal training, updating your old transceiver, or maybe an air bag is what you have set your priority at! i think that this industry attracts the types of people that want to continue expanding their toys and knowledge.

the Snow & avalanche committee has been busy since the end of last winter. having listened to industry feedback it was clear that last season’s new format of the info-ex was not meeting its potential and that most operations preferred the simplicity of the old format. So look out for the introduction of a cleaner revamped info-ex based on the original format, in 2012 season. this is a key tool for the avalanche community. the intellectual property now resides in New Zealand and we have the ability to tweak and build it for the future.

this is only one of many projects that the staff have been working on during the summer. we as a committee have strived to set the foundations for a strong future in place around avalanche education, public engagement and industry best practice, i believe we achieved two out of three last year, and this year we focused on getting the third one right.

i hope you all have projects or toys to add to your tool box this winter. all the best and have safe, enjoyable experiences out there!

cheers - Chris Emmett Snow and Avalanche Committee Convenor

Convenor: Peter Bilous (Otago Polytech & AEWG rep)

Members: dr i owens (University of Canterbury)don Bogie (DOC) arthur tyndall & Nick Jarmin (Club Ski Fields) wayne carran (Works Infrastructure)chris emmett (SAANZ Nth Island and outgoing Convenor)Pete Zimmer (LandSAR)Kevin Boekholt (NZMGA)andrew hobman & Gordon Smith (NZMSC)

The mission of MSC’s Snow and Avalanche Committee:to provide expert advice and support to the council on appropriate strategies to foster public safety in snow environments including:

• overseeing the training, assessments and qualifications of instructors to ensure that national standards are maintained and enhanced

• overseeing the professional training programmes of all providers as required

• monitoring, research and review trends in snow and avalanche activities to ensure the council remains the leading authority for safety in this environment.

SharpEN yOur TOOlS SNOw aNd avalaNChE COmmiTTEE (SaC)

Above: the Snow and avalanche committee. from left: Pete Zimmer, Gordon Smith, don Bogie, art tindall (seated), chris emmett, wayne carran, Peter Bilous, Kevin Boekholt, andrew hobman, dr ian owens. absent in picture: Nick Jarmin.


ISSW 2012 ConfErEnCE the international Snow Science workshop (iSSw) is a biennial meeting of the professionals who work in the field of snow science and winter recreation. this is the only such conference which takes place and has been ongoing since 1976. the iSSw motto is ‘the merging of theory and Practice’, and this year’s event will be in anchorage, alaska during September. for more information visit: www.issw2012.com

earlier this year an extensive archive of presentations and articles from previous conferences was put online.

follow this link to lose yourself in this fantastic resource. http://arc.lib.montana.edu/snow-science/

AVALAnCHE CArDSthe much anticipated avalanche assessor card and avalanche rescue cards are now for sale. the avalanche assessor card provides a simple checklist to help you make evidence-based decisions in avalanche terrain, with the bonus capability of measuring the approximate angle of the slope you wish to use. the avalanche rescue card is another prompt to lead the user through the key points of companion rescue including transceiver, probe, and shovelling techniques. Both are available soon from the mSc online store at www.mountainsafety.org.nz

NEwS BiTES

TECH fILEtechnology is allowing practical use of mobile devices such as Smartphones to record location and field data. Some allow ‘sync’ functions to upload field observations. New software applications ‘apps’ and programs are continually becoming available. here are a few that have potential use within our industry. most are designed for apple devices (e.g. iPad/iPhone at this stage). head to the links below and read more

Avalanche field books - GPS, snowprofiles, weather, snowpack, avalanche observations, camera, settings to align to NZ guidelines (either fully or in part)

• maSt www.ullrlabs.com/solutions.html

• avalanchelab (free) www.avalanchelab.com

GPS

• viewranger (free, both apple and android) www.viewranger.com

• theodollite http://hrtapps.com/theodolite/

nZ’S fIrST SKIDoo HILL CLIMB EVEnTroundhill Ski area will host NZ’s first snowmobile hill climb event on Saturday 18 august. competitors will attempt to climb a 650m rise in the richmond range. for info email: [email protected]

will this herald the arrival of the Sled community to our shores? efforts are also being made to form a ‘Snow machine user Group’. email Phil wiel for more details:[email protected]

nEW AVALAnCHE DoWnLoADSwe have recently produced a number of avalanche Safety material such as the new avalanche Safety and avalanche rescue pamphlets. these pamphlets are now available as a free download for easy and fast access. make sure you head to www.mountainsafety.org.nz/resources to check out the new avalanche safety info.

Above: Some screenshots of various digital field note book apps. Recent AvAlAnches:

The strongest indicator

of avalanche conditions

are avalanches running.

This is the best clue that

a particular slope or

similar one is dangerous

signs of instAbility:

Collapsing snow

(whumpfing sounds),

shooting cracks and

hollow drum like sounds

are natures warning

signs that the snowpack

is unstable.

heAvy snowfAll oR RAin in the pAst 24hRs:

Significant new snow or

rain can overload and

weaken the snowpack.

Avalanches often occur

naturally during or

immediately after a storm

but they are commonly

triggered by people, on the

first fine day after it.

wind: Wind can deposit

snow ten times more

rapidly than snow falling

from the sky. It deposits

snow on lee slopes and can

rapidly create dangerous

conditions even under

clear skies.

RApid wARming:

Rapid increases in the

temperature of the

snowpack can weaken the

bond between the snow

crystals causing unstable

snow conditions.

Wind

Loading

Instability

Avalanches

conditionscould it AvAlAnche?

In most avalanche accidents one

or more of the following signs were

present.

Te mperature

www.mountainsafety.org.nz

www.avalanche.net.nz

03


after a late start, the 2011 winter was a boom and bust type of snow year for most as only a handful of storms formed the basis of our snowpack. By and large they were characterised by good snowfalls to low elevations, but also by gale force winds which ended up stripping ridge top snows back to ground in windward areas. it sounds like most enjoyed some of the best turns in the mid and lower elevations as cold airflows allowed the unusually large amounts of low elevation snow to hang around and remain in good shape.

avalaNChE.NET.Nz - 2011 wiNTEr SummaryBelow are the detailed regional summaries from our 2011 forecasting crew. they did a great job last year as we implemented a large redevelopment to the avalanche.net.nz website. the new forecasts offer more detail using graphics and text to convey specifics on danger, risk, and consequences from the threat of avalanches.enjoy the summaries below.

- Gordon Smith Assistant Avalanche programme manager New Zealand Mountain Safety Council

rUAPEHU AnD TonGArIro CroSSInG By denham Stewart

WEATHEr the season was dominated by three major storm systems with Sw flows. these storms were the major producer of snow for the season, bringing snow to low elevations as not seen for a number of years. the first of these low pressure systems arrived early July and parked itself over the region through to mid July. this brought large accumulations of snow and gale force w1/2 winds. the rest of July saw an unsettled weather pattern. the next significant storm arrived mid august as a polar blast engulfed the country bringing larger amounts of low density snow to very low elevations and light winds. following this throughout mid august to mid September, high pressure dominated the region bringing clear skies and a return to our prevailing Nw winds. mid September saw another low pressure system bring large amounts of snow above 1400m with strong w1/2 winds, as for the rest of September high pressure dominated the region. overall we experienced limited rain events and lighter winds than usual.

SnoWPACKSmall amounts of snow through June created a very shallow snowpack giving the perfect conditions for near surface weaknesses, which could be found on many aspects above 2000m. the first of our major storm systems arrived early July bringing snow to low elevations with gale force winds, creating stiff wind slab on slopes lee w1/2 at depths of up to 3m. this deep instability persisted for a week, until failing under its own weight on a facet layer in the old snowpack and producing a natural avalanche cycle above 2000m. for a few days from the end of July to mid august, small accumulations of snow combined with strong w1/2 winds to create very sensitive wind slab on leeward slopes with Natural avalanches occurring at low elevations (1300m). mid august saw a polar blast with light Southerly winds and large accumulations of snow to very low elevations (500m) this distributed snow on an array

of aspects up to 80cm deep but fell with very little wind.

No significant instabilities were observed within this new snow. (Some would say the best day skiing on ruapehu in the last decade) mid-august through to early September saw a generally stable snowpack. large accumulations of snow returned to the region in mid-September during a week-long storm. very sensitive wind slab formed up to 70cm deep with natural avalanches running above 1600m. late September through to early october saw the snowpack go through a melt-freeze cycle leaving a generally stable snowpack at all elevations.

DAnGEr rATInGthe danger rating spent a majority of its time on low this season while fluctuating between moderate and considerable as storm cycles passed over the region. the rating of high used only a number of times through intense stages of storm cycles.

AVALAnCHE ACTIVITYmultiple Natural and explosive triggered avalanches were observed on an array of aspects averaging from size 1 to 3 during the months of July, august, and September. avalanche paths reached threshold on multiple aspects within the 1600m - 1900m elevation band late July early august. these lower elevation paths became the more active as the higher smaller paths became self-supporting with reduced angles.

a natural avalanche cycle occurred on the 7th of July above 2000m on aspects lee to the westerly half, these avalanches occurred during a storm system so observations were limited but evidence of debris indicated up to size 3 avalanches had ran. currently alpine winter conditions still exist in the mt ruapehu/tongariro regions and daily forecasts will continue through into November. i would like to thank the snow safety crew at turoa and whakapapa for their contribution and information sharing, without their shared knowledge these forecasts wouldn’t exist.


TArAnAKIBy todd cations-velvin

oVErVIEW2011 winter saw some excellent days on the mountain with great snow conditions and excellent coverage of snow with the splash of fine weather thrown in. a couple of record-breaking snowfalls and it was a season to remember.the new avalanche advisory website was a successful addition to the resources available for mountain users and avalanche professionals alike. this was a great season for those wanting to play in the snow.

WEATHErthe weather in taranaki was highlighted by several cold snaps that crippled the country this winter. the first major snow to low levels for the region came at the start of July as a cold westerly flow hit the country. this was followed a few weeks later by a very cold southerly blast pulling cool air all the way from antarctica. it spread snow to low levels across New Zealand and even to the beaches of taranaki, which was the first time in over eighty years. in mid august we saw the next significant weather event to hit the region which again had snow settling on local beaches. in between these significant weather events we saw some great clear days.

AVALAnCHE ACTIVITYSeveral avalanches were sighted around the mountain this winter but unfortunately records were not kept. with the new avalanche website i would hope in the future recreational and professionals in the taranaki region embrace information sharing and use this new website as a tool to record and share information.

SnoWPACKfor the most of winter we saw a generally stable snow pack, the exception to this was around the several major storm cycles of July and august. during these storms new snow instabilities were present in the snow pack and quite often buried deep, with the potential to create large avalanches. these instabilities settled out quickly after the storms had past. late august and early September saw the snow pack turn isothermic and spring conditions remained on the mountain through September. with the heavy snowfalls received through July and august the mountain has a significant amount of snow. this remains on the upper mountain leading into october.

ConCLUDInG rEMArKSa generally good season for all on the mountain this winter with plenty of snow which made for some great skiing and riding. with great cover this opened up some avalanche terrain on the lower mountain, which rarely sees enough snow to reach threshold, providing a new set of terrain hazards for mountain users. it was a mostly incident free winter, with mountain users respecting the conditions presented to them. thanks to all those that provide information to help in the forecasting for the mountain and those that continue to provide feedback on the service provided. remember large volumes of snow still exist on the mountain and care will be needed heading into late spring as large avalanches can still happen around significant rain events.

Avalanche awareness, advisories & info

Avalanche Centre campaign winter 2012

on the right is an example of one of many print adverts to appear in magazines over

winter 2012. this particular example is for adventure

magazine.


nELSon LAKES nATIonAL PArKBy matt wilkinson

oVErVIEWthis winter was slow coming but despite that it was of historical significance in that deep snow extended to low elevation for a large part of the winter. this was mainly due to the July storm that broke the snow drought here and elsewhere in New Zealand. this is the third winter of the Backcountry avalanche advisory in the Nelson lakes National Park. continuing improvements in both the web based format and the support of both the department of conservation and the rainbow Ski area have seen this program continue to grow. the new web based format i believe is a significant step forward in terms of presenting the information to the public.

WEATHErthere was basically no snow in the National Park for may and June with rain to high levels when precipitation did occur. the temperatures were generally higher than normal leaving people wondering whether winter was going to come at all. the “winter making” storm that lasted several days from the 6th of July saw about 1.5 to 2 meters of snow deposited in the Park with a little more in the western ranges. Strong associated wind from the west and southwest saw significant loading onto North eastern aspects which is still evident to low elevations at the time of writing this report.

western aspects have been quick to lose snow cover over ridge crests and spurs due to the more shallow snow distribution. more settled weather dominated until 15th of august when a strong southerly flow arrived. this produced moderate snow fall in the park with increased snow coverage further east. again the storm was associated with strong winds distributing snow to the north and western aspects. cooler “spring like” conditions have dominated since with a slow progression towards an isothermic snow pack. the 2nd and 3rd of September has seen rain to high levels in significant volumes. this will see a complete transition of all aspects to an isothermic spring snow pack for the first time.

SnoWPACKdue to the lack of snow cover and moderate temperatures during may and June and the large single snow fall that set up the majority of the total snow pack in one event the snowpack has been predominantly very strong. there has been very little evidence of faceting at any stage during the winter and the majority of the snow pack all the way to ground has been small well sintered rounds with a pencil resistance and no evident weaknesses. there has been occasional near surface weaknesses due to crystal form or density variation during the small storm cycles that occurred. the majority of snow pack weakness has been due to solar radiation on northern aspects and ground release wet slabs on north eastern aspects at lower elevations. the later was due to the large volumes of snow to mid and lower elevation during the July storm. then warm

temperatures and rain in September has caused both glide cracks and climax wet avalanches on lower north-eastern aspects. this has been most pronounced on aspects which have significant tussock cover and deeper soils which are less free draining. this phenomenon will be exacerbated by the rain in early october.

