Glaciated Landscapes Flashcards
(224 cards)
1
Q
What is a glaciated landscape?
A
Glaciated landscapes include any landscapes that are being affected by the action of glaciers. This course also includes ‘post-glacial landscapes’ which do not have glaciers currently acting on them but still have distinctive features from their presence.
2
Q
What is a glacier?
A
They are huge flowing bodies of ice that move downhill and carve out landscapes over thousands or millions of years.
3
Q
What is the importance of glaciers?
A
- They are a good fresh water source
- They carve out beautiful landscapes
- They create valleys that can be used for dams - hydroelectric power.
- Leusire activities support local economies
- reflect sunlight to keep planet cool
- Melt into the sea causing sea level to rise
- Habitat for many ecosystems
- Create stunning places for towns and people to live.
4
Q
What properties does a glaciated valley have?
A
- Flat bottom to the valley’s
- Steep sided mountains
- Jagged rock faces and ridges
- Bare rock faces
- Little vegetation
5
Q
Where do we find glaciated landscapes?
A
HIGH ALTITUDE - LOW LATITUDE
LOW ALTITUDE - HIGH LATITUDE
Above the permenant snow line
6
Q
5 What are the types of glacier?
And description
A
- Vallery glaciers: tounges of ice confined within valleys in mountainous regions. Constrained glacier - its path and form determined by the landscape.
- Ice sheets: Can be over 2 miles thick and cover whole continents (Antartica, Greenland contain 96% of ice). Unconstrained glacier. Often have valley glaciers coming off side. Greater than 50,000km2
- Ice Caps - cover entire mountainous regions. Up to 50,000km2.
- Piedmonet glaciers - valley glaciers that have spilled out into lowland regions.
- Cirque glaciers - small glaciers that occupy a bowl shaped hollow at the top of the glacial valley.
7
Q
How much is mountaintop glacier ice disappearing in some parts of the world?
A
90%
8
Q
What is the proccess that forms glaciers?
A
Diagenisis - snow turning into ice.
9
Q
Explain the process of diagenisis.
A
- Snowfall remains frozen throughout the year. Every fresh layer of snow falls on top of the previous year. Snow has a density of 0.05g/cm3
- As more and more layers fall, they compress the layers below them. If snow survives one summer without melting it compresses into firn which is more dense at around 0.4g/cm3
- After more years of compaction, the firn becomes glacial ice with a density between 0.83 and 0.91g/cm3. This process takes between 40 - 1000 years. The hardest ice is found around 100m deep into a glacier.
10
Q
What climatic conditons are required for diagenisis?
A
Cold enough so that snow doesn’t melt in the summer.
11
Q
How does pressure impact the temperature that ice melts?
A
As pressure increases the temperature that ice melts decreases. At high pressures, ice will turn into water at temperatures below 0C. The melting point is lowered by 0.072C per MPa. This increases the production of meltwater which aids glacier flow.
12
Q
What are typical properties of warm based (temperate) glaciers?
A
- High altitude locations
- Steep relief
- Basal temperatures above pressure melting point
- Rapid rates of movement, typically 20-200m.
Typically found in locations such as the Alps and Rockies where there are high rates of accumulation and ablation, so very active. Large volumes of ice being transferred across the equilibrium line, and significant seasonal differences. Fast processes.
13
Q
What are typical properties of cold based (polar) glaciers?
A
- High latitude locations
- Low relief
- basal temperatures below pressure melting point so frozen to the bedrock
- Very slow rates of movement, often only a few metres a year.
Typically found in Antartica and Greenland, where there is very low accumulation and ablation, so not very active. Small seasonal differences, and very limited processes.
14
Q
Why does temperature vary with depth in a glacier?
A
Due to the increasing pressure of the layers of ice as you go deeper.
15
Q
Where does a glacier move fastest and slowest?
A
Fastest at the top and in the middle, slowest at the battom and the sides. This is because there is less friction.
16
Q
What are the three main types of glacier movement?
A
- Basal sliding
- Internal deformantion
- Bed deformation
17
Q
What is basal sliding?
A
The act of a glacier sliding over the bed due to meltwater under the ice acting as a lubricant.
18
Q
What is internal deformation (creep)?
A
Gravity and the pressure of the ice causes the ice crystals to slide over each other in a series of parallel planes in a ‘crumpling’ deformation.
19
Q
What is bed deformation?
A
The deformation of soft sediment of weak rock beneath the glacier causes it to slip downhill due to gravity.
20
Q
What are the 3 types of basal sliding
A
1 - Basal Slip: When a thin layer of water builds up at the ice-rock interface and the reduction in friction enables the ice to slip forwards.
2 - Enhanced basal creep: Ice squeezes up against a larger (>1m wide) obstacle the increase in pressure causes the ice to plastically deform around the feature
3 - Regelation: When ice presses up against a smaller (<1m wide) obstacle and reaches pressure melting point, and rather than deforming, the ice melts on the stoss side, and refreezes on the lee side where pressure is lower.
21
Q
How do ice sheets move in comparison to valley glaciers?
A
- Similar processes (basal sliding, internal deformation, bed deformation), except much slower due to far colder temperatures.
- The whole ice sheet doesn’t move, instead there are streams of ice movement in the sheet that often follow topographic features.
- They are thicker in the middle so gravity pulls ice downhill towards the sea.
22
Q
Why do some glaciers move faster than others?
A
- Gravity: The fundamental cause of the movement of an ice mass.
- Gradient: The steeper the slope, then the faster the ice will move.
- Thickness of ice: This influences basal temperature and pressure melting point, which in turn influences how the glacier moves. Also influences stress on ice which can impact internal and bed deformation.
- Internal ice temperature: This allows the movement of one area of ice relative to another if they are different temperatures and thus different speeds of movement. Internal deformation happens 100x faster at 0 degrees than -20 degrees.
- Glacial budget (mass balance): A positive mass balance allows glacial advance at the snout.
23
Q
How does relief impact a glacier?
A
- As a glacier flows over a steep slope it can’t deform quickly enough so stretches and fractures forming crevasses. This is known as extending flow.
- As the gradient of the slope decreases the ice thickens and compresses closing the crevasses. This is known as compressing flow.
24
Q
How does climate (seasons) impact a glaciers movement?
A
- During summer there is a higher level of melting due to higher temperatures, so this causes more basal sliding and thus causes the glacier to have greater velocity. Strong correlation between metling and velocity.
- Internal deformation happens faster in higher temperatures due to greater temperature differences in the ice.
25
What type of system are glaciers?
Open system as they allow inputs and outputs of energy and matter.
26
What are inputs into a glacier system?
- KE (wind)
- Thermal Energy (sun, geothermal)
- GPE (altitude)
- Precipitation
- Debris
- Meltwater
- Avalanches
27
What are the throughputs of a glacier system?
* Snow
* Ice
* Debris
* Meltwater
* GPE (Altitude)
* KE (movement of glacier)
28
What are the outputs of a glacier system?
- Thermal energy (friction with base)
- Meltwater
- Water vapour (evapouration and sublimation)
- Icebergs
- Debris
- KE (movement of glacier)
29
What are the energy transfers involved with HEP and glaciers?
