LITHOSPHERE

LANDSCAPE FEATURES RESULTING FROM GLACIAL AND FLUVIOGLACIAL ACTION

Glacial Action by ice Fluvioglacial

Action by Meltwater

Erosion Deposition Corries Ground Moraine Kames Arêtes Moraine Ridges Eskers Pyramidal peaks Drumlins Outwash Plains Hanging Valleys Erratics Ribbon Lakes Fiords U-shaped valley

Snow collects in the north facing slopes in hollows as more snow falls in winter than melts in summer. North/north-east facing slopes are more shaded so snow lies longer. As more snow falls it is compacted into ice(neve). The ice will then begin to move downhill due to gravity and meltwater lubricating the glacier.

Before GlaciationCorrie

During Glaciation

The erosive forces of the ice erode the hillside, widening and deepening the hollow. As the glacier moves downhill it freezes onto the back wall and tears rock away eroding the steep backwall by plucking, deepening and widening the hollow into a basin shape by abrasion. This is when material trapped in the ice grinds away at the solid bedrock below like sandpaper. Rotational sliding further deepens the central part of the hollow floor asgravity causes the ice to move.

After Glaciation

Formation of an Arête

When two corries form back to back(use corrie note), narrow ridges called arêtes form.eg Striding Edge

Corrie with tarn

Grib-Goch Arête, North Wales

Corrie formation

arete formation

Slide 74

Friction causes the ice to slow down at the front edge of the corrie, allowing a rock lip to form, which traps water as ice melts, leaving a lochan or tarn.eg Corrie Cas

Formation of a Pyramidal Peak

When 3 or 4 corries erode back to back around a hillside(use corrie note), the arêtes between the corries rise to a central peak, called a pyramidal peak.eg Angels Peak

Formation of a U-Shaped Valley (Glacial Trough)

Arêtes

Pyramidal Peak

Matterhorn

V-shaped valley

Formation of U-shaped valley

U-Shaped Valley

Slide 71

Glen Coe

Hanging valley

Many small glaciers join to form a large main glacier which deepens and widens and straightens a V-shaped valley, forming a U-shaped valley. The valley is eroded by plucking when the glacier freezes onto rocks and tears away when it moves away. It is also eroded by abrasion when material trapped inside the glacier scrapes away at the valley. This main U-shaped valley has a wide flat bottom and steep sides called truncated spurs which are eroded interlocking spurs. On the flatter valley floor, a stream will meander called a misfit stream. It is called this because it could never have eroded the valley. If the U-shaped valley has been dammed by an end moraine then a moraine damned lake is formed. When a U-shaped valley meets the sea a fiord is formed when sea water rose after the last ice age.

Fiord pictureSlide 82

Formation of a Hanging Valley

A small glacier flows down from a corrie eroding by plucking and abrasion to join the main glacier found in the main u-shaped valley. This smaller glacier doesn’t erode as much as the main valley glacier and after the ice melts this small tributary valley is left hanging above the main valley. A small stream flows from the corrie and over the hanging valley, forming a waterfall. At the bottom of the waterfall an alluvial fan is formed by deposition.

Scree

In glaciated areas there is a constant process of freeze-thaw action (frost shattering). This is where water enters cracks in the rock, freezes and expands by 9%. This forces the cracks slightly wider. This is repeated many times and pieces of rock are broken off. This builds up at the front of the slope as scree.

• Occurs on very steep slopes above 40˚.• Where there is a lack of soil and vegetation.• It is often found in areas of high altitude with low

temperature which causes frost-shattering or freeze-thaw action.

• Roots of trees can sometimes get into the cracks in the rock and cause the formation of scree.

Scree

LANDFORMS created BY GLACIAL DEPOSITIONGROUND MORAINE (Boulder Clay)Ice carries moraine beneath it and on top of it. When the ice melts it deposits the moraine. This forms a covering of soil called boulder clay or till. This is clay soil with stones of different sizes in it.

FORMATION OF TERMINAL MORAINE

Direction of ice movement

Terminal Moraine

Animation

END MORAINES (or recessional moraines)Formed behind the terminal moraine. They mark interruptions in the retreat of the glacier, when it remained stationary for long enough to form a further small ridge.

ERRATICS (Rocks out of place)

Large boulders that are transported by glaciers and deposited many miles away.

Erratic

Fluvioglacial landforms

A terminal moraine marks the maximum advance of a glacier to the point where the climate was warm enough for it to melt. This ridge was formed as ice bulldozed loose soil and rock in front of it and from the constant deposition of melting ice at the glaciers snout. All the material was deposited where the ice melted building up a ridge. This ridge is made up of unsorted rocks. This is called Terminal moraine

Fluvioglacial (action by meltwater)

Outwash Plain

When the glacier melts large amounts of water flows beyond the terminal moraine. The water carries sand and gravel beyond the terminal moraine, which is deposited by the river. Larger pieces are dropped first followed by smaller ones.

Eskers

A meltwater stream flows in a tunnel beneath the melting ice sheet. The stream carries and deposits moraine filling up the tunnel. When all of the ice melts along ridge of moraine is left in the shape of the stream’s tunnel. These long ridges of deposited material are called eskers.

Bedshiel Esker

What fluvioglacial feature is this?

location of Bedshiel Esker

Direction of flow

Drumlin

Drumlins are smooth, elongated mounds of material formed parallel to the direction of ice movement. They often consist of stones and clay, and are believed to result from load, carried by the glacier, becoming too heavy and being deposited. They owe their streamlined shape to later ice movement.