Glaciation Part 2 Flashcards
Weathering
Uses heat energy to produce physically or chemically altered materials from surface or near surface rock.
What are the processes for physical or mechanical weathering?
Freeze-thaw, frost shattering and pressure release.
Physical or mechanical weathering
The break down of rock that produces small fragments of the same rock.
Freeze thaw
Water enters cracks and expands by almost 10% when it freezes. In confined spaces, the exerts pressure on the rock, causing it to split or break.
Frost shattering
At really low temperatures, water trapped in rock pores freezes and expands. So disintegrates the rock due to stress.
Pressure release
When the weight of overlying ice in a glacier is lost to melting, the underlying rock expands parallel to the surface.
Chemical weathering
The decay of rock.
What are the processes of chemical weathering?
Oxidation, carbonation, solution, hydrolysis and hydration.
Oxidation
Minerals in rock react with oxygen, either in the air or in water. The rock becomes soluble under acidic conditions and the original structure is destroyed.
Carbonation
Rainwater with dissolved carbon dioxide produces a weak carbonic acid. Then reacts with calcium carbonate in rocks to produce calcium bicarbonate with is soluble.
Solution
Some salts are soluble in water so minerals such as iron dissolves.
What is Biological weathering?
It may consist of physical actions such as the growth of plant roots.
What are the processes of biological weathering?
Tree roots and organic acids.
Tree roots
Grown into cracks in rocks and exert outward pressure.
Organic acids
Produced during decomposition of plant and animal litter which causes soil water to become more acidic and react with some minerals.
What is geomorphic?
Related to the form of the landscape
Geomorphology
The study of landscapes/ landforms and how they form.
What is Erosion?
The wearing away and removal of soil, rock or dissolved material.
Where does material carried by glaciers come from?
Rockfall
Avalanches
Volcanoes
Debris flows
Abrasion
Plucking
Aeolian deposits
Material deposited by lactation is known as what?
Drift
What are the two types of glaciation drift?
1) Till- directly deposited by the ice
2) Outwash- deposited by meltwater
What are the two types of glacial Till?
Lodgement till and ablation till
Lodgement till
Deposited at the base of advancing glacier due to melting
Ablation till
This is the more common glacial till. Material is deposited as the ice melts away from retreating or stagnant glacier.
What are the characteristics of glacial till?
Unsorted and ungraded.
Angular- sharp edges
Ranging in size from rock flour to angular rock.
Unstratified
Hydrolysis
Minerals in rock can undergo a chemical reaction when in contact with water
Hydration
When water molecules are added to rock minerals they create minerals of larger volume.
Mass movement
Occurs when the forces acting on a slope material exceed the forces acting to keep material on the slope. It causes downslope movement of material.
What is rockfall?
It occurs on slopes of 40 degrees or more and is due to gravity and physical weathering. The rock then accumulates at bottom of the slope.
What are slides?
Occur when there’s a movement along a slight line slip plane. Might also occur where erosion at the base of slope undercuts valley side increasing force of gravity.
What are slumps?
Where there’s more rotational movement along a curved slip plane.
What is solifluction?
Gradual mass wasting process which occurs on slopes.
What is erosion?
The wearing away and removal of soil, rock or dissolved material.
What are the two main processes of glacial erosion?
Plucking and abrasion
what is plucking?
An erosional process that removes larger fragments of rock. Meltwater gets into cracks and joints in the rock and as the water freezes around pre-weathered rock it becomes part of the glacier. Plucks rock away as it advances.
What are the factors affecting rates of plucking?
Nature of bedrock
Weakening of bedrock by weathering making rock more susceptible to erosion
Pressure melting point
What is abrasion?
A type of erosion where rock fragment in glacial ice scrape along the valley bed and sides. The coarse material will create scratches in rock called striations.
What are the factors affecting rate of abrasion?
Presence of basal debris.
Debris size and shape
Hardness of particles and bedrock
Ice thickness
What is nivation?
