glaciers Flashcards
(112 cards)
1
Q
what is the Earth’s complete ice age history? (5)
A
Huronian - 2.4-2.1 million years ago
Cryogenian - 850-635 million years ago
Andean-Saharan 460-430 million years ago
Karoo - 360-260 million years ago
Quaternary 2.6 million years ago to present
2
Q
glacial meaning (1)
A
time period within an ice age where ice is expanding
3
Q
interglacial meaning (1)
A
time period within an ice age where ice is retreating
4
Q
negative feedback meaning (2)
A
- if we view a glacier as a system, negative feedback processes will work to reduce the impact if there is sudden change
- for example more meltwater in the summer will occur if there is excess accumulation in summer
5
Q
positive feedback meaning (4)
A
- an increase in temperature leads to the reduction of ice coverage
- white surfaces relflect heat
- once the ice has melted a darker surface is revealed, altering the albedo of an area
- as less solar radiation is reflected, the temperature increases which leads to further ice loss
6
Q
what is shown in a glacial budget? (4)
A
- the level of accumulation across a year
- the level of ablation across a year
- if a glacier is shrinking or growing
- the mass balance within the glacier
7
Q
what are the inputs of a glacier? (6)
A
- snowfall
- blown snow
- solar radiation
- avalanches
- rockfall
- geothermal heat
8
Q
what is between inputs and erosional landforms in a glacier? (1)
A
ice movement and erosional processes
9
Q
what are the erosional landforms of glaciers? (4)
A
- corrie
- arete
- u shaped valley
- drumlin
10
Q
what is between erosional landforms and depositional landforms in glaciers? (1)
A
ice and meltwater transport
11
Q
what are the depositional landforms of glaciers? (3)
A
- medial moraine
- lateral moraine
- terminal moraine
12
Q
what is between depositional landfroms and outputs in glaciers? (1)
A
melting, sublimation and calving
13
Q
what are the outputs of glaciers? (4)
A
- evaporation
- meltwater
- icebergs
- sublimation
14
Q
ice sheet definition (2)
A
- a body of ice larger than 50,000 sqquare kilometres
- there are two on Earth - Greenland and Antarctica
15
Q
ice cap definition (2)
A
- a body of ice smaller than 50,000 square kilometres
- found in Iceland, Russia, and Canada
16
Q
glacier definition (1)
A
a ‘river’ of slow-moving ice
17
Q
how does glacial ice form? (4)
A
- each year snowfall lands on top of the previous years
- this compresses the snow underneath with its weight and pushes out the air from it
- this snowly turns the snow into ice
- it goes from snow to coarse-grained snow to firn to glacial ice
18
Q
types of cold environment - describe the arctic environment (5)
A
- found at latitudes of 66°N and above it
- includes the Arctic Ocean and the northern extremes of North America, Europe, and Asia
- the central area is continuously covered by drifting ice pack approximately 3 metres in thickness
- during the winter months to ice pack extends to 14 million kilometres
- temperatures range across the area with a mean range of 4°C to -28°C
19
Q
describe the antarctic environment (4)
A
- the largest ice sheet covers the 13 million kilometres over the continental land and periodically freezes the surrounding ocean
- due to the large uninterrupted expanse of ocean, temperatures are much colder in Antarctica
- sea ice in the region ranges from 2 million square kilometres in February to 16 million square kilometres in September
- winter sea ice in Antarctica is increasing
20
Q
describe the alpine environment (3)
A
- tend to be found in tectonically active mountain ranges with peaks over 3000 metres
- older mountain ranges in more tectonically secure regions have eroded down and tend to be lower
- mountain ranges include: Himalayas, Rockies, Cascades, Alps, Norweigan mountains, Andes, and New Zealand
21
Q
types of cold environment - describe the periglacial environment (4)
A
- periglacial areas, including tundra regions, are usually found in dry, high latitude areas
- the cold conditions create permenantly frozen ground called permafrost
- the low levels of precipitaition, cold temperatures, and poor soil leads to sparce vegetation
- can be found in: Scandanavia, Siberia, North America, the southern tip of South America, and New Zealand
22
Q
what is permafrost? (1)
A
land that has been frozen constantly for at least two years
