Stone Age mass graves on UK islands might be filled with the victims of a prehistoric tsunami, according to a controversial new study.
Shetland and Orkney are archipelagos that lie off the north coast of Great Britain. Both have been inhabited for thousands of years. Orkney is home to prehistoric villages including Skara Brae, while Shetland boasts Jarlshof among others.
There are many stone cairns on Orkney, containing multiple graves: one may hold over 300 bodies. Cairns are also found on Shetland but they are less well preserved.
Advertisement
Most archaeologists think the cairns are a sign of religious practices, or that they had a social function such as asserting ownership over land. But of the University of Oxford, UK and her colleagues have an alternative suggestion: that some of them, at least, are the mass graves of tsunami victims.
“It is entirely plausible that there are coastal mass burial sites around the world that we can attribute to catastrophic tsunamis throughout history and into prehistory,” says Cain.
Tsunamis can be devastating: the 2004 Asian tsunami left over 200,000 people dead. They are most common in tectonically active places, like the Pacific, because submarine earthquakes can set them off, and there is evidence of causing havoc in these places. But tsunamis do also occur in the seas around the UK, albeit rarely.
The largest known is the Storegga Slide from about 8150 years ago. A submarine landslide off the coast of Norway triggered a tsunami that swamped coastlines around the North Sea. However, the archaeological record on Orkney and Shetland doesn’t go back quite that far.
So Cain and her colleagues focused on a more recent tsunami, which happened . Geological evidence from Garth in Shetland suggests sea levels rose by 10 metres, enough to swamp coastal communities. In the face of such a disaster, bodies must have been buried hastily in mass graves.
“There are many mass burial sites and their ages at least approximate the timing of the Garth tsunami,” says Cain. “This has never been proposed as a cause, largely because the sites were not studied with this in mind.” She admits the link is currently “speculative” and wants to look for marine microorganisms called diatoms in the graves, as this would suggest the people drowned in seawater.
“If it did inundate Shetland and Orkney as we think, then it probably affected the majority of the coastal communities – and to be honest, most of the communities in the islands are coastal,” says co-author of the University of New South Wales, Australia.
Waves of doubt
Other archaeologists are intrigued but highly sceptical.
“The architecture of the tombs themselves does nothing to suggest anything carried out in haste,” says of the University of Aberdeen, UK. “They are sophisticated and complex structures, indicative of careful planning.”
“I would be extremely cautious,” says of Cardiff University in the UK. He accepts that coastal mass graves elsewhere, especially in the Pacific, could hold prehistoric tsunami victims, but says the evidence on Orkney and Shetland is scanty.
In , Whittle and his colleagues reviewed 692 dating measurements from Orkney to build a detailed picture of how the islands’ prehistory played out. They found that the mass burials took place at widely separated intervals, and did not cluster around 5500 years ago. “It’s not looking at the moment like a single event, it’s a process, a sequence,” he says.
Whittle’s team did find a “potential slackening of settlement” on Orkney’s largest island, confusingly called Mainland. But this happened around 4800 years ago, “too late for their claimed Garth event based on the Shetland site”. Besides, it was limited to Mainland: “the one part of Orkney which would be more naturally protected”.
