To what extent are fluvio-glacial deposits and landforms distinctive?

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Sarah Bewers

Distinguish between the processes of erosion and weathering in an area undergoing glaciation:

Weathering is the decomposition of ,  and their  through direct contact with the . Weathering occurs in situ, or "with no movement", and this is how it differs from , which involves the movement and disintegration of rocks and minerals by agents such as water, ice, wind and gravity.

There are two important classifications of weathering processes; physical weathering involves the breakdown of rocks and soils through direct contact with elements heat, water, ice and pressure.  However Chemical weathering, involves the direct effect of atmospheric chemicals, or biologically produced chemicals, in the breakdown of rocks, soils and minerals.

There are also two different types of erosion, classified into the same two categories; mechanical erosion and chemical erosion.  Each of these has a different effect on the environment.  Mechanical erosion would include water, wind, sun, ice, natural disasters such as earthquakes and shoreline erosion. Chemical erosion would be acid rain, over use of fertilizer, human land use, deforestation and overgrazing.

With regards to glacial regions weathering processes, such as Dilatation and Freeze-Thaw can provide the debris, or rock weaknesses that are required for glacial erosion to occur successfully.  Weathering can also occur after glacial erosion, possibly in de-glaciated areas, where the processes decompose and wear away the landscape and features left behind after glaciation.  Glacial erosion is the processes whereby the glacial ice itself alters the underlying bedrock beneath the glacier.  The two main processes of glacial erosion are Abrasion and Plucking.

Examine the impact of glacial erosion on the evolution of landscapes:

Many regions today have been shaped by glacial erosion, whether or not they are currently experiencing glaciation, or whether they are post-glacial regions.  Erosional processes occur as glaciers move forward; advance downhill due to gravity.  This movement and subsequent erosion can have impacts on a wide variety of scales, and varying implications can be seen over short and long periods of time, or repeated cycles of glaciations.  This essay will attempt to describe and explain the processes of glacial erosion and the significance of the impacts on landscapes and their development.  Examples will be drawn upon with reference to areas currently undergoing glaciations as well as areas that were once, but are no longer glacial regions.

There are two main types of glacial erosion; Plucking and Abrasion.  Plucking occurs when sub-glacial melt-water enters weaknesses in the rock, mostly on the valley floors, and the water then re-freezes and attaches itself to the ice above (on the actual glacier).  Ice continues moving downwards due to gravity and pulls along the attached melt-water, and thus the rock too.  The melt-water is initially produced due to the temperature reaching the pressure melting point of the ice, but after a short period of time falling again to cause the re-freezing of the water.  Due to the particular conditions and temperature changes required for this to happen this process occurs in very specific areas.  Abrasion is where the ice, or glacier, wears the rock away gradually, similar to the effect of sand paper on wood.  As well as the ice itself eroding the bedrock, the debris within the basal layer of the glacier also erodes.  Evidence for this process includes the polished appearance and texture of the rock in post-glacial regions.  

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These processes are dependent upon various factors. For example the geology of the underlying rock; the less resistant the rock type the greater the rate of erosion and therefore the greater the impact on the landscape.  The rate or success of plucking is quite heavily influenced by the structure, or amount of jointing present in the rock, as greater jointing creates greater opportunity for the process to occur; thus greater rates of erosion and greater impacts on the landscape.  The size of the debris within the basal layer of the glacier determine their individual affect on the rate of erosion, ...

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