A process of freeze thaw, solifluction, transport by running water and possible chemical weathering.
It leads to initial enlargements of hollows on hillsides to the development of corries.
Glacio-fluvial deposits
The result of deposition by glacial meltwater during a period of retreat or stagnation.
What is a corrie?
An armchair shaped hollow with a steep back wall. The hollow itself is over-deepened and is often characterised by a rock lip.
Diameter of between 0.5 and 1 km.
Depth of between 100 to 400 m.
Example: Cwm Idwal, Snowdonia
What is an arête?
A knife edged ridge which separates two corries.
Example: Crib Coch, Snowdonia
What is a pyramidal peak?
An angular glaciated mountain peak with three or more steep sides, which are usually back walls of corries.
Example: summit of mount snowdon
What is the formation of a U-shaped valley?
As a glacier moves through a river valley it erodes he sides and floor by abrasion and plucking. Pre-exciting spurs are cut off creating truncated spurs.
Example: Nant Ffrancon Valley, Snowdonia
Length of between 1 and 50km
Width of between 0.5 and 3 km
What is a Roche moutonnée and example?
Masses of more resistant rock that are smooth and rounded on the up valley side often with striation marks whereas the down valley side is steep and jagged.
Example: Nant Ffrancon Valley, Snowdonia
Often up to 1km in length and 100m high
What are glacial striations?
Scratches made in rock by debris embedded in the base of the glacier.
What are glacial grooves?
Large striations. They are gouged into the rock as debris in the base of the ice is pushed and pulled along.
What are chatter marks?
A series of crescent shaped gauges chipped out of the bedrock as a glacier drags rock fragment underneath it.
What are ellipsoidal basins?
Deep elongated lakes that are formed by sub glacial activity.
Example: Great Lakes of North America
How are the Great Lakes of North America formed?
Due to glacial over deepening. In this case it was due to the presence of vulnerable softer geology.
As retreating ice sheets carved basins into the land and they became filled with meltwater.
Approx size of the Great Lakes?
Lake Superior covers and area of the approx size of Austria with an average depth of 147m.
What are moraines?
Landforms that develop when material is carried by a glacier and deposited.
What are Lateral moraines, and how are they formed?
Run along the edge of a glacial valley.
Formed by debris that is frost shattered from the valley slopes. Material falls onto the surface of glacier and carried along the edges. The debris is then deposited as melting occurs.
What is our example and size of a lateral moraine?
Example: Athabasca glacier, Canada
Size of 1.5km long and 124m high.
How are medial moraines formed?
Where two glaciers meet resulting in the mergence of two lateral moraines. Material is often on the top (super glacial) and about 1m of coarse debris.
What is our example of a medial moraines and their size?
Athabasca glacier, Canada.
Length of up to 20km, width of up to 100m and height of up to 10m.
What is a terminal moraine?
A ridge of till extending across a glacial trough, usually steeper on up valley side and tend to be crescent shaped. It arks the maximum extent of the glacier, forming at the snout.
What is our example of a terminal moraine and its size?
Cromer ridge
Height of 400m, length of 15km and width of 20m.
What is a push moraine?
If a glacier readvances, previously deposited material may be pushed back up.
What are recessional moraines?
Series of ridges running transversely across a glacial trough.
Material is deposited as it retreats.
The longer the pause, the greater size of moraine.
What is an erratic?
Pieces of rock that are geologically out of place. They can vary from huge boulders to small pebbles.
How do erratics form?
Initially supra-glacial debris, either from plucking or rockfall. Then transported and deposited into an area of differing rock type.
Example: Norber erratics, Yorkshire Dales
How are till plains formed?
When large masses of unstratified drift is deposited at the end of an advance, smoother surface.
Example: East anglia covered by chilly till.
How’s till transported to become till plains?
Transported as supra-glacial debris which is then later deposited to form a moraine.
What are drumlins?