AVALAnCHE oCCUrAnCESit is believed that a substantial avalanche cycle occurred during the early July storm but observation within the park was not possible, and any evidence was lost due to continuing snow fall and snow cover to very low elevations. the southerly storm in august is expected to have produced avalanches in the upper elevations of the park but the weaknesses that caused these settled rapidly after the storm. September has seen some loose snow activity. most notable has been the climax wet slabs on North eastern aspects during September. this has been evident from the air over a large part of the region on mid to lower elevations. it is expected that this will continue to occur during the month of october when significant rain fall occurs.

TrAVEL ADVISorYthis winter has seen predominantly low and moderate danger rating with most increases related to solar and rain related loss of surface cohesion. this will be the case as spring continues. Substantial snow cover on north and northeastern aspects will continue to see increasing avalanche danger during times of warm air temperatures and high solar radiation. rain and warm temperatures will also accelerate snowpack creep and glide which will see an increase in larger climax wet slabs during spring.

caution is advised on solar aspects during the afternoon when air temperatures are high and during rain when the snowpack becomes unsupportive on skies or while walking. Generally the number of park user’s increase as the passes clear of snow and days become longer. it will be important for people to remember that there is still significant snow in the basins above. most caution will need to be exercised during intense rainfall to high elevation.

ConCLUDInG rEMArKS this advisory will continue until there has been a significant decrease in total snow cover. i would like to again recognize the substantial support from the department of conservation, N.i.w.a. for the remote access to weather information and rainbow Ski Patrol continued support of the program.


ArTHUr’S PASSBy alex Geary

oVErVIEWthe winter got off to a slow start with almost no snow until July 6th. this marked the beginning of a large cold North westerly storm and then regular top ups throughout the rest of the winter, providing excellent coverage until the end of September. the snow pack was generally stable, with the normal storm snow instabilities being short lived and no significant persistent weak layers.

WEATHErthe largest storm affecting the entire south island in 12 years lasted for 7 days starting July 6th and brought 349mm of precipitation in arthurs Pass accompanied by winds mostly from the Nw and w gusting over 150kph. the middle of July brought no significant weather events until July 26th - 30th, when 65mm of rain was recorded in arthurs Pass with freezing levels rising to 1800m. another settled period followed until august 5th - 7th, when 42mm of rain fell in arthurs Pass and freezing levels up to 1900m.

the next weather event was august 13th-17th, which was very cold and brought approximately 40cm of storm snow accompanied by gale force winds from the South and South east. relatively settled weather followed until august 27th – 30th, when another 30mm of rain fell in arthurs Pass and freezing levels rising to 2000m. September was characterised by several small storms bringing snow and rain in the mountains interspersed with warm and sunny weather.

SnoWPACKthe snow pack before July 6th was non-existent below 1700m, with small pockets above this elevation and no skiing to speak of. the July 6th storm resulted in ridge tops being scoured and deposits of over 4.5m being measured in sheltered areas lee to the Nw, with some of the best coverage in deep gullies and creeks in the last several years. on august 13th a thick melt freeze crust was buried, which turned into a persistent weak layer on w, Nw, N, Ne above 1500m where it had a couple of centimetres of facets on top of it, then 40cm of storm snow on top of this. isolated whumphing was observed on this layer immediately following the storm, where sudden planar compression tests in the moderate to hard range persisted until the end of September also showing a good likelihood of propagation.

this aug 13th layer began to be absorbed into the dominant melt freeze crust near the surface by September, although isothermal snow down to the ground beneath this crust on

w, Nw and N aspects above 1600m continued to react to similar test results, sometimes on a layer of hail from the July 6th storm up to 120cm deep. despite these test results indicating avalanches were possible, the melt freeze crust continued to bridge over these deeper isothermal layers of concern and no avalanche activity was noted. this lack of activity is likely also due to the lack of large steep terrain on these aspects between 1600-2000m with enough snow to create a large avalanche. the snow pack for the remainder of the season was typified by a melt freeze cycle and occasional top ups of snow with no significant layers.

AVALAnCHE ACTIVITYthe July 6th storm resulted in a widespread natural avalanche cycle up to size 3.5 dry storm slabs on Se and e aspects by the end of the storm, the largest running on the east face of mt temple to valley bottom. on July 29th a significant avalanche cycle occurred when several dry storm slab avalanches up to size 3.5 were observed on e and Se aspects between 1600-1800m elevations. during the morning of September 1st a size 2.5 avalanche was observed at 1500m elevation, Se aspect, Scott’s ridge, 2.7m deep x 50m wide running 200m.

a glide crack was previously observed on this slope and it failed on the ground. this appears to have been an isolated event, although numerous other glide cracks had been observed. the spring brought the normal cycle of loose wet avalanches triggered by solar and daytime warming, peaking on September 20th with lots of entrainment from the N aspect of rome ridge up to size 2.5 on September 18th. Several other storm slab avalanches up to size 2 were observed on this day, and doc closed the St James walkway in the lewis Pass area as size 3’s were reported to have “swamped” the track for the first time in 5 years.

ConCLUDInG rEMArKS 2011 has been a great winter for snow coverage to valley bottom and stability, allowing many fantastic lines to be skied throughout the winter including the Bealey face and chockstone route on mt rolleston, mt Phillistine, Phipps Peak and the list goes on. thanks for a great winter!

Avalanche awareness, advisories and info


CrAIGIEBUrnSBy damian Jackson

oVErVIEWthe 2011 winter in the craigieburns was a unique one in many ways. a pair of record breaking storms provided for a bit of excitement at times. really though, it was the extended periods of settled weather and a lasting cover of snow (well into the subalpine) that characterized the season, opening the door to some unique lines and day after day of less hassle backcountry travel. the New Zealand avalanche centre’s updated backcountry avalanche advisory was an excitement as well. it was great to see the new tools, greater detail, and better consistency it provided- also good to see a format more aligned to that of other international avalanche centres.

WEATHEra mainly “high and dry” pattern in late June/ early July had many wondering when or if winter would arrive. all questions were answered on 7 July, as a powerful westerly trough with numerous embedded fronts barreled across the tasman. By 14 July, 2m or more of snow had accumulated around the region, and severe w and Nw winds with unique loading patterns had left a great covering of dense “base builder” snow well below bush line, while stripping clean most ridgelines and some of the more exposed upper elevation slopes and basins- these effects seemingly more drastic at the southern end of the range. Settled weather had returned by 15 July- this remaining the general pattern through to mid august.

on 14 august, much of New Zealand was on alert as another powerful storm system approached- this one an unprecedented “Southerly”. By 19 august, another 1m or so of snow had accumulated to all elevations in the craigieburns and for the first time of the season, there was more than adequate snow cover in the regions westerly facing basins. Nothing too exciting in September- besides a mild, “spit and sputter” west flow during the latter half of the month, conditions remained generally mild and “spring like”.

SnoWPACKin essence, July’s storm set the tone for the season. as far as the snowpack is concerned, going from 0 to 2m in less than a week, usually leads to favourable long term stability. certainly there were some storm snow interfaces (12 July Stellars, 14 august Graupel) that proved plenty reactive during and just following July and augusts’ storms. there were also several periods of near surface instability related to wind redistribution (mostly w and Sw events) and surface/ near surface loosening by radiation/ melt water. otherwise, the snow structure was favourable, allowing for safe travel over a wide variety of aspects, elevation, and terrain type.

there were a few periods where persistent type weaknesses developed in the regions high and shady zones- diurnally recrystallised facets (7 august), melt layer faceted grains associated with the 1 September crust, as well as a thin

layer of radiation recrystallised facets (15 September) below a brittle radiation crust (originally buried 18 September). to now (late September), these weaknesses lack an overlying slab, and are thus unable to bear fruit.

AVALAnCHE oCCUrAnCESas one would guess, there were significant avalanche cycles during both of the season’s large storms. the July storm was seen to produce plenty of storm and wind slabs (to size 2), out of mid and upper elevation S to e facing terrain- these occurrences likely running on the 12 July stellar interface. augusts’ Southerly storm was responsible for both natural and controlled wind slabs to size 2.5, once again, all of these related to weaknesses within the recent storm’s snow (14 august Graupel). most occurrences were reported out of N- Ne facing mid and upper elevation zones with some sizable cross loaded slabs reported out of e aspects as well.

TrAVEL ADVISorYin spring, weather factors seem to have an amplified effect on stability. Snow and blowing snow can be fierce and temperature spikes can quickly loosen previously strong interfaces. during unsettled weather, storm snow and wind slab is usually the main concern- watch for storm weaknesses to be especially sensitive to the lee of ridgeline and features of the dominant wind direction. if weather becomes intense, you’ll need to think about avoiding avalanche terrain all together. when the sun comes out, turn your focus to radiation related instability. look for signs of slopes preparing for a shedding of their winter coat (snowballing, lubricated feel underfoot) – that’ll be the time to retreat to lower angle terrain.

ConCLUDInG rEMArKS with generally good stability, and a consistent cover of snow to well below bush line for much of the season (rarely observed in New Zealand), it was a good winter to get into the hills. this did however open the door to a different set of hazards in the craigieburns. access into some of the regions more abrupt terrain is often made difficult by a lack of snow cover below the level of the regions controlled and patrolled ski fields. this winter, easy and obvious access to terrain surrounding the ski fields was enough to entice many into the craigieburn’s numerous natural bounties- some of these folks possibly unprepared for the hazards that nature can dish out. learning the subtleties of terrain, and being prepared with the proper equipment and knowledge will keep the odds in your favor and allow you to travel in the backcountry with greater safety.

a quick thank you is in order to the mountain community of canterbury. much thanks to the many teams and individuals who contributed snow, weather, and avalanche information, vital to the cause. information from ski area snow safety teams, guides, avalanche/ mountain educators, and of course recreational parties is irreplaceable. taker easy’


MT HUTT/TAYLorS/ArroWSMITHSBy Jamie robertson

oVErVIEWwith snow to low levels early in the season and no deep instabilities this provided some great skiing/riding opportunities for those keen to earn their turns. cameron hut had snow around it for most of the season and further east the skiing off the back of mt hutt and walking the short distance to the road provided some great turns. as it was mostly a dry season the major influence was wind that accompanied the storms making east facing aspects look like a normal season yet look towards the west facing aspects and you would think summer was still here. Some great skiing/riding has occurred throughout the region as long as you played the aspect.

WEATHErmay and June provided no snow to the region with very warm temps causing a late start for the ski areas. after a very slow/dry start to the season the 1st major storm of the season set up the rest of the season, arriving early July with over 3m of snow near the divide tapering to the east, for over 3 days it snowed and blew with gale Nw winds.

temps during this storm ended cool and this caused the snow level to be low with snow to the valley floor. cool temps for the next period kept the snow in the valley floors and made for some long runs. the other major storm of the season was in mid aug with snowfalls to sea level. this provided snow in the higher mountains but was again accompanied by strong winds.

at the head of the rakaia 65cm of snow settled in the valley, methven had 20cm on the ground which saw everybody excited about some fresh powder. again the temps stayed cool with snow staying to the valley floors. later season (Sept) saw small snowfalls usually in the 10cm range with lighter winds and again often with cool temps, keeping the snow light and dry.

SnoWPACKthe season generally had a very stable snowpack. Starting with nothing then getting major snow accompanied by strong winds helped to prevent any deep instabilities. Some faceting was observed later in the season on the eastern hills but never became reactive, mostly due to not becoming overloaded with new snow. the winds associated with the earlier storms provided a varied loading pattern over the region, and caused areas to be stripped (west facing) and other areas to have deep snowpack (east facing). Generally with the westerly winds the snow tapered to the east with deep snowpack closer to the divide. Spring has yet to see a big rainfall event (this may be happening at present) that usually produces a large wet slab avalanche cycle. Solar aspects have slowly become isothermal and we are unlikely to see any issues for the rest of the season on these aspects other then with new snow.

AVALAnCHE oCCUrAnCESoverall it was a very quiet season for avalanche activity. in the arrowsmiths the early season storms produced the usual mid storm cycles with avalanches to size 3 but after this, only small events were observed (due to no deep instabilities). the mt hutt region was similar, having some isolated storm events but generally a quiet season. Spring in the arrowsmiths has been consistent with other years; wet slides on solar aspects following the small snowfalls in the last few weeks but nothing over size 2.

TrAVEL ADVISorYthe advisory has often had very little change from day to day. consistent conditions have made the forecasting straightforward. the challenge during the season was the range of hazard throughout the region. often the mt hutt region would be low while the arrowsmiths region had a high hazard with heavy snow falling. this often meant reading the text provided was important to get the right information for the area you wanted to venture into.

during the season the usual high hazard during storm cycles would quickly drop with clear weather. the later part of the season has had moderate to low danger rating with the expected rise to considerable and daytime warming on steep solar aspects as the solar effect increased with longer days. forecasting for the future: expect solar aspects to fall off after any new snow and quickly change to a melt freeze cycle. Still waiting on the big rain event to high elevations that will sort all aspects, but without the usual deep instabilities we don’t expect to see the large events to valley floor which are usual for this time of the season.

ConCLUDInG rEMArKS overall the season was good for those looking in the right place. the mt hutt Patrol reported a number of people touring from the ski area and finding some great skiing. the arrowsmiths had snow to lower elevations meaning touring from the cameron hut was fun. this provided longer runs than the last few seasons. Stability was generally good making a low stress season for all those working in the snow, while still providing some great skiing/riding conditions. let’s hope for another similarly low stress season next year.


AorAKI /MT CooKBy trev Streat

SUMMArYeyebrows were raised early July as pretty much the only snow lay high up on the glaciers and permanent snowfields after an autumn that was far too warm and far too long. that all changed on the July 8 with the onset of a cold westerly storm that set things up for the rest of the winter putting a ton of snow in low elevation lee areas and stripping windward slopes bare. this provided some unusually easy ski touring access for much of the winter. long spells of settled weather characterized the rest of the season punctuated by a few relatively weak Nw storms and of course the big southerly in late august. the wind remained a dominating theme, with few snowfalls remaining untouched by her raking nails.

