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1. Permafrost This can be continuous permafrost (Siberia where it reaches 1500m) where the active
layer is still able to melt, discontinuous permafrost where only some areas will not have permafrost,
such as lakes, or near the sea. Mean temps need to be below zero for at least 2 years. Or finally
sporadic permafrost where only some areas will contain it.
2. Ice wedges when temps drop very low in Winter, causing the ground to contract and crack. Then
when temps rise, melt water seeps in the these cracks. When the water freezes ice wedges will
form. As this occurs year after year, ice wedges will thicken and increase in size.
3. Frost heave When the active layer freezes, as as ice takes up 9% more space than water, it
causes the ground to rise. Also, ice lenses form due to the sudden cooling and heating of stones,
therefore it is often colder beneath stones. Therefore as the ice lens expands, they push stones
towards the surface of the ground forming stone polygons.
4. Patterned ground Formed by frost heave or frost contraction. This forms when frost heave has
occurred, and the stones roll down the mound that has been formed, forming a circle. If the
mounds are close together, they form polygons, and if the ground is on a gradient, they form lines.
5. Solifluction lobes Form when waterlogged ground causes one section of soil to move faster due
to the presence of melt water.
6. Pingos Conical hill which has an ice core and can reach 80 metres high and 500m wide. There are
two types, open and closed pingos:
1. Open pingos are found where there is discontinuous permafrost and ground water is forced up
the gaps between permafrost, then as it freezes, a core of ice forms, pushing the ground upwards.
2. Closed pingos form where there is continuous permafrost and a lake present. The lake insulates
the ground, but when it dries up, permafrost advances around the area. A pool of water will form
in the middle of the dried up lake, but as it freezes, the ice core forms, pushing the land upwards to
form a pingo. If it collapses, it will form a lake again.