P1 - Glaciation Flashcards
Name 4 pro glacial landforms
- pro-glacial lakes
- kettleholes
- sandurs (outwash plains)
- Meltwater channels
Describe how a pro-glacial lake is formed
- Formed along the front of glaciers and ice sheets where melt water from the glacier becomes impounded with a deposition blocked by glacier ice and bounded by high grounds
Describe how kettles are formed
During ice retreat, blocks of dead ice become detached. Sediment builds up around the dead ice and when they eventually melt, a small hollow is formed in which water accumulates to form a lake
Describe how a sandur (outwash plain) is formed
What is it?
- a flat expanse of sediment deposited in form of a glacier
How does it form?
-as the melt water streams gradually lose energy due to entering lowland areas, they deposit their material. The largest material is deposited nearest the snout and the finest further a way.
Describe how a melt water channel is formed
Melt water on the surface of the glacier melts its way through the glacier to the base through a ‘moulin’. Once the melt water comes out from the base of the glacier it forms a channel in front of to the glacier
Name three fluvioglacial landforms
Esker, Kame, Kame terrace
Describe how an esker is formed
Subglacial streams carry large amounts of rock debris due to their hydrostatic pressure inside the tunnels. The stream often meanders beneath the glacier, when the glacier retreats, the debris load is deposited at a consistent rate and forms a ridge.
Describe what an esker is
A long, narrow, sinuous (widening and meandering) ridge of sand and gravel
Describe how a Kame is formed
A meltwater stream emerges into an outwash plain or peri glacial lake at the glacier snout, their velocity falls and energy is lost causing sediment to be deposited.
Describe what a Kame is
An undulating mound of sand and gravel deposited on the valley floor
Describe how a Kame terrace is formed
During the summer, the valley sides radiate heat. This melts the edge of glacier forming a meltwater stream. This deposits sediment. When the glacier retreats, the sediment will fall to the valley floor, forming a Kame terrace.
Describe what a Kame terrace is
A flat, linear deposit of sand and gravel along the valley sides
Name 3 peri glacial landforms
Pingo (open and closed), patterned ground, ice wedges
Describe how a closed system pingo is formed
The lake insulates the talik preventing it running to permafrost. Water begins to drain from the lake reducing the amount of talik. Pressure from the advancing permafrost allows land (talik) to settle above.
Hydrostatic pressure causes the water to turn to ice. Hydrostatic pressure also pushes the land above causing the land to be disformed.
What is talik
Unfrozen ground in a periglacial area that surrounds the permafrost
Describe how ice wedges are formed
A thin piece of ice (around 3-4 metres in length) causes a crack in the rock. In the winter, ice freezes and expands. When the temperature rises, the ice melts. More water fills the crack and permafrost freezes it. This process repeats itself until a polygon of ice goes deep into the ground.
Describe what an ice wedge is
It is a wedge of ice extending 3-4 metres underground, usually in a polygon shape
Describe how patterned ground is formed
Ice wedges form underneath granite. As the ice wedges continue to expand (by 10%) the land above buckles and creates a trough with small mounds. Ice wedges melt causing land to fall in its place. This leaves new mounds in between where the ice wedges used to be.
Describe how an open system pingo is formed
Groundwater moves through the ground and eventually finds a weakness in the permafrost. Hydraulic pressure causes the water to rise up through the cracks. As the water gets closer to the surface, the temperature decreases turning into ice. Hydrostatic and hydraulic pressure causes the ice to continue moving upwards. This creates an open system pingo
Name 5 macro erosion landforms
U-shaped valley, hanging valley, ribbon lake, pyramidal peak, corrie/cirque
Describe how a ribbon lake is formed
Meltwater at the glacier base plays a role, and where PMP is exceeded, the glacier can basically slide encouraging even more erosion.
Differential erosion= some parts of the valley floor are over dependant creating ribbon lakes.
Describe how a corrie is formed
Snow accumulates in a hollow. Snow compacts making a neve/firn and glacial ice. Ice becomes too big for the hollow and moves down the slope. It will move in a rotational slip. The hollow deepens through invasion, abrasion and plucking. Freeze thaw shatters rocks above the hollow and delivers shattered rock (scree) to the ice - abrasion. Pressure melting point is often surpassed allowing melting to exist which allows basal slippage. This creates a steep back wall and a hollow known as a corrie.
Describe how a pyramidal peak is formed
If three or more corries development on all sides of a mountain a pyramidal peak is formed. The feature has steep sides and several arêtes radiating from the central peak.