Solar -> GPE -> Kinetic -> GPE -> Kinetic -> Electrical
30
Explain the transfer of energy in a glacier?
- Solar energy is the driver of the whole glacial system. It drives the hydrological cycle which causes precipitation in the form of snow. This snow turns into glacial ice via diagenisis and aquires GPE.
- This GPE is then converted to KE as the ice flows down the valley once the glacier is large enough. As the glacier flows it erodes the bedrock and shapes the valley.
- Solar energy then melts the glacier once it reaches a lower altitude to produce meltwater, which once again converts GPE to KE. Meltwater transports material down the valley in streams to create new landforms.
- Solar energy also drives the physical weathering process.
- In the post-glacial period vegetation converts solar energy into chemical energy by photosynthesis and then into kinetic energy as roots penetrate into bedrock causing biological weathering modifying glacial landforms.
31
What glacier may be the most dangerous glacier in the world and why?
* Thwaites glacier in Antartica.
* Because it is on the brink of collapse due to the land it rests on being below sea level. As sea water seeps in below the glacier it causes it to break up and the speed of this is increasing.
* It is already contributing to 4% of sea level rise.
32
What is the definition of accumulation?
The accretion of snow and ice onto a glacier. Occurs at high latitude and altitudes where the temperature prevents melting.
33
What is the definition of ablation?
The loss of ice mass due to melting and sublimation (small contribution)
34
What is the defintion of mass balance?
The annual mass balance of a glacier is the difference between accumulation and ablation over one year.
35
What processes are dominant at the source of the glacier?
Accumulation
36
What processes are dominant at the snout of the glacier?
Ablation
37
What part of the glacier sees more accumulation?
zone of accumulation
38
What part of the glacier sees more ablation?
The zone of ablation
39
What point on the glacier sees equal ablation and accumulation?
The equilibrium line
40
What state of equilibrium do glaciers exist in?
Dynamic equilibrium
41
What is dynamic equilibrium?
The idea of a system adjusting to bring itself back to equilibrium if either the inputs or the outputs change and equilibrium is disturbed. It does this through negative feedback loops to counteract the change.
42
How does air temperature impact precipitation?
A 1C rise in temperature means the air holds 7% more water vapour, leading to 14% less precipitation. This reduces the rate of accumulation in summer months. Reaches dew point less easily.
43
Why is seasonal variations in glacier mass balance much less in higher latitude glaciers?
Precipitation rates are much lower.
44
Where is the South Cascade Glacier and what type is it?
A cirque glacier in the Cascades range in Washington, USA.
45
How far has the South Cascade Glacier retreated from 1958 to 2013?
1.1km
46
What is the reason for the retreat of the South Cascades glacier?
Global warming
47
What is a positive feedback loop?
A feedback loop that takes a system further away from dynamic equilibrium.
48
What is a negative feedback loop?
A feedback loop that returns a system to dynamic equilibrium.
49
What is a positive feedback loop linking glaciers and climate change?
* Glacial system in equilibrium, mass balance in dynamic equilibrium.
* Increased Carbon dioxide in the atmosphere raises global temperatures
* Melting of the glacier begins at the top and base as ice passes PMP.
* Warm based glaciers flow faster due to lubrication from meltwater. The total amount of ice in the glacier decreases
* The glacier gets stretched out and thins, increasing the number of crevasses
* This increases the absorption of solar radiation causing more melting at the glacier surface. The glacier begins to melt faster and thin out more.
* Over time the rate of melting speeds up. This reduces the albedo effect.
* Darker surfaces absorb more of the solar radiation, raising global temperatures.
BACK TO STEP 3
50
What is a negative feedback loop linking solar flares and glaciers?
* Glacial system in equilibrium, mass balance in dynamic equilibrium.
* A solar flare occurs.
* Increased inputs of solar radiation heat the glacier above the PMP causing melting at both top and base of the glacier.
* This causes meltwater at the base of the glacier to appear and flow down the valley.
* Ablation exceeds accumulation and the glacier is in negative mass balance.
* Glacier retreats up the valley leaving deposits of moraine.
* Temperatures decrease at the higher altitude in the valley reducing ablation.
* Ablation equals accumulation.
* Dynamic equilibrium is restored.
* BACK TO THE START.
51
What factors affect how a glacier shapes glaciated landscapes?
* Aspect
* Precipitation and Temperature
* Geology of the Landscape
* Relief
* Altitude and latitude
52
How does aspect influence glaciation?
- Aspect is the direction a slop faces.
- Cirque glaciers are more likely to build up on the shaded side of a mountain as they recieve less thermal energy so there is less ablation so have a positive mass balance.
- In the northern hemisphere the north side is shaded, and in the southern hemisphere the southern side is shaded.
- In the UK most corries are located facing north-east. This is also partly because of snow being blown by the prevailing wind from the south-west over mountain ridges and settling in corries on the far (lee) side of mountains increasing accumulation.
53
How does precipitation and glaciation influence glaciation?
* In warmer temperatures, glacier movement is at a higher velocity
* This is because of increased melting which increases basal sliding and bed deformation
* Increased temperature also increases internal deformation due to greater differences in temperature throughout layers of ice.
* If the temperature rises above 0C then accumulated snow and ice will start to melt and become an output. In polar regions this is why they are so thick despite low precipitation.
54
How does geology influence glaciation?
Areas of less resistant rock will be eroded at a higher rate than areas of more resistant rock, due to the rock having a weaker lithology and structure. This means the landscape can be shaped depending on rock types, with the resistant rock making up more prominent features.
55
What is lithology
The physical and chemical composition of rocks
55
What is the structure of rocks?
The properties of individual rock types such as jointing, bedding and faulting.
55
How does releif influence glaciation?
- As a glacier flows over a steep slope it can't deform quickly enough so it stretches and fractures forming crevasses. This is extending flow.
- As the gradient of the slope decreases the ice thickens and compresses closing crevasses. This is known as compressing flow.
55
How does altitude and latitude influence glaciation?
- Locations at high latitudes, mainly beyond the artic and antartic circles have cold dry climates with little seasonal variation. Landscapes develop under the influence of large, stable ice sheets.
- Locations at high altitude but lower latitude have higher precipitation (releif) inputs, and more summer receding due to greater seasonal variation in temperature. They are also normally located in steep valleys and have a very steep releif compared with cold based glaciers. Much faster erosion rates due to greater velocity.
56
How much does temperature decrease with altitude?
0.6C /100m
57
What are the 'big 5' geomorphic processes that shape the earth and what factors affect rate and intensity?
- Erosion: velocity of glacier, resistance of rock, mass balance, thickness of ice, friction, temperature and PMP, amount of basal debris.
- Mass movement - releif, precipitation, weight, and permeability.
- Deposition: velocity of glacier, amount of debris, mass balance
- Transportation: velocity of glacier, amount of debris, mass balance
- Weathering: precipitation, temperature, resistance of rock
58
What is a nivation hollow?
Shallow depressions left underneath snow patches and are thought to be the starting point for the development of cirque glaciers. Mainly formed from weathering and transportation. Whole process is called 'nivation'.
59
Explain the three types of glacial erosion?
* Abrasion: Debris in the glacier's base/sides slides across the bedrock wearing it away.
