PeriglacialPermafrost II

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Periglacial/Permafrost II
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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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Upland sorted nets
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Lowland sorted nets

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

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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)
• Slope)

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Frost heave/creep
Fine

• Movement f(
• Time)
• Slope)

Coarse
Coarse
Fine
Transect across a flow lobe
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Sorted nets on slopes - steps
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Yipes stripes!
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Soli-/Gelifluction

• Well-drained boulders trap finer sediment.
• Roll down hill like caterpillar track

2340130
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Examples soli-fluction
Cryoplanation?
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Stone lobes

• Stones move?
• Water?
• Fines?

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Block streams

• Weird!

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Avalanche/Debris Fans

• Lateral levees
• Terminal lobes
• Undisturbed ground
• Run on snow?

• On/above the surface redistribute as lobes
  levees.

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Talus

• Ubiquitous slope deposit
• Note natural levees

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Case study Sacajawea cirque
NOTE talus adjacent to ongoing debris flows
why?
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Protalus ramparts

• Positioned below talus
• Ridge transverse to slope
• Composition talus
• Origin ?

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Protalus ramparts

• Positioned below talus
• Ridge transverse to slope
• Composition talus
• Origin ?

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Rock-glaciers

• Transition between ice-glaciers, protalus
  ramparts and talus cones
• Lobate rock masses downhill from talus
• Often totreeline
• Orienteddue north Why?

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Rock-glacier features head

• Transitional to talus coarse surface

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Evidence of flow

• Arcuate ridges vegetation(?)

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Rock-glacier toe

• Angle of repose fine/frozen core

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Lobate rock-glacier CO
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Rock-glacier vs. talus

• Comparable orientation, source area So?

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Rock-glacier movement
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Lava Lake rock-glacier(?)
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Deflated Rock-Glaciers Why?
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Mountain Basins

• EX Sawatch Rge, CO
• Name those features!
• Talus
• Debris flows
• Lobes
• Levees
• Rock-glaciers
• Active
• Ancient

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Application Alaska Pipeline

• Permafrost regimes
• Tectonics

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145F