Periglacial Process and Landforms

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Periglacial Process and Landforms
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Permafrost distribution in the Arctic
high latitudes
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(No Transcript)
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Periglacial (tundra) environments

• Alpine tundra

• Arctic tundra

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Permafrost

• 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
• also common within the Arctic Oceans continental
  shelves and in parts of Antarctica
• Most of the worlds permafrost has been frozen
  for millennia and can be up to 5,000 ft thick.

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Active Layer vs Permafrost Thermal State

• Active layer thermal boundary layer near
  surface, seasonally thawed
• 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
• Material at lt 0C for 2 yrs or more
• Sub-freezing thermal state

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Temperature Profile

• 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
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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
depth scale f(thermal diffusivity, period) 3m.
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Ground temperatures

• Mean T increases with depth
• Permafrost
• Active layer to
• Base of pfrost
• Seasonal
• Geomorphic work
• Active layer
• Above ZAA

25C/km .025C/m
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Depth of the active layer

• Solve for depth

Zdepth scale
Pperiod of oscillation, 1 yr kthermal
diffusivity of regolith, 1mm2/s Z 3m
If Tamp lt mean surface temp, active layer depth
0 That means its frozen all the time, all
permafrost
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Below the active layer

• There is no liquid water so heat moves by
  conduction,
• Q-k(dT/dz)
• Why do model and data vary near surface?
• Variation in k with depth?
• Msmts say no
• Long-term Arctic warming

Lachenbruch and Marshall, 1986
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Types of Ice

• Pore
• Frozen in interstitial space between particles
• Segregation
• Lenses of ice in fine grained sediment, commonly
  parallel to ground surface
• Ice content can exceed porosity
• Massive ground ice

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Frost Heave

• Water migrates through fine grained (silty)
  material to lenses of ice (segregation ice)
• Even against gravity (capillary action)
• Ice lenses redistribute moisture
• As lenses grow, they deform soil and lift ground
  surface
• Frost heave
• Slower rates of freezing allow for more time for
  water migration
• Amount of heave f(water content, soil texture,
  rate of freezing)

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Upfreezing of stones

• Frost heave is the process that enables upward
  transport of stones to the ground surface
• Upfreezing or frost-jacking
• Sorting occurs due to long-term effects of
  upfreezing on unsorted mixed grain size sediments

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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
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Patterned ground

• Geometric or repeated patterns on the ground
  surface
• 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
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Yipes stripes!
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Boxes A and B Lateral sorting Boxes A, C, and
D Lateral squeezing and confinement
Stones creep to stones Soil moves toward deeper
soil
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
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Self 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)

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Ice Wedge Polygons

• Tapering vertical wedges of ice
• Grow by repeated thermal contraction cracking of
  frozen ground
• Ice growth in the cracks from summer meltwater

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Thermal contraction produces horiz. tensile
stress Tensile stress gt tensile strength of froz
ground Crack Crack propagates downward Fills
with snow, water, and freezes
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Fossil Frost Wedges
Cover sand (eolian)?

• Big Horn Basin
• Pipeline trench

Bkb (caliche)
Preglacial soil
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Polygon Geometry

• 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
• Random orthogonal networks
• Scale of cracks related to depth of crack

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Alpine Felsenmeer (CO Front Range)

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

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Solifluction

• 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/cryoplanation-terrace

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Soli-/Gelifluction
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Planview map of solifluction lobe, NE Greenland
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Examples soli-fluction
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

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Stone lobes
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Block streams
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Pingos

• Conical mound
• Cored by massive ice
• Height 1-10 m., Dia. 50-150 m.
• Require permafrost
• Often found on the bed of drained lakes
• Closed system pingo
• Water derived from talik (localized unfrozen
  ground)
• Open system pingo
• Water derived from groundwater

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How to make a pingo

• Step 1 Lake drains
• Step 2 Ice segregation by pore water movement
  into talik
• Step 3 Ice grows from top fed by talik water

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Hydrolaccoliths
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Periglacial Landforms in Google Earth

• Arctic coastal plain, Point Barrow, AK
• Kings Hill, ID
• Northwest Territories, Canada