Features of erosion These slide-shows are all on the Prepwork folder if you wish to copy any notes from them; we will not be stopping in class for you to do this 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
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 by abrasion to become a corrie. A corrie is a deep, rounded hollow with a steep back wall.
Features of erosion Read the section about corries in the booklet, pages 28 and 29. There is a bullet-pointed list of actions explaining in order how a corrie is created. Learn this at home! Also learn how to draw and label sketches like a),b) and c).
MAXIMISE YOUR MARKS ! Features of erosion NOTE;- the labels on the first two sketches are not just naming the features, like in sketch c). They describe what is happening in the sketch, naming the processes. This makes these labels -and the diagram- worth more marks than one where bits only are named!
Features of erosion Answer these questions in the usual way;- 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.
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.
Features of erosion 12 Formation of a corrie Take a handout of the diagram and stick it into your jotter.
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.
Features of erosion On an OS map, corries are shown as horseshoe-shaped features. scree Note the east-facing aspect; snow lasts longer before melting. N Note the contours are very close together, especially on the steep backwall. Note also the bare rock symbol. tarn
Features of erosion Red Tarn
Features of erosion ARETE An arete is a narrow, sharp-edged ridge which forms the side walls of corries or separates different glacial valleys.
= arete scree bare rock horn Features of erosion On a map an arete is hard to see. It is a long ridge between to corries or valleys. The red lines mark the spines of the three aretes. These corries and arete are in the Cairngorms.
Features of erosion arete Striding Edge Striding Edge arete on Helvellyn, Lake District
Features of erosion MATTERHORN Pyramidal peaks are also called horns.
Features of erosion A VALLEY GLACIER The next few slides will help to explain the formation of this feature.
Features of erosion 13 Stages in the formation of a U-shaped valley Take the handout and use page 284 of ‘Wider World’ to add the labels.
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.
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.
Features of erosion A U-shaped valley in Canada.
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
Features of erosion A hanging valley Vertical 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 waterfall Can you spot the river delta,too?
Features of erosion Truncated spur U-shaped valleys have few contours on their floors. There is a hanging valley here. Note the very steep sides. waterfall Misfit stream
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. The English Lake District owes its character to these narrow ribbon lakes along its valley floors. Ribbon lakes
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 (This is really a depositional feature.) alluvium = silt deposited by a river
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.
Features of erosion Now play the glacial erosion dominoes game! There is a mapping question sheet to try at this point. You will need a copy of the questions and the map extract supplied. 14 A ruler may also be quite useful. The extract is of the area you will need to know for the Rural Land Use section of the course.
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.