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Sunday, 6 July 2014

The Valley of the Rocks




Close to Lynmouth in Devon the cliff scenery is very spectacular, with one dry valley in particular making the grade as a "must see" tourist attraction.  This is the Valley of the Rocks -- a deep dry valley with steep sides, one of which has been partly eroded away by cliff retreat.  Many attempts have been made to explain this feature away as a "normal valley" -- but it is anything but normal, and more and more geomorphologists nowadays are interpreting it as a meltwater spillway, formed when the ice of the Irish Sea Glacier was pressed up against the coast.

There are other similar valleys -- but not as spectacular -- at Hartland Quay, Dalehole Point, Speke's Mill Mouth and Bideford.  These also suggest considerable erosion by meltwater that has come from melting glacier ice.

How old are the features?  It's very difficult to say, but I think I would go for an Anglian age, since that is the date of most of the glacial features in the South-West.  That having been said, we know that the Devensian ice reached the Scilly Isles, and I am open to the idea that the Devensian ice of the Irish Sea Glacier also pressed up against the coasts of Cornwall, Devon and maybe Somerset as well.  Watch this space......

2 comments:

Constantinos Ragazas said...

Brian,

These landscape features seem to be too fresh and well defined to be Anglican dating back 400,000 years ago. And these 'meltwater channels' drain directly to the sea. And likely carried considerable volume of meltwater from inland. Suggesting the contributing glaciers were likely extensively covering the land.

In your expert opinion what would the volume and extend of the contributing land glaciers need to be to carve out such 'meltwater channels' ?

Kostas

BRIAN JOHN said...

The "fresh features" have been created by coastal erosion intersecting with the flank of the channel. The coastline is younger than the channels. As for the volumes of meltwater needed to cut channels of this size, either a lot of water over a very short time or a little water over a very long time. I favour the former -- melting ice edges are pretty catastrophic places. Decades or centuries maybe...