23
Q
why are Polar environments cold? (4)
A
- low levels of insolation
- in the summer, the sun remains low in the sky and even though there is continuous sunlight, the rays hit the surface obliquely, meaning there’s a wider surface area to heat
- the longer passage through the atmosphere allows for increased absorption, scattering, and reflection of radiation - less insolation therefore reaches the ground
- the high albedo of the snow and ice covered ground reflects solar radiation, reducing the amount that can contribute to the warming of the atmosphere
24
Q
why are polar environments cold? (2)
A
- the domination of high-pressure systems in polar regions prevents any frontal systems from forming in the area, which leads to low levels of precipitation
- cold air can’t hold much moisture and when precipitation does occur, it’s usually no more than a light, powdery snow
25
why are polar environments windy? (2)
- katabatic winds are those which flow down mountains into valleys
- as there is very little vegetation or barriers to block the winds, they can reach up to speeds of 200km/hour
26
describe tundra soils (4)
tundra soils can be characterised by:
- lack of clearly differentiated soil horizons
- an acidic surface layer
- a blue-gray colour
- waterlogged in summer
27
explain why tundra soils are the way they are (4)
- very little 'litter' is added each year due to the lack of vegetation
- only a few organisms can live in the soil breaking down material and it happens very slowly due to the temperature, meaning there is very little organic material
- the lack of organisms means very little soil mixing occurs, which leads to the lack of defined horizons
- in some areas, frost heave can cause the soil to swell upwards
28
describe vegetation in tundra environments (5)
- low level of productivity
- low biodiversity
- no fully grown trees although there are some dwarf species
- plant species produce hard shelled seeds
- lichens and the pioneer species colonising bare areas and beginning the process of soil formation
29
what are cold glaciers? (4)
- found in areas of high latitude where the temperature of snowfall is far below zero
- the ice of the glacier remains at below zero throughout the year
- they stay frozen to the bedrock all year and there's very little ice movement and erosion
- greenland and the antarctic have cold based glaciers
30
how do cold glaciers move? (4)
- internal deformation
- they're frozen to the bed and therefore only move 1-2cm a day
- the ice crystals within the glacier orientate themselves in the direction of ice movement, allowing the ice crystals to slide past one another
- where the ice movement is fast enough, crevasses may develop
31
where are warm glaciers found? (3)
- in areas of high altitude
- they have water present thoroughout the ice mass and this acts as a lubricant
- this may be for a period of the year or all year and allows for much greater rates of movement and thus more erosion
32
what is regelation? (1)
the phenomenon of melting under pressure and freezing again when the pressure is reduced
33
describe basal slippage (4)
- if the glacier moves, this can raise the temperature of the base ice through pressure and friction
- the basal ice can then melt, this water helps to allow the ice to slip easier out of its bed
-can move at 2-3m per day and pick up material that erodes out its bed
- related to regalation
34
why can basal slippage occur? (2)
- the melting point of ice is 0 degrees C at the surface, but this can vary within the ice profile because of the pressure that the mass exerts
- this means ice below the surface can mellt at colder temperatures, allowing the ice to move with the help of mel water even if the air temperature is below freezing
35
what are polythermal glaciers? (4)
- they're between the extremes of hot and cold glaciers
- they have both types of movement and are particularly dangerous because there's more crevasses
- the very cold temperatures mean that high basal pressures must be reached if the pressure melting point is to be attained
- the thinner edges of these glaciers tend to have cold bases and experience limited movement, whilst the thicker ice in the middle may have a warm base due to increased pressure
36
what is the net balance of a glacier?
