Cold Environments Landforms Flashcards
Describe the weathering of rocks?
It is the breakdown of rocks in situ. The finer particles produced can be moved away by agents of erosion such as water and wind
In cold environments physical weathering processes dominate name the main one
Frost shattering
Describe Frost shattering
Water enters a crack in a rock. At night when temperatures drop below 0°C the water expands by approximately 9%. Exerting pressure on the rock. This will happen thousands of times, widening the crack and eventually will cause pieces of the rock to break off.
What is the collection of material produced by Frost shattering known as?
Scree
Describe the process of abrasion (in glaciers)
When angular material embedded in the glacier rubs against the valley floor wearing it away finer material leaves are polished surface while course the material leaves striations. The material caught up in the ice and worn down by abrasion is known as rock flour.
Describe the process of plucking
When glacial ice freezes on to rocky outcrops and as the glacier moves away it takes the piece of rock with, it is mainly found at the base of the glacier where pressure and friction result in the melting of ice. It can also result in plucking.
What rocks is plucking common in and what does it leave?
It is common in weldjoint rocks that have been weakened by Frost shattering and leaves a jagged surface.
Describe a corrie
An arm chair shaped hollow with a steep back wall and deep base and it may contain a tarn and often has a raised lip
Describe the process of corrie formation
- Snow accumulation on NE and E facing slopes with little insolation
- The hollow is deepened by nivation
- Snow accumulates and the pressure causes it to turn to ice
- The weight of the ice causes it to rotate and move
- The ice pulls away from the back of the hollow, plucking occurs
- Frost shattering causes rock to drop onto the ice, this material supplied by plucking allows the glacier to abraded the floor and over deepen the Corrie basin
- A large crevasse forms at the back of the hollow called a Bergschrund
- The front of the corrie the ice is thinner and failed to produce the same level of abrasion and the rock lip develops
Give an example of a tarn
Red tarn in the Lake District
Describe and arête
When two or more corrie glaciers erode back to back from opposing side they produce a knife edge ridge called an arête
Give examples of and arête
Striding edge in the Lake District
What happens when three or more corries erode back towards each other and what is an example of this?
Pyramidal peak forms and example of this is the Matterhorn in Switzerland
What do glaciers do to pre-existing river valleys?
They straighten, widen and deepen these valleys, they change the original V shape to a U shape
How does glacial erosion differ to river erosion?
Wild Rivers Road vertically any of the sections glaciers erode horizontally as well as vertically they are better able to road obstructions that streams and rivers would meander around
Does the action of ice have a great erosive power than that of water?
Yes, along with meltwater and subglacial debris
What is the technical term for a Valley shaped by a glacier
A glacial trough
Why are some places in glacial valleys deeper than others?
Compressional flow means that more erosion will occur leading to the formation of rock basins
over deepening can also occur at the confluence of two glaciers
In post glacial times what mate over deep parts of the valley be filled by?
Ribbon lakes
Give an example of a ribbon lake
Wastwater in the Lake District
What may extension flow leave?
Less eroded, more resistant rock steps
What happened to some glacial troughs once sea levels rose?
They became submerged and fjords formed
What is it called when a glacial Valley ends abruptly and what lies above it?
It is called trough end and above it lie a number of corries
What is left when a tributary glacier joins a larger glacier after both glaciers have disappeared?
A hanging valley is left due to differing rates of erosion, they may be marked by a waterfall
In some areas glaciers do not remove small areas of resistant rock what does this leave?
Roche Moutonnées with an upvalley side (stoss) and a downstream side left jagged from abrasion
What may abrasion have left on the upValley side of the Roche moutonnees?
Striations
What is another feature similar to a roche moutonnees and give an example of it
A crag and tail is the same thing only the opposite way around and an example is in Edinburgh on the site of the castle and the Royal mile
Name the three types of glacial debris
- Supraglacial debris- on the surface of glaciers
- Englacial debris- inside glaciers
- Sub glacial debris- beneath the ice
What are glacial deposits often called?
Drift, to distinguish them from the underlying geology
What are the two types of glacial deposit?
Number one: till or boulder clay
Number two: fluvioglacial material
Describe boulder clay
All material deposited directly by the ice, it is unsorted.
Describe fluvioglacial material
Sediment deposited by meltwater streams that they are usually sorted with coarser material deposited near the glacier snout and with finer particles carried further
How would till have been transported in a glacier?