WEATHEr2011 feels a little like a one storm winter, such was the dominance of the huge westerly storm in early July. when the skies finally cleared on July 14, over 300mm had been recorded in mt cook village with 2-4m of snow to low elevations, on lee aspects of course. w/Nw gales were unrelenting throughout the storm. we had to wait till late July for the next weather event, the prelude to which was a cold, mostly dry and very windy S/Sw change. a weather station up the murchison valley recorded 80 knots from the south on the 25th. this was quickly followed up by a run of the mill Nw storm that put 66mm in the gauge and up to 75cm in the hills. once again wind was the winner on the day with surface conditions left largely corrugated and windswept. the next system rolled in august 6 and left 39mm in the village over a couple of days with about up to 60cm on the divide. the Sw clearance came through with some punch. old ski tracks were looking like railway lines in places. the next event was the big ol’ southerly that got the media really frothing.

the village largely escaped the bulk of it with about 20cm falling to valley floor between the 15th and 18th. Gale southerlies dominated the period and of course seldom seen intense cold, with lows of -15c recorded at 1800m. Given the wind during the storm we were surprised and delighted to find about 50cm of cold smoke overlaying much of the ski terrain. an extended period of fine weather following ensured we made the most of it. late august wind preceding the next weak Nw system took care of the snow quality. September saw the usual potpourri of spring weather and Nw gales with a few welcome cold snaps that produced snow to low elevations. of note was a prolonged cold and unstable Sw air stream between the 9th and 15th that began with Nw storm dropping 90mm in the village, followed by several days of unsettled Sw’sters with a further 33mm over four days, falling as snow above 1200m. we are still awaiting the really big spring storm to fill those crevasses right up and ensure a long climbing season.

SnoWPACKthe storm of early July set the tone for the rest of the season, with the bulk of the snow pack arriving over a few days. where the new snow stuck it was packed in tight and was good base building material. where there was snow it was deep while in exposed areas nothing stuck. the distribution was unusual with the best coverage at low elevations. a wee ski tour up hoophorn stream in late July, (5km down the valley from the village), revealed an impressive 240cm snowpack at 1200m elevation, skiable to within 5 minutes of the car. the trend set by the July storm generally continued with most precipitation coming in with an excess of wind. So the fat areas got fatter and the shallow zones did not really recover. with a lack of persistent weaknesses this season instabilities were generally confined to the more predictable storm snow/windslab sequence that healed up over a few days.

AVALAnCHE oCCUrEnCESBy and large the pattern of avalanching was fairly predictable and limited to the big storm events. the oliver and Kitchener paths above the village, as well as Stocking Stream and the hayter path on the divide ran to d3 during the large July storm. interestingly there was a heli remote on the north aspect of liebeg dome to d2.5 during the same period. a week later a deep slab released to d2 at 2600m on hochstetter dome as a result of an ice cliff collapse. Nw to Sw gales and about 40cm of new snow on august 8 led to a d2.5 natural slab pulling out of the murchison headwall on about the 10th or 11th during a spell of settled weather, possibly triggered by solar sluffing out of bluffs above and running on the old facetted snow surface. a handful of slabs pulled out during the cold southerly cycle of mid august to d2, interestingly on windward aspects. around mid September a couple of deep slabs released to d3 on the divide after a Nw storm and several days of intense Sw loading.

TrAVEL ADVISorYtypically spring instabilities are relatively easy to predict with avalanching directly related to the intensity of the weather. expect slab avalanching during or just after the storm on lee slopes followed by a round of loose snow avalanches on solar slopes, or all slopes if it really warms up post storm. Big precipitation whether or not it’s rain or snow will result in big avalanches, in fact in spring it is often the big rain events that produce the big slides as the moisture lubricates those buried crust layers that have lay dormant over the winter.

CLoSInG rEMArKSit has been great to have a stack of low elevation snow in the region that stayed around for most of the winter, combined with generally good stability and none of that early season facet crust combination that have plagued recent winters. have a great summer.


WAnAKABy Simon howells

oVErVIEWthe 2011 season in the wanaka region was unusual for a number of reasons. the winter commenced with an alarming lack of snow. this period was followed by a Nw storm of remarkable severity and duration. the last two thirds of the season was characterised by extended periods of mostly settled weather, predominately light winds and very limited precipitation. this weather pattern as a whole ensured that avalanche activity across the region was limited. also notable, was the introduction of the new mSc avalanche advisory. the new format has been well received by backcountry enthusiasts in this region.

WEATHEr in may we experienced a Northerly flow, warm temperatures and very limited amounts of precipitation. this pattern persisted throughout June and into early July. on the 7th of July it finally started snowing and we received around two meters of snow over the next 7 days. an interesting feature of this storm was that although it was Nw in origin, we received large amounts of snow to unusually low elevations (600m). the second half of July saw a return to mostly settled weather with a Southerly flow and light to moderate winds. very little precipitation fell during august or September and winds were generally light.

AVALAnCHE ACTIVITYit is pleasing to be able to report that there were no accidental avalanche involvements recorded in the wanaka area, during the winter. there was very little natural activity across the region during the early part of the season due to the lack of snow. following the major storm cycle of the winter in July, there was an increase in wet slide activity

particularly on the solar aspects below 1700m. only limited amounts of slab avalanche activity occurred during this period. this situation was largely attributable to the lack of buried sliding surfaces or significant hidden weaknesses in the pack. in the latter half of the season, storm cycles generally failed to produce snow in sufficient quantities to create dangerous hazard.

SnoWPACKthe most notable feature of the pack this season was the manner in which it increased from virtually nothing too at least, two meters in depth in the course of a single storm cycle (July 7th - 14th). this in turn, produced generally favourable conditions for the rest of the winter. the rapid growth of the pack, to a substantial depth in most areas, helped to retard the development of deep instabilities such as facet layers and depth hoar. areas which subsequently became wind scoured and shallow and therefore weak, failed to receive significant additional loading. during the early weeks of Spring, temperatures were relatively mild and heavy rainfall uncommon. as a consequence, large wet slides were a rarity.

ConCLUDInG rEMArKSthe unusual weather patterns we experienced during the early weeks of the season when combined with the limited amounts of snow and wind we received later ensured a quiet few months as regards avalanche activity. with the mSc advisory seldom elevated to considerable or higher, parties could venture out with confidence on most days. i would like to thank my co forecaster richard raynes for his efforts and all the people who provided me with information during the season.

QUEEnSToWnBy chris cochrane

oVErVIEWthe winter of 2011 in the Queenstown region was unique in many ways. at the start of winter many thought it would be the winter that never was, could this be the first ever winter that it never snowed? well, the winter turned out to be a record in many ways. record snowfalls to low levels and a low level of avalanche activity were some of the highlights, but there were some other strange facts to emerge from this season, a season in many ways that set records and patterns that have not been seen since the 1960s.

WEATHErearly season snow was absolutely nonexistent. temperatures were so warm during June and early July that snowmaking was impossible, day temperatures were in the mid teens and no overnight frosts. the mountains around the Queenstown region were brown and bare with no snow,

even the high peaks showing just scree. on July 10th a major winter storm deposited up to 2 m of snow with over 15 cm’s in town its self, July 15th the fields opened, 6 weeks later than usual. Strong w to Sw winds at upper elevations scoured the tops but at lower levels the skiing was unbelievable, skiers using terrain that had not been skied since the 1960s.

temperatures stayed cold for weeks and so did the snow at low elevations, then in august another record snowfall, a blizzard that deposited 30 cm’s of snow at the airport. Skiers and boarders skied/rode the full length of coronet Peak from the summit to the valley, runs up to 1400 m in length. these two storms were the only major weather events for the season, two falls!

September delivered very little in the way of snow, very unusual as the past 3 or 4 seasons saw spring snowfalls at record levels, killing thousands of lambs, not so this season. two other major variances for the season were the lack of the traditional Nw storms, the two major falls were


from the Sw, meaning cold snow. without the Nw winds meant there was no rain event this season, very unusual as rain events have created sliding layers that persisted in the snowpack over the past 3 seasons, there were no such layers present in the ‘11 snowpack. the other abnormality was there was No snow from the east this season, last year easterly snow was very common, with a majority of snow coming from this direction.

SnoWPACKterrain to the west was devoid of snow at upper elevations for most of the season, the snow being so light that is was virtually blown away, heliski operators struggling with scree at ridge top landings. mid to low elevations and the lower peaks producing by far the best skiing conditions and of course opening up terrain that had not been skied in decades. the air flow in between weather events continued from the Sw, the snow cover at lower elevations remaining. the next weather event in august was almost a replica of the July event. these two events were the main contributors to the snowpack for the season. there was the occasional 5 to 10 cm falls in September but none of the major snowfalls that we have seen over the past few seasons. there was certainly a lack of slab snow development this season.

without a slab forming meant there was very little tension in the snowpack and nothing to trigger in the way of stiff snow avalanches. there was also very little in the way of a natural avalanche cycle this season (although some small events immediately after the two main weather systems were noted), perhaps it had something to do with the lack of significant snow in start zones or the lack of a hard sliding layer within the snowpack. there was some slab development from the September snowfalls, but events never got above size 2. ‘Slide for life’ conditions which can be of concern (for several weeks) around this region were also a rare occurrence this season. the remarkables being south and east suffered from a lack of snow this season and has closed early, coronet Peak still has great coverage and will continue well into october.

AVALAnCHESthere were 3 reported involvements (very low involvements for this region) resulting in 1 full burial. a man buried 2m deep was rescued by companion rescue techniques after a burial time of almost 20 minutes. well done to all those involved in the rescue. this event was on an easterly aspect at around 1600 m with a crown wall of approx. 2m, evidence again of the significant snowpack depth at mid elevations.

ConCLUDInG rEMArKSthe 2011 season has surpassed may peoples pre season predictions and has set new records of its own, however another season goes by without a dump of our classic ‘knee deep’ powder, suppose you can’t always have it your way, next year, let’s hope. Stay safe if you are doing some spring touring and tune in for the 2012 season in June next year.

Seen to produce plenty of storm and wind slabs (to size 2), out of mid and upper elevation S to e facing terrain- these occurrences likely running on the 12 July stellar interface.

augusts’ Southerly storm was responsible for both natural and controlled wind slabs to size 2.5, once again, all of these related to weaknesses within the recent storm’s snow (14 august Graupel). most occurrences were reported out of N- Ne facing mid and upper elevation zones with some sizable cross loaded slabs reported out of e aspects as well.

TrAVEL ADVISorYin spring, weather factors seem to have an amplified effect on stability. Snow and blowing snow can be fierce and temperature spikes can quickly loosen previously strong interfaces. during unsettled weather, storm snow and wind slab is usually the main concern- watch for storm weaknesses to be especially sensitive to the lee of ridgeline and features of the dominant wind direction. if weather becomes intense, you’ll need to think about avoiding avalanche terrain all together. when the sun comes out, turn your focus to radiation related instability. look for signs of slopes preparing for a shedding of their winter coat (snowballing, lubricated feel underfoot) – that’ll be the time to retreat to lower angle terrain.

ConCLUDInG rEMArKS with generally good stability, and a consistent cover of snow to well below bush line for much of the season (rarely observed in New Zealand), it was a good winter to get into the hills. this did however open the door to a different set of hazards in the craigieburns. access into some of the regions more abrupt terrain is often made difficult by a lack of snow cover below the level of the regions controlled and patrolled ski fields. this winter, easy and obvious access to terrain surrounding the ski fields was enough to entice many into the craigieburn’s numerous natural bounties- some of these folks possibly unprepared for the hazards that nature can dish out.

learning the subtleties of terrain, and being prepared with the proper equipment and knowledge will keep the odds in your favor and allow you to travel in the backcountry with greater safety. a quick thank you is in order to the mountain community of canterbury. much thanks to the many teams and individuals who contributed snow, weather, and avalanche information, vital to the cause. information from ski area snow safety teams, guides, avalanche/ mountain educators, and of course recreational parties is irreplaceable. taker easy’


in february 2012 Porters Ski area obtained the necessary resource consents and plan changes to develop New Zealand’s first on-mountain alpine village and to expand the ski area into the adjacent crystal valley. the development is worth $500 million over 10-15 years.

crystal valley is scheduled for opening in the winter of 2015. the new ski area will comprise of a snowmaking system, chairlift, gondola and day lodge. visitors will access both Porters and crystal valleys by gondola from the village thereby closing off the existing ski area access road.

the development will see a huge expansion into the current snow safety management programme, both in size of area and the amount of resources and risk management. the ski area avalanche control boundary expands from 3 km² to over 9 km² and this is not including the avalanche control boundary along the lower road.

the project was first unveiled in 2009 and since this time Porters patrollers have been documenting and mapping all the avalanche events within crystal valley, however, with approvals the development of the crystal valley avalanche management Programme enters the next phase, consequently there been a few key personnel changes at Porters this winter.

after many years as lead avalanche forecaster i begin a new role and duties this winter as Snow Safety development officer for crystal valley. Brad carpenter, who been with us for a number of years, takes the role as lead avalanche forecaster.

as Snow Safety development officer my responsibilities include: the management of information and data collected during the development phase, the design and developmentof a professional snow safety

programme, the design and development of management tools and process systems within the programme to assist with the daily operation, and designing and developing a programme that will manage the avalanche risks and hazards.

the development of the snow safety programme composes of a number of projects including weather stations/snow study plot, meteorological data, summer mapping, avalanche flow paths/avalanche defence, remote avalanche control system, avalanche events, avalanche start zone/snowpack, avalanche control, avalanche forecasting and avalanche rescue.

