PeriglacialPermafrost

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Periglacial/Permafrost
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Periglacial (tundra) environments

• Alpine tundra

• Arctic tundra

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Treeline
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Permafrost distribution

• Continuous
• -6C MAAT isotherm
• Discontinuous
• Note bed of Greenland Ice
• Sporadic
• Mountains

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The periglacial environment

• Air temperature lt-6C
• Albedo follows cycle affects surface T
• Snow cover drives albedo
• Result surface and subsurface temps!

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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

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Local distribution

• Absent beneath water
• Absent beneath forest
• Present beneath moss - hummocks

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Processes of the Active Layer

• Short summer season!
• Saturation
• Dessication
• Dehydration
• Frost tables

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Needle Ice
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Freeze-thaw cycles

• Weathering
• Frequency
• Intensity
• Maximum
• Mountains
• South!
• Minimum
• North
• W. coast

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Alpine Felsenmeer(CO Front Range)
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Frost Sorting

• Ubiquitous!
• Stone walls fences
• Multiple explanations
• Frost table penetration

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Frost Sorting
X
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Frost Sorting

• Ubiquitous!
• Stone walls fences
• Multiple explanations
• Frost table penetration
• Selective crystal growth
• Heat transfer through rock allows nucleation at
  base
• Once nucleated, crystals grow vertically
• Stones are Jacked up!

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Frost Sorting

• Ubiquitous!
• Stone walls fences
• Multiple explanations
• Frost table penetration
• Selective crystal growth
• Rapid process!

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Tombstones
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Patterned Ground

• Frost wedging (after Lachenbruch, 1960)
• Expand/contract
• Add water
• Repeat
• Upon warming, fill in with noncohesive sediment

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Fossil Frost Wedges
Cover sand (eolian)?

• Big Horn Basin
• Pipeline trench
• Also evident in aerial photographs
• Evidence of former MAAT lt-6C

Bkb (caliche)
Preglacial soil
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Frost Boils

• Sorting and circulation
• Fines in center (dont step there!)
• Stones around the margin

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Sorted nets

• Like mud cracks and columnar jointing
• May be high-center or low (seasonal)
• May be fine or coarse

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Upland nets
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Pingos

• Cycle lt10,000 yr
• Feedback loops?

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Periglacial Slopes

• Landscape f(
• Freeze-thaw cycles)
• Slope angle)
• Water saturation)
• Sediment size)
• Sediment supply)
• Snow/water/ice supply)

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Frost heave/creep

• Heave f(
• Moisture)
• Grain size)
• Creep f(
• Saturation)
• Grain size)

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Frost heave/creep
Fine

• Movement f(
• Time)
• Slope)

Coarse
Coarse
Fine
Transect across a flow lobe