* Plucking: Meltwater seeps into cracks in the bedrock, and freezes becoming attatched to the glacier. As the glacier advances it pulls pieces of rock away. Particularly effective at the base of a glacier due to PMP.
* Nivation: A combination of freeze-thaw action, chemical weathering, and transport water is responsible for the initial enlargement of hillside hollows and corries.
60
Explain the three types of glacial transportation.
- Supraglacial: Debris being carried on the surface of a glacier
- Englacial: Debris being carried within the glacier
- Subglacial: Debris embedded in the base of the glacier.
61
Explain the three charachteristics of till deposition.
- Angular or Sub-angular in shape because it was embedded in the ice so not subjected to further erosion processes.
- Unsorted (deposited by advancing ice) and has no pattern. This contrasts to water which deposits material in size based sequence as it loses energy progressively.
- Unstratified (dropped in mounds rather than layers).
62
How much of the earths surface is covered by glacial deposits?
8% (30% in Europe)
63
What are the two types of glacial till?
- Lodgement till: this material is deposited by advancing ice. Due to the downward pressure exerted by thick ice, subglacial debris may be pushed into the existing valley floor.
- Ablation till: material deposited by melting ice from glaciers that are stagnant or in retreat. Most glacial depositional landforms are formed this way.
64
What are the three types of weathering?
- Chemical
- Biological
- Physical
65
Explain the three types of physical warming.
1. Freeze-thaw ~ Water enters cracks and expands by nearly 10%. This exerts pressure on the rock causing it to split or break off.
2. Pressure release ~ When the weight of overlying ice in a glacier is lost due to melting, the underlying rock expands and fractures parallel to the surface.
3. Frost shattering ~ Water trapped in rock pores freezes and expands and disintegrates individual rocks.
66
Explain the two types of biological weathering.
1. Tree roots ~ Tree roots grow into cracks or joints and exert outward pressure and when trees fall they can exert leverage on rock and soil.
2. Organic acids ~ These are produced during decomposition of plant and animal litter causing soils to become more acidic and react with minerals (chelation).
67
Explain the 5 types of chemical weathering.
1. Oxidation ~ Some minerals in rocks react with oxygen either in the air or water breaking them down.
2. Carbonation ~ Rainwater and dissolved carbon dioxide from the atmosphere produce carbonic acid which reaves with rocks dissolving them.
3. Solution ~ Minerals dissolving in water.
4. Hydrolysis ~ Silicates combine with water producing secondary minerals such as clays. Chemical reaction between rock minerals and water.
5. Hydration ~ Water molecules added to rock minerals create new minerals of a larger volume. Causes surface flaking in many rocks.
68
Explain the two types of mass movement.
Slides ~ Sediment, soil or rock slides down the mountain. May be linear with movement along a straight line slip plane or rotational. Rotational slides are known as slumps. Slides may occur due to steepening or undercutting valley sides.
Rockfall ~ On slopes 40 degrees or more rocks may become detached from the slope by physical weathering processes. These then fall to the foot of the slope due to gravity.
69
How is a landscape 'prepared' for glacial erosion when there aren't glaciers.
1. Sub-surface rotting - occurs in warm periods and causes the weathering of the bedrock
2. Frost action
3. Overburden and dilatation (pressure release)
4. Wind weathering and mass movements
70
What is the spatial variation of the 5 geomorphic processes in a glaciated landscape?
- Erosion: At the ice-rock interface on the valley floor and walls.
- Weathering: Occurs on the valley floor and walls, sourrounding rocks, debris.
- Deposition: Largely at the ice-rock interface or at the snout of the glacier, or beyond the glacier.
- Transportation: Either on top of the glacier, in the glacier, or at the base of the glacier.
- Mass movement: Valley walls - steeper areas - transports material onto the top of the glacier.
71
What are temporal variations in geomorphic processes.
Seasonal: Geomorphic processes happen faster in the summer due to greater glacier velocity and warmer temperatures.
Interglacial and glacial cycles: During interglacial periods, weathering will be the most prominent geomorphic process as rock is exposed to the weather. When there is a glacier much of the rock is covered, however erosion, transportation, deposition and mass movement are far more rapid.
72
What are the three types of glaciated landforms.
Erosional, depositional or periglacial.
73
What is an example of a Roche Moutonnee?
The Roche Moutonnee in the Nnant Ffrancon valley, Snowdonia.
74
What is a Roche Mountonnee and how do they form?
- A roche mountonnee is mass of resistant rock which sits in the base of a U-shaped valley. They have a smooth rounded side which faces up the valley (stoss side), and a jagged side facing down the valley (lee side)
- As the more resistant rock erodes slower than the rock around it, it sticks out higher than the sourrounding valley floor.
- Pressure melting point is reached on the stoss side causing meltwater to move round and freeze on the lee side, causing plucking to occur creating the jagged side. Abrasion occurs on the stoss side, acting like sandpaper and making it smooth, with some striations parallel to the ice flow.
75
What are striations and chatter marks and how do they form?
* Striations are a series of scratches in the bedrock as a result of abrasion from a glacier
* The scratches are parrallel to the direction of ice flow
* Chatter marks are just when a lump of bedrock is chipped out.
* Form when subblacial debris attactched to the glacier base scratches and chips the bedrock.
* Debris must be angular and resistant
76
What are examples of where striations and chatter marks can be seen?
- Nigardsbreen, Norway
- Moiry Glacier, Switzerland
76
What is a corrie and how do they form?
- Horseshoe shaped valley located on the shaded side of the mountain. Usually north east facing in the UK.
- Weathering of exposed rock faces by frost shattering generates debris which falls onto the ice that has accumulated, and down the backwall crevase providing 'tools' for abrasion.
- A hollow in a mountain side is deepend by Nivation, and as the ice in the hollow moves downhill in a rotational motion and plucks rocks from the backwall causing the hollow to deepen, and abrades with a grinding action.
- Summer and diurnal meltwater helps the ice to move by lubricating the base, as well as disintigrating rocks through freeze thaw weathering and frost shattering and allows basal sliding.
- At the front edges of the corrie the ice thins due to GPE converting to KE, and deposition at the snout of the cirque glacier creates a corrie lip.
- In interglacial periods, the ice melts to form a tarn in the bottom of the corrie.
77
What is an example of a corrie?
- Cwm Llwch, Brecon Beacons
- Cwm Idwal, Snowdonia
78
What is an arete and how do they form?
- The ridge between two corries, made of more resistant rock than the two corries either side.
- Same process of formation as a corrie due to it being what is left between two corries.
79
What are example of aretes?
Grib Coch, Snowdonia.
80
What is a pyramidal peak and how do they form?
- When three corries erode back to back, with three aretes seperating them and forming a sharp peak.
- Formation processes of three corries back to back.
81
What are examples of pyramidal peaks?
- The Matterhorn, Switzerland
- Mount Snowdon, Snowdonia
82
What are the main erosional landforms of glaciated landscapes?
- U-Shaped Vally
- Roche Mountonnee
- Striations and Chatter Marks
- Corries
- Aretes
- Pyramidal Peaks
83
What are U-Shaped valleys and how do they form?
- They are flat bottomed valley formed by glacier erosion which have very steep sides meaning the cross sectional profile is likened to a 'U' shape.
