Glacial depositional landforms
Glacial depositional landforms are formed from the action of glaciers. Most of the Glacial depositional landforms are formed by the movement of large ice sheets.
Most of the famous areas for such glacier landforms are Fennoscandia, Andes, etc.
The unsorted sediments, unassorted coarse and fine debris are dropped from the glacier melting. This is called Glacial till. The rock fragment in large numbers in the Till is in form of angular or subangular form.
Due to the melting of ice at the bottom, sides, lower ends of the glaciers, the streams are formed. In these streams, small rock debris is carried, washed down, and deposited. Such glacial-fluvial deposits are called Outwash deposits.
Outwash deposits are stratified and assorted. Also, the rock fragments in the outwash deposits are rounded at their edges.
Glacial depositional features
Moraine is are the left behind materials by the moving glacier. These materials are usually soil and rocks. The glacier moves all types of boulders, dirt which are built up to form moraines. Moraines are simply long ridges of deposits of glacial till.
Moraines are of four types and are Terminal Moraines, Lateral moraines, medial moraines and Lateral Moraines. Examples of Moraines are the Side Glacier of the Gorner Glacier in Zermatt Switzerland, Kettle Moraine Wisconsin USA, Harbor Hill Moraine in Long Island USA, etc.
Terminal Moraines are found at the endpoint of the glacier. These are long ridges of deposits of glacial till are formed along the sides parallel to the glacial valleys.
In some cases, the lateral moraines and terminal moraine may join and form a horseshoe-shaped ridge.
These moraines are found on either side of the glacier and there can be many lateral moraines. The lateral moraines partly or fully owe their origin to glacio-fluvial waters that push up the material to the sides of the glacier.
The ground moraines are rocks of different sizes and types. These are formed when different glacier’s valleys retreat rapidly. This leaves an irregular sheet of till over the valley floors. These deposits differ greatly in thickness and in surface topography.
These Moraines are found at the centre of the glacial valley / at the junction between two glaciers flanked by lateral moraines. Medial moraines are imperfectly formed compared to lateral moraines.
In some cases, the ground moraines are indistinguishable from the medial moraines.
Eskers are ridges that are made of stones, sands, and gravel. These are deposited by the water which is melted from the glaciers. Eskers are carried by the water through the tunnels underneath or within the glaciers.
Formation of Eskers
During the summer, the glaciers melt and the water flows over the surface of the Ice. Also, the water seeps down along the margin or through holes in the ice. This water accumulates below the glacier and flows like a stream below the glacier.
These streams also flow over the ground that forming ice in its banks. These streams carry coarse materials like boulders, blocks, and other rock debris and make them settle in the valley of ice beneath the glacier.
After the ice melts these coarse materials can be found as a sinuous ridge called Esker.
Outwash plains occur in front of melting glaciers. These are deposits of sand and gravel carried by running water. The glacial mountains plain at the foot or beyond the limits of the continental ice sheet are covered with glacio-fluvial deposits.
These glacio-fluvial deposits were in the form of broad flat alluvial fans that may join to form outwash plains of gravel, silt, sand, and clay. The outwash plains are expansive, dominated by braided rivers when glaciers melt.
The outwash plain extends several miles beyond the glacier margin. The outwash plains were often used for specialized kinds of Potato cultivation. Example in Montcalm County. This plain favors plants that grow well in well-drained soil.
Drumlins are oval-shaped hills, that are composed of glacial drift that is formed under the glacier or ice sheets. These are aligned in the direction of ice flow.
Drumlins are smooth have the feature of the oval-shaped ridge. It is made of glacial till of gravel and sand. The long axes of drumlins are parallel to the direction of ice movement and measure up to 1 km in length and 30 m or so in height.
One end of the drumlins facing the glacier called the stoss end is blunter and steeper than the other end called the tail. The drumlins form due to the dumping of rock debris below heavily loaded ice through fissures in the glacier or ice sheets. The stoss end gets blunted due to pushing by moving ice.
Thereby, the Drumlins give an indication of the direction of glacier movement.
This is Ncert’s notes for the topic ‘Glacial depositional landforms‘ for Upsc and other state service exams. Due to the deposition actions of the Glaciers, several types of landforms are formed. They are Moraines, Eskers, Outwash Plains, and Drumlins.
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