Glaciated Landscapes Flashcards
What is a glaciated landscape?
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.
What is a glacier?
They are huge flowing bodies of ice that move downhill and carve out landscapes over thousands or millions of years.
What is the importance of glaciers?
- 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.
What properties does a glaciated valley have?
- Flat bottom to the valley’s
- Steep sided mountains
- Jagged rock faces and ridges
- Bare rock faces
- Little vegetation
Where do we find glaciated landscapes?
HIGH ALTITUDE - LOW LATITUDE
LOW ALTITUDE - HIGH LATITUDE
Above the permenant snow line
5 What are the types of glacier?
And description
- 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.
How much is mountaintop glacier ice disappearing in some parts of the world?
90%
What is the proccess that forms glaciers?
Diagenisis - snow turning into ice.
Explain the process of diagenisis.
- 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.
What climatic conditons are required for diagenisis?
Cold enough so that snow doesn’t melt in the summer.
How does pressure impact the temperature that ice melts?
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.
What are typical properties of warm based (temperate) glaciers?
- 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.
What are typical properties of cold based (polar) glaciers?
- 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.
Why does temperature vary with depth in a glacier?
Due to the increasing pressure of the layers of ice as you go deeper.
Where does a glacier move fastest and slowest?
Fastest at the top and in the middle, slowest at the battom and the sides. This is because there is less friction.
What are the three main types of glacier movement?
- Basal sliding
- Internal deformantion
- Bed deformation
What is basal sliding?
The act of a glacier sliding over the bed due to meltwater under the ice acting as a lubricant.
What is internal deformation (creep)?
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.
What is bed deformation?
The deformation of soft sediment of weak rock beneath the glacier causes it to slip downhill due to gravity.
What are the 3 types of basal sliding
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.
How do ice sheets move in comparison to valley glaciers?
- 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.
Why do some glaciers move faster than others?
- 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.
How does relief impact a glacier?
- 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.
How does climate (seasons) impact a glaciers movement?
- 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.
What type of system are glaciers?
Open system as they allow inputs and outputs of energy and matter.
What are inputs into a glacier system?
- KE (wind)
- Thermal Energy (sun, geothermal)
- GPE (altitude)
- Precipitation
- Debris
- Meltwater
- Avalanches
What are the throughputs of a glacier system?
- Snow
- Ice
- Debris
- Meltwater
- GPE (Altitude)
- KE (movement of glacier)
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)
What are the energy transfers involved with HEP and glaciers?
Solar -> GPE -> Kinetic -> GPE -> Kinetic -> Electrical
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.
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.
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.
What is the definition of ablation?
The loss of ice mass due to melting and sublimation (small contribution)
What is the defintion of mass balance?
The annual mass balance of a glacier is the difference between accumulation and ablation over one year.
What processes are dominant at the source of the glacier?
Accumulation
What processes are dominant at the snout of the glacier?
Ablation
What part of the glacier sees more accumulation?
zone of accumulation
What part of the glacier sees more ablation?
The zone of ablation
What point on the glacier sees equal ablation and accumulation?
The equilibrium line
What state of equilibrium do glaciers exist in?
Dynamic equilibrium
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.
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.
Why is seasonal variations in glacier mass balance much less in higher latitude glaciers?
Precipitation rates are much lower.
Where is the South Cascade Glacier and what type is it?
A cirque glacier in the Cascades range in Washington, USA.
How far has the South Cascade Glacier retreated from 1958 to 2013?
1.1km
What is the reason for the retreat of the South Cascades glacier?
Global warming
What is a positive feedback loop?
A feedback loop that takes a system further away from dynamic equilibrium.
What is a negative feedback loop?
A feedback loop that returns a system to dynamic equilibrium.
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
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.
What factors affect how a glacier shapes glaciated landscapes?
- Aspect
- Precipitation and Temperature
- Geology of the Landscape
- Relief
- Altitude and latitude
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.
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.
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.
What is lithology
The physical and chemical composition of rocks
What is the structure of rocks?
The properties of individual rock types such as jointing, bedding and faulting.
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.
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.
How much does temperature decrease with altitude?
0.6C /100m
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
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’.
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.
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.
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).
How much of the earths surface is covered by glacial deposits?
8% (30% in Europe)
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.
What are the three types of weathering?
- Chemical
- Biological
- Physical
Explain the three types of physical warming.
- Freeze-thaw ~ Water enters cracks and expands by nearly 10%. This exerts pressure on the rock causing it to split or break off.
- 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.
- Frost shattering ~ Water trapped in rock pores freezes and expands and disintegrates individual rocks.
Explain the two types of biological weathering.
- 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.
- Organic acids ~ These are produced during decomposition of plant and animal litter causing soils to become more acidic and react with minerals (chelation).
Explain the 5 types of chemical weathering.
- Oxidation ~ Some minerals in rocks react with oxygen either in the air or water breaking them down.
- Carbonation ~ Rainwater and dissolved carbon dioxide from the atmosphere produce carbonic acid which reaves with rocks dissolving them.
- Solution ~ Minerals dissolving in water.
- Hydrolysis ~ Silicates combine with water producing secondary minerals such as clays. Chemical reaction between rock minerals and water.
- Hydration ~ Water molecules added to rock minerals create new minerals of a larger volume. Causes surface flaking in many rocks.
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.
How is a landscape ‘prepared’ for glacial erosion when there aren’t glaciers.
- Sub-surface rotting - occurs in warm periods and causes the weathering of the bedrock
- Frost action
- Overburden and dilatation (pressure release)
- Wind weathering and mass movements
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.
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.
What are the three types of glaciated landforms.
Erosional, depositional or periglacial.
What is an example of a Roche Moutonnee?
The Roche Moutonnee in the Nnant Ffrancon valley, Snowdonia.
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.
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
What are examples of where striations and chatter marks can be seen?
- Nigardsbreen, Norway
- Moiry Glacier, Switzerland
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.
What is an example of a corrie?
- Cwm Llwch, Brecon Beacons
- Cwm Idwal, Snowdonia
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.
What are example of aretes?
Grib Coch, Snowdonia.
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.
What are examples of pyramidal peaks?
- The Matterhorn, Switzerland
- Mount Snowdon, Snowdonia
What are the main erosional landforms of glaciated landscapes?
- U-Shaped Vally
- Roche Mountonnee
- Striations and Chatter Marks
- Corries
- Aretes
- Pyramidal Peaks
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.
When were glaciers most recently in Snowdonia?
11,500 years ago
What are the glacial depositional landforms?
- Eratics
- Till Sheets
- Drumlins
- Moraines
