Glacial processes

The figure below shows a valley-glacier and the most common sediments and sedimentary forms developed by and at a glacier.

Moraine, marked with gray-green and gray color, is deposited directly from the glacier. Basal till forms when sediments frozen to the bottom of a glacier drop off by ice-melting. A typical basal till contains, except the coarsest boulders, all grain-sizes. Due to contact between the particles, grains are typically smoothed by glacial movement into a sub-angular shape. Ablation till consists of sediments that has been transported above the glacier-base. When the glacier melts down melt water streams remove the finest grains. Most of clay and silt is therefore absent in the ablation till, in contrast to basal till. Due to little contact between the particles the typical grain-shape is angular.

The glacier transports sediments towards the ice-margin, both to the glacier front and to the sides (laterally). Much sediments are deposited at the ice-margin when the glacier melts in the summer-season. If the glacial position is constant during several years a marginal moraine is formed (a depositional moraine), in the front and sides called lateral and terminal moraines, A moraine may also be formed by the glacier when it advances in the winter-season and pushes till into a»bulldozer-moraine». Meltwater-rivers deposits material as glaciofluvial sediments. A sandur is glaciofluvial sediments deposited in front of a glacier (orange color in the figure). The small, rounded pond is developed by melting of a fragment of ice isolated in the sediments, and is called a kettle hole. 

Bresedimentasjon_engelsk

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