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physical geography > periglacial environments > Flashcards

periglacial environments Flashcards

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1
Q

how much of Earth’s surface can be described as periglacial

A

25%

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2
Q

what are periglacial environments

A
  • around glacial environments and has permafrost
  • lots of seasonal temperature variation - above 0C in summer
  • geomorphic processes dominated by cycles of freezing and thawing
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3
Q

distribution of periglacial environemtns

A
  • high latitude areas
  • continental interiors e.g. Siberia
  • high mountains at a low latitude
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4
Q

what is permafrost

A
  • perminantly frozen ground
  • the sub soil temperature must be below 0C for two consecutive years for the permafrost to form
  • the extent, depth and continuity varies
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5
Q

what are the types of permafrost

A
  • continuous / permanent
  • discontinuous
  • sporadic
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6
Q

continuous permafrost

A
  • permafrost upto 700m deep
  • 1500m in Siberia
  • winter temp is -50C
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7
Q

discontinuous permafrost

A
  • temp range from -5C to -1.5C
  • break up around river, lake and coastal areas
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8
Q

sporadic permafrost

A
  • isolated spots of permafrost
  • temp is 1.5C to 0C
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9
Q

what is the active layer

A
  • in the summer the surface layers of the permafrost melt
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10
Q

what is talik

A
  • unfrozen ground surrounded by permafrost
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11
Q

what happens with active layer due to the permafrost

A
  • the water from the active layer is unable to drain away through the impermeable layer of frozen ground
  • soil becomes saturated creating a boggy marsh land
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12
Q

what are the periglacial processes

A
  • frost action (due to freeze thaw cycle)
  • frost heave
  • ground ice development
  • ground contraction
  • solifluction (gelifluction)
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13
Q

what does frost action occur due to

A

seasonal fluctuations in temperature around 0C

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14
Q

how does frost action work

A
  • small crack in rock fills with water at day. during the night, the water freezes at the top sealing the crack
  • as water freezes completely, it expands the crack by 9%
  • as water thaws, it wont fill the crack as its bigger
  • process begins again, this time with a larger crack to fill
  • again crack expands, eventually does significant fracturing of the rock
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15
Q

what does frost heave occur due to

A

under the surface and results in the upward movement of material through the active layer

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16
Q

how does frost heave work

A
  • fine material heats up and cools down faster than their surroundings ( due to lower specific heat capacity)
  • as temp falls, water beneath the stones freezes, it expands, pushes the stone above upwards
  • on surface finer material creates dome, large material accumulates around sides of dome
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17
Q

how does ground ice development work

A
  • due to melting in summer, water goes into rocks below
  • this freezes and expands by 9%
  • cause ground surface to be pushed upwards
  • permafrost stops the downward movement of rocks
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18
Q

how does solifluction/gelifluction work

A
  • active layer melts in summer
  • the water cant move down due to impermeable permafrost below
  • so active layer becomes saturated and slowly moves downslope
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19
Q

features of periglacial landforms

A
  • pingo
  • patterned ground
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20
Q

what is patterned ground due to?

A

linked to ground contractions and frost heave

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21
Q

small scale features of patterned ground

A
  • stone garland
  • ice wedges
22
Q

stone garlands

A
  • typically 1-2m in diameter
  • stones from frost heave create polygon shape as they roll into gaps between domes
  • domes then sink and create level land
  • slopes of 6° or more, the stones create stripes
23
Q

ice wedges

A
  • water fills the cracks and freezes, expanding the gap
  • e.g. North West Territories, Canada
24
Q

Pingo

A
  • isolated hills with core of ice (lens)
  • can be quite large - 50-500m diameter, 10-70m high
  • when collapse, create ognips and might have a pond, might resemble crater
  • if ice lens melts the pingo will collapse, forming ognip
25
Q

features from pingos

A
  • generally occur in groups
  • land is almost flat
  • grow as water is drawn in from sediment
  • if the covering sediment splits and exposed the ice core, it might melt. it will then collapse
26
Q