- Initially a river forms a V-shaped valley, with debris accumulating in the bottom.
- As ice tends to take the easiest route downhill, glaciers follow the path of the V-shaped valleys, eroding the base and side in the process via abrasion using the debris and plucking more debris from the bedrock.
- More debris falls ontop of the ice and down the sides of the glacier aiding abrasion.
- When the ice retreats, the valley has been deepend and widened with very steep sides and a flat base.
84
When were glaciers most recently in Snowdonia?
11,500 years ago
85
What are the glacial depositional landforms?
* Eratics
* Till Sheets
* Drumlins
* Moraines
86
Why might a glacier deposit material?
- Increase in pressure leads to more lodgement of till
- Once carrying capacity is reached
- Increase in ablation
- Drop in velocity
87
What are the three types of moraines and how do they form?
- Terminal Moraine (ridge of till extending across a U-shaped valley): Mark the position of maximum ice advance; deposited at glacier snout; cresent shape due to ice moving faster in middle; usually higher at the sides.
- Lateral moraine (ridge of till running along the edge of a U-shaped valley): Material accumulates on top of glacier side due to weathering; when glacier retreats it is deposited at side of valley
- Recessional Moraine (ridges running across U-shaped valleys): Form during temporary pauses in retreat; deposition of material at glacier snout.
88
What are examples of moraines?
- Franz Josef glacier in new zealand has left terminal moraine 430m high
- Athabasca glacier in Canada has left lateral moraine 1.5km long and 124m high
89
What is moraine?
- A mass of rocks and sediment carried down and deposited by a glacier, typically as ridges at its edges.
- As the glacier flows down hill, it picks up and erodes sediment and transports it. It then deposits the sediment at the edges of the glacier to form moraines, which are ridges due to the build up of the sediment. The glacier must be in equilibrium over a period of time to allow the sediment to build up.
90
What is hummocky moraine?
When a large chunk of glacier breaks off and melts, its debry is suddenly deposited. This is why they have a random and erratic appearance with not sorting or stratification.
91
What is an erratic and how do they form?
- An individual piece of rock, varying in size that is composed of a different geology to its sourroundings.
- They were eroded, ususally from plucking, or added via weathering or rockfall to the supraglacial debris.
- They are then transported by the glacier to an area of differeing rock type.
-
92
What is a good example of where erratics are found?
The Norber erratics in the Yorkshire Dales. These are blocks of Silurian shale perched on top of younger Carboniferous Limestone.
93
What are till sheets and how do they form?
- Till sheets are large expanses of thick unsorted glacial till deposited by an ice sheet as it retreats.
- The composition of the till sheet is determined by the area over which the ice sheet flowed so analysing it can help to reconstruct past ice sheets.
94
What is a good example of an area covered by Till sheets?
East Anglia is covered by glacial till and many of the cliffs in North Norfolk reveal layers of till deposited over several glaciations.
95
What is a drumlin and what are the ways the could form?
- A mound of glacial debris that has been streamlined into an elongated hell that can be 1km in length and 100m high.
- Stoss end is steeper and faces direction ice is coming from
- Elongated eggshape formed by moulding of till, with ratios of 2:1 up to 7:1
- Lee side faces in direction of ice flow and is streamlined and more gently sloping as till is dragged down slope by moving ice or fluvial streams.
1. Lodgement of subglacial debris as it melts out of the basal ice layers.
2. Reshaping of previously deposited material during a subsequent re-advance.
3. Accumulation of material around a bedrock obstruction - these are known as rock-cored drumlins.
4. Thinning of ice as it spread out over a lowland area, reducing its ability to carry debris.
96
What are good examples of where drumlins can be found?
North Yorkshire, New York State in the hills of Elslack
97
What key analysis points must be considered for glaciated landforms?
Climatic ~ Temperature and whether snow will form or how fast the glacier is flowing. Will the ice melt for deposition? Is the glacier advancing or retreating?
Geomorphic ~ Can processes occur? What type of rock or landscape is it? Is it predominantly deposition or erosion? What different types of transportation to the snout?
98
Summarise UK past glaciation.
* The glacial landforms we see today are the outcome of the pleistocene epoch glaciation, which begain 2.4 million years ago and ended around 10,000 years ago.
* Within this there are periods of glacial and interglaical for the UK. These major glacials also see local fluctuations known as stadials and interstadials which are short lived warmer and coller periods.
* The Devensian period is the most recent glacial period and started around 115,000 yeas and ended 10,000 ears ago.
* Last peak in glacitation was the Devensian period 18,000 years ago, where ice covered around 30% of the Earth's land surface. An ice sheet at this time covered much of the British Isles as far south as South Wales.
* Most recent stadial was the Loch Lomond stadial from 11,000 - 13,000 years ago.
* Glaciers remained in Scotland until 10,000 years ago.
99
What two statements can we make as a result of compating landforms left by glaciation and current processes?
1. Medium and large scale erosional landforms are likely to have been influenced by successive glacial advances
2. The form of depositional features tends to result from conditions and processes at work during the most recent glacial-interglacial cycle.
100
What causes fluctuations between glacials and interglacials?
Milankovitch cycles
101
What are hanging valleys and truncated spurs and how are they formed?
Tributary valleys that used to flow into a v-shaped valley, until a glacier came and turned this into a far deeper and wider valley, leaving these tributary valleys far above the new valley floor. Truncated spurs are the ridges betreen these tributary vallys that decend towards the valley floor. However, the glacier action has effectively cut the ends of them.
102
what three stages can the devension glaciation be thought of having in Snowdonia?
1) Last glacial maximum: 18,000 years ago. The large Welsh (Merioneth) Ice Cap joined with other ice caps to form part of the British Ice Sheet. During this period the glacial troughs of Nant Ffrancon will have eroded. They would have been occupied by outlet glaciers from the welsh ice sheet. Major peaks such as snowdon will have stuch out as nunatacks, such as Snowdon.
2) Late glacial: 13,000 years ago. After the last glacial maximum, there was a period of around 6,000 years where cirque glaciers fed valley glaciers which occupied Nant Ffrancon until they disappeared around 12,000 years ago. It was during this period that the nine cirques, such as Cwm Idwal along the western flank of Nant Ffrancon were further developed. The Loch Lonomd stadial enhanced the shapes of the corries and resulted in the deposition of hummocky moraine.
3) Present day landscape: No ice remains but the glacial features are clear and distinct as they are relatively recent.
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What is a nunatak?
A lonely peak that sticks out above an ice sheet or cap.
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What is an example of a corrie, tarn and hanging valley in Snowdonia.
Cwm Idwal, Llyn Idwal, Cwm Cywion
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What is an example of a glacial trough (U-Shaped valley), misfit stream, and arete in Snowdonia?
Nant Ffrancon, Afon Ogwen, Y Gribin
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What is an example of a glacial trough (U-Shaped valley), misfit stream, and arete in Snowdonia?
Nant Ffrancon, Afon Ogwen, Y Gribin
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What in an example of a ribbon lake, terminal moraine and nunatak.
Lyn Ogwen, Cwm Coch, Tryfan
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What are the impacts of geology, climate and aspect on the formation of corries such as Cwm Idwal and Cwm Coch in Snowdonia?
