A thousand years ago, the breathtaking Isles of Scilly were actually a single, large island.
Now, the isles are slowly sinking into the ocean, and could even disappear completely in the centuries to come.
Researchers studying coastal changes due to seal-level rise recently found that today's Isles of Scilly emerged from a single island. It only became the current configuration of more than 140 islands less than 1,000 years ago.
Led by the University of Exeter, they developed a new 12,000-year sea-level curve for the Isles of Scilly. They also looked at new landscape, vegetation and human population reconstructions created from pollen and charcoal data and archaeological evidence. The new research extends and enhances data collected by the Lyonesse Project (2009 to 2013), a study of the historic coastal and marine environment of the Isles of Scilly.
The new findings suggest that, between 5,000 and 4,000 years ago, the island was rapidly becoming submerged by the ocean.
Land was being lost at a rate of 10,000 m 2 per year - which is equivalent to a large international rugby stadium.
But, instead of abandoning it, people seemed to adapt to the new landscape.
By the Bronze Age (after 4400 years ago), the archaeological record suggests the area had a permanent population – and instead of leaving the islands, it appears that there may have been a “significant acceleration of activity”.
The reasons for this are unclear, but one possibility is that new shallow seas and tidal zones provided opportunities for fishing, shellfish collection and hunting wildfowl.
This period of rapid land loss happened at a time of relatively slow sea-level rise – because lots of Scilly’s land at that point was relatively flat and close to sea level.
Charlie Johns (Cornwall Archaeological Unit) co-director of the Lyonesse Project said: “This new research confirms that the period immediately before 4,000 years ago saw some of the most significant loss of land at any time in the history of Scilly — equivalent to losing two-thirds of the entire modern area of the islands”.
After 4,000 years ago, the island group continued to be submerged by rising sea levels, even during modest (e.g., 1 mm per year) rates of sea-level rise.
While a considerable part of Scilly's land has already disappeared, the islands are still at risk of sinking into the ocean.
Due to the sea-level rise, climate change and winter storms, the archipelago is expected to become uninhabitable in the future. The highest point on St Mary’s, the main island, is just 49 metres above sea level; 30% of the island is below five metres.
The community is in “managed retreat”. Two of the smaller islands – Tean and Samson – which were once inhabited have been left to wildlife and tourists.
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Hugh Town, the biggest settlement on St Mary’s, could be one of the first to disappear into the ocean.
The capital is built on a sand spit, and in the February 2014 storms came close to being inundated. It is anticipated that by 2080 the maximum wave height in the deep waters around the islands will be a metre more than at present.
“We have a number of flood defence plans that have already been started," a spokesperson said at the time.
“There is some managed retreat, though not in populated areas. This is a serious, long-term plan. We are not fire-fighting.”
A councillor added at the time: "We used to be part of the mainland, and we are being slowly inundated. But it won’t happen for hundreds of years."
According to the Cornish folklore, there is a city - off Land's End, in the Isles of Scilly area - that disappeared into the ocean centuries ago.
The legend, immortalised in the poetry of Alfred Lord Tennyson, says that the lost land of Lyonesse was engulfed by a huge tidal wave.
It was a rich land with fair-sized towns and as many as 140 churches.
Some say that it is where King Arthur fought his last battle against Mordred and others, like Thomas Mallory, claimed it was the birthplace of Iseult's lover Tristan.
Lyonesse is said to have been swallowed by the sea in a single night, never to be seen again.
The catastrophe left only two survivors - a man called Trevillian and his white horse.
Since then, local fishermen have been said to have pulled up stones from the buildings of the lost city in their nets and, to this day, the bells of long-submerged churches can be heard ringing beneath the waves on still nights.
Others say the domes and spires of Lyonesse can be seen in the sea when standing on the cliffs at Land’s End.
This is the legend which inspired the Lyonesse Project. You can read more about it here.
The coastal changes the Isles of Scilly have been through for thousands of years show how other territories, including Cornwall, could be affected by the sea-level rise and how critical the fight against climate change is for coastal populations.
The lead author of the study, Dr Robert Barnett, of the University of Exeter said: "It is clear that rapid coastal change can happen even during relatively small and gradual sea-level rise."
But with climate change now driving rapid sea-level rise, the team says the effects will not always be as simple as a forced human retreat from coasts.
“When we’re thinking about future sea-level rise, we need to consider the complexity of the systems involved, in terms of both the physical geography and the human response” Dr Barnett said.
“The speed at which land disappears is not only a function of sea-level rise, it depends on specific local geography, landforms and geology.
“Human responses are likely to be equally localised. For example, communities may have powerful reasons for refusing to abandon a particular place.”
Dr Barnett added: "The current rate of mean global sea-level rise (around 3.6 mm per year) is already far greater than the local rate at the Isles of Scilly (1 to 2 mm per year) that caused widespread coastal reorganisation between 5,000 and 4,000 years ago.
“It is even more important to consider the human responses to these physical changes, which may be unpredictable. As can be seen today across island nations, cultural practices define the response of coastal communities, which can result in polarised agenda, such as the planned relocation programmes in Fiji versus the climate-migration resistance seen in Tuvalu.
“In the past, we saw that coastal reorganisation at the Isles of Scilly led to new resource availability for coastal communities. It is perhaps unlikely that future coastal reorganisation will lead to new resource availability on scales capable of supporting entire communities.
“More certain though, is that societal and cultural perspectives from coastal populations will be critical for responding successfully to future climate change.”
The research was funded by a grant from English Heritage (now Historic England) to the Cornwall Council Historic Environment Service (now Cornwall Archaeological Unit). Outputs from the original project (The Lyonesse project: A study of the historic coastal and marine environment of the Isles of Scilly (2016)) are also available from the Cornwall Archaeological Unit.
It was led by the University of Exeter in partnership with Cornwall Archaeological Unit, Cardiff University and 14 other institutes.
The paper, published in the journal Science Advances , is entitled: “Non-linear landscape and cultural response to sea-level rise.”