Above: an example of the initial avalanche path mapping within crystal valley, presenting the avalanche flow paths, the frequency and a terrain features analysis.

in this article, Simon morris, Snow Safety development officer for Porter Ski area explains more about developing a snow safety programme for New Zealand’s first on-mountain alpine village.

dEvElOpiNg a NEw avalaNChE maNagEmENT prOgrammE// SimON mOrriS

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during the development phase we intend to have a transparent internal development programme involving management, patrollers and the avalanche management team. this will benefit the programme allowing us verification and review of our data. the collaboration will make for a more dynamic development phase, creating more efficient formation of new concepts and doctrines. however, the principal benefits will be increasing our team knowledge of crystal valley.

our objectives during the initial development phase are to enhance our knowledge, to evaluate explosive requirements and to create a foundation to identify the factors which affects the stability and hazard within crystal valley. this phase comprises primarily of monitoring meteorological data and the collection of snowpack, storm events, avalanche events and avalanche control data.

the development will see New Zealand’s first static remote avalanche control system being installed in both Porters and crystal valleys. this system is a gas-operated avalanche release system which is unaffected by weather conditions and is completely automatic. the system will comprise of six to eight exploders.

we are investigating the use of the more environmentally friendly o’Bellx exploders. these exploders produce no pollution or residues produced by the blast. they allow for a very light foundation and are removable during the summer and/or for maintenance operations. the o’Bellx exploders are removed with a helicopter through the use of a specific hook without the need of ground operators.

the exploders should work well with the New Zealand snowpack as the shockwave initially forms an overpressure wave followed by a underpressure wave. this will have a double effect on the snow; first to break its resistance and then to lift it and ease its motion. any result is confirmed by a network of seismometers.

the development will also see the installation of two new automatic weather stations within crystal valley for the avalanche management programme. this will increase our network to five stations within the avalanche control boundary and will provide us with a high level of detail and enhanced meteorological data.

we plan to collect additional snowpack data by locating one of the new automatic weather stations in close proximity to our start zones. this data will include snowpack temperatures, snow surface temperature, snowpack height, free water outflow, new snow height and density.

we are attempting to design management tools within the snow safety programme that will assist with the daily operation and provide additional information on the stability and hazard of the ski area.

two of these tools we are evaluating are a snow lysimeter (monitoring rain on snow events and monitoring rapid warming events) and a snow drift sensor.

many of the projects require a high level of mapping. for this we are using our lidar data and high resolution aerial photograph. the lidar data provides as with a digital elevation model to an accuracy of about 20 centimetres and the aerial photograph has a ground sample distance (GSd) of 60 centimetres.

we will investigate spatial variation of wind speeds, precipitation amounts and snow depths using a number of different methods. we will use full length avalanche path snow profiles after storm events from different wind directions to help determine areas of wind loading and stripping. we will examine the meteorological data between Porters and crystal valley to determine variation between the two valleys.

other significant projects that we will look at are; the evaluation and compilation of a new explosive management programme, compiling a new rescue plan, avalanche dogs and the summer mapping of avalanche paths to provide general descriptions of the paths.

the next few winters at Porters developing the new snow safety programme will be very demanding, interesting and exciting. it will allow Porters to incorporate the latest technology, to computerise data management system and to design management tools within the snow safety programme that will directly assist with the operations of the ski area.

- Simon Morris Snow Safety Development Officer Porter Ski Area [email protected]

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avalanches which occur during periods of cooling are important because they can surprise people.

the subject first piqued my interest several years ago. i was sitting outside a ski lodge at the end of a hot spring day, watching the sun leave a steep slope on the opposite side of the valley. a few minutes later, a large slab released from the slope. it seemed incongruous, as no obvious trigger was present: no recent loading by wind, snow or rain, no person and no bomb. the only change i could perceive was a rapid drop in temperature as the slope moved from full sunshine to shade and into its associated early evening chill. a few days later, i saw the exact same thing on the exact same slope.

in 2005, i took on the role of avalanche forecaster at Broken river Ski club. lingering in the shadows of my mind was an avalanche which had occurred there 13 years beforehand. the week preceding the avalanche had been stormy, with 142 mm of precipitation. fluctuating freezing levels eventually led to a rain-soaked snowpack. on the day of the avalanche, the weather cleared, temperatures dropped and the snow surface became slick and icy. Staff decided to open the area based on conventional wisdom: cooling and surface re-freezing promote stability. at lunchtime, a size d4 avalanche failed near the ground on depth hoar, pulling out the entire Broken river basin with a crown up to 2.2 m deep, which propagated 800 m wide into low-angled terrain, leaving a deposit 20-30 m deep. a snow groomer and skiers were in parts of the basin, and may have been the trigger, but they were far from the fracture line.

amazingly, only one person (the ski area manager) was killed, as almost all the other skiers were inside having lunch. a photo of the avalanche hung on the wall in the forecasting

office, leaving me chilled and uncertain. doesn’t an icy, frozen surface mean the snowpack’s locked up? why did the avalanche fail then and not during the warm storm? why did it propagate so widely?

So began my investigation. i started by turning to the books, to read up on this phenomenon and learn about the mechanisms behind such events. Beyond some passing references to rapid temperature changes, the standard volley of avalanche reference books left me empty-handed. i tried scientific journals, asked academics and searched online. very little came to light. So i began to ask my colleagues. a few

Above: treble cone Ski area. Saddle Basin was closed during the day due to creep and glide concerns. at 5pm the surface was starting to refreeze, so the forecaster gave the oK for groomer operators to go into the basin to work. the avalanche occurred sometime during the night, failing on depth hoar at ground. it damaged the lift bull wheel.

people had experienced something like that. many hadn’t. a more formal questionnaire followed. in the end, 40 avalanche professionals from around the world responded. the questionnaire focussed specifically on ‘re-freeze’ type events (where the snow surface goes from 0° c to below 0° c). i called this a “cool-down avalanche” or cda for short. the responses alerted me to the prevalence of surprising, large avalanches during periods of rapid cooling, not just when the snow surface goes from melt to freeze, but also at overall lower temperatures (e.g. a drop from -5° c to -15° c).

NZ research into the effects of ‘rapid cooling’ to initiate avalanches. Penny Goddard is an avalanche forecaster, educator, author, ski patroller, mountaineer, and soon to be ‘mum’. we wish Penny and Jamie all the best for their upcoming new arrival.

COOliNg aNd avalaNChES // pENNy gOddard

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this article firstly summarises the results of the questionnaire, then highlights a round of cooling-related avalanches in western canada during the 2010-2011 season.

Part 1: The results of the CDA questionnaire:

• in order of descending quantity, observations came from New Zealand, North america, europe, asia and antarctica.

• 15 of the 40 respondents had never experienced a cda. (many more people elected not to answer the questionnaire at all, due to having never experienced a cda).

• about 360 cda were observed (this number is approximate, as the bulk of observations were poorly recorded, based instead on observers’ memories).

• 98% of observed cda were described as slab avalanches, 2% as loose.

• the bulk of the observed avalanches were size d2-d3. 14 were size d4 and 3 were size d5.

• 61% were described as ‘glide’ releases.

• 20 cda events occurred within 15-60 minutes of the sun leaving the slope. a further 7 occurred less than 15 minutes after the sun left the slope.

• 21% of respondents had experienced a close call involving a cda. these included very large avalanches hitting an open highway, burying a ski lift in an area which was open to staff and fully burying people in guided groups.

• 38% of respondents factor cda into their decision-making while managing the exposure of people and infrastructure to avalanches. 44% said they do not.

• 7 people who had never had a close call involving a cda factor the possibility of cdas into their decision-making. interestingly, 3 people do not factor cdas into their decision-making, in spite of having had a close call involving a cda (including involvement in fatal incidents).

• the following comments were made by respondents help address some of the reasons why cdas are rarely factored into operational forecasting:

• “[this is] much too speculative a theory to apply in an operational forecast”.

• “i see ‘cool-down’ as the more stable end of the curve”.

• “i don’t factor cdas into management due to a lack of understanding and observations”.

• “i don’t factor cdas in, as it seems a very rare event”.

• “i don’t factor cdas in, as there’s no knowledge base, therefore they are hard to estimate”.

• “the funny thing is, i probably still guide and operate considering cooling down as a good tick for stability”.

CDA Conclusions

• cdas (surface refreezing avalanches) were observed around the world.

• accidents and near-misses have occurred when operators have re-opened previously closed terrain assuming that cooling means dramatically improved stability.

• Some operators actively manage the cda hazard through closures or explosives control, which are timed to coincide with rapid cooling or surface refreezing.

• they were rarely observed overall – many experienced practitioners have never experienced a cda.

• there’s a feeling that they are too difficult to predict, so there’s a tendency to ignore them when making decisions.

Above: Ski patroller ed Nepia at the crown wall of the treble cone avalanche. hard refrozen snow jutted out like a diving board above soft, moist snow below. other similarly shaped crown walls were reported from various cda events.

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Part 2: Cooling Events in Western Canada during winter 2010-2011

Before i launch into Part 2, it’s important to distinguish a key difference between Part 1 and Part 2. the questionnaire in Part 1 asked specifically about ‘re-freeze’ cda events (snow surface going from 0° c to below 0° c). the events listed in Part 2 occurred during periods of rapid cooling within an overall colder temperature regime and did not involve a clear melt-freeze process at the surface.

the following photos show a succession of large avalanches which occurred during periods of rapid cooling in western canada. operators described these events as very surprising, eye-opening, historic and unusual.

Above: monashee Powder Snowcats, Southern cross Path, overnight 8/9 Jan, 2011. overnight there was no appreciable new snow, no sign of wind, skies were clear most of the night, and temperatures dropped from -8.5° c to -15° c by morning. it was a size d4 step-down slab, with very wide propagation. the trigger was a small cornice or small slope above. the lead forecaster said “i’m busy rethinking my assumptions/intuition” (the guides were considering expanding their scope of terrain use that day)”

Above & right: Kicking horse mountain resort backcountry, 18 Jan, 2011. these paths did not avalanche during the preceding prolonged warm storm. they occurred overnight 17/18 Jan during rapid cooling and strong winds. the air temperature dropped overnight from -5.6° c to -16.4° c at the ski resort’s nearby weather station.

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Above: mistaya lodge, western rockies. overnight 17/18 Jan, 2011 after a storm ended which had deposited 1 m+ snow. there was overnight air temperature cooling from -3° c to -13° c and wind (however, many of these slopes were not lee to the wind). more than 20 avalanches released, size d1 to d3.5 (many d2-2.5) with crowns 100-150 cm; some up to 200 cm deep. Several avalanches were observed in unusual locations.

Left & above: lanark path, rogers Pass, 8am, Jan 18, 2011. the avalanche was size d4.5 and damaged 10 acres of forest. it failed on facets/crust at ground. the air temperature dropped from -3° c to -17° c overnight prior to the event. the avalanche cycle was considered to be over. this one failed near the time that sun first hit the slope.

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Right: castor Peak, Glacier National Park, 8am, Jan 18, 2011. under the same weather conditions affecting the lanark Path, this widely-propagating avalanche occurred. a second, historic avalanche occurred around the same time on nearby crawford Peak, destroying mature timber in the runout. the surprising nature of these events led to the canadian avalanche centre issuing a warning message to operators on Jan 18: “Notable avalanche activity: we have received a couple of reports of large, unusual avalanches that occurred this morning as the temperatures were cooling…”.

Right: hilda Peak, valkyr range, 20 Jan, 2011. this size d4 avalanche

was an isolated event which occurred post-cooling. there were no other large

natural avalanches during the cycle. it destroyed mature forest.

Above: Golden backcountry: “dogtooth range, overnight feb 7/8, 2011. there had been no avalanche activity during warming on feb 7th. overnight, the air temperature

dropped from -10° c to -17° c and these and other large slabs released.

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Some common factors in the events of 2010-2011:

• heavy storm loading occurred prior to the event.

• all but one failed on a Persistent weak layer.

• rapid air temperature cooling occurred, often around 7-10° c overnight.

• they were mostly very large events with wide propagation.

• in every case, experienced locals were surprised by the events.

In conclusion

So what does all this mean? is there anything more than a sense of vague paranoia to take away?

it seems clear that avalanches sometimes occur during periods of rapid cooling, both when the snow surface is going from melt to freeze and at overall colder temperatures. it is unclear whether, or how, cooling itself triggers avalanches - and that is a topic for a whole different study. what does seem apparent to me is that many near-misses and possibly some serious accidents were caused by faulty decision-making around cooling. the premise that cooling stabilises the snowpack after a storm (or solar warming) ends is not always correct. always basing decision-making on this premise can lead to premature exposure of people to avalanche terrain.

the most constant element in these events was that of surprise. in many cases, professionals were just about to (or just had) opened up terrain previously off-limits for public, guests and staff access.

this research is mostly a collection of anecdotes. in order to really understand the mechanisms behind avalanches which occur during periods of cooling (and from there, to be able to forecast them), as a community we need to better document this type of event. i hope that this preliminary investigation will spark some discussion, spawn some more focussed research and perhaps encourage decision-makers to take a ‘second look’ at conditions during periods of rapid cooling.

i presented this topic at conferences in Penticton, Bc, canada and New Zealand last year. on both occasions, numerous audience members revealed that they, too, had experienced surprising avalanches during times of rapid cooling. my feeling is that this phenomenon, while sporadic, is more common than one might expect.

acknowledgments

Thanks to the following people for their contribution: Bill Atkinson, Mark Austin-Cheval, Ried Bahnson, BC Ministry of Transportation – Avalanche and Weather Programs, Canadian Avalanche Centre, Peter Bilous, Dave Birnie, Stewart Blennerhassett, Kevin Boekholt, Jay Bristow, Wayne Carran, Howard Conway, Rosco Davies, Jef Desbecker, Thomas Exner, Ryan Glasheen, David Hamre, John Hooker, Andy Hoyle, Damian Jackson, Dan Kennedy, Karl Klassen, Mark Klassen, Brett Kobernik, Gary Kuehn, Chris Landry, John Mletschnig, Jane Morris, Shaun Norman, Tom O’Donnell, , Christine Pielmeier, Tarn Pilkington, Nicholas Rapaich, Tim Robertson, Davie Robinson, Mike Rubenstein, Mark Sanderson, Mark Sedon, Ron Simenhois, Jim Spencer, Dean Staples, John Stimberis, Frank Techel, Craig Wilbour and Henry Worsp.