- the difference between accumulation and ablation
- if the summer and winter budgets cancel eachother out, the glacier appears to be stationary
- the snout of the glacier would remain in the same position while ice is still advancing down the valley
37
what is freeze-thaw weathering? (5)
- it rains and water gets into a crack in a rock
- it freezes and expands by 9%, cracking the rock ever so slighty
- this process repeated again and again eventually fully cracks the rock into multiple pieces
- the pieces fall off cliff sides or stay in place
- its impact on glacial environments is it adds material to the glacier, helping it to erode further down
38
what is acid rain? (3)
- CO2 is released into the atmosphere and goes into clouds
- this creates carbonic acid within the clouds, which dissolves certain rocks such as limestone when it rains
- this process doesn't really affect glacial environments, but affects alpine & periglacial environments
39
what is plant root action? (3)
- roots of plants seek out weaknessews within rocks and cause them to break apart
- the pieces just lie there
- this isn't a major process in glacial environments due to the lack of vegetation
40
what is nivation? (4)
- in hollows filled with snow (north and eastern facing in the northern hemisphere), freeze-thaw and chemical weathering happening underneath the snow disintegrates the rock
- in spring, the meltwater flushes the rock away
- this process repeats yearly creating nivation hollows
- its impact on a glacial environment is it creates nivation hollows which look like craters on the landscape
41
what is abrasion? (4)
- occurs when rocks and stones become embedded in the base and sides of the glacier
- these are then rubbed against the bedrock/rock faces as the glacier moves
- this causes the wearing away of the landscape as the glacier behaves like sandpaper
- it leaves behind smooth polished surfaces which may have scratches in them called striations
42
what is plucking? (3)
- occurs when rocks and stones become frozen to the base or sides of the glacier and are plucked from the ground or rock face as the glacier moves
- particularly common where a localised reduction in pressure under the ice has led to regalation
- it leaves behind a jagged landscape
43
how does the temperature of the ice control ice movement? (2)
- in some environments such as greenland and antarcticaa, the ice is so cold that it's frozen to the bedrock
- such cold based glaciers tend to move slower than warm based glaciers where meltwater may be present at the base of the ice
44
how does gravity control the movement of ice? (2)
- this is the downhill force that encourages ice to move
- the steeper the gradient, the greater the pull of gravity
45
how does friction control ice movement? (1)
if the ice as a whole is to move forward, the friction exerted by the ice on the ground has to be overcome
46
how does the mass of the ice control ice movement? (2)
- the heavier the ice, the more potential energy it has to move
- however, more force will also be needed to overcome the increased friction caused by the extra weight
47
how does melltwater control ice movement? (2)
- it lubricates the base of the icce, enabling it to slip downhill
- an increase in water pressure beneath the ice may also help to overcome friction by creating a buoyancy effect
48
what is supraglacial? (1)
on the surface of the glacier
49
what is subglacial? (1)
beneath the glacier
50
what is englacial? (1)
within the glacier
51
what is glacial deposition? (3)
- the huge amounts of material carried by a glacier will eventually be deposited
- deposition takes place when the ice melts, primarily in the ablation zone close to the glaciers snout
- material deposited directly by the ice is known as till
52
how do corries form? (7)
- snow accumulates in a sheltered hollow on a hillside, especially on north facing slopes
- over many winters, the snow is continually added to and compressed into firn/glacial ice
- the hollow is continuously weathered by freze-thaw and other processes of nivation, allowing more snow to collect
- eventually, a small hollow is formed and by a process of rotational slip, it gouges out and deepens the hollow, just like an ice cream scoop
- rocks (moraine) trapped in the ice erode the hollow by a process of abrasion, an erosional action
- erosion is less powerful at the front of the corrie so a rock lip is often formed: moraine can build up here
- after the glacier has melted, a tarn (corrie lake) may be formed by the high rainfall that's found in Snowdonia. the lip of the corrie and any moraine built up acts like a dam/barrier
53
what is a tarn? (4)
- a lake that's found inside a corrie
- when the glacier melts, the combination of the rock lip and terminal moraine forms a natural dam with a corrie lake
- the lake drains over the rock lip/moraine dam and erodes a v shaped notch
- the lake begins to silt up
54
what is u shaped valley? (2)
- shows the path that a glacier took through rocks/mountains
- ribbon lakes which are long and narrow can often be found in them
55
what is an arete? (1)
- a knife edged ridge between two corries
56
what is a pyramidal peak? (1)
- when three corries are next to eachother
57
what are hanging valleys? (3)
- a landform of glacial erosion
- a tributary glacier fed into the main flow which was eroding the valley floor
- now the ice has melted, the tributary glacier valley is left hanging
58
what is a fjord? (1)
- when the sea has broken in and flooded a u shaped/glacial valley
59
what are Roches Moutonnees? (1)
- tough rocks that couldn't be plucked or eroded
60
describe glacial deposition (5)
- the collective name for all the sediments and debris deposited under glacial conditions is glacial drift
- sediments that were deposited by melting ice or by glacial streams are called fluvio-glacial
- debris deposited directly by the glacier, such as moraine and intra-glacial materia dropped 'in situ' by retreating ice is known as till
- the term till is used to describe an unsorted mmix or rocks, clay, and sand
- the material tends to be angular and reflects the character if the rocks over which the ice has passed
61
what are erratics? (4)
- stones and rocks that were transported by a glacier and left behind after it melted
- they don't fit the landscae they're deposited in
- they can be carried fro hundreds of kilometres and can range in size from pebbles to large boulders
- scientists sometimes use erratics to help determine ancient glacial movement
62
what is medial moraine? (3)
- found on top of and inside an existing glacier
- only found when glaciers join together
- the lateral moraine from the different glaciers are pushed together to form it
63
what is lateral moraine?
