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What are "Roches Moutonnees" and "Bedded Pyroclastics" and where specifically can you find examples in the British Mountains?

Submitted by:Elaine Pearson
Date:30-08-2003
Answered By:Simon Jowitt

Roches Moutonnees are rocks shaped by glacial action, where the side of the rock facing the glacier's place of origin is sharp and heavily eroded, with the rock then sloping gently away from this heavily eroded and 'plucked' face being smooth and polished. This shape is formed by the glacier, and material that the glacier has transported such as rocks and soils, passing over a rock outcrop, and eroding it into the characteristic roche moutonee shape.

Bedded Pyroclastics are rocks formed from pyroclastic flows. Pyroclastic flows are moving flows of ash and other debris produced by volcanic eruptions. These ash and rocks often flow downslope away from a volcano during an eruption, as the ash and rock are blown out of the vicinity of the volcano. In the case of a series of eruptions, large numbers of pyroclastic flows can be produced, eventually forming a pile of pyroclastic deposits that over time harden and form rocks - bedded pyroclastics - with each individual bed representing an individual pyroclastic flow.

Roche Moutonnes can be found in any upland glaciated area of the United Kingdom, and Bedded pyroclastics are common in areas that were once volcanic. Both can be found together in Borrowdale, in the Lake District.

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