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Right: an example of a alpine & avalanche education advert that is set to print in

numerous local newspapers.


the 2011-12 utah season began hot-on-the-heels of a relaxing NZ season. after a fairly straight-forward 2011 austral winter, in utah things could not have been more diverse, or unusual. a series of small storms occurred in october with a more significant storm around November 9. interspersed with cold, clear high pressure systems, a weak basal layer formed that persisted all season.

the previous season (2010-11) in utah had started in a radically different fashion with massive early snowfall – and frequent storm systems all winter (the more typical situation). with such positive memories, skiers were chomping at the bit with the arrival of November’s snow.

a powder-frenzy occurred on the not yet opened slopes of Snowbird and alta with two significant avalanche incidents on November 12 – including utah’s first fatality for the season – famous free-skier Jamie Pierre.

a tedious winter had begun – of infrequent top-ups and tip-toeing on the egg shells of 20 cm basal facets. i wrecked a pair of skis for the first time ever in North america - the quality climbing granite of little cottonwood canyon being a nasty rock to ski over. the cold smoke powder we know and love arrived on occasion but with it, a price. we awaited the massive storm that would bury the facets far below the stress bulb (spatial variability notwithstanding). it never really came.

waiting for snow, as the existing 60cm rotted to the ground, was an exercise in reflection. i worked on a lot of avalanche classes with some experienced avalanche practitioners (Bruce tremper, don Sharaf, Kelly elder and others). all agreed that it would be one of those low-angled seasons. it was a great season to take an avalanche course and a terrific season for teaching.

the first significant storm in late January caused massive cracking, collapsing and wide-spread avalanching. repeaters became common as chronically large high-pressure systems moved in post-storm and avalanche bed surfaces re-faceted. Near-surface-faceting also created issues following storms

(buried NSf being the most common weak layer in the wasatch mountains).

the trickiest periods were post-storm, as the snow pack ‘tightened’ and the likelihood of triggering a slide was reduced, the classic situation of ‘low probability-high consequence’.

test results were often hazy (i mostly use ct and ect and i oscillate between the american system of rating the failure quality and the canadian system of fracture character). i began to use the Sharaf-mccammon stability wheel – in both teaching and thought.

discussion with friends and colleagues revolved around the fact that the mere existence of the weak layer meant that strength tests (alone) are insufficient for decision-making.

much of the time post-storm, 30 taps on a column were insufficient to cause failure. add a boot stomp (or even continue tapping beyond 30: canadian deep tap test) and a fast, clean (Sc) shear would result 60cm-120cm below the snow surface. it’s dodgy stuff when unorthodox test methods produce high energy results. the number 30 is arbitrary. accidental avalanches occurred with relatively frequency when technically, test results were negative.

false stable results. during avalanche classes i bleated endlessly about the enduring weak layers.

i emphasised the weak snow pack structure, and field days easily demonstrated the incongruity of strength during tests. my own words would echo in my mind as i planned back-country trips. i frequently used my probe to establish snow depth – thus applying some of mccammon and Sharaf’s “five lemons”: Persistent weak layer crystal type, down 100cm or less, weak layer <10cm thick, grain size (=/>1mm) and one step or more hand-hardness between layers. Not all of these categories applied – the weak layer being more like 20cm thick – but other boxes checked out. Given the wide publicity of avalanche issues in utah this season, my clients would eagerly watch as i probed, impressed with a sudden dive as the stick hit basal facets. Structure demonstrated with minimal fuss!

a reminder on the importance of snow structure to guard against false/Stable results. anna Keeling is an ifmGa guide based in both utah and NZ’s craigieburns.

Slim piCkiNgS iN uTah’S waSaTCh // aNNa kEEliNg

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So enter the human factor. you get bored with a dangerous snow pack. you even get used to it. you begin to imagine, hope and assume that it’s bridged (hence the probe – it doesn’t lie about snow depth). as the season progressed with additional snow accumulation, crux times, where the weak layers re-activated became harder to call and attention to crucial areas pre-storm were essential. i used more discipline to manage travel – ensuring that clients practiced beacon searches, digging regularly and using my probe to establish weak layer depth. i frequented familiar

places and remained wary of anything new. my clinometer was kept handy in my leg pocket – it wouldn’t lie about slope angle. it was the season of tree skiing.

i was keen to have it over with by april. interestingly, control work on the little cottonwood canyon road (home of alta and Snowbird ski resorts) brought down big slides in the last week of april – the weak layer being wet basal facets. as the forecasters predicted – this weak layer will only be history once we drink it (the cottonwood canyons are the water source for Salt lake city).

“you get in zee pit, you get zee information, you get out” – Peter Schaerer told one of us during a training course. along with his advice that you should never stop observing changes within the snowpack was the stern admonition that snow pits should be focused, efficient, and QuicK.

for years, avalanche educators have taught students to dig snow pits to look at stratigraphy, identify snow crystals, and perform stability tests. But correlating snow profiles with stability has never been an exact science, and many students came away unsure of exactly how they were supposed to use snow stratigraphy in their stability decisions. moreover, many of them lacked clear objectives for their pit analysis and ended up wasting time collecting tedious and semi-relevant information. the result fell far short of Peter Schaerer’s sage advice. rather than training people to make quick, informed decisions, we seemed to be creating an army of winter recreationists who could spend half an hour or more in one snow pit, but couldn’t tell you how, why, or when they would use the information they found.

two years ago, we began teaching a simple approach to interpreting snow profile results on upper level avalanche courses and professional training seminars. many students said the approach produced an “a-ha!” moment for them and they were excited to learn a simple way to focus their efforts in their snow pits. in this article, we’ll describe our approach and how we teach it, in hopes that others may find it useful in helping their students to make quick and informed stability decisions.

A three-part model

the discipline of fracture mechanics tells us that three things need to happen in order to produce the large-scale shear fracture that initiates a slab avalanche:

1. the fracture must begin at some point under the slab where the shear strength of the weak layer is overcome by applied stresses,

2. the shear fracture must liberate enough energy from the snowpack to sustain its own propagation, and

3. there must be a “path of least resistance” in the snowpack structure along which the shear fracture can propagate.

these three components of strength, energy, and structure are a simplification of the complex inter-relationships that produce slab avalanches. But from a teaching standpoint, they provide an effective way of summarising important stability information that students can gather from a few simple field procedures.

Strength

the backbone of most level 1 stability classes is the standard stress-strength model. this model says that a weak layer will fail when you apply enough stress to it. an important implication of this model is that when stress and strength are very nearly balanced, unstable conditions will exist and slabs may be easily triggered by the weight of a skier or snow machine. in this model, the role of stability tests is to assess whether stress and strength are in a critical balance.

if your stability test scores are low, the weak layer is in a critical state of balance. But if your stability scores are consistently high, the weak layer is less likely to be triggered. many students come away from avalanche courses with a simple rule of thumb: low scores are bad, high scores are good. thus it’s no surprise that some of them come to base their go/no go decisions almost entirely on cursory avalanche observations and test scores from one or two snow pits.

integrating strength, energy and structure into stability decisions.

SO yOu dig a piT aNd ThEN whaT? // iaN mCCammON & dON Sharaf

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research has shown that the stress-strength model works pretty well most of the time: high test scores generally do correlate with stable conditions. But not always. a disturbing number of accidents occur during “false stable” conditions, where tests indicated stability but avalancheswere still triggered by a skier or rider. in these cases, practitioners in the know say “well, that’s spatial variability for you” and shake their heads in recognition of the tough job they have chosen. But for decision makers who rely on stability tests the message is deeply troubling – the stress-strength model is not the whole picture.

Energy

in 1998, ron Johnson and Karl Birkeland described a formal rating system for a phenomenon that field practitioners had noticed over the years: when stability tests fractured with a clean and fast shear, triggered avalanches were more likely. in 2001, Schweizer and weisinger described a similar system used with rutschblock tests in Switzerland and in 2002, van herwijnen and Jamieson described a system of fracture character used in canada. exactly what these schemes are measuring remains unclear, but one trend stands out: fast and clean shears release their fracture energy quickly, and are more frequently associated with unstable conditions. See Karl Birkeland’s article on stability, shear quality, and fracture character in the reference section for more details.

fracture mechanics tells us that the higher the fracture energy release rate, the greater potential the fracture has for propagation. Shear quality and fracture character may only provide a very rough estimate of the fracture energy release rate, but when used in conjunction with stability tests, shear quality seems to provide valuable information regarding the likelihood of avalanche triggering.

Sudden Planar: SP Sudden Collapse: SC Resistant Planar: RP

Progressive Compression: PC Non-‐Planar Break: B

NZ and Canadian Fracture Character Classifications

Structure

imagine two snow profiles. in one, an interface between light-density storm layers produces a moderate and sudden planar fracture 30 cm from the surface. in the second, a layer of facets beneath a hard wind slab produces the same fracture character and score at the same depth. even though the two weak layers have the same strength and release their energy at the same rate, few practitioners would treat the two snow packs the same.

in an effort to characterize some of the “red flags” that professionals use in comparing such profiles, mccammon and Schweizer (2002) described five stratigraphic features of weak layers that statistically correlate with skier-triggered avalanches (table 1). these features, referred to here as “lemons”, appear to be rough indicators of how well a snowpack might concentrate shear stresses in a weak layer. the more lemons in a weak layer, the more structurally weak the snowpack... Schweizer et al. (2004) extended the initial concept, and refinement of the system continues.

Weak Layer Depths ≤ 1m Weak Layer Thickness ≤ 10cm Hardness Difference ≥ 1 step

Weak Layer Grain Type: Persistent (SN, DH, FC) Grain Size Difference ≥ 1mm

Table 1: Five Structural “Lemons”

Above: figure 2. a fracture mechanical model of slope

Above: figure 3. two profiles with similar strength and energy, but different structural properties

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taken alone, strength, energy and structure only do a fair job of predicting skier triggered avalanching. But fracture mechanics tells us that when all three factors are present, shear fractures are more easily initiated and are more likely to propagate large distances.

Bruce tremper uses the analogy of a combination lock; when all three tumblers of strength, energy and structure fall into place on a particular slope, conditions are primed for avalanching. false stable conditions exist when the tumblers of energy and structure are present, but strength tests indicate stability. under these conditions, wandering onto an isolated weak spot can cause localized fracture that can propagate into an avalanche.

Teaching

the standard way that we approach teaching mechanics and stability assessment using strength, energy and structure typically goes like this:

1. review the stress-strength model and its limitations

2. describe shear quality as a way of quantifying elastic energy release

3. introduce the lemons as a method of analyzing snow structure

4. incorporate the lemons into a quiz for strength, energy, and structure

5. introduce the concept of the ‘test +’ pit as an efficient way to analyze snow strength, energy and structure in a snow pit.

as always, information from a snow profile shouldn’t override class 1 information (natural avalanches, recent loading, shooting cracks). however, we have found that when students look at snow profiles within a larger mechanical framework, their efforts are more focused, efficient, and productive. So get in those snow profiles and then… get out!

The Test + Pit In Snow Sense, Jill Fredston and Doug Fesler describe three questions to ask when digging a test pit:

1. What is the weakest (significant) layer? 2. How much force does it take to make that weak layer fail? 3. What is the depth and distribution of that weak layer?

These are very good questions to help focus snow pit observations and keep the observer from analyzing layers that are unimportant for an immediate go or no go decision. A test + pit takes the three questions and then asks you to get more structural information about the weak layer. To answer the five lemon categories, you need this additional information about the weak layer only. Obtaining this information shouldn’t take more than a few minutes.

1. What is the hardness of the weak layer and the layer immediately above it? 2. What is the grain size of the weak layer and the layer immediately above it? 3. What is the grain type of the weak layer? Persistent? 4. What is the weak layer depth (answered before with the previous questions) 5. What is the weak layer thickness?

Helpful hint: When teaching about the lemons we strongly encourage the students to write down the lemons into the back of their field books (along with the three objectives of a standard test pit).

Test results Strength Energy Structure Stability

RB6 Q3 L2 Strong Slow Strong Good

RB2 Q1 L4 Weak Fast Weak Poor

RB6 Q1 L5 Strong Fast Weak False stable?

Left: table 2. examples used in introducing the fracture mechanics model of slope stability. Students are encouraged to consider all three aspects of stability in their snowpits.

acknowledgmentsThanks to the following people for their contribution: Reprinted by permission of the authors

Birkeland, K., 2004, comments on using shear quality and fracture character to improve stability test interpretation. The Avalanche Review, Volume 23 #2,

Johnson, r. and Birkeland, K. 1998. effectively using and interpreting stability tests, Proc. ISSW, Sunriver, or.

mccammon, i. and Schweizer, J. 2002. a field method for identifying structural weaknesses in the snowpack, Proc. ISSW, Penticton, Bc., pp.477 - 481

Schweizer, J., fierz, c. and Jamieson, B. 2004. assessing the probability of skier triggering from snow layer properties, Proc. ISSW, Jackson, wy.

Schweizer, J. and weisinger, t. 2001. Snow profile interpretation for stability evaluation, Cold Regions Science and Technology, 33 (2-3): 179–188.

van herwijnen, a. and Jamieson, B. 2002. interpreting fracture character is stability tests, Proc. ISSW, Penticton, Bc., pp. 514 - 520

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managing ‘sidecountry’ challenges, misconceptions, and lessons.

