Why Have Glaciers Affect Erosion?

LO2
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Erosion
Moving masses of ice (glaciers) cause erosion, and as a result change landscapes dramatically. There are 3 processes that cause direct glacial erosion: o Abrasion o Crushing o Plucking
Meltwater erosion is an indirect process of erosion.
Abrasion
Rock fragments at the base of the glacier grind against the bedrock wearing down it’s surface. As a result, the surface becomes smooth. These smoothed bedrock surfaces are called striations. Fine silt particles are formed, called rock flour. This causes meltwater streams to look ‘milky’.
Some of the factors that influence abrasion include: o Ice velocity – faster flowing glaciers create more abrasion simply because more debris is passing a given point at any one time. o Basal rock debris – needs to be present between ice and rock for abrasion to occur as smooth ice will not scour the rock bed. The more debris there is, the more affective the abrasion. The debris must be harder than the rock surface.
o
Crushing
Basal rock fragments put pressure on the surface of the bedrock beneath causing fractures (chattermarks).
Plucking
When loose blocks of bedrock freeze onto the base of the glacier and are removed or ‘plucked’ as the glacier moves. These plucked rocks then cause abrasion. Plucking can occur when frost weathering has already weakened the bedrock.
Meltwater erosion
Meltwater streams at the base of a glacier are much more erosive than surface water streams because they flow much faster. This is due to the weight of the ice causing hydrostatic pressure. Erosion is caused by a combination of: o Abrasion o Hydraulic action o Attrition o Solution