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Evidence from the coast of Devon Looking for the Ice Age Shore Line Magnetic Reversals and Crustal Overturn Evidence from the coast of Devon |
Underwater investigations off the coast of Devon in the UK show cliffs, but they don't line up. This paper suggests that these cliffs have another cause. The South Hams of Devon, the region between the granite moorland of dartmoor and the South Coast, is a gently rolling countryside: .
The ridges are mostly smooth, level, rounded.
But the coast shows a steep slope to the sea. A wave cut shelf into this slope marks the present sea level - but this demonstrates that the slope itself is not wave cut. Notice how smooth the much older top edge of the slope is compared to the wave cut notch at sea level. Notice also the angle of this slope.
Between Prawle Point and Start Point - Lannacombe Bay - the same angle of seaward slope is visible, with a wave cut platform marking the current sea level. Here an older wave cut platform exists just above the current one, which is being exposed as the well accreted gravel bank that covers it is washed away.
Further west beyond Bigbury, there is no sign of this seaward slope, or of a previous higher sea level, but the rocky outcrops demonstrate clearly how rough a coastline is produced by erosion by the sea.
East of Dartmouth the seaward slope is clearly visible, but with no signs of higher wave cut platforms. Notice again how the recent erosion at sea level produces a much steeper cliff than that of the smooth seaward slope.
By contrast the shore of Northern Brittany on the other side of the channel shows the gently rounded contours of granite running out to sea without any signs of the high seaward slopes of the UK side of the channel. In many places there is barely any erosion to produce a seaward cliff.
I am putting forward the hypothesis that the lack of any consistent ice age sea level cliffs, is because of major faulting of the rocks that took place in the past, and again on the same fault lines at the end of the last ice age. Different sections of the Devon coastline rose or fell by varying amounts so that there is no consistent level to earlier wave cut platforms. I am suggesting that the steep seaward slope of Bolt Tail to Bolt Head, and Salcombe to Prawle point were created by the sinking of the rock strata on the seaward side. The offshore cliffs detected along this coast are further fault lines and do not represent earlier sea levels. Flooding of the Estuaries such as Kingsbridge may be the result of tilting of the land surface behined this fault line, rather than a rise in sea level. This same tilting may be why old erosion terraces in the inland rivers of the region don't show the expected slopes.
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