Periglacial Process and Periglacial Process and LandformsLandforms

Permafrost distribution in the Arctic

high latitudes

Periglacial (tundra) Periglacial (tundra) environmentsenvironments

Arctic tundraArctic tundra Alpine tundraAlpine tundra

PermafrostPermafrost

Perennially frozen ground that remains at or Perennially frozen ground that remains at or below 0 C (32 F) for two or more years below 0 C (32 F) for two or more years

Forms in regions where the mean annual Forms in regions where the mean annual temperature is colder than 0 C temperature is colder than 0 C

Permafrost underlies about 20% of the land Permafrost underlies about 20% of the land in the Northern Hemispherein the Northern Hemisphere also common within the Arctic Ocean’s also common within the Arctic Ocean’s

continental shelves and in parts of Antarctica continental shelves and in parts of Antarctica Most of the world’s permafrost has been Most of the world’s permafrost has been

frozen for millennia and can be up to 5,000 frozen for millennia and can be up to 5,000 ft thick. ft thick.

Active Layer vs Permafrost: Active Layer vs Permafrost: Thermal StateThermal State

““Active layer”: “thermal boundary Active layer”: “thermal boundary layer”; near surface, seasonally layer”; near surface, seasonally thawedthawed Depth at which annual max temp = 0CDepth at which annual max temp = 0C Water content, soil strength, and bulk Water content, soil strength, and bulk

density of soil change dramaticallydensity of soil change dramatically Produces patterned ground/solifluctionProduces patterned ground/solifluction Drives hydrology of periglacial Drives hydrology of periglacial

landscapeslandscapes Perenially frozen ground: permafrostPerenially frozen ground: permafrost

Material at < 0C for 2 yrs or moreMaterial at < 0C for 2 yrs or more Sub-freezing thermal stateSub-freezing thermal state

Temperature ProfileTemperature Profile Base of active layer = Base of active layer =

depth where Tmax = depth where Tmax = 0C0C

Below active layer, Below active layer, mean annual temp mean annual temp increases (geothermal increases (geothermal gradient) to 0Cgradient) to 0C

This is the base of This is the base of permafrostpermafrost

Thickness of permafrost Thickness of permafrost most strongly most strongly controlled by mean controlled by mean annual surface tempannual surface temp

As mean annual surface temp decreases, permafrost deepens, active layer thins

What sets the depth of the What sets the depth of the active layer?active layer?

T (z, t) Ts Q

kz Tamp exp

zz *

sin2tP

z

z *

Temp (depth, time)Thermal behaviorOf Periglacial Landscapes

Oscillation of temp about the meanOscillations decrease with depthTime lag of oscillations

geothermal heat flow

Mean annual surface temp

depth scale = f(thermal diffusivity, period) ~ 3m.

annual temp swings (Tamp) falls off exponentially with depth

at a depth of z*, the amplitude or temp swing is 1/3 of that at the surface

Ground Ground temperaturestemperatures

Mean T increases Mean T increases with depthwith depth

PermafrostPermafrost Active layer toActive layer to Base of p’frostBase of p’frost

SeasonalSeasonal Geomorphic workGeomorphic work

Active layerActive layer Above ZAAAbove ZAA

25C/km = .025C/m

Depth of the active layerDepth of the active layer

Solve for depthSolve for depth zactive z * ln TsTamp

Z*=depth scale z* P

P=period of oscillation, 1 yrthermal diffusivity of regolith, 1mm2/sZ* ~ 3m

If Tamp < mean surface temp, active layer depth = 0That means it’s frozen all the time, all permafrost

Below the active layer…Below the active layer…

There is no liquid water There is no liquid water so heat moves by so heat moves by conduction,conduction, Q=-k(dT/dz)Q=-k(dT/dz) Why do model and data Why do model and data

vary near surface?vary near surface? Variation in k with depth?Variation in k with depth? Msmts say noMsmts say no Long-term Arctic warmingLong-term Arctic warming

T Ts Q

kz

Lachenbruch and Marshall, 1986

Single borehole at E. Teshekpuk Lake, AK70 degrees latitudeClow, 2008

Types of IceTypes of Ice

PorePore Frozen in interstitial space between Frozen in interstitial space between

particlesparticles SegregationSegregation

Lenses of ice in fine grained sediment, Lenses of ice in fine grained sediment, commonly parallel to ground surfacecommonly parallel to ground surface

Ice content can exceed porosityIce content can exceed porosity Massive ground iceMassive ground ice

Frost HeaveFrost Heave Water migrates through fine Water migrates through fine

grained (silty) material to grained (silty) material to lenses of ice (segregation ice)lenses of ice (segregation ice) Even against gravity (capillary Even against gravity (capillary

action)action) Ice lenses redistribute moistureIce lenses redistribute moisture As lenses grow, they deform As lenses grow, they deform

soil and lift ground surfacesoil and lift ground surface Frost heaveFrost heave

Slower rates of freezing allow Slower rates of freezing allow for more time for water for more time for water migrationmigration

Amount of heave = f(water Amount of heave = f(water content, soil texture, rate of content, soil texture, rate of freezing)freezing)

Upfreezing of stonesUpfreezing of stones

Frost heave is the process that Frost heave is the process that enables upward transport of stones enables upward transport of stones to the ground surfaceto the ground surface Upfreezing or frost-jackingUpfreezing or frost-jacking