- Geology: Tough ignous rock makes up the side and back walls. Siltstone at the base is less resistant so gets eroded faster and hollows out.
- Aspect: North east facing, so doesn't receive much sun over the course of the day, as well as being on the far side of the mountaing to the prevailing wind so snow isn't blown away.
- Climate: Requires a cold enough climate to support glacier formation and not have a negative mass balance. Also needs to move across 0C to allow freeze thaw weathering and frost shattering to weaken rock and increase debris
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How does geology, climate and aspect influence the formation of tarns such as Llyn Idwal?
Geology: Less resistant and impermeable bedrock at base of corrie - clay and mudstone.
Climate: Requires a warm post glacial climate because they form when the glacial ice melts and gets trapped in the hollow of the corrie.
Aspect: Forms in the hollows of corries, so its location is impacted
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What geological rock sequence dictates the location of corries on the west flank of Nant Ffrancon valley?
Cambrian and Ordovician rock sequence
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What are examples of igneous rock found in Snowdonia?
Felsic Tuffs, Basalts, Microgranites
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How does geology, aspect and climate influence the formation of U-Shaped valleys such as Nant Ffrancon?
Geology: U shaped valleys are often located where there is softer sedimentary rock such as siltstone, between harder igneous rocks
Aspect: Aspect has very little impact on U shaped valley formation, unless it forms off a corrie
Climate: Requires a cold enough climate to support glacier formation and not have a negative mass balance. Also needs to move across 0C to allow freeze thaw weathering and frost shattering to weaken rock and increase debris
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How does geology, climate and aspect influence the formation of misfit streams such as Afon Ogwen?
Geology: Forms as small streams that run off Ribbon Lakes in hollows in U shaped valleys created by glaciers eroding less resistant rock, but do not erode the valley they are within.
Climate: Must be a warmer climate because misfit streams form in post glacial landscapes, and are formed when meltwater runs into the base of the U shaped valley.
Aspect: Very little impact
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How does geology, climate and aspect influence the formation of ribbon lakes such as Llyn Ogwen?
Geology: Meltwater builds up in hollows in the base of U shaped valleys
Climate: Must be a warmer climate because ribbon lakes form in post glacial landscapes, and are formed when meltwater runs into the base of the U shaped valley.
Aspect: Very little impact
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How does geology, climate and aspect influence the formation of aretes such as Tryfan and Y Gribin?
Geology: Formed when there is harder and more resistant igneous rock that erodes more slowly, causing there to be sharp ridges formed. The more resistant the rock, the steeper and sharper the ridge.
Climate: Requires a cold enough climate to support glacier formation and not have a negative mass balance. Also needs to move across 0C to allow freeze thaw weathering and frost shattering to weaken rock and increase debris
Aspect: Forms between corries that are heavily influenced by aspect, so therefore it impacts Aretes
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How does geology, climate and aspect influence the formation of pyramidal peaks such as Snowdon?
Geology: When there are 3 corries with softer sedimentary rock, formed alternately with 3 aretes between them, made of harder igneous rock
Climate: Requires a cold enough climate to support glacier formation and not have a negative mass balance. Also needs to move across 0C to allow freeze thaw weathering and frost shattering to weaken rock and increase debris
Aspect: Has some impact, however there are corries facing in 3 directions, so altitude is more of a factor than aspect in the formation of pyramidal peaks
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How does geology, climate and aspect influence the formation of Roche Moutonees such as the one in the Nant Ffrancon valley?
Geology: A small strip of harder igneous rock erodes slower than the softer sedimentary rock sourrounding it on the valley floor.
Climate: Requires a cold enough climate to support glacier formation and not have a negative mass balance.
Aspect: Very little impact
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What harder rock is the Nant Ffrancon roche mountonnee made of?
Felsite as an igneous intrustion within softer siltstone.
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Why is aspect particularly important in Snowdonia?
- In the more recent glacial periods since the glacial maximum 18,000 years ago, mainly in the Loch Lomond stadial, it was only really cold enough for glaciers to form in the shaded hollows facing north east.
- Also Snowdonia is at a relatively low altitude.
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What is the most important factor that decides the shape of a corrie?
Geology
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What is the most important factor for the location of a corrie?
Aspect
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What are the most important factors influencing the shape of a U-Shaped valley?
Releif and Geology
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What are two examples of landforms that are heavily interconnected?
Corries->Aretes->Pyramidal Peaks
Corries->Tarns
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How may a landscape be influenced over minutes, months, years, centuries, millenia and millions of years?
Minutes
- Mass movement events
Months
- Mass balance changes
- Changes in rate of weathering and erosion
Years
- Start to see impacts of geomorphic processes such as weathering, erosion and deposition
Hundreds of years
- Development of smaller land forms such as a roche moutonnee
Thousands of years
- Weathering of glaciated landscapes
- Development of larger land forms such as corries and aretes.
Millions of years
- Multiple glaciers and ice sheets in different ice ages
- Tectonic movement and changes in locations of landforms
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Where was the laurentide ice sheet located?
Much of Canada and Northern USA
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How thick was the laurentide ice sheet?
4km
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How many times has the laurentide ice sheet advanced and retreated in the last 2 million years (Pleistocene epoch of the Quateranry Period).
4 times
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When was the most recent advance of the Laurentide Ice Sheet?
Wisconsin glaciation 100,000 years ago.
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Describe the underlying geology of Minesota
- Northern part is covered by alternating parts of granite (igneous) and gneiss (metamorphic).
- South western part is sedimentary - shale, siltstone and sandstone.
- South eastern is limestone.
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What were the four lobes of glacial advance in the wisconsin glaciation?
- Wadena Lobe from north west
- Rainy Lobe from north east
- Superior lobe from east
- Des Moines lobe from west
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What happened druing the Wisconsin glaciation?
- Four ice lobes advanced and retreated a number of times across Minnesota.
- These lobes transported and deposited large quantities of glacial till across the state.
- The different origins of the different lobes resulted in tills with different charachteristics.
- The south west of Minnesota largely avoided ice cover so remains steep hills and river eroded valleys.
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What was the impact of erosion from the Laurentide ice sheet lobes.
- Wore down the mountains to form scoured mountains around 500-700m high.
- Highest peak is 701m
- Formation of low lying ellipsodial basin in north-east which now houses lots of lakes such as the upper and lower red lakes.
- Tectonic tilting aided the erosion of basins as it exposed less resistant shales that eroded quickly to form these basins.
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What was the depositional impact of the Wadena lobe?
- Deposited a till sheet with reddish-iron rich sediment (red sandstone and shales).
- Formed the Wadena drumlin field which tends southwest showing the direction of movement.
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What was the depositional impact of the Rainy Lobe and Superior Lobe
- Left a coarse-textured till with fragments of basalts, red sandstone and slate.
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What was the depositional impact of the Des Moines lobe
- Deposited till (160m deep) a tan coloured, clay-rich and calcareous, passed over shale and limestone.
- In Southwest, Moraine at Prairie Coteau.
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What was Glacial Lake Agassiz and how did it form?
- As ice retreates, vast amounts of meltwater are released an may be trapped by ice or a moranic dam.
