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Geomorphology > Periglacial geomorphology > Flashcards

Periglacial geomorphology Flashcards

1
Q

Periglacial

A

Result from seasonal thawing of snow in areas of permafrost, the runoff from which refreezes in ice wedges and other structures.

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2
Q

Key elements

A
  • Permafrost
  • Dominant process: frost action
  • Creation of very distinctive features
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3
Q

defining periglacial

A
  • those in which frost action and permafrost related processes dominate
  • located in extra-glacial area at high latitudes and/or altitudes
  • periglacial landscapes are usually considered synonymous with permafrost (Frozen ground)
  • many are not directly associated with Quaternary or present day ice sheets
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4
Q

processes

A
  • growth/melt of ground ice + temperature induced ground deformation = periglacial disturbance and dives the preglaical debris system
  • weathering (mechanical, chemical, biological)
  • slope processes (solifluction/genlifluction)
  • fluvial action (Arctic nival flood)
  • aeolian action (strong winds, low rainfall, little vegetation
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5
Q

extent of perglaciation

A
  • periglacial is defined by a set of processes, not by area or climatic type
  • currently 25% of the land surface
  • 82% of Alaska and 50% of Canada
  • in glacial periods of Quaternary an additional 20-25% of land area was affected
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6
Q

Permafrost

A
  • perennially frozen ground
  • one that survives for >2 years
  • not permanently because climate changes and the depth and spatial extent of permafrost changes with it
  • ground that has remained at or below 0oC for 2 or more consecutive years
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7
Q

arctic permafrost distribution

A
  • effects extend up to thickness of 1000m

- can be; isolated, sporadic, discontinuous, continuous

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8
Q

types of permafrost

A 
Isolated
- 0-10% of affected area
Sporadic 
- 10-50% of affected area
Discontinuous 
- 50-90% of affected area
Continuous
- 90-100% of affected area
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9
Q

Permafrost structure

A
  • surface layers subject to annual freezing and thawing, as seasons progress
  • active layer (most importation where processes take place = landforms)
  • active layer varies in thickness with climate
  • dynamic layer, usually has high water content; leads to freeze that cycles and results in formation of landforms.
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10
Q

Blockfields

A
  • boulder cover
  • no soil/vegetation cove visible
  • development requires 2 basic processes
  • detachment of the block from bedrock
  • movement of the block towards the surface
  • lower limit linked to upper limit of glacial ice cover (ice protects/erodes: frost weathering/heave above ice)
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11
Q

frost weathering of rock

A
  • breakdown of rock through repeated freezing and thawing
  • water in rocks expands by 9% on freezing
  • 2 effects: Macrogelivation & Microgelivation
  • landforms: frost shattered bedrock, blockfield and other forms of frost weathered detritus
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12
Q

Microgelivation:

A

small-scale breakdown of rock into particles (Silt, sand) by freezing of water in pores and by formation of ice lenses
- often causes rounding of rock surfaces by granular disaggregation

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13
Q

Macrogelivation

A

breakdown of rock into angular clasts by water freezing in joints

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14
Q

Upland feature: Patterned ground

A
  • sorted circles or unsorted hummocks, stropes
  • common where boulders cover mountain top
  • 1-15m in diameter
  • vegetated cell
  • forming by mass displacement of soil fines (freeze thaw)
  • class occupy troughs
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15
Q

freezing model

A

during freezing, frost penetration is uneven. clasts are heaved upwards to the surface and outwards towards cell margins

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16
Q

Thaw model

A

during thaw an unstable density configuration set convection cells in the soil

17
Q

soil convection

A

warmed (more dense) surface waters descends - melts frozen beneath - undulating lower surface projected to surface
- sorting occurs if soil particles move with water during convection

18
Q

patterned ground

A
  • some forms grade into others

- as gradient increases, nets becomes elongated forming ovals then stripes

19
Q

solifluction

A

slow downslope movement of soil due in cold region to freezing and thawing

20
Q

frost heave

A
  • vertical rise in position of material ins oil due to volume expansion that accompanies freezing of pore water
  • results in net downslope movement because lifting by heave occurs perpendicular to the slope which back-dropping after thawing occur vertically
21
Q