Sorting occurs due to long-term Sorting occurs due to long-term effects of upfreezing on unsorted effects of upfreezing on unsorted mixed grain size sedimentsmixed grain size sediments

Frost pullFrost pull

Clast adhered to froz soil

Void beneath clast fills upon thaw

Clast moves up with frost heaving soil

Requires frost susceptible soil with scattered large stones

Patterned groundPatterned ground Geometric or Geometric or

repeated patterns on repeated patterns on the ground surfacethe ground surface Sorting, variations in Sorting, variations in

vegetation, vegetation, microtopographymicrotopography

Seasonal heaving of Seasonal heaving of the active layer and the active layer and radial surface motionradial surface motion

Controlled by depth Controlled by depth of active layerof active layer

Sorted circles: self organized

Yipes – stripes!Yipes – stripes!

Boxes A and B: Lateral sorting

Boxes A, C, and D: Lateral squeezing and confinement

Lateral frost heave

Vertical frost heave

Stones creep to stonesSoil moves toward deeper soil

Areas of concentrated stones uplift by lateral sqeezingStones avalanche off sides and move along stone axis Kessler and Lerner, 2003

Self organizationSelf organization

“nonlinear, dissipative interactions among the small- and fastscale constituents of a system give rise to order at larger spatial and longer temporal scales” (Kessler and Lerner, 2003)

Ice Wedge PolygonsIce Wedge Polygons

Tapering vertical Tapering vertical wedges of icewedges of ice

Grow by repeated Grow by repeated thermal contraction thermal contraction cracking of frozen cracking of frozen groundground

Ice growth in the Ice growth in the cracks from summer cracks from summer meltwatermeltwater

Thermal contraction produces horiz. tensile stress

Tensile stress > tensile strength of froz ground: Crack

Crack propagates downward

Fills with snow, water, and freezes

Fossil Frost Fossil Frost WedgesWedges

Big Horn BasinBig Horn Basin Pipeline trenchPipeline trench

Preglacial soil

Bkb (caliche)

Cover sand (eolian)?

Polygon GeometryPolygon Geometry

A crack relieves stresses that A crack relieves stresses that led to its formation (normal led to its formation (normal to the crack)to the crack)

Remaining stress is || to the Remaining stress is || to the crackcrack

New cracks intersect New cracks intersect perpendicular to crackperpendicular to crack

““cracks nucleate in random cracks nucleate in random directions, but intersect one directions, but intersect one another at right angles”another at right angles” Random orthogonal networksRandom orthogonal networks

Scale of cracks related to Scale of cracks related to depth of crackdepth of crack

Alpine Felsenmeer (CO Front Range)Alpine Felsenmeer (CO Front Range)

Making Felsenmeer (out of ice cubes and a Hershey bar)Making Felsenmeer (out of ice cubes and a Hershey bar) http://www.sciencefriday.com/videos/watch/10299http://www.sciencefriday.com/videos/watch/10299

SolifluctionSolifluction Lobate features produced Lobate features produced

by slow creep assoc. with by slow creep assoc. with frost actionfrost action

Fronted by rocks or rolls of Fronted by rocks or rolls of tundra vegetationtundra vegetation

Can occur in “sheets” on Can occur in “sheets” on low gradient slopeslow gradient slopes

Often in hillslope Often in hillslope hollows/concavities where hollows/concavities where flowlines convergeflowlines converge

Higher moisture content Higher moisture content than surrounding ground, than surrounding ground, denser vegetationdenser vegetation

http://http://pyrn.ways.org/cryoplanationpyrn.ways.org/cryoplanation-terrace-terrace

Soli-/GelifluctionSoli-/Gelifluction

Planview map of solifluction lobe, NE Greenland

ExampleExamples: soli-s: soli-fluctionfluction

Cryoplanation?

step- or table like residual landforms consisting of a nearly horizontal step- or table like residual landforms consisting of a nearly horizontal bedrock surface covered by a thin veneer of rock debris, produced bedrock surface covered by a thin veneer of rock debris, produced

by frost actionby frost action

production of an erosional surface by freeze-thaw and other periglacial processes

Stone lobesStone lobes

Block streamsBlock streams

PingosPingos Conical moundConical mound Cored by massive iceCored by massive ice Height: 1-10 m., Dia.: Height: 1-10 m., Dia.:

50-150 m.50-150 m. Require permafrostRequire permafrost Often found on the bed Often found on the bed

of drained lakesof drained lakes Closed system pingoClosed system pingo

Water derived from talik Water derived from talik (localized unfrozen (localized unfrozen ground)ground)

Open system pingoOpen system pingo Water derived from Water derived from

groundwatergroundwater

How to make a pingoHow to make a pingo

Step 1: Lake drainsStep 1: Lake drains Step 2: Ice Step 2: Ice

segregation by segregation by pore water pore water movement into movement into taliktalik

Step 3: Ice grows Step 3: Ice grows from top; fed by from top; fed by talik watertalik water

““Hydrolaccoliths”Hydrolaccoliths”

3

42

max

1

16

3

ET

RgTPW bw

Periglacial Landforms in Google Periglacial Landforms in Google EarthEarth

Arctic coastal plain, Point Barrow, AKArctic coastal plain, Point Barrow, AK Kings Hill, IDKings Hill, ID Northwest Territories, CanadaNorthwest Territories, Canada