- Ice retreated 11,000 years ago causing meltwater to be relesed.
- The edge of the Laurentide Ice Sheet and the lobes blocked the meltwater from its natural passage to the sea so lakes were formed, with the largest being Lake Agassiz.
- At its maxium it was 400m deep and covered 440,000km^2
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What was the Glacial River Warren Valley and how did it form?
- Formed as glacial lake Agassiz burst its banks 9000 years ago at Browns valley cutting a deep chennel (Traversal gap) and drained.
- Left deposits of fertile silt in the valley
- Eroded a valley 7 miles wide and the river itself was miles wide in places.
- Now valley holds Minnesota river which is far smaller.
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What are the waterfalls formed by the Glacial River Warren (now Minnesota river)
- Minehaha and St Aurthon waterfalls
- Formed due to more rock
- Moving up stream 2-4 ft a year due to erosion
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How did climate impact the Minnesota landscape?
- Occured due to latitude and cooling global temperatures.
- Temperatures were on average 8.5°C cooler than the current interglacial allowing expansion of the lobes
- Short warmer periods where temperatures are 5°C warmer led to retreat depositing till.
- Temperature rise caused retreat forming lakes from meltwater and isostatic readjustment due to the weight of ice being lifted.
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What is isostatic readjustment?
When the downwards pressure of an ice sheet due to its vast weight is taken away by melting, the land slowly rebounds back upwards over thousands of years.
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How did geology impact the Minnesota landscape?
- Weaker rocks (shales) exposed by tectonic tilting eroded faster reated a knock & lochan landscape creating deep lakes such as lake Vermillion depth of 23m, and up to 60m deep.
- Harder igneous rock areas remained higher and formed pyramidal peaks such as Eagle mountain 701m high
- Rock types influence the till sheets deposited
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How did relief impact the Minnesota landscape?
Highland areas diverted lobes to follow low, flat areas due to gravity.
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What is a knock and lochan landscape?
A glaciated landscape of low relief which is made up of ice-moulded hillocks and intervening lochans (small lakes) eroded along zones of rock weakness.
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How many km^2 did the Laurentide ice sheet cover at its peak?
13 million
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What is the key difference in the glaciated landscapes seen in Snowdonia and Minnesota?
Snowdonia is associated with valley glaciers, while Minnesota is associated with the Laurentide Ice Sheet.
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How does climate influence glaciation in Snowdonia and Minnesota differently?
Snowdonia:
- Determines mass balance of a glacier
- Requires a long period of glacial climate to form large landforms due to glaciers being spatially smaller.
- Warm based glaciers so erosion is faster
Minnesota:
- Climate must be cold enough for tens of thousands of years to from an ice sheet 4km thick
- Fluctuation of the temperautre caused formation of lobes that have eroded and shaped the landscape through deposition.
- Lake Aggasiz was created due to warming climate, and meltwater created Glacial River Warren valley.
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How does altitude influence glaciation in Snowdonia and Minnesota differently?
Snowdonia:
- Has great importance as in 13,000 to 11,000 years ago temperatures were too warm to sustain a glacier at lower altitudes in Snowdonia.
Minnesota:
- Has little influence as ice sheet is 4km thick and mountains were flattened to under 700m.
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How does releif influence glaciation in Snowdonia and Minnesota differently?
Snowdonia:
- Allows the glacier to move downhill and thus erode a U-Shaped valley
- Dictates glacier routes and velocity, which has a large impact on the location of landforms.
Minnesota:
- Releif caused the ice sheet lobes to spread from areas of higher altitude to lower altitude
- Influenced the flow of the Glacial River Warren.
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How does aspect influence glaciation in Snowdonia and Minnesota differently?
Snowdonia:
- Large impact on the formation of corries, especially at lower altitudes where glaciers can only form on the shaded north east side of mountains.
Minnesota:
- No impact of note
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How does geology influence glaciation in Snowdonia and Minnesota differently?
Snowdonia:
- Reistance of rocks has a huge impact on the location and shape of landforms
- Mainly sedimentary rocks so valleys can erode quickly
Minnesota:
- Restant rock areas remain higher, while ellipsodial basins form in softer areas
- Rock types eroded by lobes influences the composition of till sheet depositions.
150
How does climate influence glaciation in Snowdonia and Minnesota differently?
Similar latitudes, so little difference. Snowdonia is 53 degrees north while Minnesota is 47 degrees north.
151
How does continentality influence glaciation in Snowdonia and Minnesota differently?
Snowdonia:
- More precipitation as located near coast, so diagenisis is faster.
Minnesota:
- Colder winters due to continental climate, so ice melts less and cold based. This means the ice could build up to be incredibly thick.
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What is the name of the current interglacial we are in and how long ago did it start?
Holocene, 11,000 years ago.
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What is the devensian period called in the parts of America impacted by the Laurentide ice sheet
Wisconsion period
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What is a period called when large ice sheets start shrinking?
Post glacial - covers the end of the last glacial period and the current interglacial.
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What has the retreat of ice sheets in the last 20,000 years resulted in?
Huge amounts of meltwater creating glaciofluvial landforms.
156
What has happened to the meltwater output of the Greenland Ice Sheet in the last 5 years?
It has more than doubled
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What is a moulin and how do they impact the greenland ice sheet?
- Holes where meltwater runs deep into the ice sheet, and they lubricate the base of the ice sheet.
- They also add heat to the ice which softens it and makes it flow more under its own weight.
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How much could the greenland ice sheet influence sea level rise by 2100?
Contribute 1m
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What does glacio-fluvial mean?
Glacio-fluvial is a term which refers to the processes, sediments and landforms produced by meltwater flowing through glaciated landscape systems
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What five charachteristics can define a glacial fluvial landscape, and how do these differ from glacial landforms?
- Stratification: Sediment has distinct layers in it due to phases of deposition, where as glacial landforms are unstratified
- Sorting: Sediment is all of a similar size, where as glacial landforms are poorly sorted.
- Imbrication: Sediments have their long axis aligned in one direction. Glacial landforms have no imbrication.
- Shape: Rounded shaped rocks and sediment. Glacial landforms have more angular sediment.
- Grading: Large sediment is deposited first, and smallest sediment is deposited last leading to a sequence fromed from top to bottom. Smaller sediments are carried furthest. Glacial landforms have no grading.
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What factors increase meltwater?
* increased temperatures increase the amount of meltwater.
* Increase in dust creates a darker surface absorbing more heat.
* Increase in lakes causes absorption of more heat due to darker surface. Moulins (water plunging deep into the ice) soften the ice making meltwater more likely.
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What are Kames and how do they form?
- A deposited mound of sediment left in the path of a retreating glacier
- Meltwater streams accumulate in depressions on the surface of the ice.
- Crevasses may become filled with debris carried by the meltwater.
- When the ice melts, these deposits of glacial-fluvial sediment are left on the valley floor as a raised mound.
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What are eskers and how do they form?
- A sinuous (winding) trail of deposited material from a subglacial channel. It shows the channels course.
1) A subglacial stream forms due to increased pressure
2) The channel carries sediment into the glacier and also takes sediment with it
3) When the glacier retreats, the subglacial stream stops flowing because the hydrostatic pressure from the glacier is lost
4) It deposits all its material now because it doesn't have the energy to carry it and it is dumped in the path of where the channel was in a long line
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What is an example an esker?
