METHODOLOGY

METHODOWGY

Since 2002, annual surface mass balance measurements have been carried out on

Chhota Shigri Glacier at the end of the ablation season i.e. end of September or

beginning of October. The direct glaciological method is used here (Paterson, 1994 ), an

insitu method that is more accurate and widely accepted throughout the world. Also

exsitu method, Equilibrium Line Altitude (ELA) and Accumulation Area ratio (AAR)

method is used in this study, that includes satellite imagery and GIS tool to calculate

the mass balance of a glacier.

4.1 Glaciological Method

The direct glaciological method provides information on mass changes for several

locations on the glacier surface which is extrapolated to the total area of the glacier.

The changes in the mass were known by the stake network. The net

accumulation/ablation data from each stake measurement within a time interval of one

year was recorded. The difference in level (accumulation/ablation) was multiplied by

the near surface density which yielded an estimate of the mass balance of that point.

Changes in the levels were measured in a variety of ways, including stakes drilled into

the glacier in the ablation zone and snow depth relative to a known stratigraphic surface

(e.g. previous summer surface) by means of snow pit in the ablation zone. Density

value for the ice was assumed constant at 900 kg m·3• Snow density was measured in

snow pits, which was dug down to a reference surface. Density was also measured from

cores taken with a drill or a cylinder of known volume.

Glaciological method includes different steps, here's an attempt to describe each and

every step one by one.

4.1.1 Creating Stake Network

In order to know the ablation and accumulation of the glacier a network of 14 stakes at

different altitude ranging from 4932 m to 4981 m were placed through out the glacier in

2002 which was further raised to 26 in 2006 to monitor the glacier more efficiently.

The stake network was created in such a manner the each stake was representative of

that part where it was installed.

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METHODOWGY

Stake Type

In the present study bamboo stakes are used because it is light, durable, cost efficient

and easily available in country like India. The stakes may be of different materials such

as steel, aluminium, PVC and wood or bamboo, but wooden stakes are considered to be

the most reliable (Fig.4.1 ). Metallic stakes if left unsupported then it can cause errors

by "self drilling" due to solar heating.

Stake Location

The ablation pattern is much more uniform as compared to the accumulation and thus

point measurements can be representative over large areas keeping this in mind, the

stakes were installed along the centre line of the glacier at suitable intervals, some of

the stakes were placed transversely to the central longitudinal axis in order to monitor

the difference in accumulation pattern resulting due to wind distribution, shading or due

to avalanching. The stakes were installed more in the ablation zone in order to calculate

the rate of ablation more precisely. Each stake was installed in such a manner that it

represented that part of the glacier well, where it stands (Fig. 4.2). Finally the exact

position of the installed stake on the glacier surface was known by using differential

GPS ( Ashtech Pro Mark II).

:: ~ 200 t ! 150

~ 50 c. <

- -t:-.

- -0-.

---0---

- -·-.

PLASTIC

WOOD

ALUMINIUM

STEEL TRUE W.eq

----------.....

-.

; 100 lr

0 ~------~~--------~~------~~--------~ 125 150 175 200 225

JULIAN DAY 1990

Fig.4. 1: Effect of stake type on measured ablation; wooden poles are the most reliable as

compared to steel, plastic and aluminium poles. {Ostrem and Brugman, 1991)

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(a) (b) (c)

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METHODOLOGY

Fig.4.2: Distribution of stake network throughout the glacier.

Fig.4.3: Different methods for joining two individual stakes (a) By rubber hose (b) By clamp (c) By metallic wire.

METHODOLOGY

Plate 4.1: Measurement of installed stake position on the Chhota Shigri Glacier, using

differential GPS

Plate 4.2: Installation of ablation stake on the ablation zone of the Chhota Shigri Glacier

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METHODOLOGY

Numbering system

To easily identify each stake, it is necessary to have a logical system of numbering.

Tropical glaciers throughout the world generally show ablation ranging from few

meters to several meters during the ablation season. In order to know the ablation on

the Chhota Shigri glacier several stakes of 1.8 - 2 meters were attached to form a chain

of stakes of 10 to 12 meters in length. The stakes of different year were marked

differently (apart from the number of the individual set of stakes) .In 2002 and 2003 no

markings were done, in 2004 all the stake pieces at its neck were marked my engraving

a ring above the stake number, in 2005 two rings were engraved, in 2006 three rings

were engraved and in 2007 again no rings were engraved. This was done in order to

differentiate two different stakes of same number but of different years.

