New underwater research carried out by the universities of Bradford, Warwick, St Andrews and Wales has for the first time discovered that the tsunami devastated parts of East Anglia and adjacent land which is now submerged beneath the southern part of the North Sea.
Indeed, the new research suggests that two-thirds of the land inundated by the tsunami was in that newly investigated southern area of submerged territory, sometimes popularly dubbed Britain’s North Sea Atlantis.
Up till now, scientists only had evidence of it affecting eastern Scotland and northern England. Some models of the event had suggested that East Anglia and the southern North Sea might have also been affected – but the new underwater archaeological research suggests that the impact was much more extensive for that southern area than the models had predicted.
It is also estimated that in some places on Scotland’s east coast the tsunami wave was up to 20m high, and in Shetland, between 30m and 40m high.
The catastrophe unfolded in about 6200BC, when Britain’s population was made up of thousands of very small hunter-gatherer communities – perhaps a total of around 50,000 people, concentrated predominantly in coastal areas, especially river estuaries and floodplains along the east coast.
Most people were at least partly dependent on marine resources, so they tended to live in small temporary or semi-permanent encampments and settlements relatively close to the sea.
That made them particularly vulnerable to the disaster. It’s possible that, in total, up to 12,000 prehistoric Britons lost their lives.
The tsunami was caused by a huge underwater landslide which occurred off the west coast of Norway. Scientists believe that three factors combined to trigger the slide.
Firstly, the end of the final glacial period of the Ice Age led to a warming of the climate which turned vast quantities of long-frozen methane under the sea bed into millions of cubic metres of gas, which destabilised the edge of Norway’s steep continental shelf.
These increased temperatures had also melted thousands of cubic kilometres of glacial ice in Scandinavia. That second process removed billions of tons of weight from the surface of Norway, allowing the land to rise. In doing so, it seems to have potentially triggered earthquakes.
Such an earthquake was the likely immediate cause of the catastrophe in 6200 BC. It is estimated that about 767 cubic miles of continental shelf collapsed in just a few hours, causing the tsunami.
The event affected the coasts and river valleys of eastern Britain, western Denmark, northwest Germany, Norway, Shetland, Orkney, the Faeroe Islands, Iceland and Greenland.
In Britain, many east coast estuaries and river valleys were inundated. Many temporary encampments and semi-permanent settlements in these areas would have been wiped out.
“Our new research suggests that a significant proportion of the British Mesolithic coastal population almost certainly suffered fatalities,” said Dr Simon Fitch, an archaeologist and prehistoric population modeller from the University of Bradford.
The key estuaries and river valleys affected would have included the Moray Firth, the lower Spey Valley, the Firth of Tay and the Tay Valley, the Firth of Forth and the Forth Valley, the Tees Valley, the Humber estuary area, the Wash and three valleys in land which is now covered by the southwestern North Sea.
“The multidisciplinary investigation we carried out reveals that the tsunami wasn’t just a single wave – but impacted the now submerged southern North Sea area we examined in three successive inundations, probably spread over just a few hours at most,” said geophysicist Dr Richard Bates, of the University of St Andrews.
In some parts of Britain the tsunami penetrated far inland. Geomorphological evidence shows that it surged inland along Scotland’s Forth river for some 20 miles.
It is thought that it probably took hundreds of years for Britain’s population to recover. The waves may also have temporarily and very severely disrupted coastal food resources – especially the shellfish on which a substantial part of the population depended. As a result, it is conceivable that competition for surviving resources temporarily increased and resulted in low-level warfare. Certainly evidence from the tsunami-affected west coast of Denmark for that period suggests that such interpersonal violence increased.
The 6200 BC tsunami event, known as the Storegga Slide, is of particular interest to scientists because of the possibility it may happen again. Continental shelf landslides do still occur in parts of the world, and current global warming increases the risk through methane release. Although earthquakes in the North Sea and in Norway are relatively rare, they do sometimes occur – the most recent substantial ones being off the coast of Norway in 2012 and 2018 (magnitude 6.6 and 6.8 respectively) and in the southern North Sea in 1931 and 1958 (6.1 and 5.1).
“By investigating the former terrestrial landscapes now submerged beneath the southern North Sea, we have succeeded in shedding important new light on British prehistory, on climate change and on the continuing potential threat from tsunamis, sea level rise and storm surges,” said the leader of the research project, archaeologist Professor Vince Gaffney of the University of Bradford.
The multidisciplinary team’s investigation into the tsunami’s impact on now long-submerged land in the southern North Sea is published this week in the international scientific journal, Geosciences.
The wave height and coastal impacts of the Storegga Slide were similar to the 2004 Indian Ocean tsunami – although the kinetic energy levels, speed and distance covered by the 2004 wave was much greater, as was the loss of life.