How Britain became an Island (Brexit 1.0)
A catastrophic megaflood separated Britain from France hundreds of thousands of years ago, changing the course of British history
For much of our pre-history, a permanent land bridge existed between Britain and France at the Dover Strait. How and when it was removed, however, was previously unknown. Following a grant for a suite of high-resolution sonar equipment, we conducted the first ever multi-beam bathymetric survey of the UK continental shelf, which led to the discovery of a megaflood landscape carved into the floor of the English Channel. This feature could only be formed by a catastrophic failure of the rock ridge, resulting in the abrupt isolation of Britain from continental Europe. This dramatic event significantly altered the pattern of human colonisation of Britain.
Our work revealed spectacular images of a huge valley tens of kilometres wide and up to 50 metres deep carved into bedrock on the floor of the English Channel (Fig.1). The carving of this feature around 450,000 years ago resulted in the geographical separation of Britain from continental Europe.
We analysed a new regional bathymetric map of part of the English Channel derived from a compilation of both single- and multi-beam sonar data, which shows the morphology of the seabed in unprecedented detail. We observe a large bedrock-floored valley that contains a distinct assemblage of landforms, including streamlined islands and longitudinal erosional grooves, which are indicative of large-scale subaerial erosion by high-magnitude water discharges. Our observations support the megaflood model, in which breaching of a rock dam at the Dover Strait (Fig.2) instigated catastrophic drainage of a large pro-glacial lake in the southern North Sea basin. This flow was one of the largest recorded megafloods in history and could have occurred 450,000 to 200,000 years ago. We suggest that megaflooding provides an explanation for the permanent isolation of Britain from mainland Europe during interglacial high-sea-level stands. The breaching likely affected patterns of early human occupation in Britain by creating a barrier to migration which possibly explains the complete absence of humans in Britain 100,000 years ago. The breach of the ridge, and subsequent flooding, also may have initiated the large-scale reorganisation of the river drainages in north-west Europe by re-routing the combined Rhine-Thames River through the English Channel to form the Channel River.
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Gupta S, Collier JS, Garcia-Moreno D, Two-stage opening of the Dover Strait and the origin of island Britain, Nature Communications, Vol: 8. See here for the Press Release., 2017,
Collier JS, Oggioni F, Gupta S, ., 2015, Streamlined islands and the English Channel megaflood hypothesis, Global & Planetary Change, Vol: 135, Pages: 190-206.
Gupta, S., Collier, J.S., Palmer-Felgate, A., & Potter G 2007. Catastrophic flooding origin of the shelf valley systems in the English Channel, Nature, Vol: 448, Pages: 342-345.
Channel 4 Walking Through Time (2016 Episode 1)
How Britain became an Island (Imperial College Festival Talk - video)
UK Hydrographic Office (UKHO) and the Maritime Coastguard Agency (MCA)
Data collected by the MCA and archived by the UKHO was originally sourced for civil safety at sea.