As supraglacial or englacial material
Where do some deposits in Norfolk come from?
Norway
What is till formed from subglacial material that was deposited by and actively moving glacier known as?
Lodgement till
Name five types of moraine
- Terminal moraine
- Push moraines
- Lateral moraine
- Medial moraine
- Recessional moraine
What are erratics?
They are rocks in the wrong place and maybe very different to the local geology, they are fragments of glacial debris that have been carried large distances before being deposited for example Shap granite erratics are found on the Holderness Coast in East Yorkshire that originally came from Cumbria
What is a lateral moraine?
Debris fallen on the sides of a glacial valley after glaciation and it looks like long embankment of debris at the side of the valley
What is medial moraine?
It is formed when two places meet and the two lateral moraines may join to form a medial moraine
What is a terminal moraine?
It is often a series of high mounds of debris that extends across the valley marking the point that a glacier reached
What is recessional moraine?
They are essentially the same as terminal moraines and are formed by glacier retreat
What are push moraines?
Again essentially the same as terminal moraines but are formed by glacial advance
What are drumlins?
They are rounded oval-shaped hills which look like the top half of an egg they are formed from insulted till deposited by a moving glacier
How long and how high can drumlins be?
Up to 1.5 km long and 50 m high although most are smaller
What are the two ends of a drumlin called?
The steep end is the stoss and the sloping end is the Lee
In which direction are drumlins elongated?
In the direction of ice advance
What is it called when there are multiple drumlins in an area?
A swarm or “basket of eggs topography”
Where are drumlins often found?
On lowland plains such as the central lowlands of Scotland
How is it believed that drumlins are formed?
When ice becomes overloaded with debris. The ice becomes unable to carry all of the material and so deposition occurs at its base. Once it has been deposited the material becomes streamlined as the ice advances over and around it
Give five reasons why meltwater is important
- Helps enlarge nivation hollows
- Lubricates the base of a glacier
- If it refreezes, melt water can bind the base of a glacier to broken rock
- It can form ‘meltwater’ rivers
- It will for several depositional features
What is different about fluvioglacial deposits from till?
It is sorted
How deep can subglacial streams erode and why?
They can form valleys deeper than 15m. They carry much more debris than a normal river of the same size and flow under great pressure with a turbulent flow
Describe an outwash plain?
An extensive, gently sloping area of sands and travels that form in front of a glaciers snout, they are formed from sediments deposited by meltwater rivers
How are outwash plains composed?
The coarsest material is deposited first and the finest material is deposited last, they reflect the seasonal flow of meltwater streams as they carry coarser deposits further in the summer
Where can outwash plains be found?
Iceland and Alaska
Describe an esker
Long, sinuous ridges of sorted material, mainly sand and gravel that run in the direction of ice advance, they are often stratified
Give potential measurements of eskers
The can be up to 30 M high and can run for several KMs
How is it thought that eskers are formed?
By subglacial rivers in the final stages of glaciations, when the ice was melting away and no longer moving forward.
Why can eskers sometimes run up gentle gradients?
The subglacial stream they were formed by were under considerable hydrostatic pressure and so could flow uphill for short distances.
How do eskers often appear now?
As discontinuous hills, as meltwater and postglacial rivers have eroded them away
What are Kames?
Deposits of sorted and often stratified sand and gravel left by meltwater along the front of a melting ice sheet
Why do kames often collapse?
As the ice supporting them melts
What shape are kames, often?
Conical
What are the three types of Kame?
- Kame Terrace
- Kame delta
- Crevasse Kame
Describe a Kame Terrace
Long, bench like features on the side of the valley. They’re formed when a gap between the valley side and ice is filled with fluvioglacial deposits, leaving behind a Terrace as the glacier melts. When the ice finally melts, the Kame Terrace is abandoned as a ridge on the valley side.
Describe a Kame delta
A Kame delta is a smaller feature that forms when a stream deposits material on entering a marginal lake. Kame deltas form small mound-like hills on the valley floor, and can be identified by their deltaic sedimentation characteristics
Describe a crevasse Kame
Some kames arise from the fluvial deposition of sediments in surface crevasses. When the ice melts, they are deposited on the valley floor to form small hummocks
What is the key to identify Kames and eskers?