2010 SADDLE PEAK AVALAnCHE - CASE STUDY // dOug ChaBOT, mark STaplES, karl BirkElaNd & EriC kNOff

1. pre-event

Bridger Bowl Ski area, near Bozeman, montana opened the new Schlashman’s lift to its southern flank during the winter of 2008-2009. this expansion resulted in a new backcountry boundary gate accessing forest Service land. this new gate was located at the ridge crest, eliminating both the need for skins and a chance to think about stability on the climb up. Schlashman’s added expert skiing terrain within Bridger Bowl boundaries and greatly improved sidecountry access. it was hugely popular with hundreds of skiers a day lapping the sidecountry of the adjacent Saddle Peak (9,162’) after fresh snows. the descent lines are in full view of the lift and the sight increased the popularity of sidecountry terrain (figure 1).

Bridger Bowl requires all riders on Schlashman’s to wear an avalanche transceiver since the in-bound terrain is serious and avalanches are possible and it aids Search and rescue operations outside the boundaryif people are buried. Bridger has had a beacon policy for all skiers accessing their in-bounds ridge since 1976. consequently, most locals own transceivers and wear them regularly at the ski area.

Bridger is a local ski hill with a large population of adolescents who ski the “ridge”, a two mile long crest above lift served terrain. they own beacons, hike to get turns and most are expert skiers. the adolescent population was the avalanche center’s and Bridger Bowl’s primary concern with the new boundary gate. there was never any doubt that the sidecountry of Saddle Peak would be popular, even though the slopes were uncontrolled and required snow assessment and travel skills that many adults and most adolescents do not have. Parents routinely drop the kids off at the ski area without appreciating the ease or risks of entering the sidecountry. adolescents’ inexperience and immaturity in making complex decisions about avalanche danger is a grave concern. Because of their adventurous spirit, we anticipated that many would head out-of-bounds first chance they got with far less avalanche judgment than the rest of the Saddle Peak skiers who ranged from montana State university students to middle aged adults with decades of Bridger history.

although the backcountry gates were always open, the lift accessing them was not, especially after larger storms. this time lapse between storm and skiers sometimes but not always allowed the slopes to stabilize before they laid tracks.

from the summit of Saddle Peak a skier can descend 2,000 feet of powder and traverse back to the lift without any

specialized touring gear. this increased traffic on slopes laced with terrain traps prone to avalanche presented a new education challenge for the avalanche center.

1.1 Avalanche Education and Awareness

in early 2008, eight months before the scheduled opening of the new lift, the avalanche center began working with Bridger Bowl to put together a sidecountry education package for the community. Parents

not familiar with the avalanche potential outside the boundary were our first target, followed by the teenagers themselves and then the general adult population.

1.2 Sidecountry user Challenges

the skiers and snow boarders who used this new access point into the sidecountry had concerns of their own. Because Saddle Peak is expansive, descending one at a time is impossible with heavy traffic and the terrain provides no true safe zone on the descent. Safe travel protocol is often discarded with solo skiers also frequenting the sidecountry. our avalanche awareness and education programs work, but not with everyone. cognitive dissonance and self justification play roles in skiers’ decision making (tavis and aronson, 2007). despite our best efforts, we watched the sidecountry experience turn into a free-for-all----everyone skiing at the same time and bumps on the most popular lines. this was unthinkable a year ago when this was truly backcountry and not so easily accessible.

Above: a view of Saddle Peak from the top of the Schlashman’s lift.

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1.3 Weather, Snowpack and Avalanches

although these human factor and terrain challenges exist every day, an avalanche hazard requires an unstable snowpack, and the 2010 winter’s snowpack was the most unstable in the 20 year history of the avalanche center. the snowpack began with small storms from the end of September through october, followed by a three foot storm on November 12th. at the beginning of december five days of -25° f temperatures (-32° c) created large facets throughout the snowpack that persisted all winter. on december 17th a snowpit on Saddle Peak showed a 30 cm thick P+ hardnessslab capping 50 cm of fist hardness facets (figure 2). we made a video of the stability test (ectP14, Q1) viewed 5,000 times on youtube, pointing out that skier compaction would not affect this capped weak layer.

for the Bridger range, and specifically Saddle Peak, the real event began on friday, february 12th and ended two days later. a storm dropped 2 ½ feet of snow (3.5” of Swe) with strong westerly winds which loaded Saddle Peak’s east face and triggered avalanches throughout the Bridger range (figure 3). the new lift did not run over the weekend, shutting down access to the sidecountry. the lift reopened

Above: december 17, 2009 snowpit.

Below: figure 3: daily snow water equivalent measured at Bridger Bowl Ski

area’s alpine weather Station.

Above: figure 4: crown line on Saddle Peak. the path of the triggering cornice off the ridge can be seen in the center of the photograph.

monday morning, february 15th. Saddle Peak had a lot of traffic that day, even though the avalanche danger was rated considerable. the mountain range had a stubborn, deep slab instability exacerbated by the massive load. 1.4 Skier Compaction, misconceptions

observations and conversations with folks prior to the avalanche revealed some widespread misconceptions about the danger. the terrain, weather and snowpack all pointed to unstable conditions, yet the “human factor” acted as blinders to the instability (fredston and fesler, 1994).

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a robust “herding instinct” had skiers unquestionably following one another all season long and added a false sense of security (tremper, 2009). Skiers and boarders consistently descended on top of each other, despite education efforts pointing out the dangers of this behavior. the most deeply held belief was that a tracked slope was safe—it would not slide because others already skied and tested it. folks believed that months of skier compaction would make it stable, even though the weak layer was deeper than skis could reach. this belief was even shared by some fellow avalanche/ski patrol professionals who verbally expressed it to us. in fairness, we know that skier compaction matters, especially in a ski area where tracks are numerous and a slope’s history is carefully tracked. however, the key is that the skier compaction affects the weak layer, but we knew from our december snowpack investigations that a hard slab capped the weak layer which would be unaffected by skiers.

2. Event

at the normal opening time of 10 a.m. on tuesday, february 16th, the public rode the lift and hiked out-of-bounds to the summit of Saddle Peak. Skies were clear and tracks from the day before were in full view. they immediately started skiing the east face. at 11 a.m. a snowboarder hiked too close to the edge and accidentally broke off an ever growing van-sized cornice. to everyone’s horror, it tumbled downhill 100 feet and fractured the slope at a buried rock band five deep and 1,000 wide and it ran 2,000 feet vertical down one of the most popular and heavily skied slopes on Saddle Peak (figures 4 and 5). as predicted, it broke on the layer of facets formed in december. the avalanche danger was rated considerable that morning. twenty to thirty people were estimated to be on the ridge when it released, with less than ten folks having already skied it that morning.

2.1 who were these people?

on the day of the slide many of the folks on Saddle Peak were older and experienced and thought they were savvy to the current snow stability. an informal study weeks

later showed 70% of folks skiing Saddle Peak were repeat customers. Surprisingly to us, adolescents and college students were anxious about the event and questioned us repeatedly about the circumstances leading up to the slide. much of the older crowd had a different reaction: they felt like they knew the terrain and snowpack better than anyone else and were the most likely to self justify being there.

2.2 Search and rescue

a full Sar response ensued and at 3 p.m. we called off the search for rescuer safety because of rapid wind-loading. it was, thankfully, a victimless avalanche.

3. post event

the fact that no one was caught, injured or died provided the avalanche center with a unique opportunity to educate the community since the slide was front page news. had

someone perished, it is unlikely we could have been as critical or brutally honest about the situation. we wrote about it in our daily advisories for the next week. our web traffic spiked 680% (950 hits to 6,500) the day after the slide. we posted pictures and video clips that day, did a live radio interview the next week, went back and did a post avalanche investigation, and held an hour long public forum at the library to present our findings and answer questions. this forum was filmed and posted online. we uploaded a total of six different videos on youtube that have over 24,000 views, and one additional video posted by a person on the slope was viewed an additional 4,600 times. our goal was to let as many people as possible know why the avalanche released and how luck was a large reason why no one died that day. we had to challenge some tightly held misconceptions about snow, avalanches and the terrain on Saddle Peak.

verbal and written comments on the avalanche were varied. Some skiers acknowledged that they made serious mistakes. others claimed the slide was a fluke or that the adjacent line they regularly skied was really okay.

Above: figure 5: full track of Saddle Peak.

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3.1 misconceptions

1. tracks on a slope create stability by breaking up the weak layer. also, a season of tracks will always make a slope even more stable.

2. the stress from a skier’s weight was not enough to trigger this avalanche. only something enormous like a large cornice could have fractured the slope.

3. the ski area needed to open the lift, and consequently access to the backcountry, days earlier so it would have been further tracked and further stabilized.

4. Self justification: it was safe when i skied it the day before; or, because i ski this terrain all the time i inherently know about the snowpack and its potential danger.

5. herding instinct: others skied it without consequence so it must be safe.

the first and second misconceptions have grains of truth to them. yes, skier compaction is known to help stabilize slopes, but not after the weak layer is deeply buried under a hard slab. Bigger triggers increase the odds of triggering an avalanche, but small triggers in the right spot trigger them as well. as educators, we focused our lessons away from these nuances of avalanches since they were not helping the public make good decisions.

the avalanche center confronted these common and dangerous misconceptions in our advisories, media interviews, articles and in our post avalanche public forum. even so, we were surprised at how strongly people held onto these views even after it slid!

3.2 lessons and Solutions

in the future we can teach the public better ways to identify information that matters most. making safe decisions involves searching for “Bulls eye” data to determine if a slope is stable (fredston and fesler, 1994). we hope to get people away from assessing the snow using outlier data such as what type of trigger is needed or how many tracks are on a slope. we’re focusing the discussion on the fact that it snowed a lot in a short period of time, that there was a known weak layer, and that there was ample evidence of recent avalanche activity on similar slopes in the range. we are also highlighting the lurking cornice and wind pillow hazard that is a regular occurrence in the Bridger range.

3.3 Sidecountry versus Backcountry

Sidecountry terrain creates special challenges for both ski areas and backcountry avalanche centers. we have come to the conclusion that this terrain is more dangerous than backcountry terrain for two reasons. first, because there are so many people on this terrain, it is almost impossible to follow standard backcountry protocols like skiing one at a

time. Second, the increased traffic creates a sense of safety that is often unwarranted, and this sense of safety leads to poor decision-making and poor travel habits. a challenge we face at the avalanche center is to effectively convey this message to the public.

4. Concluding thoughts

after this avalanche we mistakenly believed that everyone would take a giant step backwards and give this area the proper amount of respect. fortunately, some people have done this. however, much to our amazement, there is a sizable population that cannot or will not be reached. even with the massive avalanche clearly evident, people continued skiing adjacent terrain that did not slide in the days following the avalanche. for some people, no amount of avalanche education or in-your-face evidence will dissuade them from their powder turns or the certainty of their belief that they know exactly what is going on in the snowpack. we need to realize that these people exist, but our time, our energies and our message will only reach those members of the public who are willing to listen. we do not have all the answers, but our strength lies in our ability and willingness to quickly adapt to learning and teaching opportunities as they arise.

5. acknowledgements

this avalanche summary is made possible by the exceptional support of Bridger Bowl Ski area and ski patrol. we also could not have created this paper without the help of the Bozeman community who provided us with an incredible volume of pictures, videos and firsthand accounts, some of which arrived at our office as emails even as rescue attempts were being launched.

referencesfredston, J. and d. fesler. 1994. Snow Sense, alaska mountain Safety center, Anchorage, 115 pages.

tavis, c. and e. aronson, 2007. mistakes were made (But Not By me): why we justify foolish beliefs, bad decisions, and hurtful acts, Harcourt Books, orlando, florida, 292 pages.

tremper, B. 2009. Staying alive in avalanche terrain, The Mountaineers, Seattle, wa, 284 pages.

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Necessity, they say, is the mother of invention. certainly that sentiment held true during the early stages of explosive engineering. while seaside forts were concerned over static predetonation of their black powder caches in the 14th century¹, the mining industry in the 1800s were plagued by accidents surrounding the ignition methods for their black powder blasts.

william Bickford had no immediate connection with the mining industry. his financial well being was attributed to his career as a currier and leather merchant. Nonetheless, he was keenly aware of the accidents occurring in the tin mines in england during the early 1800s and he set out to find a solution.

during this period, the black powder shots were being ignited by crudely fashioned fuses made of black powder filled goose quills or paper straws. after some initial failures, Bickford found providence when he saw a rope making machine in action around 1830. he soon fashioned a machine that wound jute, a plant fiber, around a core of gunpowder. completing the process, a varnished outer sheath was added to waterproof the assembly.

in an unfortunate twist of fate, Bickford perished in 1834, just prior to the opening of his first safety fuse factory. it would have made the ingenious Bickford proud to know that in his tuckingmill factory’s first year, almost 45 miles of his invention was produced.

Several years after opening the first commercial safety fuse factory in the world, the corporation took their business overseas to the united States. it was at this point that the company became ensign-Bickford, with its headquarters relocated to connecticut.

as an avalanche and explosive specialist, i have heard many times that safety fuse is an old and antiquated technology. while the former is certainly true, i adamantly disagree with the latter. from its humble beginnings, safety fuse saw immense growth over the many decades that followed. the simplicity of use, cost effectiveness and reliability are several of the factors that can be attributed to its continued success.

reliability of safety fuse cannot be understated. in his excellent article “in defense of Safety fuse” published in the international Society of explosive engineering’s Journal, fred hynes states:

“As a field employee of the Du Pont Company and, later, the Ensign Bickford Company, I investigated many safety fuse accidents, mostly fatalities, and never once was there any evidence of fast burning fuse, although fast burning fuse was always the claim of the survivors. I realize that what I am going to say hereafter flies in the face of old, treasured mining folklore, but it needs to be said in order to convince the younger generations of miners, most of whom have never seen safety fuse, that safety fuse is just that, it is safe; it never burns faster or slower than it is designed to burn. However, safety fuse is only as safe as the man who is using it, and that is where the problem lies².”

one of the world’s largest producers and users of safety fuse in recent years has been africa. in an ironic twist that would see the old Bickford grinning proudly from the grave, a used tuckingmill fuse fabrication machine was sold to the african explosive behemoth ‘african explosives limited’ (ael) in the early 1960s. ael not only began production of safety fuse, but they also manufactured their own black powder for their product. this seems to be a typical trait of fuse manufacturers as wano, a fuse manufacturer from Germany, has been making black powder since 1682!

during ael’s fuse plant’s heyday in the mid 1980s, over 1.4 million meters of fuse were spun each day! at this point, it took 182 fuse manufacturing machines to meet the market demands. while production has slowed at ael to only about 700,000 meters per day, it can be clearly seen that safety fuse is in no imminent danger of extinction in africa.

indeed, aside from the geocentric philosophy of most u.S explosive users, safety fuse manufacturing is still alive and well in many other countries around the world. india is a major manufacturer, with numerous producers of black powder and safety fuse. annual country-wide production numbers are in the hundreds of millions of meters. Peru deserves mention at 60 million meters a year. and, while Germany manufactures a quality fuse, their production numbers are only in the 1000 kilometer a year range.