- forms along the sides of a glacier
- found in matching ridges on either side of the glacier
64
what is terminal moraine? (4)
- aka end moraine
- forms at the very end of a glacier, telling us important information about the glacier and how it moved
- all the debris that was taken and pushed to the front of the glacier is deposited as a large clump of rock, soil, and sediment
- terminal moraines are used to see where the glacier flowed and how it moved
65
describe the three ways in which moraines are formed (3)
- push moraines- form at the snout of glaciers, rock and sediment debris at the ice margin is moulded into ridges by the bulldozing of material by an advancing glacier
- dump moraines- form where debris flows or falls from a glacier surface due to gravity and accumulates at the ice front or sides as a ridge. they form where the ice front is stationary and theres a regular supply of debris to the snout, normally due to melt-out/rock debris stored in the ice
- ablation moraines- form where rock and sediment debris accumulate on the glacier surface near the margin and subsequently undergo melt-out. the dark coloured material on the glaciers surface lowers the ice albedo and increases the amount of solar radiation absorbed at the glaciers surface, which causes ice melt to speed upp
66
what are drumlins? (3)
- drumlins are generally found in broad lowland region, with their long axes roughly parallel to the path of glacial flow
- although they come in a variety of shapes, the glacier side is always high and steep, while the lee side is smooth and tapers gently in the direction of ice movement
- drumlins can vary widely in size, with lengths from 1-2km, heights from 15-30m, and widths from 400-600m
67
why are there multiple theories on the formations of drumlins?
- the internal composition of drumlins reveals a perplexing array of different sediments and structures
- some have rock cores surrounded by a concentric sheath of till, but they're mostly filled with unconsolidated sediments that are poorly sorted, and may contain silts, sands, gravel, and boulders
- tectonic structures such as thrusts and folds have also been found and have been taken to imply the sediments have been deformed during the drumlinisation process
68
what is theory one of drumllin formation? (2)
- in a previousglacial advance, hummocky ground moraine is deposited
- as the glacier advances again (perhaps the next winter) the ice moulds the moraine into the classic drumlin shape
69
what is the second theory of drumlin formation? (3)
- there's a nucleus of rigid material under the glacier
- it would be frozen till or a Roche Moutonnee
- material is deposited on and around the nucleus whilst the ice continues to move over it, forming the drumlin
70
what is the third theory of drumlin formation? (3)
- in some drumlins, the material is sorted
- fluvioglacial processes transport material underneath the glacier to be deposited in mounds
- as the ice moves over it, it moulds the material into the drumlin shape
71
what is the fourth theory of drumlin formation? (5)
- its the most widely accepted theory
- drumlins were formed when the ice became overloaded with sediment
- when the competence of the glacier was reduced, material was deposited, in the same way that a river overloaded with sediment deposits the excess material
-the glacier may have experienced a reduction in its competence for several reasons, including melting of the ice and changes in velocity
- if theres a small obstacle on the ground, this may act as a trigger point
72
what are the differences between glacial and fluvioglacial deposits? (6)
glacial deposits are:
- unstratified (difficult to identify layers)
- unsorted (random sorting as ice melts and deposits material regardless of size)
- material is angular from physical weathering and erosion, and various shapes and sizes
fluvioglacial deposits are:
- stratified (vertical layering due to seasonal variations in sediment accumulation)
- sorted (larger rocks and boulders are deposited first as the melt water loses energy
- material is smooth and rounded, it's sorted and graded
73
why are fluvioglacial deposits different to glacial deposits? (3)
- ice is a solid and doesn't flow in the same way that water does
- englacial material isnt subject to erosion such as attrition in meltwater
- water has less energy and it needs more energy to carry the same amount of material
74
what are eskers? (4)
- long ridges of material running in the direction of ice advance
- have a sinuous (winding) form , 5-20m high
- consist of sorted coarse material, usually coarse sands and gravel
- often stratified (layered)
75
how are eskers formed?
