Presentation on theme: "Glaciation Learning Intentions"— Presentation transcript:
1Glaciation Learning Intentions Be able to understand the processes which occurred during the last ice age.Be able to describe and explain the formation of features formed during glacial periods.
2Processes Of Weathering Freeze-Thaw Water enters crackIce freezes and exerts pressure from inside rockRock breaks upover time
3Processes Of Erosion Plucking Water can enter cracks in the rock and freeze, as it does so it freezes the glacier and rock together.As the glacier moves it literally pulls the rock out and is likely to occur more when temperatures fluctuate around 0ºC.
4Processes Of Erosion Plucking The water from this process often comes from the friction between ice moving over rock.Another source of the water is a result of melting of the ice; during the day it melts, but refreezes at night.Plucked Rock
5Processes Of Erosion Abrasion This is when rock under the ice or stuck in the bottom of it, scrape away at the surface of the bed rock surface.The rock comes from the debris produced by Freeze Thaw and Plucking.The bedrock is scratched, polished, smoothed and eventually worn away by the scouring action.
6Processes Of Erosion Abrasion Striations or scratches can be left on the rock
7A corrie is a deep, rounded hollow with a steep back wall. Features of erosionCORRIESSnow collects in hollows, especially on the less sunny north and east facing slopes, turns to glacial ice and moves downwards under the force of gravityRocks are plucked out and the hollow is widened by abrasion to become a corrie.A corrie is a deep, rounded hollow with a steep back wall.
8Match the letters to the descriptions. Corries Task 3 Q2Match the letters to the descriptions.Flat BaseHorse shoe shapeSteep sidesCliffs/ Outcrops/Screebdac
10Corrie Formation Stage 1 Snow collects in hollows high up in the mountains, usually in north facing slopes.Pressure causes the lower layers of iceto turn to ice.Gravity and reduced friction cause the iceto move downhill.The hollow in which the snow and ice collected is eroded by the ice to form a much deeper, steeper hollow called a Corrie.
12Corrie Formation Stage 2 As meltwater under the ice seeps into cracks the rock in the hollow is weathered by freeze thaw action.Then when the meltwater freezes onto the rock plucking takes place.The backwall and sidewalls of the hollow are eroded quickly by these two processes.Abrasion due to rocks taken in by frost shattering and plucking deepens the hollow.The glacier slips in a rotating movement, which means that it is eroding the most at the back wall and base. So with less erosion at the base so a lip starts to form, which has deposits of rocks left on it by the glacier
14Corrie Formation Stage 3 When the ice melts a corrie can clearly be seen.It is an armchair shaped hollow in the mountainside with steep sidewalls and steep backwall and a flat base.Sometimes after glaciation, corries fill with meltwater to form corrie lochs or tarns.
18Features of erosionARETEAn arete is a narrow, sharp-edged ridge which forms the side walls of corries or separates different glacial valleys.
19Arete FormationAretes are formed when two corries are found back to back or side by side in the mountain area.Plucking and freeze thaw action erode the backwalls of both corries towards each other.The land between them gets narrower and narrower until all that remains is a steep knife-edged ridge of rock.
20Striding Edge arete on Helvellyn, Lake District arete Features of erosionStriding EdgeStriding Edge arete onHelvellyn,Lake District
21Pyramidal peaks are also called horns. Features of erosionMATTERHORNPyramidal peaks are also called horns.
22Diagram Of Pyramidal Peak Pyramidal PeaksDiagram Of Pyramidal PeakbPyramidal PeakErosioncca
23Pyramidal Peak Formation Found where 3 or more corries are located in the same mountainside.Plucking and freeze-thaw action of the backwalls of each corries occurs to such an extent that the rounded summit is eroded into a sharp peak or point.The rock erodes back so that the mountain becomes steeper and the three corrie walls come close enough to convergeThis leaves a pointed and jagged (freeze thaw) peakeg. The Eiger (The Alps)
24U Shaped Valley b Steep sides d Deep valley c a Loch in wide valley Straight valley
27Features of erosionA VALLEY GLACIERThe next few slides will help to explain the formation of this feature.