A particular stake consisted of several independent pieces and each set of stake was

numbered in a logical manper. Each piece was engraved with symbols at its neck using

a hacksaw blade like I II III 1111 IIIli etc which represented stake piece number 1, 2, 3,

4, 5 respectively. Each set of stakes throughout the glacier were numbered using roman

digits as I II Ill IV V ...... XXIV etc.

The installation of the bamboo stakes were done by putting the segment I at the bottom

and the rest in ascending order from bottom to top i.e. II III 1111 IIIII etc. Adjacent

segments of a stake were tied together with the help of an iron wire drawn through

holes drilled at the end of each piece (Fig.4.3). The wire was so tied as to make easy

fall-out of the upper stake avoiding any breakage (Fig.4.4 ). The numbering of the

segments was done with the help of a hacksaw blade as I, II, III, 1111 and IIIII at the top

end of each piece. For more clarity a pictorial presentation of one of the installed stake

is shown in figure (Fig.4.5).

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SNOW SURFACE

rings for 2006 Stake number P ieee number

SNOW SURFACE

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METHODOLOGY

Fig.4.4: Pieces of stake falls freely during the ablation season.

Fig.4.5: Example of stake no IX that was installed in 2006.

METHODOLOGY

Technique for Inserting Stakes

The stakes should be inserted vertically in the glacier. The technique used for this

depends on the kind of surface where the stake is located. In general there are two

different ways of inserting stakes (Ostrem and Brugman, 1991).

1. In the firn area a stake could simply be pushed into the snow or fim, but recent

investigations have shown that such stake tends to sink into the glacier during

the melt season. Therefore, the stak~s must be supported at their lower ends to

prevent such sinking. Details of the procedure are given below.

2. In the ablation area the stake should be placed in a narrow hole drilled with an

ice drill (hand- or motor operated mechanical drill) or a hot point.

In this study a light portable steam driven ice drill suitable for drilling holes in ice and

firn (Heucke, E., 1999) was used (Fig.4.6). The working pressure of this drill is

between 0.7 and 0.17 bar. The boiler capacity is 4.4L, which can make approximately

one hour of drilling possible. This means that a hole of 12m in depth can be drilled in

ice or 25m deep in firn without interruption. This steam drill was used successfully for

drilling stakes in ablation as well as in accumulation zone in the present work.

Before drilling, the steam drill is prepared by filling water in the boiler and by

connecting the hosepipe. The boiler is allowed to heat up till the pressure reaches 2

bars. The drilling pipe is held perpendicular to the snow surface (to avoid the tilting of

the hole) and the vapour valve is released is order to start drilling. When the desired

depth is acquired, the drilling pipe is pulled out and the pre-connected numbered stakes

are put into the hole and is fixed properly using some stone chips and pebbles in the

gap (if it persists) between the drilled hole diameter and the bamboo stake.

While drilling was in progress, sometimes the drilling pipe failed to penetrate for more

than five minutes, or sometimes the drilling pipe descended suddenly, this was due to

boulder or crevassed area, which lied underneath respectively. In both the cases, the

drilling points were changed.

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filler cap with safety valve

bowl for prwrannlng of water tor next drillng operation and cartridge containers

METHODOLOGY

Fig. 4.6: Diagram of the portable steam driven drill designed by Heucke.

Replacement of old Stake

If it is necessary to replace a stake which has disappeared or where there is possibility

that it will disappear in the next ablation season, new stakes were inserted as close as

possible to the "original" stake position that existed in the last ablation season.

Generally it was found that the annual shift of the stake was between 30 to 45 meters,

so new stakes were inserted 30 to 45 meters above the old stakes. In the ablation zone

the newly inserted stake where exposed not more than Y2 meter.

Stake Extension

In the accumulation zone where the rate of accumulation was more than the rate of

ablation, the stakes that were inserted were further extended using another long stake;

this was done in order to know the accumulation at that point in the coming year.

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- -- ~

(a)

(b)

Plate 4.3 (a) & (b): Heucke steam drill, used for drilling on the Chhota Shigri glacier in this

study.

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... '-.