- Munro Esker in Canada
- Blakeney Esker (3.5km in length, up to 20m tall and 100m wide)
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What are delta kames and how do they form?
- An terrace that is formed when melted water flows around or through a glacier and deposit materials (sediments) called kame deposits.
- A subglacial channel is formed from the glaciers pressure
- It entrains the material and transports it downstream
- As the subglacial channel meets the proglacial lake, it looses its energy and therefore deposits the sediment
166
What is a proglacial lake?
A lake that forms when meltwater is trapped by moraine and/or ice
167
What are kame terraces and how do they form?
- A flat-topped mound or hill composed of stored sand and gravel, often down along the edges of glacial valleys.
- Pressure between the valley sides and glacier forms a ice marginal channel/lake
- As water (carrying sediment) travels into the valley, it collects here.
- The ice-marginal lake/channel is not flowing so it deposits the material
When the glacier retreats, it leaves the sediment at the valley sides
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What are examples of kame terraces and delta kames?
- KT: Fenton river valley Kame Terrace
- DK: The Fonthill Kame Delta in the Niagara Peninsula region
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How do climate and geomorphic processes influence the formation of kames and eskers?
- Rapid melting increases formation of eskers and kames
- Delta and Terrace kames do not require as warm an environment as they form between the glacier and the valley wall by filling in ice marginal lakes
- Weathering of valley walls and mass movement events causes debris to fall onto the glacier
- Transportation mainly englacially and supraglacially, apart from delta kames
- Deposition when the meltwater looses energy
- Attrition makes sediment more rounded
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What are outwash plains and how are they formed?
- A large expanse of wide open land formed of glacio-fluvial sediment
- Supraglacial and subglacial meltwater carries debris and sediment and deposits it past the snout of the glacier
- Larger debris is deposited by braided streams (winding streams of meltwater running from the snout of a glacier) first, and smaller sediment last as the streams lose energy and disperse.
- This means horizontal sorting occurs of the sediment found on the outwash plane
171
What are kettle holes and how do they form?
- A hollow, typically filled lake, resulting from the melting of a mass of ice trapped in glacial deposits.
* Formed when large blocks of ice are calved away from the glacier onto an outwash plain.
* As the glacier retreats the ice is left stranded and then surrounded or buried by the outwash deposits.
- When temperatures increase the block melts leaving a large depression in the ground which can be filled by rainwater.
172
What is calving?
The process when large lumps of ice brek off the snout of the glacier into the sea as ice bergs, or just onto the groumd leading to the formation of kettle holes.
173
How does a warming climate influence landforms?
- More postglacial landforms and glaciofluvial landforms will form.
- Weathering of newly exposed landforms previously coevered by ice
- More space and better climate for vegetation
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How does colonisation by vegetation influence landforms?
- Biological weathering and covering of landforms
- Can hold some landforms together due to roots
175
How does mass movement influence landforms?
- Removal of ice supporting lateral moraine and debris leads to debris reaching the base of the valley and altering the landscape.
- Infill of tarns, ribbon lakes and misfit streams from debris
- Flattening of eskers due to mass movement
176
How does weathering influence landforms?
- Warmer temperatures may increase rate of freeze thaw weathering
- Increase in biological weathering
- Rates of chemical weathering increase in warmer temperatures (other than carbonation)
177
How does human activity influence landforms?
- Buildings on land that is now uncovered may stop natural processes
- Footpath erosion
- Fumes and greenhouse gas emissions create enhanced greenhouse affect that warms climate and leads to more ablation
- Farming on till sheets
- Extraction of materials
- Building dams and flooding valleys
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What are periglacial landscapes?
Periglacial refers to the processes and landforms associated with the zones found within cold climates which are not permanently covered with snow or ice. Usually taken to be the presence of permafrost: permanently frozen ground.
179
What percentage of the worlds landscapes have been shaped by periglacial land?
15%
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During the devensian, what type of landscape was southern England?
Periglacial
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What is permafrost
Permafrost is frozen ground which remains frozen all year round for at least 2 consecutive years - can be as deep as up to 1500m
182
What is permafrost made of
Rock, sediment and soil, and various quantities of ice
183
What is the active layer?
The thin layer of soil above the permafrost - it thaws each summer, and re-freezes each winter - ranges from 30-200cm
184
What often indicated the presence of permafrost
Ice wedged polygons and ice veins
185
How much of the exposed northern hemisphere land surface is currently permafrost?
25%
186
What is continuous permafrost?
Where there is no break in the permafrost. Temperatures usually below -5C on average
187
What is discontinuous permafrost?
Contains patches of unfrozen ground. Temperatures are between -5°C and -1°C.
188
What is sporadic permafrost?
Sporadic permafrost - Islands of permafrost found at the fringes of discontinued permafrost. Temperatures fluctuate around -1°C and 0°C.
189
What is talik?
An area of unfrozen land sourrounded by permafrost
190
Why is the active layer often boggy in the summer?
Because the water cannot penetrate the permafrost beneath
191
Where is talik ususally found?
normally when there is something insulating the area such as a lake.
192
What are ice lenses and how do they form
- Bodies of ice withing the active layer
- Free moisture in the soil freezes
- Water seeps through the ground (talik) by capillary movement towards frozen sediments and comes into contact with frozen water.
- The water cools and freezes when it contacts the lens causing it to grow and the ground to swell as water expands by 10% when freezing.
193
What is frost heave and how does it work
* Where the repeated freezing and thawing of the ground can push stones upwards through fine sediment, causing rocks to form patterns on the ground.
* Once rocks reach the surface as a result of Frost Heave, they then move down undulating ground due to GPE, forming circular patterns.
194
Explain frost push and pull
Frost pull ~ The top of a rock freezes to the ground which then expands (10%) and pulls the rock upwards. Due to low thermal conductivity freezing passes through the ground more easily in winter.
Frost push ~ As a result of the rock being pulled upwards there’s a small cavity below the rock which becomes filled by sediment and water which then freezes expanding and pushing the rock up. This continues in a cycle.
195
How does freeze thaw weathering impact perglacial landscapes?
* Water seeps into cracks and fractures in rock.
- When the water freezes it expands by 10% wedging apart the rock.
- With repeated freeze/thaw cycles, rock breaks into pieces.
196
How doe ice wedge polgons form?
- 1st winter: Water freezes in a crack in the ground causing it to exert pressure as the ice expands, widening the crack.
- 1st summer: This water melts as the ground thaws, leaving water trapped in the crack. Water seeps into the crack and it fills up.
- 2nd winter This water then re-freezes, once again exerting pressure and widening the crack.
- 2nd summer This water melts as the ground thaws, leaving water trapped in the crack. Water seeps into the crack and it fills up.
- 100th winter The process repeats anually, leading to cracks in the ground becoming wider and wider
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What is patterned ground?
· As frost heave repeats over many years it forms stone circles, polygons or stripes. This is due to gravity pulling the rocks into small depressions where they accumulate.
198
What are pingos?
ce cored hills that rise abruptly out of flat landscapes in periglacial landscapes such as the Arctic.
