Dover Straits Waterfall

7 Apr 2017

At www.bbc.co.uk/news/science-environment-39494740 ... we have a regurgitation of an old story that has been updated by some new thinking by geologists from Imperial College. This concerns the breaking up of the chalk downs that connected Kent to Calais, 450,000 years ago. It emerges this figure may actually be completely guesswork as at the end of the story we are told the researchers want to drill into the bottom of Dover Strait and analyse the age of the sediment on the sea floor. We now there is still a chalk ridge in existence as the Channel Tunnel made use of it. In this story we are told a huge waterfall poured over this chalk ridge and hollowed out deep gouges into the chalk at the bottom - rather like the Scablands in the US NW. Not only that it scoured out a line of holes (according to the story) where the water landed as it fell over the scarp edge. Then, much later, around 150,000 years ago, there was a second catastrophic flooding event in the Dover Straits. This time the water carved out a deep valley at the bottom of the English Channel, 8 to 10km wide. This was still in existence after the end of the last Ice Age - and around 8000 years ago water once again broke through the Dover Straits after flooding the southern basin of the North Sea. Why the third event is not mentioned in the story is unclear - but presumably, they do not want to pose the idea some of this scouring was more recent than meets the eye. In fact, geologists tend to downplay the narrowness of the English Channel in the first half of the Holocene, but archaeologists are well aware that people were able to move from northern France to southern England without too much of a problem (during the Mesolithic).

Getting back to the storyline we have the idea that a huge lake formed above the chalk ridge - the latter holding back the water. At some stage the water overflowed and poured down the other side in a cascade. Presumably it rapidly filled what is now the English Channel. This occurred roughly at the end of what is known as the Anglian ice advance - when the ice sheet extended to its furthest point across Britain. It is well known from the geology of East Anglia (hence the name applied to it).  This region is just north of the Dover Straits and one can see, on the beach for example and in the cliffs, that chalk extended all the way from Norfolk across the North Sea in the direction of Denmark and N Germany. Now we might speculate that if the Anglian Ice Age ended catastrophically and very rapidly it would have created a lot of meltwaters. Is that where all the water that fell over the ridge came from? Invoking a huge lake may be unnecessary - although a lake could have briefly built up. The problem here is that Britain was really still attached to the continent from Norfolk to Kent so meltwaters would appear to be a more likely explanation. Of course, working in a uniformitarian straightjacket geologists are restricted in their explanations and hypothetical lake appears to be a neutral option.

In addition, in a catastrophist model, a changing geoid can explain the comings and goings of ice sheets across northern Britain and Ireland - as a result of changes at the axis of rotation and redistribution of sea water. In such a scenario there is no mystery about the advance and retreat of ice sheets - or their rapid disappearances. Neither is there any mystery about rapid change in sea levels - as earth's geoid is forced to reposition itself, especially the waters of the oceans. This is an integral part of the geological history of southern Britain. Over long periods much of it was submerged. At other times it has been above sea level. One explanation for this is changes in the earth's geoids - but another explanation might be rapid continental drift, plate movement in jerks rather than infinitesimally slowly.