Bulk fuse is currently imported into North america through Petro explo inc. in arlington, texas. their staple fuse products from tec harsheim in chile were recently cut as that factory, most recently owned by dyno Nobel international, shut their doors in 2003. they now import similar products from mexico.

a history of the humble fuse wire. John Brennan is an avalanche and explosive specialist at the Snowmass Ski area in colorado, uSa. he founded avalanche mitigation Services, inc. in the summer of 2005. his company has recently sold their 22nd avalauncher.

BurN, BaBy, BurN // jOhN BrENNaN

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the majority of uSa bulk fuse users are now using the dyno uSa owned compania mexicana de mechas Para minas fuse sold under the trade name ‘cobra fuse’. Previously, tec harseim produced a military spec fuse that found favor with avalanche control programs who liked its hotter spit and burning characteristics. while compania mexicana produces a similar product, contractual agreements with ensign Bickford aerospace make it unavailable for commercial use until at least 2012.

despite the staggering amounts of safety fuse still being produced worldwide, users should resist being lulled into a false sense of product availability. Shock tube initiating systems are drastically cutting into the safety fuse market. Several countries, such as russia and the united States, have prohibited the use of safety fuse in some mining applications. (Sweden too has regulated that all snow blasting be performed using Shock tube or Non El initiation – Ed)

african explosives limited, the largest manufacturer of safety fuse in the world, has invested heavily in the manufacturing of shock tube - a thin plastic tube lined with a dusting of high explosive. when initiated, the detonation signal is passed through the tubing at 6500 feet per second without rupturing it. the tubing is an inexpensive, highly reliable and safe way to initiate a blast. unfortunately, it is a system that doesn’t lend itself readily to avalanche control. the need to couple the blaster to the explosive charge is an obvious challenge as is the need to collect the spent tubing.

an interesting characteristic of the core of some safety fuse is its ability to carry a static charge- a phenomenon that canadian authorities feel could cause predetonation. Because of this concern canada, and only canada, mandate the use of pre-manufactured blasting cap/ safety fuse assemblies that has a shunting staple installed. this staple provides a preferential pathway for the static charge to ground itself through. it is important to note that blowing snow can generate in excess of 20,000 volts of static electricity³.

there is quite a bit of commercial interest in the cap and fuse market that exists in North america and around the globe. a better educated consumer can ask their explosive distributors about the availability and cost of other international product alternatives. it is avalanche mitigation Services aim to be apprised of the safety fuse options available. Please contact us with your comments and concerns. [email protected]

Related reading:

“increasing explosive Safety”, John Brennan, 2002, http://www.avalanchemitigationservices.com/articles.htm

“in defense of Safety fuse”, fred hynes, iSee, march/april 1985. contact John Brennan for copies of the article

references¹ electrostatic discharge association, http://www.esda.org/

² “in defense of Safety fuse,” international Society of explosive engineers, march/april 1985

³ Personal communication with r.a. Schmidt, 2/02

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assessing avalanche size can be like telling a fish story. to one person the fish is the monster of the deep that almost dragged the boat over, while to another person that same fish was a minnow. however, with avalanches, an accurate and unbiased assessment is critically important to improve communication between avalanche workers and also to maintain consistency in our databases.

although most observers do a great job of assessing avalanche size, we have noticed an unfortunate increase in the incorrect use of avalanche size, especially the relative (or r-) scale. descriptions of the size scales are included in SwaG (Greene et al., 2010), but we are writing this short article to try to help clarify the use of each of the size scales, and to discuss how they complement each other.

The r-Scale

the r-scale, or relative-size scale, has served as the standard size classification in the united States since at least the start of the westwide avalanche Network data in 1968. at its core, the scale is a simple estimate of the size, based on volume, of an avalanche relative to the path in which it occurs.

Sizes range from r1 (very small relative to path) to r5 (maximum or major, relative to path). when estimating the relative size of an avalanche, remember that you are trying to compare the current avalanche with the largest avalanche that path could produce. the size is not just the proportion of the start zone that released. the r size is a function of the depth and width of the slide, as well as the conditions in the track. for example, an r5 slide would run far past where you would normally expect. for paths ending below tree-line, an r5 (major or maximum, relative to the path) avalanche would remove a significant amount of timber. likewise, an r4 slide (large, relative to the path) would generally run full track and might also take out a few large trees. a slide where the whole start zone releases but the crown face is only a foot deep is unlikely to be an r4 or r5 slide unless the conditions in the track are such that a large volume of snow ends up at the end of the runout zone.

The d-Scale

the d-scale, or destructive-size scale, has been the standard size classification in canada for many years. when the first version of SwaG was released in 2004 the working group decided that using both scales would be the most complete way to describe avalanche size, so the d-scale was added to uS guidelines.

the d-scale is an assessment of the destructive potential of an avalanche. Sizes range from d1 (relatively harmless to people) to d5 (could gouge the landscape, largest snow avalanche known). a d4 avalanche could destroy a railway car, large truck, several buildings, or a substantial amount of forest. the description of the potential damage produced by avalanches in each size category is a very useful tool for classifying an avalanche in the field. it also helps all of us select similar categories and thereby maintain consistency between operations and regions.

with the d-scale, half sizes are sometimes reported. the scale also provides the typical mass (which increases exponentially) and typical path length for each d-size, though these can occasionally vary quite a bit from avalanche to avalanche.

Combining The Scales: why use Both?

classifying avalanche size resulted in numerous discussions for the SwaG working group. in the end, we decided that using both scales gives operations flexibility and provides the most complete picture of avalanche activity.

Note that both scales are qualitative assessments of avalanche size. as such, they are useful if you are communicating recent avalanche activity within or between operations or if you are looking back and assessing historical cycles. however, the utility of the scales is only as good as the consistency between observers, past and present.

while we can use the categorical values of the scales in some statistical analyses, saying a specific avalanche was an r3d4 is closer to saying the water was warm than it was 16.8 degc. this is true for both scales since numbers associated with the categories are simply estimates meant to give each level some context.

a comparison of the relative and destructive size scales, and why they are both important. Karl Birkeland is an avalanche scientist with the uSda forest Service National avalanche center, and ethan Greene is the director of the colorado avalanche information center.

r2D2 - aCCuraTEly aSSESSiNg avalaNChE SizE // karl BirkElaNd aNd EThaN grEENE

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Above: a slab avalanche triggered by explosives. this slide involves about 70% of the start zone, but stopped well inside the boundaries of the runout zone. we would classify the avalanche as an r3d2.5.

each scale has its advantages. the r-scale is especially useful for forecasting if the forecaster is not familiar with the particular avalanche path, and it can also give a hint of the current avalanche character (atkins, 2004). for example, a report of an r4 avalanche would tell a forecaster that avalanches are running deep, propagating far, or both. on the other hand, the advantage of the d-scale is that it tells us the destructive potential of a particular avalanche. this is critically important for engineering applications and it may be easier for avalanche workers to visualize the destructive potential of a particular avalanche rather than its size relative to the path.

utilizing the strengths of both scales can be valuable for avalanche forecasting operations. imagine you are forecasting for a mountain range. you know you have a buried layer of faceted grains and the next snow storm is rolling into your area from the north. an observer on the north end of the range reports three natural avalanches, and two of them are r4s. as the storm progresses through your mountain range,you know there is the potential for more avalanches to release that are large with respect to the path. if there are big paths in the central and southern portions of your mountain range, these are going to be dangerous and destructive avalanches. like we say in all of our avalanche awareness classes, recent activity is the best predictor of further activity. large avalanches in small paths are likely to be good predictors of large avalanches in large paths with similar snow conditions.

in contrast, hearing about a d4 avalanche makes all of us pay attention. however, a forecaster has to know the particulars of the path to extrapolate the d size to other areas. for example, a d3 avalanche could be a small avalanche involving only new snow in a large avalanche path, or it could be a large, deep slab avalanche in a small path. in short, neither scale gives the complete story by itself, so using both scales is advantageous. for uS avalanche operations, keeping the r-scale is especially important because it provides consistency with other data collected for many years.

however, the uS was not the first to use both scales. the operation at canada’s rogers Pass has been using an avalanche classification system that includes both an absolute and relative size for many years (mcmahon, pers. comm., 2009). they document avalanche size with a d scale size and a qualifier of large, medium, or Small, which describes the size of the avalanche with respect to the path. thus, they might describe a specific avalanche as a “Small d3” or a “large d2.”

Conclusionas a community, we need to do our best to accurately

and consistently estimate avalanche size. having a good understanding of the r- and d-scales can help us to do that. however, the most effective tool for improving size estimates is good mentoring from experienced avalanche workers. those folks have likely seen a multitude of conditions and a wide variety of avalanche sizes in both relative and destructive terms, and that gives them the perspective to better assess the size of various avalanches. accurate size assessments are important for communicating between and within various avalanche operations and for maintaining useful long-term avalanche databases.

referencesatkins, r. 2004. An avalanche characterization checklist for backcountry travel decisions. Proceedings of the 2004 international Snow Science workshop, Jackson hole, wy, 1 – 10.

Greene, e. m., d. atkins, K. w. Birkeland, K. elder, c. c. landry, B. lazar, i. mccammon, m. moore, d. Sharaf, c. Sterbenz, B. tremper, and K. williams. 2010. Snow, Weather and Avalanches: Observation guidelines for avalanche programs in the United States. 2nd ed. Pagosa Springs, colorado: american avalanche association, 2nd printing.

mcmahon, B. 2009. Personal communication.

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my name is luke lennox, at the relatively late age of 18 years old i became an addict. i became hooked on the thrill of skiing and experiencing challenging situations in a mountain environment. around this age i chose to pursue a career and a lifestyle in line with my habit. eventually through a lot of directive learning, mentorship of others, five professional seasons of ski patrolling and of course my own trial and error experience; i have dedicated myself to an interest for snow study and avalanches.

i believed i had learned and experienced enough of this terrifying and intriguing natural phenomenon to take on more responsibility and commit to a higher career path in the snow study business. little did i know i had been sheltered from reality. the exact people that were teaching me were doing such a good job in protecting and controlling the avalanche environment around me that in seven years i had not seen the full chaotic potential of this industry.

in the last week of November 2011 i was offered the opportunity to work as the assistant snow safety officer and intern avalanche forecaster for Gulmarg ski area in Kashmir india, an opportunity of a lifetime. i thought i understood what this would entail and embraced the challenge, but as i look back in hindsight, i realise how bold and naive i was!

all of my learning and experience i gained from my time in Gulmarg is a list too long to write but a couple of examples really stick out…

Scale

the first snow profile i dug in early January made my head spin. observing 40cm of depth hoar reacting to light loads and the beginning of a storm setting in, i looked around at the 1000 meters of vertical gain and imagined huge avalanches pouring down the slopes.

the aphrawat mountain consists of a series of ridges and sub ridges all flowing into their own gullies/terrain traps at a consistent pitch of around 35 degrees and eventually out onto a large plateau. as i stared around and focused on the inbounds area i realised that completing avalanche control work in the himalayas with a snow pack like this would be challenging.

how do i throw a charge that far to get to a sweet spot? how do i get to a safe zone without using 50 shots to protect a traverse? this place is huge!! these questions

were all answered on our first control route of the season as i found out what a real size four avalanche looked like.

reading through the snow safety plan and doing dry runs through the control routes with Brian Newman (Snow Safety officer) gave me more of an understanding of a mountain this big, but on the front line when the 1kg of military plastic explosive detonated? the ‘crack’ that sounded as the crown wall failed sounded louder than the actual explosives shot itself. a 200 meter wide, up to 2.5 meter high wall appeared at the end of my ski tips, and the rock i was standing on seemed a lot smaller. So many thoughts went through my head i wasn’t thinking at all. thoughts like dear lord what have i got myself into! how did that slab propagate around that ridge? i’ve never seen snow move that fast! oh, so that’s how an avalanche diversion wall works, you would not survive if you were caught in that, i’d better take a photo!

the entire upper main slopes of the ski field, all except one bowl just transformed into combination of boulders, left over snow blocks the size of cars and sugary depth hoar crystals as its snow pack was stripped away, what’s more the powder cloud that swept over the areas that

weren’t part of the debris field formed a 1cm wind crust on the snow surface. i was almost speechless for a day.

the general weather patterns for the past five seasons in the himalayas Pir Pinjal range have supported this event to be normal. in the previous four seasons a large storm occurs, dropping at least 1 meter of snow which cleans out most of the depth hoar layer in a large natural avalanche cycle. one thing in my mind was certain, that i was not going anywhere near the alpine terrain in the back country until this depth hoar layer was gone and a new snow pack had formed. unfortunately this storm never came this season, which leads me to the next experience worth noting.

treble cone Ski Patroller luke lennox shares his steep learning experience from Northern india this summer. luke currently works at treble cone Ski Patrol, but has also styled in the hair salons of whitewater (caN) and Gulmarg (iNd) Ski Patrols. we wish him well in the re-growth of any hair lost this past Northern winter.

iN ThE dEEp… ENd // lukE lENNOx

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insanity!

