Solving the mystery of Shetland's tsunami sands

Map of Basta Voe

Map showing Basta Voe's depths and yellow pinpoints marking tsunami sands

6 November 2017 by Sarah McDaid

Shetland's wild, rugged landscape has long fascinated scientists, but for one British Geological Survey (BGS) marine geologist, it's the seabed around the islands that have ignited his interest.

Around 8,200 years ago, a submarine landslide off the coast of Norway caused a 20-metre high tsunami to sweep across Shetland's isles. Sands that were found at various points across the isles, and in Norway, the Faroe Isles and elsewhere, proved the towering height of the tsunami.

Now, BGS scientists are trying to trace the origin of much younger sand that has been discovered at different points across Shetland. They are taking a closer look at Shetland's seabed to find out whether the islands have been subjected to more giant wave events than previously thought.

Sands aged 5,000 and 1,500 years old have been discovered at three locations at up to 13 metres above sea level: Garth Loch and Dury Voe on mainland Shetland, and Basta Voe at Yell. Professor David Tappin, a marine geologist with BGS, believes these sands could prove that there were later tsunamis in Shetland, and that the answer lies on the nearby seabed.

Marine surveys carried out by the Maritime & Coastguard Agency (MCA) in the nearshore area provided a background to focused surveys by the BGS White Ribbon. The White Ribbon is a nine-metre catamaran that can survey the UK's shallow waters, and which recently sailed around Shetland on a research mission to hunt for the signs of submarine landslides.

Small survey ship

THE WHITE RIBBON

  • Surveys the shallow waters bigger ships can't reach

  • Nine metres long

  • Uses sound waves to create super accurate seafloor maps

  • Has also been used in lochs and lakes

David said:

We're hoping the White Ribbon will help us identify slumps that, on collapsing, could have triggered tsunamis, thereby washing the 5,000 and 1,500 year old sands up onto the islands. It could be that we discover a previously unknown way that tsunamis happen, or we are plunged deeper into the mystery of these sands.

They're in very small areas, which could mean the source of the tsunami was very close by, or simply that the sands that might tell us, have been lost. The sands are preserved in the peat of Shetland, much of which was disturbed and used for fuel, so it could be we're missing evidence. It's a bit like trying to solve a jigsaw puzzle, but with only a quarter of the pieces.

The BGS team is still analysing the data collected by the MCA and the White Ribbon, and David Tappin is determined to get to the bottom of the 'enigmatic' sands located around Shetland.

There are numerous coastal communities on the banks of the voes, and there's a major oil terminal nearby at Sullom Voe, so it's critical that we clarify whether there are any potential tsunami hazards in these areas. The White Ribbon can survey even the shallowest waters, so we'll soon have a complete picture of what lies beneath the waters of Shetland.


UnEarthed

In November, White Ribbon will set sail on a different type of mission. The nine-metre catamaran will be berthed outside Dynamic Earth in Edinburgh as part of NERC's free, interactive showcase event UnEarthed - external link. Members of the public will see its state-of-the-art facilities up close, and learn more about the exciting environmental science it has unearthed around the coast of the UK.