- made from deposits from subglacial streams
- the channel of the subglacial streams is restricted by ice walls
- high hydrostatic pressure means the streamn can carry a large load and can flow gently uphill, explaining why some eskers run up gentle gradients
- the stream's load builds up the bed of the channel, builds up above the surrounding land, or close to the snout as hydrostatic pressure may drop, leading to deposition
- a ridge is left after deglaciaiton, sometimes combined with mounds of material. in this case it's known as a beaded esker
76
what are kames?
- kames are amongst the most varied landfroms resulting from deposition by glacial meltwater
- a kame may occur as an isolated hill but more generally each kame is one mound in a low-lying terrain of many hummocks, ridges, and hollows
- kames often occur in association with kettle holes in kame and kettle topography
- eskers may also occur between the kames
- meltwater channels may cut into and between the kames
- these associations indicate that kames are formed close to ice margins in situations where there are large volumes of both meltwater and debris
77
what are deltaic deposits? (2)
- meltwater flows into a lake between the glacial snout and recessional moraine
- the meltwater is forced to deposit its load, buiding up a mound of material on the valley floor
78
how do kames slump? (2)
- as the ice melts, the kame begins to emerge as a hump but its sides are saturated and no longer supported by the ice
- therefore slumping is possible
79
how do kame terraces form? (3)
- deposits from meltwater streams which ran along the sides of the glacier
- they look like lateral moraine, but the material is sorted and stratified
- when the glacier melted, the material at the bottom of these streams was lowered to the valley floor
80
how do outwash plains form? (6)
- an extensive, gently sloping area of sands and gravels formed in front of the glacier's snout
- as the name implies, it results from the outwash of material carried bby meltwater streams
- material originally carried by the glacier is deposited by the meltwater streans running from the ice
- coarsest material is dropped first, found nearest the glacier
- fine material (clay) travels further across the plain
- deposits are layered vertically, reflecting the seasonal flow of meltwater streams
81
how are braided outwash plains created? (2)
- meltwater streams that cross the outwash plain are braided
- streams becomes choked with coarse material due to changes in meltwater variations
82
how are kettle holes formed? (3)
- dead ice is no longer attached to the glacier and melts slower for some reason, like vegetation blocking solar radiation
- outwash builds up over this dead ice
- when the dead ice finally melts, it causes depressions in the surface of the outwash called kettle holes, with kettle lakes inside
83
what are varves? (6)
- lakes on the fringe of the ice are filled with deposits that show a distinct layering
- a layer of silt lying on top a layer of sand represents one year's deposition
- the coarser, lighter-coloured layer is the spring and summer deposition - when meltwater is at its peak, the max load is being carried
- the thinner darker-coloured and finer silt settles during autumn and through the winter
- as stream discharge decreases, the very fine sediment in the lake settles to the bottom
- good indicator of the age of the lake sediments
84
what are periglacial areas?