Gulmarg has 320 degrees of back country skiing from the top of the gondola at 4000masl with 1000 vertical meters of consistent steep pitches. this draws back-country skiers from all over the world. throw in a bunch of un-aware resort skiers, local ski guide operators and western ski guide operators, a late snow season and you have the perfect combination to witness the ‘human factor’ in all its glory.

despite community work by Gulmarg Snow Safety which includes: a daily backcountry avalanche advisory, running awareness evenings, and offering basic and aaa certified courses, the hunger for powder and the power of the human brain causes incidents like this to happen: 21 January 2012 was a day when the most luck i have seen was dished out in one serving. two avalanches occurred in the back country. the first one was a destructive size 4 then twenty minutes later a second one occurred, a size 3. Both were skier triggered and a total of five people were captured. my role in the rescue that followed was to interview the six groups involved and source any information that could lead to the need for further rescue planning and resources. in doing this task i got an insight into the decisions people made that day.

the examples of simple heuristic traps that appeared to blind people were these:

Scarcity: a late snow season forced pressure on people to get into the alpine region as soon as possible which happened as soon as the snow cover was sufficient.

Commitment: People had objectives to ski specific lines, a limited time to actually be in Gulmarg or worse, commercial pressure of guaranteed powder for clients.

Social proof: Guided parties followed each other (sucker tracks) into the same areas which may be the reason so many people (three involvements from two different) were caught in the second avalanche.

Expert Halo: this was obvious as clients followed their guides or bosses and handed their lives over to them literally as they entered a clearly dangerous environment.

even though people went for extraordinary rides and one victim was buried up to 15 minutes, no lives were lost. on this day, white ghost like faces showed that lessons were learned by some individuals but this example was not enough to stop the chaos.

throughout the rest of the season i was frequently amazed by the decisions people made/didn’t make while traveling in the back country. every pre and early season, personally i get fit to ski, read about snow pack histories, practice the latest slope test etc. Something i, and i suspect many people in the example above fail to do,

is we don’t learn about ourselves enough. our decisions and thought process in this environment are the factors that will keep us safe or kill us in the end.

persistant deep instabilities:

watching large avalanches gave me sleepless nights, seeing people caught in avalanches in the backcountry gave me sweaty palms and a racing pulse whenever i thought of it, but arriving on scene at a Sa triggered size 2 Pcr (Post control release) with poor visibility on terrain that was in my control route … made my heart stop and all my hair fall out!

in late february the 40cm of dh that formed all the way back in November had once again become a living nightmare.* every storm that we received, activated this layer which resulted in large avalanches and settlements in the back country. inside the ski area things were looking much better. explosives control work had caused avalanche results in most start zones and flushed the slopes clean of the dh layer. however, one area of snow was reluctant to move. a single skier had skied just next to the bomb crater made by the 1kg of power gel just one hour prior.

after placing charges and making informed decisions about this and all the other start zones on this control route, then having all my confidence pulled out from underneath me was worse than being caught in an avalanche myself. fortunately no one was caught.

my specific thoughts and the largest mistake i made was that throughout the season i had bombed this start zone many times and seen/felt the depth hoar layer settle, i had assumed that it had done enough to stabilize the slope. again from the learning perspective of this incident two main factors stand out for me:

1. Never trust a deep instability in a ski resort environment, bomb the snot out of them, use larger charges in all areas (including low down near staunch wall areas) of potential start zones. unfortunately, Gulmarg is located in a military occupied state 30km from the line of control with Pakistan and explosives resources are hard to come by. this season alone, a period of seven days went by after a storm when the alpine area was kept closed due to the unavailability of explosives. this problem has been mitigated for future seasons by the implementation of a commercial explosives program.

2. avalanches can never be 100% guaranteed not to happen. if they do happen, even in a ski resort, the best chance of being found alive by an organized rescue team is through a transceiver search which is why i always recommend everyone wears a transceiver at all times in avalanche terrain.

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i consider myself fortunate to experience and learn about less common situations. it’s valuable to learn from not only your own mistakes and experiences so i offer my accounts here and welcome feedback from others’ perspectives.

i was particularly lucky not to experience any fatalities this season as this concept terrifies me. But… as i share a common feeling with others is this industry, will quote Bruce tremper from his book Staying alive in avalanche terrain as a closing comment.

“I don’t think it’s possible to witness a huge natural event, especially a cataclysmic one, without having the experience change your life. Volcano watchers, tornado

chasers, eclipse junkies… they all saw their first one and nothing was the same anymore. The unspeakable power, the beauty, the horror and the insignificance of humanity in the face of it all. They/we spend the rest of their lives trying to find it again”.

referencesfor any information regarding the avalanche incidents listed above, or any other information on Gulmarg please visit www.gulmargsnowsafety.com

Bruce tremper, Staying alive in avalanche terrain

the guy on the door at delhi’s airport won’t let us in, it’s 5am and we were there to check in for our flight to Srinagar, ‘wrong airport’ he says. damn hotel taxi had taken us to the wrong place. taxi across delhi, check in, security check, pat downs, wait, wait some more, pat down, go to departure gate, load the bus, drive out onto tarmac, around the plane, and back into the arrival gate. what?? the flight is cancelled, get bags off conveyer belt, queue up again, re-book on another flight, then start process again........

welcome to india. But by later that evening we arrived into Gulmarg, blanketed in metres of snow, one or two fresh metres. later the next morning we are riding up the old clackety gondola, skis poking out through the roof, snowboard out the door, as the baskets aren’t big enough. the top stage is closed, ‘the ski patrol can’t get any explosives’ said tim casually. ‘we’ll get the heli to pick us up at the mid-station, -it’ll be good marketing.’ he wasn’t joking, 30 minutes later we had been dropped off at almost 4000m on the top of the mountain. we skied north, down into the trees, spaced like utah, up to our armpits in steep deep dry powder. almost 1000m later, with burning legs and smiles as wide as india’s poverty gap, we ski up to the helicopter and Jason drops us back at the mid-station. wow!!

from here we head out into what’s known as drang valley and ski 10-15kms down a massive gully to tangmarg township, eat a curry and taxi back up to Gulmarg. Nice welcome!!

a couple of days later i’m working for Kashmir heli-ski, leading a load of russians for a few heli-ski runs. we are dropped off at over 4000m, near the Pakistani border and the size of the avalanche paths hits me immediately (not to mention a slight feeling of being watched through a 303 rifle scope). thankfully there are lots of nice mellow 20-25 degree runs with champagne powder up to our knees. i am awestruck as we fly over Gulmarg’s big 1000-1500m plus vertical avalanche paths, big bowls funnelling down through tight gorges. Get this wrong and the avalanches would be so big it’d probably rip off your arms and legs!!

the snowpack in february is also a bit like utah’s. the sunny slopes seem to stabilise quite quickly, while the shady north facing slops take longer, and dry out at night, re-crystallise and get better and better quality snow to ski. in January, instabilities can linger, but the milder temperatures in february usually assist in stabilising the snowpack. like anywhere, wind can affect the snow and quickly load up the slopes with massive fetches. there is no rescue of any sorts, no matter how well insured you are, so it’s best to ski in a small group and look after each other.

when Bollywood comes a calling, who ya gonna call? heliski guide mark Sedon recounts his indian soap opera debut. mark is a wanaka based ifmGa guide, who this year, together with wife Jo, will run their 10th annual NZ mountain film festival (July 6th-11th) mountainfilm.net.nz, he also does cameo roles in front of the camera.

avalaNChES, pOwdEr aNd Curry... // mark SEdON

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the touring from the top of the gondola is amazing. But finding a safe passage down can be a challenge. Getting your route-finding right is critical, and even then you have to watch out for flying Swedes or russians who centre-punch the unstable bowls, 1000m high above your escape route. But there are some nice safe ridges, and once you get down a bit, perfectly spaced Paper trees and Pines.

then when it storms we hire a taxi and hit the Bararishi trees. it’s a 500m run below Gulmarg, through the trees, down to the road where you find your taxi and ride back up to the top again. when the taxi is full, you hold onto the spare tyre rack (usually empty) and get a tow back up on the un-gritted road. the taxis somehow manage to get oK traction, even with their one chain and it’s chaos with road jams, stuck taxis and deep snow.

three weeks pass quickly and before we knew it we were heading down to Srinigar for a night on a house boat and a long flight home...... But we’ll be back...…

the international classification for Seasonal Snow on the Ground for ‘rime’ states: ‘thin breakable crust forms on snow surface if process continues long enough.’ clearly the authors haven’t sat out a solid storm cycle on mt ruapehu, where the stuff builds up so thick, dense and fast, that it collapses brand new lift towers, encases your skis in 10 centimetres while you’re eating lunch, and that the ‘breakable crust’ is more like boiler plate ice.

i don’t know of many other ski areas that offer a job titled ‘de-icer’, with ice axe and crampons as standard equipment in the patrol pack. there is no doubt, that as far as NZ ski areas go, the North island takes the cake for riming. Powder is overrated... right?

when good rimes go bad – how to spot the good, the bad, and the ugly. while keeping one eye on any potential Graupel events, ryan focuses his other to oversee the Snow Safety for whakapapa Ski Patrol, New Zealand.

wiNTEr - TimE TO rimE // ryaN lEONg

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riming is a fairly common part of the winter (and sometimes summer) experience in the mountains of New Zealand. due to the geography of our country and the weather patterns that line us up, we get a fair amount of riming in all its forms.

as systems roll in from the surrounding sea, clouds bank up over the ranges, in some cases rising so fast that the droplets don’t get a chance to freeze onto a nucleus such as a dust particle, and remain in a liquid state, despite being below 0°c.

as these clouds move over the mountains, the super-cooled droplets freeze on contact with any surface or object, and that’s when we wind up with surface rime. as it continues to accumulate, it grows into the wind. this gives us a good indication of the history of the storm by using the direction and size of the rime as a guideline. the amount of rime depends heavily on both the strength of the wind and the density of the cloud.

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Left & above: Spot the chairlift – extreme riming on lift towers in Northern Sweden. Spooky rime monster about to swallow the editor.

Above: overnight rime ice build up, inconvenienced the running of this turoa chairlift in June 2010.

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Left: Get out your yeti sticks – a little, light turoa rime straight off the tasman. t-bar spring boxes slump to head height, weighed down with excess baggage.


the riming process also plays a fairly important role in affecting snowpack stability, both for the better and for the worse. the following are some of the good, and the bad sides of the riming process relative to snow stability.

The goods

riming of the snow’s surface can aid stability depending on the strength of the rime layer once deposited. a good ‘welded’ layer of rime ice will essentially cap the snowpack significantly reducing the likelihood of triggering weaknesses in the upper snowpack. this increase to stability is brought about not only by the bridging effect, but also by the rime layers tensile strength.

for example, a near surface storm snow weakness capped by a Knife – impenetrable hardness (think ruapehu) rime layer. in a compression test, this may fail in the easy range due to both the lack of strength and its proximity to the surface, and the stiffness of the rime layer on top may make the weakness exhibit increased propagation propensity.

however these observations and results do not take into account that the test column has been isolated at the back, and that the rime layer’s (and other subsequent layers) tensile strength is no longer part of the equation. whereas in reality, in this given situation you would confidently drive a cat down the middle of a start zone and nothing would be triggered.

on the other hand, the deeper the weakness, the more tensile stress there is in the slab above. So therefore, as the weakness depth increases, confidence in the stability aiding tensile strength of the solid rime layer decreases. it goes without saying that just because there is a good strong rime layer on the surface, we can’t forget about what is happening further down in the snowpack.

The bads

a layer of rime on the snow surface can easily become the perfect bed surface for an avalanche once it is buried, even more so the harder that layer is. it is not uncommon to have multiple avalanche events on it as it reloads during a storm cycle. often times the hardness difference between this rime layer and the overlying snow means a good bond cannot be achieved until a warmer weather system deposits relatively warm wet snow to glue it all in place. as is often more common in the ranges of the South island, a thinner softer rime will form providing a loose crumbly texture as the rime crystals grow into the wind. as well as providing the bed surface, these more fragile rime crystals can also provide the weak layer, and are often characterised by large irregular crystals, with poor bonds, and large pore spaces to facilitate constructive metamorphism.

as with other buried ice layers, a buried rime ice layer will exaggerate the temperature gradient immediately above and below it, opening the door for a potentially nasty facet/crust combo. in addition to this, a buried rime layer also has the potential to cause problems in spring as things warm up. free water introduced to the snowpack by either melt or rain can pool and run along these layers, creating a well lubricated bed surface for the overlying snowpack.

riming can also occur on snow crystals as they form and are moved through turbulent air before falling to the ground. this can range from lightly rimed precipitation particles, through to graupel. aside from peeling off layers of exposed skin, as it pelts down (or sideways) at you, and providing some unique skiing conditions when in deep drifts (our version of powder), there are various forecasting considerations around graupel.

it exhibits very low cohesion, has relatively large pore spaces between grains, and a low amount of bonds per unit volume. this tends to make the sintering process slower than other types of precipitation particles. all of this combines to create a substantial weak layer once buried.

Quite possibly the crux of dealing with a buried graupel layer is figuring out its spatial distribution. due to its low cohesion and spherical shape it has a lower angle of repose than most other forms and tends to run down steep slopes and pool in areas such as depressions, at the base of rock bands, in gullies and similar terrain features. vary rarely does it accumulate uniformly. hunting down these pockets of graupel once buried (or ideally before they are buried) is key, as they can provide good trigger points for slabs which can then propagate into areas where these layers do not exist.

rime may not be the most enjoyable substance in the mountains, but it does provide some interesting challenges and benefits in terms of snow safety, and is always worth keeping a good eye on.

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crystal ball issue 21 vol june 2012

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