Mass graves dating back to Neolithic times have been found on two islands off the Scottish coast, but archaeologists aren't really sure why they exist. In a paper published in the Journal of Archaeological Method and Theory, researchers have put forward a new (and controversial) theory suggesting ancient tsunamis could be to blame.
Stone cairns found on Orkney and Shetland are some of the most prolific surviving infrastructures from the Neolithic period. They were used as repositories for the dead, with some containing more than 300 skeletons. Yet, while the consensus appears to be that these were sites of religious practice, no one really knows for sure.
Now, Genevieve Cain, a graduate at the University of Oxford, and co-workers have compared characteristics of these sites to mass burials in other parts of the world, finding evidence to suggest they are, in fact, mass graves built in the wake of a natural disaster, specifically a tsunami.
Tsunamis most frequently take place around tectonic plates (think: Japan, Indonesia, and Central America) but they can, occasionally, occur in Northwestern Europe, including sites in the UK. These are usually caused by underwater landslides, like the Storegga slide (8,400 to 2,200 years ago). The incident highlighted in the paper, the Garth tsunami, occurred roughly 5,500 years ago.
“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,” said James Goff, co-author and adjunct professor at the University of New South Wales, New Scientist reports.
In the paper, the researchers say "the nature, chronology and location" of the burial sites fits with the Garth tsunami theory. They also point out certain commonalities between tsunami-related mass burials that seem to defy time and place – for example, the 2004 Indian Ocean tsunami and the 1896 Sanriku tsunami. These comparisons show that these mass burials can usually be found by the coast, in shallow trenches or pits, and are carried out with little to no thought to religious and cultural sensitivities. Also, because the most common cause of death in a tsunami-type scenario is asphyxiation, there may be little to no physical sign of trauma on the skeletons.
At this stage, the theory is entirely speculative and there are reasons to remain skeptical. For example, as Rebecca Crozier from the University of Aberdeen told New Scientist, the architecture of the tombs are sophisticated, which would suggest they are the product of careful planning and not a rushed mass burial.
The next steps are to search for any marine microorganisms that might be lurking in the burials, suggesting the people died from drowning. As the study authors mention: "The argument here is not that every mass burial is tsunami-related, but that in a coastal context in particular, there is the danger of not considering it and, as such, misinterpreting much about human-environment interactions in prehistory."