periglacial environments Flashcards
1
Q
how much of Earth’s surface can be described as periglacial
A
25%
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
3
Q
distribution of periglacial environemtns
A
- high latitude areas
- continental interiors e.g. Siberia
- high mountains at a low latitude
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
5
Q
what are the types of permafrost
A
- continuous / permanent
- discontinuous
- sporadic
6
Q
continuous permafrost
A
- permafrost upto 700m deep
- 1500m in Siberia
- winter temp is -50C
7
Q
discontinuous permafrost
A
- temp range from -5C to -1.5C
- break up around river, lake and coastal areas
8
Q
sporadic permafrost
A
- isolated spots of permafrost
- temp is 1.5C to 0C
9
Q
what is the active layer
A
- in the summer the surface layers of the permafrost melt
10
Q
what is talik
A
- unfrozen ground surrounded by permafrost
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
12
Q
what are the periglacial processes
A
- frost action (due to freeze thaw cycle)
- frost heave
- ground ice development
- ground contraction
- solifluction (gelifluction)
13
Q
what does frost action occur due to
A
seasonal fluctuations in temperature around 0C
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
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
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
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
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
19
Q
what are the periglacial landforms
A
- pingo
- patterned ground
20
Q
what is patterned ground due to?
A
linked to ground contractions and frost heave
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
features from pingos
- 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
example of open system pingo
East Greenland
27
type of permafrost in open system pingos
discontinuous
28
water source in open system pingos
from outside the system as it's an open system
29
location of open system pingos
- on valley bottoms
- on sandier soil
30
example of closed system pingos
Mackenzie Delta
31
type of permafrost at a closed system pingo
continuous
32
water source in closed system pingo
- inside the system
- trapped between ice layer and permafrost
33
location of closed system pingos
low lying or flat areas
start as small scale lakes
34
case study for human activity in periglacial environments
Alaska oil extraction
35
Trans Alaska pipeline
- 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
what is the need for oil in alaska
- 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
area 1002
- 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
for drilling into Area 1002
- 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
against drilling into area 1002
- 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
solving problems with Alaskan pipeline
- 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
impact of Alaskan pipeline on glacial material flows
- 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
what are gravel pads
- 1-2m thick
- act as substitute for insulating effect of vegetation
- reduce thaw of permafrost
43
impact of Alaskan pipeline on glacial energy flows
- 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
Effect of buildings in Alaska on the permafrost
- 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
formation of solifluction lobes
- 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
Alaskan thaw of permafrost - the methane problem
- 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
Alaskan thawing of permafrost impact on plants
- 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
what is a thermokast landscape
a landscape that refers to the process where distinctive landforms are made from thawing of ground ice
49
development of thermokast landscapes
- permafrost thaw and degradation
- increase in active layer depth
- accumulation of water on soil surface
- retreat of permafrost table
50
thermokast landforms
- 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
cause of thawing of ground ice in alaska
- clime change
- human interference (removal of vegetation reduced insulating effect, buildings and pipelines transmit heat
52
Alaska cost of infrastructure
by 2030 infrastructure repair and replacement costs will reach $40 billion
53
what is the case study of human activity in glacial areas
Grande Dixence Scheme in Switzerland
54
details for Grande Dixence Scheme
- built in 1960s to provide Switzerland with hydroelectric power
- cost of building was 1600 million swiss francs
- high gravity dam and 5th highest dam
- 285m high, 200m wide at base at 15m at top
55
why was grande Dixence dam difficult to build
- inaccessibility
- severe working conditions - cold weather so only work in summer months
56
water details for Grande Dixence scheme
- stores over 400 million M3 of water
- water from an area of 35km2 and meltwater from 35 glaciers
- four pumping stations move water through 100km2 of tunnels into the reservoir
- Lac Des Dix us man made lake
57
energy production for Grande Dixence scheme
- glacial meltwater is stored in the summer and used for high demand periods in winter
- water behind the dam turns turbines in 4 power stations - powers 400,000 homes
- less than 5% of energy is from fossil fuels
58
impact on environment for Grande Dixence scheme
- pumping stations are mainly built underground to maintain attractive environment
- tourism has increased for helicopter rides over dam
- BUT higher pollution from domestic/agricultural sources at Les Haudere due to reduced flow in Borgne River
59
impact on glacial system for Grande Dixence scheme
- 85% of water is used for generation
- 15% used for sediment problems
- lack of water flow leads to deposition behind the dam (20-40cm/yr)
- Futher down the river, high level of turbidity and high sediment concentration
60
impact on river channel for Grande Dixence scheme
- increased channel erosion - as water isn't transporting as sediment is stuck, it has extra energy and there has more erosion
- contractions in channel size - lack of discharge in below dam river means some dry up in the summer
- risk of sudden flooding - when excess water is released, it might flood - impact tourism and development along valley floor