METHODOLOGY

Plate 4.4: Extended accumulation stake on the accumulation zone of the Chhota Shigri

Glacier

1:55PM

Plate 4.5: Stake No. III on the Chhota Shigri Glacier

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METHODOLOGY

Relocating the buried stake in the accumulation zone

In order to locate the buried stakes, microwave reflector system was used which include

two units: the detector which is a directional radio transmitter/ receiver, and a small

reflector tag. The reflector tag reflects the radio wave to the detector but at a double

frequency (Ostrem and Brugman, 1991). Thus the exact positions of the stakes were

known .All the accumulation stakes were tied with recco reflectors tags, exactly at the

snow surface. Apart from the Recco reflector tag, some blue power was also sprayed

around the foot of the accumulation stakes, this blue powder facilitated easy

identification of last year surface in form of thin blue line while digging snow pit for

accumulation measurement.

4.1.2 Accumulation measurement

In the accumulation area of Chhota Shigri glacier at altitudes more than 5300 m the

amount of accumulation was calculated in terms of water equivalent by measuring the

snow depth and by applying a snow density factor at each measuring point.

Snow Depth

Snow depths were calculated at every stake (if present) with the help of aluminium

snow probe. At every stake 5 to 6 measurements were taken around each new and old

stake, finally the average of snow depth was taken.

Pit Studies

Several pits were dug in the accumulation area. The pit was dug in such a manner that

the overlying snow cover was undisturbed. The snow pit was made down stream or on

the side of stake where the snow was present. The pits were made in order to know the

yearly accumulation by carefully studying the stratigraphy of the pit wall and by

identifying the last summer layer in form of dirty ice layer or in form of blue line, if

blue powder was used.

In order to calculate the snow density steel cylinder of 20.5 em length and 5.64 em of

inner diameter was used. Steel cylinder was kept slightly outside the periphery of the

pit. It was slightly tapped, if required, with the help of a wooden hammer until the

upper end of the cylinder touched the snow surface. Cylinder was then taken out

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METHODOLOGY

carefully with the help of a hand held flat shovel from the sidewalls of the pit. While

taking out the cylinder the snow was neither compressed nor was it allowed to escape

in order to avoid the errors in snow density measurement. The extra snow that leaped

over the cylinder was carefully scraped off with the shovel.

The snow samples thus collected were transferred into a pre- weighted plastic bag hung

through a sensitive spring balance. The whole snow was transferred into the sampling

bag by slightly tapping the steel cylinder with the wooden hammer.

While weighing the snow sample in the field the spring balance was kept away from

the direct influence of wind, so as to avoid the errors in the measurement. The final

reading gave the mass of the snow. Finally the density of snow was calculated by

known volume and known mass.

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METHODOLOGY

..

Plate 4.6: Density measurements on the Chhota Shigri Glacier

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4.1.3 Ablation Measurement

Reading of stakes

Free end to ice:

Free end to ice was measured by adding the exposed portion of the stake and the snow

depth.

Free end to snow:

Free end to snow was measured by measuring the exposed part of the stake i.e. the free

end to the surface. While taking this one thing was kept in mind, the ice cover should

not be disturbed.

Ablation:

For ablation measurements at a particular stake, the free end to ice (FE*) was measured

at the end of the ablation season (t2). The current value thus obtained was subtracted

from the last years FE*value (t1) of the same stake. The surface change thus obtained

by the difference between the free ends to ice (i.e. FE* on t2- FE* on t1) on tz. gave the

net ice ablation at that point.

4.1.4 Mass balance Calculation:

The over all specific mass balance, bn, is calculated according to:

bn= lib; ( s;/ S) (in m w .e.), (1)

Where b; is the mass balance of the altitudinal range, i , of map area s; and S is the total

glacier map area. For each altitudinal range, b;, is obtained from the corresponding

stake readings or net accumulation measurements.

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METHODOLOGY

4.2 Remote Sensing Method

Apart from the field methods remote sensing method can be also used for calculating

the mass balance of the glacier. Field methods need extensive field investigations, and

due to the rugged terrain of the Himalaya, they can provide mass balance of few

glaciers. In order to obtain the mass balance of large number of glaciers, accumulation

area ratio (AAR) method can be used (Kulkarni et. al., 2004). AAR is the ratio between

accumulation area and total glacier area (Meier and Post, 1962). In temperate glaciers,

the extent of superimposed - ice zone in insignificant and therefore, the equilibrium

line coincides with the snow line (Paterson, 1998). Snow line at the end of the ablation

season and AAR can be estimated using remote sensing method (Kulkarni, 1992;

Braithwaite, 1984 ).

In order to calculate the mass balance of the glaciers in the Lahaul and Spiti valley, the

relationship between the AAR and mass balance was developed using the field mass

balance data of the Chhota Shigri glacier at the end of the ablation season in the month

of September.

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