Describe and Explain the variety and location of periglacial landforms Essay

506 WordsOct 26, 20083 Pages
A) There are a number of periglacial landforms caused by permafrost. One of the largest, as a single object, would be pingos. These are rounded ice-cored hills that can reach up to 90 meters high. They are formed by ground ice which develops in the winter months as temperatures fall. There are two types of pingos open and closed system. Open pingos are formed in valley bottoms, where water is collected from surrounding slopes under the force of gravity. This water then freezes and expands forcing the overlying surface material to dome upwards. This kind of pingo is commonly found in Greenland. However there are other kinds of pingos a good example of which are found in the Mackenzie delta in Canada. This kind of pingo is formed beneath a lake where the supply of water is from the immediate area. Permafrost grows in the winter season and the ground water below the lake is trapped by the permafrost below and the frozen lake above. The saturated talik is compressed by the expanding ice around it and when it freezes it pushes the overlying material up. When the ice core in the pingos melts the top of the dome collapses leaving a rampart surrounding a circular depression called an ognip. Patterened ground is a collective term for a number of minor features which are thought to be the result of frost heave. Stones within the fine material heat up and cool down faster because they have a lower specific heat capacity than the surrounding material. As the temperature falls ice lenses develop under the stones and force them upwards. As the larger stones are moves upwards they push the surface into a dome shape and the large stones eventually force themselves onto the surface. When the large stones reach the surface they roll off the dome under gravity this forms a network of stone polygons typically 1-2 meters in diameter. If the slope is at an angle of 3-5° the polygons

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