- periglacial landscapes, although not actually glaciated, are exposed to very cold conditions with intense frost action and the development of permanently frozen ground or permafrost
- at present, areas such as the tundra landscapes of northern Russia, Alaska, and northern Canada, alongside high mountainous areas such as the European Alps, experience a periglacial climate
- there are three types of periglacial environment: arctic continental, arctic maritime, alpine
85
what are the conditions of periglacial areas? (5)
- persistently low temperatures - annual average between -15°C and -1°C
- average annual rainfall (exluding snowfall) is 120-1400mm
- short summers - temperatures can reach above 15° but remain well below freezing in winter, with some areas reaching -50°C
- permafrost - permanently frozen ground where soil has remained below 0°C for at least two years. if water is present in the soil, a significant amount will freeze, cementing the material and organic particles together
- the ground below this frozen layer that remains unfrozen is known as talik - the permafrost acts as a blanket preventing the talik from freezing
86
what are two local factors that could influence the depth of permafrost? (2)
- bodies of water warm up the surrounding areas, meaning they aren't as cold as they 'should' be. this means there's less permafrost around bodies of water, like lakes and oceans
- mountains in the area mean it's likely that there are glaciers in the area. ice has a low albedo, meaning its colder than it 'should' be, and there is therefore more permafrost
87
what are the three types of mass movement?(4)
- during the warmer seasons, mass movement can be a common phenomenon in periglacial environments. it usually occurs in three forms:
- frost creep
- rock falls
- solifluction/gelifluction
88
explain the process of frost creep (4)
- the slow downslope movement of soil and sediment because of frost heaving and thawing
- the process begins with the freezing of the ground surface, elevating particles at right angles to the slope
- the particles are elevated because cold temperatures cause water in between the particles to freeze and expand
- in the warm season, thawing causes the ice to convert back into water and the contracting surface drops the particles in elevation. this drop; however, is influenced by gravity causing the particles to move slightly downslope
89
explain the process of freeze thaw weathering and the impact it has on periglacial environments (7)
- water gets into the cracks of a rock
- the water freezes and expands by 9%, which cracks the rock slightly
- these two steps repeated over and over again over time break apart the rock
- as periglacial environmments are hostile to life, much of the landscape is exposed and vulnerable to weathering
- the extreme temperatures result in fractures along the bedding planes and joints in the rock
- if the fracture occurs on a gradient, then the accumulated material will form a scree slope
- if the freeze thaw occurs on flat land then a block field forms
90
what is solifluction/gelifluction? (3)
- during the warmer seasons, temperatures rise enough to melt the huge amounts of water held as ice in the upper layers of permafrost
- due to the impermeable layer of still frozen ground below, this water cannot drain away. there is little evaporation due to low temperatures, and subsequently the surface area beomes very wet
- this excessive lubrication reduces friction between soil particles, and on slopes as gentle as 2°C, the saturated layer becomes quite mobile and soil begins to move downslope
91
what are fluvioglacial landscapes? (6)
- fluvioglacial landscapes are associated with flowing water, especially meltwater, in glacial or periglacial environments
- meltwater is seasonally abundant in temperate glacial and periglacial environments and is often seen at a glacial snout flowing out from under the ice
- it's much less common in the world's coldest environments, characterised by cold based glaciers
- the mleting of ice produces a great deal of water which has the capacity to carry much debris
- as the water flows under considerable pressure, it has a high velocity and is very turbulent
- it can therefore pick up and transport a larger amount of material than a normal river of similar size
92
what happens when meltwater discharge decreases in a glacier? (4)
- when the meltwater discharge decreases, the resultant loss of energy causes the material being carried by the meltwater to be deposited
- as with all water deposition, the heavier particles will be dropped first, resulting in sorting of the material
- deposits may also be found in layers (stratified) as a result of seasonal variations in the meltwater flow
- therefore the landscapes of regions 'downstream' of glacial and formerly glaciated areas are often dominated by fluvioglacial landforms
93
what does a typical fluvioglacial landscape consist of? (3)
- wide, multi-channeled or braided river flowing over a vast area of sediment
- coarse, larger, more angular material
- typically gravelly or sandy - smaller, rounder, finer, sorted material
94
what is glacier milk?