Name an example of a pyramidal peak
The Matterhorn, Alps
Describe how a U-shaped valley?
As the glacier leaves the Corrie it moves down the old river valleys that are V-shaped. As the valley glacier moves down the valley, it plucks material from the valley sides and base. This allows abrasion to occur making the valley deeper and wider. Lateral and ground moraine abrade the valley sides and the floor further. The front of the glacier acts like a bulldozer and shifts and removes the plucked material turning the interlocking spurs into truncated spurs.
Describe how a hanging valley is formed
Hanging valleys are created due to different rates of erosion between the main valley and the tributary valleys that enter it along its sides. The floors of the tributary valleys are eroded and deepened by abrasion and plucking at a slower rate than the floor of the main valley, so the difference between the depths of the two valleys steadily increases over time. The tributaries are left high above the main valley, hanging on the edges. In the post glacial, rivers and streams return and enter the main valley by either a series of small waterfalls or a single impressive fall.
Name 3 messo erosional landforms
Roche mountonness, crag and tail, knock and lochan
Describe how a crag and tail is formed
The glacier erodes soft rock and then reaches a band of hard rock. Once the band of hard rock is reached, pressure builds and pmp is reached enabling the glacier to overcome the hard rock. This causes a rapid decrease in pressure and a fall below pmp. This causes a loss in energy, causing the glacier to drop sediment. This forms the tail of the crag and tail.
Describe how a Roche mountonness is formed
The glacier encountered the obstacle, pressure increases and allows melting to occur (PMP exceeded). This allows the ice to melt and basal slippage to occur, rocks trapped in this ice abrade the bedrock. This abrasion on the up-valley sides of the glacier can leave striations as pieces of rock debris with the ice were dragged across the surface under great pressure. Once the Lee side pressure fails and the water refreezes (regelation) and as the ice moved downhill it pulls away masses of rock; plucking the rocks underneath. This leaves a steeper sided, more jagged Lee slope.
Describe how a knock and lochan is formed
Alternating Roche mountonness and eroded hollows often containing small lakes
Give an example of a crag and tail
The royal mile, Edinburgh
Name two micro glacial erosion landforms
Crescentic gouges and striations
Describe how crescentic gouges are formed
Plucking
Describe how striations are formed
Caused by abrasion
Name 5 glacial depositional landforms
Lateral moraine, recessional moraine, terminal moraine, medial moraine and drumlins
Name the two theories of how drumlins are formed
Boulton Menzies, shaw theory
What are the 4 types of moraine?
Lateral moraine, recessional moraine, terminal moraine, medial moraine
Describe how lateral moraine is formed
Debris from freeze thaw weathering falls onto the glacier and then is transported and then deposited at the edge of the glacier when in melts
Describe how recessional moraine is formed
Debris is deposited during the interrupted retreat of the glacier, when the glacier is stationary long enough for there to be a build up of material
Describe how terminal moraine is formed
Debris is deposited at the maximum extent of the glacier, especially if the snout is stationary and the glacier is in the equilibrium. It will be continuously supplied in the same place.
Describe how medial moraine is formed
At the confluence of two tributary glaciers, the lateral moraines join together medial moraine, which is deposited during ice melt and retreat.
Describe the boulton menzies theory of drumlin formation
An obstacle gets in the way of the glacier and this leads to deposition on the Lee side. The obstacle is the core of the drumlin and the ground moraine is around it.
Describe the shaw theory of drumlin formation
Subglacial meltwater causes channels and bars to the channel which are shaped by the glacier (streamlined)
What are the three long term milankovitch cycles?
- eccentricity
- obliquity
- precession
What is eccentricity?
How the earts orbit of the sun changes from circle to oval
It changes every 96,000 years
What is obliquity?
The earths tilt
It is currently at 23.5 degrees, but it varies between w21.5 degrees and 24.5 degrees with a period of about 41,000 years
What is precession?
A process that happens between 19,000 and 21,000 years
Positive feedback
Increasing the warming or cooling rates
Negative feedback
Decreasing the warming or cooling rates
Where was the Loch Lomond stadial?
Northern Scotland
What was the date of ice sheet retreat and rapid retreat?
Ice sheet retreat- 18,000 years ago
Rapid retreat- 15,000 ago
What is the vegetation in Northern Scotland?
Deciduous woodland
What was the cause of the Loch Lomond stadial?
Drainage if the huge proglacial Lake Agassiz distrusted the THC and changed ocean currents
What were the long term effects of the Loch Lomond stadial?
It changed the landscape
What was the location of the little ice age?
Global
When was the little ice age?
1550 and 1750