Smooth elongated mounds of till that are often found in clusters called “drumlin swarm”. They range in size from small mounds to huge hills.
Long axis is parallel to direction of ice movement.
What is our example of drumlins?
Hellifield Ribblesdale, North Yorkshire.
May be a result of ice sheets coming down from the Lake District that are overloaded.
What is our case study for the landscape associated with the action of ice sheets?
Minnesota, The Laurentide ice sheet.
What’s the geology of Minnesota?
Its oldest rocks lie in alternating belts of volcanic and sedimentary rocks. Between these belts lie granite rock material.
When did the formation of the volcanic and sedimentary rock formation begin?
2500 million years ago when lava escaped through rifts.
How are the mountains in Minessota formed?
Gneisses have been folded and faulted to form some of the mountainous areas.
How did the ice sheet move across Minessota?
Through a series of loves that extended form the main Laurentide ice sheet and into Minnesota. These loves advanced and retreated a number of times.
How did the glacier affect the geology of Minessota?
As the ice sheet advanced and retreated it transported and deposited till. The lobes originate from different places so different characteristics of till.
What’s the erosion impact of the Laurentide ice sheet on the relief/altitude of the land?
The ice sheet eroded many of the mountains with the highest peaks now of 500-700m.
What’s the erosion impact of the Laurentide ice sheet on creation of lakes?
Creates an ellipsoidal basin containing many lakes.
The ellipsoidal basin was particularly deep in arrowhead region due to igneous rock.
What are pro-glacial lakes?
As glaciers retreat, large amounts of meltwater is released which may become trapped against an ice sheet.
What was the till deposits from the rainy and superior lobe?
Course textured till.
What were the till deposits from the Wadena lobe?
Left ground moraines with red coloured sediment.
What were the till deposits from the Des Moines Lobe?
Till that was tan to buff coloured, clay rich and calcareous.
What’s our example of Minnesota’s pro-glacial lake?
Lake Agassiz
How was Lake Agassiz formed?
Retreat of the Laurentide ice sheet and large volumes of meltwater is released which may get trapped onto the ice sheet. This blocks natural drainage paths to the north which forms the pro-glacial lake to the south of the ice sheet.
What’s out case study for the landscape associated with valley glaciers?
Snowdonia
What is Snowdonia’s geology?
An upland area that experienced volcanic activity, folding and sedimentary deposition. Initially the area would have been similar to the Himalayas, however recent activity has changed that.
How long ago was the last glacial maximum in the UK?
20,000 years ago
What was the erosional impact of the glacier on U-shaped valleys?
Created the Nant Ffrancon Valley- Ushaped valley that was calved by an outlet valley from Migneint ice sheet moving NW.
What is the rock step in the Nant Ffrancon valley?
A drop of 100m and there’s a waterfall. The rock type here is resistant to erosion. The volume of ice was unable to erode this section of the valley.
What are truncated spurs?
They were interlocking spurs but have been eroded by the ice creating truncated spurs.
What is the hanging valley in the Nant Ffrancon valley?
Along the west side of the valley, smaller glaciers didn’t cut the old upper courses of rivers as deeply as the main glaciers.
What’s our example of a corrie in Snowdonia?
Cwm Idwal
It is a lot deeper than other corries in the area so more erosion has occurred.
Average depth of 3m.
What’s our example of aretes in Snowdonia?
Crib Goch
923m high
What depositional landforms are in Snowdonia?
Drumlins, tills and moraines, eskers and kames.
What are the types of moraines that are in Snowdonia?
terminal, lateral and hummocky in the area of Cwm Idwal.
Where are the drumlins located in Snowdonia?
Conwy valley
What’s our example of our esker for Snowdonia?
Pentir esker
What’s our example for the Kame in Snowdonia?
Pertir kame
Why are these landscapes in Snowdonia changing over time?
Periglacial processes.
Weathering
Sedimentation
Fluvial erosion