199
What are the two types of pingo?
Closed system: formed in drained residual lake
Open system: Formed in discontinuous permafrost
200
How do closed system pingos form?
- Residual lake above continuous permafrost has been filled in and drained over time
- This means ground is less insulated so permafrost advances
- Hydrostatic pressure from permafrost forces pore water to be squeezed out and freeze into an ice lense just below surface
- As more and more water gets squeezed up into the ice lense and freezes
- Ground above swells into mound due to water expanding by 10% when it freezes
201
How do open system pingos form
- An ice lense forms in discontinuous permafrost
- Artesian pressure causes groundwater to be drawn up to the ice lense, and freeze when it reaches it leading to he ice lense expanding
- This ice lense starts to push the ground above it up as it continues to grow from ground water
202
How can periglacial landforms be modified when the climate warms?
Patterned ground:
- More vegetation causes biological weathering
- Pattern of rocks becomes more scattered due to weathering
Pingos:
- Becomes a ognip, which is a collapsed pingo after ice core melts forming a basin with a lake in
* Biological weathering
* Mass movement
* Solifluction
203
What process is the gradual movement of wet soil down a slope
Solifluction
204
Context behind Prudhoe bay
- Located in Alaska
- 250 miles north of Arctic Circle
- 800 mile Tran Alaskan pipeline runs to Valdez port to be shipped
- 1.4 million barrels of oil a day
205
Why is there oil drilling at Prudhoe bay
- Supply the increasing US population and economy with secure energy
- Sell oil for money
206
What is the impact of oil drilling on the natural flows within the periglacial landscape at Prudhoe bay?
| Materials
- Conventional construction alters the thermal balance of the ground leading to the thaw of permafrost & ground subsidence as vegetation is cleared.
- Gravel is extracted from streams and used as insulation in 1-2m thick gravel pads.
- The loss of gravel alters the rate at which it is transported & deposited downstream, also affecting the balance between erosional and depositional processes in the river stream.
207
What is the impact of oil drilling on the natural flows within the periglacial landscape at Prudhoe bay?
| Energy
- Over pressurising industrial plant equipment is dangerous so flammable gases are burnt off in flaring, releasing large amounts of CO2 & methane.
- Barrow’s (town in Alaska) population has increased from 300 in 1900 to 4600 in 2000 for the oil industry, increasing infrastructure.
- The buildings have produced an urban heat island effect with mean temperatures 2.2°C higher than surrounding rural areas.
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Impact on periglacial landscape and landforms of oil drilling at Prudhoe bay
Removal of vegetation means ground ice is less insulated causing ice lenses to collapse or melt sitting on the surface due to impermeable permafrost below. When permafrost thaws there is increasing instability resulting in a thermokarst landscape.
* Alases ~ Large, flat floored and steep sided depressions sometimes containing lakes.
* Thaw lakes ~ Small scale and shallow. Form where depressions are due to thawing ice.
- Solifluction lobes ~ Where the surface layer melts in summer, forming the active layer, it becomes mobile as it is saturated due to the impermeable permafrost below. The whole mass of material moves down slope.
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What is a thermokast landscape
distinctive landforms as a result of melting ice. Has extensive areas, boggy and hummocky ground with surface depression.
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What are solifluction lobes
- Where the surface layer melts in summer, forming the active layer, it becomes mobile as it is saturated due to the impermeable permafrost below.
- The whole mass of material moves down slope. Slow process – usually between 0.5 - 5cm/year (rarely exceeds 10cm).
- Can occur on slopes as gentle as 1-2 °. The movement produces lobes forming a terrace or stair arrangement with ‘risers’ and ‘treads’.
- Increased movement in the active layer results in gelifluction (a type of solifluction).
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What is the context of the Grande Dixence Dam?
- South west of Switzerland.
- Highest gravity dam (285m).
- Stores 400 million m3 of glacial meltwater
- HEP.
- To reduce global warming and climate change, making Switzerland carbon neutral and gaining energy security.
- They can adjust to seasonal peaks and troughs.
- Located in the Alps, which are a glaciated landscape.
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What are the impacts of the Grande Dixence Dam on flows of material through the glacial system
- There is a large impact on the flows of sediment that is transported by the meltwater coming off the glaciers that feed into the reservoir.
- As water looses energy when it is stored in the dam, it deposits sediment at a rate of 20-40cm a year.
- Meltwater is stored from the summer in the reservoir, and mainly released in winter to provide energy.
- 85% of the stored water is used for energy, where as the other 15% is used to purge the sediment, letting it flush out and not build up.
- There is also less water moving into the ground because the dam is well sealed.
- The amount of sediment that lake Geneva has recieved has halved since the dam was built.
213
The impacts of the Grande Dixence Dam on flows of energy through the glacial system
- Kinetic energy of the meltwater moving off the glaciers is converted and stored as GPE, causing deposition of sediment in the reservoir.
- This GPE is then converted back to kinetic energy and then electrical energy that is used by humans.
- Darker water absorbs more insolation into the valley
214
The impact of the grande dixence dam on (meltwater) river channels
- The trapping of sediment in the dam leads to very clear water in the rivers beyond the dam. This means the water has more excess energy due to it not having to transport sediment leading to increased erosion rates.
- There is less water in the rivers below the dam, leading to some drying up during the summer months.
- The river channels are contracting with increasing scale as you move downstream from the dam.
215
Impacts of the Grande Dixence Dam on the wider landscape - be descriptive about sediment build up and reductions across the valley
Negative impacts on ecosystems and communities downstream because of impacts such as habitat change, degradation and temperatures.
216
Difference of impacts on flows of materials between PB and GDD
PB:
Gravel extracted from river systems and used as insulation under houses
GDD:
* Sediment carried in glaciofluvial meltwater streams is deposited.
* Sediment build up occurs at 20-40cm/year behind the dam.
* Sediment concentrations are 300mg/l above the dam and 20-50mg/l below the dam.
217
Difference of impacts on flows of energy between PB and GDD
PB:
- Gas is burnt (flaring) to reduce pressure in oil extraction systems.
- Heat from buildings causes an 'urban heat island' effect around towns such as Barrow, warming the air by up to 2.2degrees C higher.
- Heat from buildings is transferred into the permafrost below.
GDD:
- KE of meltwater is converted to GPE, then back to KE and the electrical energy
218
Difference of impacts on landforms between PB and GDD
PB:
- The permafrost melts and creates depressions on the ground - these can coalesce and create alas lakes.
- Highly saturated layers of melted permafrost are created as water cannot continue to percolate through permafrost. These layers can creep downwards under gravity creating solifluction lobes.
GDD:
- Channels below the dam virtually dry up in the summer months as there is reduced discharge.
- Channels below the dam carry less sediment and have more energy to erode, causing channel scour and increased channel erosion.
219
Difference of impacts on landscape between PB and GDD
PB:
- Large scale melting of permafrost creates a hummocky landscape of saturated, boggy ground with water filled depressions called 'thermokarst' landscapes.
GDD:
- Sediment input into Lake Geneva has almost halved since the dam was built.
- U shaped valley is flooded and glaciofluvial sediment is deposited on the floor of the valley upstream of the dam.
