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There are many different glacial landforms created by glacial erosion, one of these landforms is U-shaped valleys or glacial troughs. This glacial landform has many distinct characteristics. One of these characteristics is that it has very steep valley sides caused by the glacier as it moves down the valley eroding the sides of the valley by the processes of abrasion and plucking. Abrasion is when the boulders and moraine carried by the glacier rubs and erodes the valley side as it physically moves down the valley. Plucking happens when the water in the glacier freezes inside of the cracks in the individual rocks on the valley side then the water freezes and as the glacier moves the rock is plucked or torn from the valley side producing the steep side to the valley.
The valley also has wide flat floors caused by ice movement aided by large volumes of melt water and moraine has greater erosive power than that of rivers. This results in the wide floors. The greater erosive power of the glacier than that of a river also causes the valley to be very straight compared to the valley shape that a river has eroded, it has no interlocking spurs because the shear power of the glacier has slowly smashed through the original spurs of the valley. Just before the glacier forms and when the temperatures are cold enough known as the the ?pre glacial? period the process of freeze thaw takes place, this aids the formation of the u shaped valley. Freeze thaw is when the water in the summer enters the cracks of rocks and the in winter when the temperatures have gone below 0 degrees centigrade the water freezes in the cracks and because when water has frozen the particles in the water have less movement and expand causing the rock to shatter. Freeze thaw therefore helps in the formation of the u shaped valley by breaking up the valley floor so that the floor is weakened so the glacier can easily and speedily erode the valley floor by all the conventional forms of erosion like plucking abrasion but with greater ease.
There are many of examples of u shaped valleys around the world because wherever there has been a glacier there will be a u shaped valley that has been formed as it moves down the valley. One example of a u shaped valley is that of the valley in the Swiss Alps near san moritz
This valley has the characteristic flat floor and the steep comparatively flat valley side to that of a river eroded valley and as you can see is very long.
2) One periglacial landform that I have studied is pingo`s. pingo`s are dome shaped, they are isolated hills which interrupt the flat tundra of the periglacial environment. They can have a diameter of up to 500m and may rise up to 50m they often are ruptured to form an icy core, they are also not susceptible to frost heaving as they mainly are formed in sand. Pingo`s are believed to be formed in two ways only, the closed and open system.
Firstly the closed system, pingo`s are found where ground water is trapped under advancing underlying permafrost and a newly frozen surface. This water eventually freezes, expands and is forced upwards. These pingo`s therefore grow from below and are commonly known as the `Mackenzie type and are usually found in areas of thin or dis continuous permafrost.
Secondly the open system this results from the downwards extension of permafrost into the talk(soil). The freezing of water entrapped within a lake may form them which together with any sediment on the lake floor will expand and lift up to the surface. These are sometimes referred to as the East Greenland type and are more likely to be located where the permafrost is continuous.
3) One piece of evidence that show that fluvio glacial action has occurred is the outwash plain in Edinburgh. The outwash plain in Edinburgh has terminal moraine which Edinburgh castle is situated on top of then the outwash plain which slopes away from the terminal moraine into the the city of Edinburgh it self for approximately one mile, and is therefore called the ?royal mile?.
The outwash plain occurs when the snout of the glacier is melting, streams are flowing from the ice and therefore they carry material away. The streams tend to deposit the material as it is carried. Coarser and heavier material is deposited closer to the ice and the lighter and the finer material deposited further away from the ice. As the ice retreats the stops again, outwashed plains can develop on top of till.
Another piece of evidence that fluvio glacial action has occurred is the drumlins and drumlin fields in North Yorkshire near to ingelton falls this clearly shows that fluvio glacial action has occurred.
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