Once upon a time, Britain and Europe were one. Land studded with low hills, gentle valleys and marshlands between southeast England and Belgium and the Netherlands. You could have walked from proto-London to primordial Brussels or Amsterdam, in the shade of trees and could have hunted – or been hunted by – its animals.
As the Ice Age came to its close, the land gradually shrank in area and turned into an island as deglaciation led to sea level rise. And then around 8,150 years ago, a catastrophic collapse of the continental shelf off Norway, called the Storegga Slide, triggered a mega-tsunami that apparently was responsible for sending that land below the waves forever more.
Doggerland, as the lost land has come to be called, lay submerged and forgotten – at least until 1931, when a fishing trawler pulled up a prehistoric harpoon made of antler.
Evidence that there had been firm land there once, and that its final submersion below the North Sea was caused by tsunami trauma, has been accruing ever since.
Now a new team reports in the journal Geosciences on the first evidence off the southern coast of Britain and on the undersea remains of Doggerland as well. They also found evidence, they add, that calamitous Storegga Slide didn’t generate one tsunami but three.
Landslide bigger than Scotland
During most of the last Ice Age, much of Doggerland was covered by the ice sheet and would likely not have been hospitable. As the ice retreated, the land became rich tundra – rich enough to support forests, as divers reported in 2015 (at first they thought they’d found a sunken ship).
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Doggerland also featured a richness of animal life: mammoths, cave lions and other megafauna could and did cross between today’s England and Europe on this land, according to bones dredged up from the deep. Not to mention humans.
On the one hand, where the ice sheet melted, the land rose because it was relieved of the weight of the ice. On the other, sea levels rose too.
The last glacial maximum was about 16,500 years ago. By the time of the Storegga Slide around 8,150 years ago, much of low-lying Doggerland was already submerged. Doggerland had already turned into Dogger Bank, aka an island. It was still populated by humans and animals until the continental shelf off Norway massively collapsed. Why it did so, we do not know for sure. In fact, it appears that the mid-Norwegian continental margin has a nasty habit of sliding every 100,000 years or so.
Scientists suspect the core cause of the mega-landslides involves glaciation – specifically, the weight of forming glaciers. Be that as it may, the Storegga Slide was one of the biggest tsunamigenic landslides that we know of, ever. Displacing about 3,200 cubic kilometers of sediment, “the Storegga slide is bigger than Scotland, and its headwall extends for about 300 kilometers. It dwarves even the largest slide yet found on land,” other scientists wrote in 2014.
As for those three tsunamis, multiple waves are typical following major undersea landslides. The proof lay in geochemical signatures in sediment cores, which indicated three major waves hitting and retreating from the land, the team says.
At least one of these waves towered at least 20 meters (66 feet) in height in some places – for instance, in the narrow Norwegian fjords. The wave was high enough to wash over Doggerland and to reach England, north and south.
People like to live on the coast; attraction to the sea and seafood goes back to before Homo sapiens. Likely the habitable coasts along the North Sea, and Dogger Bank itself, were robustly populated until the giant waves broke over the coasts.
Evidence of the catastrophic event had been found in onshore sediments in Western Scandinavia, the Faroe Isles, northeast Britain, Denmark and Greenland, but now for the first time confirmation of the event has been found on the U.K.’s southern coasts. To wit: The team identified tsunami sediment deposit in the southern North Sea at the head of a paleo-river system that was itself identified by means of seismic surveying, they explain.
Much of the sediment from those paleo-tsunamis has eroded, but evidence still lurks in the inland basins of the time, and deep river valley systems.
Co-author Prof. Vince Gaffney from the School of Archaeological and Forensic Sciences at the University of Bradford points out that extreme events are not the fief of the past, but lie in our future as well: “Climate is changing and this impacts on many aspects of society, especially in coastal locations,” he stated.
The latest research was led by the University of Bradford and involved the universities of Warwick, Wales Trinity St. David, St. Andrews, Cork, Aberystwyth and Tartu, as well as the Smithsonian and Natural History Museum. The paper is called “Multi-Proxy Characterisation of the Storegga Tsunami and Its Impact on the Early Holocene Landscapes of the Southern North Sea.”
Cores from an area south of a marine trough named the Outer Dowsing Deep provided nearly half a meter of tsunami-like deposits, stones and broken shells sandwiched between laminated estuarine sediments.
Dating indicated they were contemporary with the Storegga event, while analysis – including geochemical, sedimentological, paleomagnetic, isotopic, paleobotany and “sedaDNA” (sedentary DNA) techniques – showed the deposits could be readily interpreted as resulting from a tsunami.
The multi-proxy characterization was necessary as the signatures of tsunamis are often difficult to identify in comparison to those from periodic storm activity. Key to understanding the sequence was the interpretation of geochemical signatures of three major waves hitting and retreating from the land.
A number of innovative sedaDNA breakthroughs were achieved by the University of Warwick scientists: for the first time, they were able to see how biomass changes with large natural events.
In addition, a new “metagenomic assessment methodology” was developed for authenticating the sedaDNA damaged while under the sea for thousands of years. These innovations, together with assessment of the stratigraphic integrity of samples and refinement in algorithms to define ancient fragmented molecules of DNA, helped establish the sediment provenance.
Prof. Robin Allaby, from the School of Life Sciences at the University of Warwick, said: “This study represents an exciting milestone for sedimentary ancient DNA studies establishing a number of breakthrough methods to reconstruct an 8,150-year-old environmental catastrophe in the lands that existed before the North Sea flooded them away into history.”
Richard Bayes, from the School of Earth and Environmental Sciences at the University of St. Andrews, added: “The multi-proxy approach has paid off dividends here. In particular, the geochemical analysis combined with the geophysics is allowing us to see and interpret data in a way never previously possible.”
At the time the tsunami hit Doggerland, a Mesolithic hunter-gather people could have been using the remaining archipelago, and for those unfortunate enough to be caught within the tsunami runup zone, it would have been devastating. However, the paleo-topography and environmental modelling suggest that much of the landscape may have survived reasonably intact, to rapidly return to pre-tsunami conditions.
The longer term fate of these lands was to be submerged as sea level rose to those of the present day.