Periglacial Process and
Landforms
Permafrost distribution
in the Arctic
high latitudes
Periglacial (tundra) environments
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Arctic tundra
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Alpine tundra
Permafrost
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Perennially frozen ground that remains at or
below 0 C (32 F) for two or more years
Forms in regions where the mean annual
temperature is colder than 0 C
Permafrost underlies about 20% of the land in
the Northern Hemisphere
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also common within the Arctic Ocean’s continental
shelves and in parts of Antarctica
Most of the world’s permafrost has been frozen
for millennia and can be up to 5,000 ft thick.
Active Layer vs Permafrost:
Thermal State
“Active layer”: “thermal boundary layer”;
near surface, seasonally thawed
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Depth at which annual max temp = 0C
Water content, soil strength, and bulk
density of soil change dramatically
Produces patterned ground/solifluction
Drives hydrology of periglacial landscapes
Perenially frozen ground: permafrost
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Material at < 0C for 2 yrs or more
Sub-freezing thermal state
Temperature Profile
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Base of active layer =
depth where Tmax = 0C
Below active layer, mean
annual temp increases
(geothermal gradient) to
0C
This is the base of
permafrost
Thickness of permafrost
most strongly controlled
by mean annual surface
temp
As mean annual surface temp decreases,
permafrost deepens, active layer thins
What sets the depth of the active
layer?
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
Mean annual surface temp
Q
z 
 z   2 t
T (z,t)  Ts  z  Tamp exp   sin 
 
 z *  P
k
z *
Temp (depth, time)
geothermal heat flow
Thermal behavior
Of Periglacial Landscapes
Oscillation of temp about the mean
Oscillations decrease with depth
Time lag of oscillations
depth scale = f(thermal diffusivity, period) ~ 3m.
Ground
temperatures
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Mean T increases
with depth
Permafrost
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Active layer to
Base of p’frost
Seasonal
Geomorphic work
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Active layer
Above ZAA
25C/km = .025C/m
Depth of the active layer
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Solve for depth
zactive
 Ts 
 z * ln 

T
 amp 
Z*=depth scale
P
z* 

P=period of oscillation, 1 yr
thermal diffusivity of regolith, 1mm2/s
Z* ~ 3m
If Tamp < mean surface temp, active layer depth = 0
That means it’s frozen all the time, all permafrost
Below the active layer…
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There is no liquid water so
heat moves by conduction,
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Q=-k(dT/dz)
Why do model and data vary
near surface?
Variation in k with depth?
Single borehole at E. Teshekpuk Lake, AK
Msmts
say no
70 degrees latitude
Clow, 2008 Arctic warming
Long-term
Q
T  Ts  z
k
Lachenbruch and Marshall, 1986
Types of Ice
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Pore
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Segregation
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Frozen in interstitial space between particles
Lenses of ice in fine grained sediment,
commonly parallel to ground surface
Ice content can exceed porosity
Massive ground ice
Frost Heave
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Water migrates through fine
grained (silty) material to lenses of
ice (segregation ice)
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Ice lenses redistribute moisture
As lenses grow, they deform soil
and lift ground surface
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Even against gravity (capillary action)
Frost heave
Slower rates of freezing allow for
more time for water migration
Amount of heave = f(water
content, soil texture, rate of
freezing)
Upfreezing of stones
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Frost heave is the process that enables
upward transport of stones to the ground
surface
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Upfreezing or frost-jacking
Sorting occurs due to long-term effects of
upfreezing on unsorted mixed grain size
sediments
Frost pull
Clast moves up with frost heaving soil
Clast adhered to
froz soil
Void beneath clast fills upon thaw
Requires frost susceptible soil with scattered large stones
Patterned ground
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Geometric or repeated
patterns on the
ground surface
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Sorting, variations in
vegetation,
microtopography
Seasonal heaving of
the active layer and
radial surface motion
Controlled by depth of
active layer
Sorted circles: self organized
Yipes – stripes!
Boxes A and B: Lateral sorting
Stones creep to stones
Soil moves toward deeper soil
Boxes A, C, and D: Lateral squeezing and
confinement
Vertical frost heave
Lateral frost heave
Areas of concentrated stones uplift by lateral sqeezing
Stones avalanche off sides and move along stone axis
Kessler and Lerner, 2003
Self organization
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“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 Polygons
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Tapering vertical wedges
of ice
Grow by repeated
thermal contraction
cracking of frozen
ground
Ice growth in the cracks
from summer meltwater
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
Wedges
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Cover sand (eolian)?
Big Horn Basin
Pipeline trench
Bkb (caliche)
Preglacial soil
Polygon Geometry
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A crack relieves stresses that led
to its formation (normal to the
crack)
Remaining stress is || to the
crack
New cracks intersect
perpendicular to crack
“cracks nucleate in random
directions, but intersect one
another at right angles”
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Random orthogonal networks
Scale of cracks related to depth
of crack
Alpine Felsenmeer (CO Front Range)
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Making Felsenmeer (out of ice cubes and a Hershey bar)
http://www.sciencefriday.com/videos/watch/10299
Solifluction
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Lobate features produced
by slow creep assoc. with
frost action
Fronted by rocks or rolls
of tundra vegetation
Can occur in “sheets” on
low gradient slopes
Often in hillslope
hollows/concavities where
flowlines converge
Higher moisture content
than surrounding ground,
denser vegetation
http://pyrn.ways.org/cryoplanatio
n-terrace
Soli-/Gelifluction
Planview map of solifluction lobe, NE Greenland
Examples:
solifluction
Cryoplanation?
production of an erosional surface by freeze-thaw and other periglacial processes
step- or table like residual landforms consisting of a nearly horizontal bedrock
surface covered by a thin veneer of rock debris, produced by frost action
Stone lobes
Block streams
Pingos
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Conical mound
Cored by massive ice
Height: 1-10 m., Dia.: 50150 m.
Require permafrost
Often found on the bed of
drained lakes
Closed system pingo
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Water derived from talik
(localized unfrozen ground)
Open system pingo
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Water derived from
groundwater
How to make a pingo
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Step 1: Lake drains
Step 2: Ice
segregation by pore
water movement into
talik
Step 3: Ice grows
from top; fed by talik
water
“Hydrolaccoliths”
Wmax
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3 Pw  b gT  1  R

16
ET 3
2
4
Periglacial Landforms in Google
Earth
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Arctic coastal plain, Point Barrow, AK
Kings Hill, ID
Northwest Territories, Canada