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Around 10,400 years ago, when Britain was still connected to mainland Europe, people ventured into Scotland, colonizing the windswept coastline. After around 2,000 years, however, the populations of their coastal communities fell dramatically.
Archaeologists previously thought that these foragers from the Mesolithic—a transitional period before agriculture became established—abandoned the coast roughly 8,000 years ago because of a tsunami that was triggered by undersea landslides near Norway. Models suggest the tsunami, dubbed Storegga, battered the northern and eastern Scottish coasts with waves up to six meters high, which inundated areas nearly 30 kilometers inland. The tsunami was thought to have been so catastrophic that it wiped out communities or forced them to flee to higher ground.
A new study by Steven Mithen and Karen Wicks, archaeologists at the University of Reading in England, however, suggests that the tsunami was just a tipping point for people already struggling with gradually rising seas and earlier climatic events.
For their study, Mithen and Wicks reconstructed the population patterns of preagricultural societies in northern Britain by collating the dates of all existing archaeological finds in the area from the period between 10,600 and 5,800 years ago. These comprised 439 samples from 87 sites. The researchers used this information to deduce the amount of human activity, and therefore rough population levels, at different times and places.
The results suggest that populations in the eastern part of northern Britain actually dipped around 8,500 years ago—at least 300 years before the tsunami hit. The decline did coincide, however, with warming that caused Lake Agassiz, a massive glacial lake in North America, to spill into the Atlantic Ocean. The team thinks this sudden increase in the sea level destabilized coastal habitats and diminished resources, causing the population decline.
In Mesolithic Scotland’s west, however, settlements seemed unaffected by this burst of sea level rise, suggesting that the landscape there, with its abundant fjords and hilly coastline, remained habitable.
In contrast, when sea levels were at their peak 300 years later, Greenland ice core records indicate that the Earth went through a bout of dramatic cooling, which caused prolonged stormy and severely cold weather. This, the team found, is likely what caused western populations to collapse, along with what remained of Scotland’s east coast populations. Then, the tsunami hit.
Considering all of these events and environmental changes, Mithen and Wicks found that inland and upland activity increased as populations moved away from ecologically destabilized coasts. “They abandoned the coast for the hills,” says Mithen. “It took several hundred years for populations to return to previous levels and to coastal areas.”
Caroline Wickham-Jones, an archaeological consultant in Scotland’s Orkney Islands, agrees that the cooling event and the tsunami likely reduced and destabilized coastal populations. But she is unconvinced that sea level rise adversely affected coastal populations—she thinks people would have had ample time to adapt.
Sea level rise was the norm for the coastal inhabitants, Wickham-Jones says. They had no idea it would eventually stop. “Today we find sea level rise very threatening because we are much less flexible and adaptable; we have become used to stability, and population levels are much higher.”
Previous studies suggest that the cooling event 8,200 years ago did not seem to affect populations elsewhere in northwestern Europe, including in Norway. But Mithen and Wicks propose that the early inhabitants of northern Britain were more vulnerable as relative newcomers to the region with isolated, low-density populations that lacked social networks, technology, and environmental knowledge, which put them on the back foot when it came to both gradual and sudden change.
But Astrid Nyland at the University of Stavanger in Norway, who is investigating the impacts of the Storegga tsunami on coastal communities in Europe, including in Britain and Norway, disagrees that these Mesolithic Scots would have been uniquely ill-adapted to their homes. Many Mesolithic peoples, she says, developed maritime cultures and robust relationships with the sea for thousands of years. Without social institutions that worked over generations, she says, “they would not have been able to live with an unstable and unsafe sea.”
Wickham-Jones also finds the explanation unconvincing: “I do not understand why people in northern Britain would have limited social networks—that makes no sense to me, and I’m not sure there is any evidence for that.”
Mithen acknowledges their conclusion that Mesolithic Scots were likely driven out by a series of climatic shifts—rather than felled by a singular event—requires further testing. But he says the finding does resonate with modern times. “The situation today is similar, with populations around the world becoming increasingly vulnerable because of gradual climatic and environmental change, which removes resilience to sudden shock events such as floods and wildfires.”