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Introduction to Outwash Plain

Outwash plains are wide, tenderly sloping sheets of glacial sediments deposited by meltwater outwash at the snout of the glaciers. As it flows, glaciers crush the underlying rock surface and carry the scrap along with it. The sediments are accumulated at the terminal of the glaciers over the outwash plain by the meltwater, with large stones accumulated near the terminal moraine, and finest particles are carried further. 

Outwash plains are commonly found in Iceland where geothermal activity speeds up the melting of ice flow and deposition of sediments carried by melting water. The other name outwash plains are sandur (plural: sabdurs), sandar, and sandr.


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What is Outwash Plain?

An outwash plain is both an erosional and depositional surface formed by meltwater coming from the glaciers. These plains are generally identified by braided streams and found in the front of the glaciers. The streams are generally small and braided because the size of the sediment varies and the original stream gets split up. As the streams meander around, the erosion takes place left to right rather than up and down. These glaciers are generally formed beyond the terminal moraine deposited by the glaciers.


Define Outwash Plain 

A wide, tenderly sloping sheet of outwash accumulated by meltwater streams flowing in front of or beyond a glacier, and formed by coalescing outwash fans is defined as an outwash plain.


Outwash Plains Formation

A fluvioglacial landform formed by both deposition and erosion by meltwater is a glacial outwash plain or sandur that generally has braided streams. Glaciers and icecaps contain large quantities of sediments and slits, that are picked up as they erode by the meltwater that carries the sediments away from the glaciers and deposit them on a broad plain. The materials in the outwash plain are size-sorted by the surface water of the melting glacier, with small particles like a slit, being the most distantly re-deposited, whereas the largest sediments are re-deposited to the original terminus of the glaciers. 


Outwash Plains Occurrence

The Kerguelen Islands, Svalbard, and Iceland are the islands where the outward plains are found. Outwash plains are also most commonly found where geothermal activities below the ice caps accelerate the deposits of the sediments by meltwater. 


Glacial Outwash 

The considerable amount of water that flowed from melting ice deposited different kinds of materials, the most important of which are glacial outwash. Glacial outwash plains made up of outwash deposits are flat and consist of layers of sand and other fine sediments. The plains at the bottom of the glacial mountains or the reserve of continental ice sheets are covered with glacial-fluvial deposits in the form of broad flat alluvial fans which combine to form an outwash plain of sand, silt, and clay.  

The thickness of the outwash can reach 100 m (328 feet) at the end of the glacier, although the thickness is usually much less, it may extend many kilometres in length. Outwash plain may be extended for miles beyond the margin of the glaciers. 

Outwash sediments from the Wisconsin Glacial episode can be tracked down to the mouth of the Mississippi River, 1120 km (700 miles) from the nearest terminus of the glacial.


Did You Know?

  • An outwash, also known as sandur, is a plain formed by melting glaciers.

  • Outwash plain on the map is found in the southeast quarter.

  • The largest outwash plain in the world covering an area of 1300 km is Skeiðarársandur.

  • Outwash plains are commonly found in Iceland where geothermal activity speeds up the melting of ice flow and deposition of sediments by meltwater.

  • A terminal moraine, also known as end moraine is a type of moraine that is formed at the edge of the glacier, making its maximum advance.

FAQs (Frequently Asked Questions)

1. What is an Outwash?

Ans. Outwash is a deposit of sand and gravel transferred by running water from the melting ice of glaciers and laid down in stratified deposits. The thickness of the outwash can reach 100 m (328 feet) at the end of the glacier. Generally, the thickness of the outwash is much less, but it may be extended in kilometres in length. For example, outwash sediments from the Wisconsin Glacial episode can be tracked down to the mouth of the Mississippi River,120 km ( 700 miles) from the nearest terminal of the glacial.

2. What are the Three Major Depositional Landforms Formed By the Glaciers?

Ans. The three major depositional landforms formed by the glaciers are:

  • Eskers

  • Outwash Plains

  • Drumlins

3. What is the Flow Pattern of Glacial Rivers Across the Outwash Plain?

Ans. The flow pattern of glacial rivers across the outwash plain is generally not channelized and dispersed, but in the conditions where the snout of the glaciers has evacuated from the terminal moraine, the flow is more channelised.

4. What are Braided Streams?

Ans. A braided stream is a stream consisting of multiple shallow streams that divide and recombine multiple times forming a pattern that resembles the strands of the braid. Braided streams are formed where the proportion of the bedload sediment is so massive that some of the sediments are transported on the shifting islands or bars between the channels.

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