Gelifluction

A
  • seasonal thaw of the active layer saturates surficial soil as the water connot percolate into frozen soil below
  • can result in flow of active layer on slopes as gentle as 2 degrees and results in terrace like lobes
22
Q

ice wedge polygons

A
  • intense cold = thermal contraction/cracking
  • networks of vertical ice wedges shape the polygons which occur below the active seasonal freeze thaw layer
  • visible surface formation is a result of the soil slumping above the ice wedges
  • may be a few meters to over 100 meters in diameter
  • low centered if ice wedge is growing
  • high centered if thawing is more prevalent causing stream channels along ice-wedges
23
Q

Lowland feature: Pingos

A
  • dome shaped hill (when active)
  • sub-surface water freezes and expands = dome
  • up to 600 m diameter and 50 m high
  • as growth progresses, cracks appear in surface
  • ice core becomes exposed - melting
  • material slumps to edges
  • forms ramparts (ridges) with central depression
24
Q

Pingo formation: hysrostatic

A
  • closed system
  • lake underlain by unfrozen sediment in permafrost
  • lake darins = exposed to cold temps = permafrost aggrades
  • talik freezes as permafrost encroaches forming a core of ice
  • core deforms overlying soil = pingo
  • found in area of continuous permafrost (Siberia and Canada)
25
Q

Pingo formation: hydraulic

A
  • open system
  • common in area of discontinuous permafrost (Alaska, Svalbard, Greenland)
  • requires flowing water beneath permafrost
  • flows from high to low pressure
  • as freezes forms dome
26
Q

Thermokarst

A
  • characteristic landforms from thawing of ice-rich permafrost or the melting of massive ground ice blocks
  • it is characterised by an irregular topography, with irregular pits and depressions develop by thaw settlement
  • perhaps indicative of warming climate
  • thaw lakes can appear aligned due to wind/water erosion
27
Q

Ice Wedge

A 
Active: 
- modern high-latitude, periglacial areas
- mean annual temp below -8 to-6
Fossil:
- modern mid-latitude maritime areas
28
Q

Frost action

A
  • granular disintegration and flaking of rock production of 6 tonnes of sand accumulate in one valley in one winter
  • frost sorted patterned ground, regular surface patterns of fine and course debris only on bare ground
  • solifluction, downslope movement of debris (under seasonal freezing/frost creep) abover 550m in UK
29
Q

Aeolian activity

A
  • removal of material from deflation surfaces
  • Arkle and An Teallach
  • debate: activation by either little ice age or over grazing by sheep
30
Q

Dominant modern day features

A
  • rock slope failures, mainly paraglacial
  • talus slope accumulation
  • debris flows
  • solifluction deposits
  • coversand deposits
  • ploughing boulders, most widspread indication of current perglacial activity
31
Q

Primary concern: release of methane gas

A
  • large uncertainties in the budget of atmospheric methane limit the accuracy of climate change projections
  • contributors; industry agriculture wetlands, ruminants, fire, ocean
  • climate effects; absorption of infrared radiation, atmospheric warming, increase in methane output = greater effect hat equivalent increase in CO2
32
Q

Primary concern: release of CO2

A
  • frozen land: anoxic, preservation of organic material
  • degradation: oxygenation and decomposition of organic matter
  • contributors: industry agriculture wetlands, ruminants, fire, ocean
  • climate effects: greenhouse effect
33
Q

components of arctic permafrost regions

A
  • permafrost degradation and erosion enhance methane release

- extreme scenarios suggest all may have thawed by 2100

34
Q

climatic change in the arctic

A
  • predicted actic temp 4-8oC
  • annual precip increase of 20%
  • active layer of permafrost will deepen over broad areas
  • roads and pipline disrupted, populations of animal fluctuate, hunting season shorted for native people
  • boreal forest will migrate poleward and productivity will decline form drought, insects, disease, fire etc.
35
Q

positive consequences of future climate warming in cold regions

A
  • Expanded trade routes
  • Increased economic potential – oil and gas reserves
  • More land suitable for cultivation/farming – longer growing season
  • Deferring of next ice age (is this a positive?)
  • Fewer deaths/injuries from cold related illnesses
  • Increased travel/tourism to previously inaccessible areas
36
Q

Negative consequences of future climate warming in cold regions

A
  • Extinction of flora and fauna – loss of biodiversity
  • Sea level rise - flooding
  • Political tensions e.g. competition for oil and gas reserves
  • Economic impact: e.g. skiing resorts
  • Loss of resources: e.g. fresh water
  • Destruction of environmental archives & infrastructure: e.g. permafrost/ice cores
  • Instability in the landscape: e.g. rivers and volcanoes

Geomorphology (9 decks)

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