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Glaciation in the Snowdon Area
The Snowdon area is one of the finest examples of glaciated scenery
in Britain. During the Pleistocene Ice Age, between one million and
twenty five thousand years ago, valley glaciers transformed the rounded
pre-glacial surfaces into precipitous glacial peaks, lake-filled rock
basins and U-shaped valleys. Today, high waterfalls tumble down a series
of gigantic steps to link the lofty waters of secluded tarns with lakes
in hanging valleys, from which they fall again to the main, valleys
where a few people contrive to live. At the beginning of the Ice Age,
snow accumulated in the radiating river valleys, and its own weight
pressed out the air to form ice. The weight of the ice caused it to
move slowly down the valleys, scraping and grinding their floors and
sides as it went. Cirque and tributary ice fed the trunk glaciers in
the main valleys. At the edge of the ice, erosion took place by the
process of freeze-thaw. During the day, cracks in the rocks were filled
with water from the melting ice and snow. This. froze at night, expanding
and shattered the rocks. In this way, erosion changed the shape of'
landscape.
The headward erosion of the glaciers his cut great corries with steep
headwalls in the rounded mountain mass, leaving only narrow, saw-edge
ridges and pyramidal peaks (aretes). Larger valleys have been hollowed
out, making them U-shaped with steeper sides & truncated spurs.
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