The Lost land of Lyonesse revisited


13 Oct 2015 - MawKernewek

In a previous post, I mentioned the work of Shennan and Horton (2002) about sea level change around Britain through the Holocene.

I showed a visualisation of the West Cornwall coastline as it may have been around 12,000 years before present.

After downloading further bathymetry via the UKHO INSPIRE portal, I present an updated version covering the whole area around Cornwall.

Much of this came as .csv point data, which I had to grid, and use the QGIS Concave Hull plugin from the Processing toolbox to restrict the interpolated grid to where there was data.

In some areas, there are gaps in what is currently available at high resolution so it falls back to low-resolution data.

Based on my reading off the graphs in Shennan and Horton, the sea level rise at this time should be similar across the area covered here:
Site Number Site Name Lat Long RSL 1kyr RSL 2kyr RSL 3kyr RSL 4kyr RSL 5kyr RSL 6kyr RSL 7kyr RSL 8kyr RSL 9kyr RSL 10kyr RSL 11 kyr RSL 12 kyr

42 Pembroke 51.8 -5.1 -0.8 -1.6 -2.4 -3.2 -4 -9.2 -14.4 -19.6 -24.8 -30 -35.2 -40.4
43 Glamorgan 51.5 -3.7 -2 -4 -6 -8 -10 -13.6 -17.2 -20.8 -24.4 -28 -31.6 -35.2
51 Devon 50.4 -3.5 -1 -2 -3 -4 -5 -10 -15 -20 -25 -30 -35 -40
52 Cornwall 50.2 -5.5 -1.4 -2.8 -4.2 -5.6 -7 -11.6 -16.2 -20.8 -25.4 -30 -34.6 -39.2

It is clear there were substantial areas of land that were disappearing in the millenia after the reoccupation of Britain after the last glacial maximum (with this map corresponding to the cold spell of the Younger Dryas).
In the period of time, between 12kyr BP and 8kyr BP sea level rose by 20m, which corresponds to half a metre every century.
Especially in the large expanses of gently sloping terrain off the north coast, it would be likely that coastal retreat would have been noticeable by people within a single lifetime.

A version speculating about woodland colonising the lowlands:

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