They are made up of sand and gravel, rather than clay-rich till like the surrounding countryside
Describe kettle holes
A series of small depressions filled with lakes and marshes. They’re formed when blocks of ice buried beneath fluvioglacial material melt, leaving depressions
Describe kettles
They’re the opposite of kames, being depressions rather than mounds. They are often found near each other and create a ‘Kame and kettle topography’
What are varves?
Layers of sediment in meltwater lakes
What are the colours and seasons of the different varves in a glacial lake?
Heavier sand is deposited in late spring when meltwater streams reach peak discharge. The darker coloured clay is layer down in the cooler autumn, when volumes of meltwater decrease. Discharge in the autumn is lower so streams can only carry finer sediments
What are the effects of glaciation on drainage?
They can form proglacial lakes and breach drainage divides, the diversion of streams and the excavation of deep overflow channels.
When do proglacial lakes form?
When deglaciation occurs, lakes form from the accumulation of meltwater, they are known as proglacial lakes
What can proglacial lakes do to drainage basins?
They can cross the lowest points of watersheds and create new valleys. When the ice damming the proglacial lake melts, the new valleys can be left dry. In some cases however postglacial drainage patterns can be changed by them
Give the potential temperature ranges for periglacial areas
Up to 15°C in the summer and it can drop to 50°C in the winter in some areas
When can ground be called permafrost?
When subsoil temperatures fall below 0 degrees, for two years or more
How much of the earth’s surface does permafrost cover?
Around 1/4
In summer an active layer can form in permafrost areas, how deep is this active layer?
Up to 4m deep
What happens when the surface layer of permafrost thaws?
It releases water it is unable to drain and, as there’s little evaporation due to low temperatures, the surface becomes very wet
Describe continuous permafrost
Found in the coldest regions e.g. The Arctic. There’s little thawing even in the summer. It can affect the rock and soil up to depths of up to 700m in parts of Canada and up to twice this depth of Siberia
Describe discontinuous permafrost
Slightly warmer regions where freezing conditions do not penetrate such deep depths (20 to 30m). It is discontinuous as it is broken by river, lakes and the sea
Describe sporadic permafrost
Annual temperatures are around or just below 0. Permafrost only occurs in isolated spots
Describe the process of frost heave
Upon freezing, fine grained soils expand unevenly upwards to form small domes. Stones in the soil heat up and cool the surrounding materials faster. Cold can pass through the stones very quickly meaning the soil below the ground in likely to freeze and expand. This will continue until the stone reaches the surface
How is patterned ground formed?
On small domes, larger stones move outwards, effectively sorting the material which, when viewed from above, takes on a pattern.
What is solifluction?
The slumping or movement of rock and soil material in response to gravity. Most likely to occur in the summer after significant melting
When do solifluction lobes form?
When thaw melting occurs in the active layer leads to the release of great meltwater. As the water is unable to percolate downwards, saturating the soil, making it highly mobile. The soil begins to ‘flow’ due to in part the lack of substantial vegetation.
Describe a pingo
A rounded hill with an ice core
What are the two types of pingo?
Open system and closed system
How big can pingos be?
Up to 60m in height and 600m in diameter
How many pingos are there estimated to be in the Mackenzie delta region of Canada?
Over 1400
How is a pingo formed?
In discontinuous permafrost, water seeps into the upper layers of the ground and freezes and expands outwards causing the overlying soil to ‘heave’ upwards
How is a closed system pingo formed?
They form in areas with continuous permafrost where there are frozen lakes. The frozen lake insulates the ground beneath it, creating Talik. As the talik freezes in the winter, the water trapped in it expands pushing the layers of soil above it upwards, forming a pingo
What happens when a Mackenzie pingo melts?
It collapses and forms a depression which could be filled by a small lake
Describe the process of ground contraction
Essentially freeze thaw weathering in the soil where water enters a crack expands, exerting pressure on the walls of the crack, the ice then melts and the process is repeated.
How does wind action work in frozen environments?
They can cause abrasion and dislodge fine sediments, leaving polished rock surfaces
What is the name of the fine material that is transported of long distances by wind action and where is it found?
Loess, it is often found in North America and Eurasia, south of the boundary of the Pleistocene ice sheets
In England what depth do loess deposits rarely exceed?
More than 2m
In China how deep can loess deposits reach?
Depths of over 300m
What’re loess deposits known as in East Anglia and the London basin?
Brick-earth deposits
