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Glaciation 2 Selkirk High School

Glaciation 2 Selkirk High School. Features of erosion. FEATURES OF GLACIAL EROSION. These are the features you will need to be able to describe, explain their formation, draw a labelled sketch of and recognise on an OS map. CORRIES. PYRAMIDAL PEAKS. ARETES. U-SHAPED VALLEYS.

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Glaciation 2 Selkirk High School

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  1. Glaciation 2 Selkirk High School

  2. Features of erosion FEATURES OF GLACIAL EROSION These are the features you will need to be able to describe, explain their formation, draw a labelled sketch of and recognise on an OS map. CORRIES PYRAMIDAL PEAKS ARETES U-SHAPED VALLEYS HANGING VALLEYS TRUNCATED SPURS RIBBON LAKE

  3. Features of erosion CORRIES Snow collects in hollows, especially on the less sunny north and east facing slopes, turns to glacial ice and moves downwards under the force of gravity Rocks are plucked out and the hollow is widened and deepened by abrasion to become a corrie. A corrie is a deep, rounded hollow with a steep back wall.

  4. Features of erosion Read the section about corries in the textbook. There is a bullet-pointed list of actions explaining in order how a corrie is created on pages 97-98. Learn this at home! Also learn how to draw and label sketches that show the formation of a corrie.

  5. MAXIMISE YOUR MARKS ! Features of erosion NOTE;- labels in sketches can just show features or named parts of them, or they can be annotations that help to explain how the feature formed. Annotations describe what is happening in the sketch, naming the processes. Annotations make the diagram- worth more marks than one where bits only are named!

  6. Features of erosion Look at these questions with answers;- Read and remember these Q1. Where is the bergshrund and what causes it? A. It is at the top of the back-wall, where the ice is ripping away from the rock because of gravity pulling the ice downhill. Q2.What erosion process greatly affects the backwall, and how does this affect the rock texture here? A.Plucking is the main process here and it leaves the rock jagged and rough.

  7. Features of erosion Q3.The debris created by plucking is active elsewhere in the corrie- where and with what results? A.Abrasion uses the plucking products to smooth, deepen and enlarge the floor/ basin of the corrie. Q4. Describe how corries, aretes and pyramidal peaks are all related features. A. To create an arete, there has to be more than one corrie eroding the land between them into an arete. The eroded corrie back-walls eat into the summit of the mountain creating a pyramidal peak, where several aretes come together.

  8. Features of erosion Formation of a corrie

  9. Features of erosion Back wall scree lip Once the glacier retreats, the corrie may be filled with water. A small, generally circular loch is formed. This is known as a tarn or corrie lochan.

  10. Features of erosion On an OS map, corries are shown as horseshoe-shaped features. Scree – fills in the corrie post glaciation Note the east-facing aspect; snow lasts longer before melting. North Note the contours are very close together, especially on the steep backwall. Note also the bare rock symbol. tarn

  11. Features of erosion Red Tarn What direction was the camera facing?

  12. Features of erosion ARETE This is Striding Edge An arete is a narrow, sharp-edged ridge which forms the side walls of corries or separates different glacial valleys.

  13. scree bare rock horn Features of erosion On a map an arete is hard to see. It is a long ridge between two corries or valleys. The red line marks the spine of the arête. These corries and arêtes are in the Cairngorms.

  14. Features of erosion arete Striding Edge Striding Edge arete on Helvellyn, Lake District

  15. Features of erosion MATTERHORN Pyramidal peaks are also called horns.

  16. Features of erosion A VALLEY GLACIER The next few slides will help to explain the formation of this feature.

  17. Features of erosion Stages in the formation of a U-shaped valley

  18. Features of erosion These are the actions that form this feature. a) A glacier flows into an earlier 'V' shaped valley. b) The glacier abrades and plucks the sides and floor of the river valley. c) The valley is greatly deepened, widened and straightened. d) When the ice melts the valley is 'U' shaped. e) It now has very steep sides and a fairly flat floor. f) Any rivers are called 'misfit streams’ because they are far too small to have cut the valley.

  19. Features of erosion Truncated spurs Former hill spurs are ‘truncated’- their ends are cut off by the ice action to form steep, sheer cliffs. The yellow lines show where the spurs were before they were chopped off! Note how they defined a V-shaped valley.

  20. Features of erosion A U-shaped valley in Canada. U – shape of the valley

  21. Features of erosion When a glaciated valley 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-these are in Norway

  22. Features of erosion A hanging valley Vertical erosion in the main glacier is far greater than in the tributary glaciers because of their far greater power to erode downwards. So the valleys are not the same depth. After the glacier has retreated, rivers flowing down the tributary join the main valley via a waterfall Can you spot the river delta,too?

  23. Features of erosion U-shaped valleys have few contours on their floors. There is a hanging valley here. Note the very steep sides. waterfall Truncated spur Misfit stream

  24. Features of erosion When 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. A small scale map shows the radial pattern of the ribbon/rock basin lakes that characterise the Lake District Ribbon lakes

  25. Erosion/ deposition Caused 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/deltaic fan (This is really a depositional feature of rivers.) alluvium = silt deposited by a river

  26. Erosion/ deposition A crag and tail Edinburgh Castle crag tail Plug of volcanic rock These 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.

  27. Roche Moutonnee Roches moutonnée often have steep, jagged faces created by plucking on the lee (far) side and a gradual incline which is smoothed and polished by abrasion on the other (stoss) end. It may have striations on it indicating the direction of glacier movement.

  28. Features of erosion Identify the features marked on the diagram by matching them to the names of features listed below. Arête; Hanging Valley; Corrie; 'U' shaped Valley; Alluvial Fan; Pyramidal Peak; Corrie Tarn; Misfit Stream; Ribbon Lake; Truncated Spur; Screes.

  29. Features of erosion The End What’s next? After erosion? Deposition!

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