Glacial Erosion

One of the most striking forms of evidence of glacial erosion is the colour of rivers like the Waiho River in Franz Josef. The melt water of the river gains a characteristic greyish colour, sometimes known as glacier milk. This is the result of the suspension of very fine grains of rock <0.002mm in size. These particles are called glacial flour and are the result of a type of glacial erosion known as abrasion. The abrasion occurs where the glacier slides over bedrock and works much like sandpaper, as rock fragments meet at the boundary of rock and ice they grind and smooth the surface below. If a large rock is trapped, large grooves or glacial striations are engraved into valley walls and bedrock.

Another major type of erosion is known as plucking. When the ice slides over the downstream side of the bedrock, it can freeze loosened rocks from the bottom into itself and rips the rocks out from the valley floor and walls, changing its shape forever.

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