The Tsunami that Devastated Ancient Britain

A piece of seabed the size of Scotland suffered a submarine landslide off the coast of Norway about 8,150 years ago, triggering a series of giant waves. The tsunami left traces in western Scandinavia, the Faroe Isles, north-east Britain, Denmark and Greenland, and it crossed the North Sea to reach Doggerland, the drowned land that once joined Britain to Europe.

It predates any written record by thousands of years, but the proof is in the ground, in layers of sediment left behind by the tsunami.

The trail it left

The University of Bradford puts the slide at around 3,200 cubic kilometres of material. The tsunami it set off is recorded in sediment deposits in the northern North Sea, along the north-east coasts of the British Isles and across the North Atlantic.

Reaching Doggerland

In 2020 evidence was found that the tsunami hit Doggerland, the now sunken land that once joined Britain to Europe. Doggerland was low-lying and would have been ravaged by the tsunami, however the impact was temporary and somewhat softened by dense woodland. It’s difficult to imagine a forest in a place now under the North Sea, but the ancient DNA evidence backs it up. A team from the University of Warwick led by Professor Robin Allaby analysed 252 samples from 41 marine cores taken from the Southern River channel. Oak, elm, lime and hazel showed up more than 16,000 years ago, thousands of years earlier than British pollen records had suggested. There was even DNA from Pterocarya, a relative of the walnut that was thought to have vanished from north-western Europe 400,000 years ago.

Who was standing there?

When the waves came, Mesolithic hunter-gatherers were living on what was left of Doggerland. Vince Gaffney of the University of Bradford says anyone caught in the runup zone would have faced devastating consequences, and it is easy to picture whole settlements swept away. Ultimately we have no way of knowing how many people lived there or what became of them.

Did anyone watch the sea pull back and understand what it meant? Did the survivors return to the same shores once the land recovered? The Warwick team suggests that Doggerland’s woods likely supported early Mesolithic communities, and that this may help explain why so little early Mesolithic evidence survives on the British mainland. If so, much of that story is now under the sea.

Doggerland itself did not go under in a day. What remained of it was low-lying land running out from Norfolk to an archipelago centred on Dogger Bank, a landscape extremely vulnerable to catastrophic flooding. It was lost for good as sea levels rose to their present height, and the Warwick DNA work suggests parts of it were still above water around 7,000 years ago, more than a thousand years after the tsunami.

Could it happen again?

According to a research project by the University of Southampton there have been at least six mega-slides in the Norwegian Sea region in the last 20,000 years. Storegga it seems, was not the only one. The research also says the UK faces few, if any, other natural hazards that could do damage on the scale of a repeat Storegga tsunami.

Among the questions the project is asking is whether climate change has any link to when the seabed shifts. In Gaffney’s words, the events leading up to the Storegga tsunami “have many similarities to those of today”, with a changing climate that weighs heavily on coastal regions.

Questions and answers

What is a submarine landslide?

A landslide that happens underwater. A mass of sediment or rock on the seabed gives way and slides down a slope. The very largest can displace enough water to set off a tsunami, as Storegga did.

What and where was Doggerland?

Doggerland was land that now lies under the southern North Sea. Before rising seas cut Britain off, it was what joined Britain to mainland Europe. Ancient DNA evidence shows it had dense woodland more than 16,000 years ago, and Mesolithic hunter-gatherers were living on what was left of it when the tsunami arrived.

What and where were the Storegga slides?

They were a series of underwater landslides off the Norwegian coast, in the Norwegian Sea, about 8,150. Estimates put the moving mass at roughly 3,000 to 3,200 cubic kilometres, spread over 80,000 to 90,000 square kilometres of seabed, an area about the size of Scotland. The tsunami left deposits in western Scandinavia, the Faroe Isles, north-east Britain, Denmark, Greenland and the now lost Doggerland.

What caused the Storegga slides?

The final trigger is still a matter of interpretation, but researchers have explained the seabed was primed to go. The slide began on a very gentle slope, averaging only 0.6 to 0.7 degrees. Rapid sedimentation during glacial periods had left water pressure trapped in the sediment, and the marine clay layers in the area lose strength as they deformed. Modelling published in 2005 showed that these factors together make a huge slide possible even on a gentle slope, with the failure working its way upslope from where it began. Work cited by the authors points to a strong earthquake as a possible trigger. The Southampton project is looking at triggers more widely, including possible links between slides and climate change.