This is Cwm Cerwyn, a classic semi-circular cwm just beneath the highest point in the Preseli uplands -- Foel Cwmcerwyn, which we can see on the skyline. The hollow is not over-deepened, which means there never was a very active cirque glacier here, but this is a classic situation for the accumulation of snow and the transformation into firn and then ice. There are traces of till in the sediments adjacent to the stream, just beyond the edge of the shadow on the cirque floor.
I suspect that a moderately active small glacier developed here and probably survived for a few centuries, around the time of the Younger Dryas / Zone III -- around 10,500 years ago.
I doubt that there was a glacier here in the Little Ice Age, although some small ice masses did develop at this time in the hight mountains of the northern part of the UK.
Satellite image of the cwm
Key features
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