28U Shaped Valleys Ice starts to flow out of corries or off ice caps It flows down V shaped river valleys
29Ice moves down river valley Usual erosion occursAbrasion deepensPlucking erodes sides backGlacier also bulldozes rock out of the wayU shaped valley develops
30U-shaped valley formation When a glacier erodes its valley, a classic U shape is formed, the side walls tend to be steep and possibly curving inwards at the base, and the valley floor almost flat.U shaped valleys start life as V shaped river valleys that existed before glaciation. Ice moves down the V shaped valley and glaciers erode it and change its shape as the ice moves.Plucking and freeze-thaw action truncate spurs of rock and steepen the valley sides and abrasion deepens and flattens the valley floor. Over time the valley also becomes straighter.
31Misfit StreamAfter glaciation when the ice melts, the river which originally flowed on the floor of the V-shaped valley may once again begin to flow through the U-shaped valley.It is now called a Misfit Stream. It is so called because it looks out of place in the now large valley and also because it did not contribute to its formation.
32Ribbon LakeAt some points in the U-shaped valley, glaciers erode more deeply than elsewhere.This might have been because the rock was softer and more easily eroded or because the ice was thicker at this point and therefore more powerful.Where ice did this, it would create an overdeepened hollow which after glaciation filled with meltwater to become a Ribbon Lake.The lake takes on the same shape as the valley in which it was formed – so tends to be long and quite narrow.
34Truncated Spurs Bulldozed by glaciers Abrasion & plucking help with erosionPost glaciation freeze-thaw has created more scree below
35Steep Sides U Shaped Valley Truncated SpursCliff FacelScreemkSteep Sides U Shaped Valley
36These are deep U shaped valleys formed by the erosion of valley glaciers As glaciers emerge from the lip of their corries they merge and form a more powerful glacier which erodes more readilyThey follow the course of former V shaped river valleysAs they progress down the valley through their own weight (gravity) they erode like a corrie glacierThe top of the valley sides are eroded by freeze thaw weathering, mid height of the valley by plucking and the base by abrasionThis means that the former V shaped valley will widen, steepen and deepensWhen a U shaped valley cuts across a water shed it is called a glacial breechThe interlocking spurs of the river valley literally have their noses cut off by the ice, leaving a ridge descending into the valley which suddenly steepens, sometimes into an outcrop or a cliff faceThe steepest part of the valley is often at the trough head (start) where the descending corrie glaciers move quickly under gravity. Other more eroded points tend to be a result of the glacier moving over weaker rock which abrades readily, deepening the baseThis over deepening can fill in with water leaving a ribbon locheg, Loch Avon (Cairngorms)
37Stages in the formation of a U-shaped valley Features of erosionStages in the formation of a U-shaped valley
38A U-shaped valley in Canada. Features of erosionA U-shaped valley in Canada.
39Features of erosionWhen a glaciated valley by the coast is submerged or drowned by a rise in sea level, a fiord is formed.The sea lochs of western Scotland are the best examples of fiords in the British Isles.Fiord/fjord
40Features of erosionA hanging valleyVertical erosion in the main glacier is far greater than in the tributary glaciers. So the valleys are not the same depth.After the glacier has retreated, rivers flowing down the tributary join the main valley via a waterfallCan you spot the river delta,too?
41U-shaped valleys have few contours on their floors. Features of erosionTruncated spurU-shaped valleys have few contours on their floors.There is a hanging valley here.Note the very steep sides.waterfallMisfit stream
42Features of erosionWhen a glacier moves along the valley, some parts are deepened more than others.When the glacier retreats, the deepest parts fill with water and become lakes.The English LakeDistrict owes itscharacter to thesenarrow ribbon lakesalong its valleyfloors.Ribbon lakes
43Material is dropped at the ‘break of slope’ to form this fan shape. Erosion/ depositionCaused when a stream falling from a side valley reaches flatter ground on the valley floor.Material is dropped at the ‘break of slope’ to form this fan shape.An alluvial fan(This is really a depositional feature.)alluvium = silt deposited by a river
44These are partly erosional, partly depositional features. Erosion/ depositionA crag and tailEdinburgh CastlecragtailPlug of volcanic rockThese are partly erosional, partly depositional features.The rock face facing the ice is steepened by glacial erosion. Softer rock on the other slope is protected from erosion to form a tail of boulder clay.