- meltwater from a glacier which commonly has a milky appearance from suspended fine sediment
95
what is a subglacial stream?
a stream that flows beneath a glacier, and usually curs the ice underneath to form a tunnel
96
what are the two types of sub-glacier streams? (2)
N-channel - those that cut downwards into bedrock by erosion, known as Nye channels
R-channel - those that cut upwards into the ice itself by meltwater, known as Rothsligberger channels. they only leave post glacial trace if the channel becomes choked with sediment
97
what are pro-glacial lakes and overflow streams? (3)
- aka meltwater channels
- the major erosional landform created by meltwater channels/glacial overflow channels
- these form as the original course followed by a river before glaciation may be blocked by ice, or as an overflow from a proglacial lake (a meltwater lake on the edge of a glacier)
98
how does patterned ground develop? (3)
- as the active later starts to freeze, ice crystals begin to develop, which increases the volume of the soil and causes an upward expansion of soil surface
- within the soil, certain stones become chilled more rapidly than the soil due to their specific heat capacity
- water besides such stones freezes and expands, pushing up the stones. the stones roll down the mounds they formed, forming circles/polygons
99
what are ice wedges? (4)
- another type of pattern ground
- relatively narrow initial cracks are filled with ice
- over time, they grow into >10m wide into ground
- due to air bubbles, the wedge has a milky appearance
100
how do ice wedges form? (5)
- ice vein leads to a frozen crack
- the soil is frozen, and contractions lead to cracks
- meltwater fills the cracks
- repeated process causes the widening and deepening of the cracks
- cracks eventually form an ice wedge
101
what are ice wedge polygons? (1)
- patterned ground due to ice wedges much larger (15-30m)
102
what are ice wedge casts? (1)
- fine grain sediment fills the void left by a melted ice wedge
103
how do closed system pingos form? (3)
- advancing permafrost pushes up talik
- increase in hydrostatic pressure
- frozen lake pushes up lake sediment to cover lake
104
how do open system pingos form? (4)
- active layer repeatedly freezes and melts annually above permafrost and talik
- water can become trapped between the descending freezing plane of the active layer of permafrost around it, promoting ice lens growth
- water underneath permafrost can moove through talik due to capillary action
- this water migrates to the ice lens and freezes, swelling the ground above further
105
what are ognips? (3)
- both types of pingos can rupture if they become too largem and if the ground cracks it exposes the ice lens to the atmosphere and the suns energy
- this can then melt the ice causing the pingo to collapse, leaving a rupturede pingo with a depression in the middle that can fill with water and a lake, and a rampart around the edge that is prone to the mass wasting process of solifluction
- the collapsed pingo is known as an ognip
106
what are solifluction lobes? (4)
- when saturated active layer of soil is thawed, usually during summer months
- lobes form on slopes
- freeze thaw loosens material
- gradient changes again and flattens out, material flow slows and is deposited in a tongue shape
107
what are terracettes? (5)
- saturated layer can be affected by a combo of solifluction and frost heave
- this causes particles to move perpendicular towards the surface due to expansion caused by freezing and thawing
- the particles fall back vertically
- on a slope, this displacement causes individual particles to move downhill with every cycle of freezing and thawing
- on some slops, distinct steps form
108
what are drunken trees? (3)
- trees stand displaced form normal vertical alignment
- discontinuous permafrost or ice wedges have melted causing trees to tilt at various angles
- common in subarctic feign forests of black spruce
109
what are thermokarst? (3)
- a form of periglacial topography resembling karst, with hollows produced by the selective melting of permafrost
- associated with limestone landscapes
- a landscape formed by the dissolving action of water
110
how are thermokarst formed? (4)
- a landscape filled with permafrost that has ice wedges
- some of the ice wedges melt, forming small thermokarst lakes
- as more ice melts, lakes join together and they get bigger
- the lakes are dark and so they get warmer faster
111
what are the causes of a thermokarst landscape? (4)
- clearance of surface vegetation
- movement of vehicles
- urbanisation and industry
- ski resorts in the alps removes vegetation
112
what are the effects of a thermokarst landscape? (3)
- disruption of ecosystem
- increases solifluction
- in steep areas landslides are more common due to unstable ground