example of open system pingo

A

East Greenland

27
Q

type of permafrost in open system pingos

A

discontinuous

28
Q

water source in open system pingos

A

from outside the system as it’s an open system

29
Q

location of open system pingos

A
  • on valley bottoms
  • on sandier soil
30
Q

example of closed system pingos

A

Mackenzie Delta

31
Q

type of permafrost at a closed system pingo

A

continuous

32
Q

water source in closed system pingo

A
  • inside the system
  • trapped between ice layer and permafrost
33
Q

location of closed system pingos

A

low lying or flat areas
start as small scale lakes

34
Q

case study for human activity in periglacial environments

A

Alaska oil extraction

35
Q

Trans Alaska pipeline

A
  • finished in 1977
  • pumps upto 1.4 million barrels of oil a day
  • crosses 3 mountain ranges, 600 streams and rivers
  • 1300km long with over 600m built in stilts
36
Q

what is the need for oil in alaska

A
  • USGS predicts that 30% of undiscovered oil and gas is around Arctic Circle
  • Alaska has 3 billion known barrels
  • in 2014, 6.96 billion barrels of oil was used by USA with 40% as imports from other countries
  • no energy security
37
Q

area 1002

A
  • contain over 16 billion barrels of oil so need to drill it to meet the demands
  • 6070km2 in NW part of Artic Refuge and is the only part that isn’t protected
  • concerns from environmentalists as it could affect Caribou and Gwich’in Indians
38
Q

for Alaskan pipeline

A
  • oil industry and some government reps
  • many Alaskans get money from the industry - $3000 per person
  • some people from USA think it’s good for energy security
39
Q

against Alaskan pipeline

A
  • minority of Alaskans who rely on Carabou for their living are against it
  • Yukon/tourist industry
  • conservation groups
  • only 50% chance of finding oil
40
Q

solving problems with Alaskan pipeline

A
  • pipe is raised by refrigeration so there is no heat conducting into the ground and permafrost
  • animals can move below the pipeline so migration routes aren’t blocked
  • pump stations move oil over mountains
  • pipe is above river not on river bed
  • oil storage tanks are raised and built to deal with seismic movements
41
Q

impact of Alaskan pipeline on glacial material flows

A
  • permeant settlements alter the thermal temp of ground
  • lead to thaw of permafrost
  • buildings are raised to remove heat
  • Dawson settlement is built on gravel pads
42
Q

what are gravel pads

A
  • 1-2m thick
  • act as substitute for insulating effect of vegetation
  • reduce thaw of permafrost
43
Q

impact of Alaskan pipeline on glacial energy flows

A
  • release and burning of gas during drilling to release pressure
  • release large amounts of CO2 and methane which impacts global warming and permafrost
  • production of heat - Barrow produced Urban Heat Island Effect. 2° higher than rest of Alaska
  • 9% fewer days of temp fluctuation around 0°C have been recorded after drilling - warmer
44
Q

Effect of buildings in Alaska on the permafrost

A
  • buildings have heating effect - thawing of permafrost and longer period of melting active layer
  • lead to mobility of active layer and therefore solifluction
  • features such as solifluction loved form
45
Q

formation of solifluction lobes

A
  • downslope movement of water saturated soil(from meltwater)
  • when active layer melts, it becomes mobile as it’s saturated due to impermeable permafrost below
  • slow process
  • movement produces lobes forming a terrace or stair arrangement with risers and treads
46
Q

Alaskan thaw of permafrost - the methane problem

A
  • organic matter frozen in permafrost is a potential major source of methane
  • ## thawing leads to the decomposition and releases CO2 and methane into the atmosphere
47
Q

Alaskan thawing of permafrost impact on plants

A
  • as more water is available there is rapid growth of plants
  • as permafrost melts, no impermeable layer to prevent drainage
  • few months after melting, there is no water left
48
Q

what is a thermokast landscape

A

a landscape that refers to the process where distinctive landforms are made from thawing of ground ice

49
Q

development of thermokast landscapes

A
  • permafrost thaw and degradation
  • increase in active layer depth
  • accumulation of water on soil surface
  • retreat of permafrost table
50
Q

thermokast landforms

A
  • Alases - large scale, flat floored, steep sided depression
  • large scale thawing of ground ice results in large scale subsidences
  • shallow lakes may form in depression
  • many joined together form Alas Valley
51
Q

cause of thawing of ground ice in alaska

A
  • clime change
  • human interference (removal of vegetation reduced insulating effect, buildings and pipelines transmit heat
52
Q

Alaska cost of infrastructure

A

by 2030 infrastructure repair and replacement costs will reach $40 billion

physical geography (4 decks)

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