пятница, 6 октября 2017 г.

Parc National de la Jacques Cartier This river, the…

Parc National de la Jacques Cartier

This river, the Jacques-Cartier River in Quebec, Canada, drains an area north of Quebec City into the St. Lawrence River and eventually to the Atlantic. The shape of this river valley is distinctively glacial. When rivers erode downwards to create canyons, they typically leave the walls surrounding them at or near the angle of repose – the angle where if rocks are too steep they break off and fall as rockfalls or avalanches. River-carved valleys therefore have a characteristic “V-shape” with the river at the bottom of the V and walls at or near the angle of repose. Geologic units of differing strength can disrupt this pattern somewhat, but it holds impressively well.

Glaciers, on the other hand, have a huge amount of weight to them. The weight of the glacier pushes down on any surface it is exposed to, and a glacier sitting on an angled surface will press against a greater surface area than it would against a flat surface. The friction between the sliding glacier above and the rocks in the valley cause the valley to erode downwards towards a flat surface, minimizing the surface area at the contact between the glacier and the rock. Glacially carved valleys therefore tend to have flat, open bottoms and gradually develop towards steep sides, often above the angle of repose.

This photograph was taken just about 1 year ago and likely reflects how the tree colors will look here again soon.


Image credit: Eduardo Fonseca Arraes





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