Ok, in the last post I kept things short and did not actually explore periglacial processes, instead I focussed on the different types of permafrost. Therefore I will focus on the periglacial processes in this post. Before writing each of the posts for my blog, I would always check BBC Bitesize first to get an overview of the topic area. However on this occasion, the website does not refer to periglacial processes.
Unlike glaciers and their processes, there are much fewer periglacial processes that are all related to the freezing and thawing of water.
Frost shattering – This occurs in rocks that contain cracks and joints. It is a physical weathering and occurs when temperatures fluctuate around 0°C. This process is just like freeze-thaw where water gets into the cracks and joints, freezes causing the ice to expand putting pressure on the rock. The water then melts, and this process is repeated resulting in bits of the rock to break away. This leads to the formation of scree slopes.
Frost heave and contraction – This process is where water freezes in the grounds soil which expands and pushes the soil upwards. Later on the ice thaws slowly, allowing finer material to fill in the spaces below. This is a repetitive cycle that continues to push the coarser materials upwards which are constantly being replaced by smaller material. Frost contraction is the fracturing and cracking of the ground by thermal contraction at sub-freezing temperatures.
Solifluction – This was mentioned in the last post, it is the downslope movement of soil on the active layer. The active layer forming by water melting but cannot filtrate through the ground due to the underlying permafrost so moves downslope instead moving soil and other materials with it.
Nivation – The processes that occur under snow patches that erode the ground, creating a hollow. Under snow patches, frost shattering, freeze-thaw cycles and chemical weathering break away the materials on a slope, when the ice finally melts the water washes away taking the materials with it leaving behind a hollow, also known as a depression.
Ground water freezing - In areas where the permafrost is thin, water is able to seep into the upper layers of the ground and freeze. This ice expands forcing the overlying sediments upwards, creating a dome-shaped mound called a pingo which can rise as high as 50m. In some cases, the surface of a pingo will collapse leaving a hollow that is filled with melt water.
Ground water freezing - In areas where the permafrost is thin, water is able to seep into the upper layers of the ground and freeze. This ice expands forcing the overlying sediments upwards, creating a dome-shaped mound called a pingo which can rise as high as 50m. In some cases, the surface of a pingo will collapse leaving a hollow that is filled with melt water.
Now I am yet to find any useful diagrams or videos to show these processes but will return to this at a later date. However I have found a very useful revision site, however I have found a useful PowerPoint presentation that explains what periglacial areas are, the processes that occur in these areas and the landforms these processes create. I have not yet touched on the landforms, but I will focus my next post on these. The PowerPoint can be viewed on: http://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=5&ved=0CGwQFjAE&url=http%3A%2F%2Fwww.st-andrews.ac.uk%2Fitsold%2Fpapers%2Fpublic%2Fmiscellaneous%2Fprintingproblems%2FGE2011L21.pdf&ei=_L0fUOiKAcO10QXb5YCQCg&usg=AFQjCNEw-kFNFnlv03HeNRBAoIVcN1LUhQ&sig2=r8PbU9MqcdK8fComoBQPpw
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