Scientists identify hidden landslides beneath Scottish lochs

The sea bed can fail when physical conditions change, just as on land, creating an underwater landslide.

These mass movements, usually involving vast amounts of sediment, are known as submarine landslides and have the potential to threaten waterfront areas and sea-floor infrastructure.

Researchers at BGS in Edinburgh and the Scottish Association for Marine Science (SAMS) in Oban are helping to understand landslide characteristics that have never been compiled into a single study for UK waters before.

By analysing survey data, using sonar technology to map the sea floor, they have discovered evidence of at least fourteen submarine landslides occurring at five loch locations off the Scottish coast.

The data shows that Loch Eriboll, Little Loch Broom, Sound of Mull, Firth of Lorn, and Holy Loch, opposite the mouth of the Clyde estuary, have all been subject to underwater landslides.

Scientists don’t yet understand when these landslides occurred at these locations or how they were triggered.

According to the study, initial assessments of the scars and deposits on surrounding areas of the seafloor, show little evidence of any modification.

It could suggest that most, if not all of the landslides, date back to the Holocene, which is the name given to the last 11 700 years, since the end of the last major ‘ice age’. In geological terms, it is an era that is still young.

Until experts can be certain, they cannot draw conclusions about what kind of hazards these underwater landslides pose for the UK.

However, the results suggest that submarine landslides could be more common to these loch environments than previously accounted for.

Author of the research and BGS marine geoscientist, Gareth Carter, who is based at the Lyell Centre in Edinburgh, says:

“Without further data that would allow us to place exact dates on each of the landslides and understand what triggered them, it is impossible to understand what kind of hazard aspects these events might pose for the UK.

“What we do know is that quite a few of the potential trigger mechanisms that are often linked with landslides in sea lochs in other global locations are still present across the sea lochs of Scotland, so we cannot absolutely rule out another landslide event occurring.”

In locations like Canada, Alaska and Norway, which share similar geological histories and fjord environments to those found near Scotland, nearshore submarine landslides have potential to cause thousands to millions of pounds worth of damage to seafloor infrastructure, like cables and pipelines.

In some cases they have resulted in significant damage to coastal and waterfront developments, and in the most extreme cases, resulted in loss of life.

“As subsea and coastal engineering has advanced, these locations have been favoured as landfall sites for subsea cables and pipelines, sites for aquaculture industry installations, and continued waterfront development,” explains Gareth.

“It’s not untrue to say that the submerged slopes of a fjordic domain can pose a hazard to infrastructure, and even life, but the diverse styles of slope failure identified in this study are based on a relatively small dataset and further work is required.

“What is important is that the study highlights additional evidence of the issues surrounding subaqueous slope instability within coastal and fjordic environments, and particularly those around the UK that have never been studied before.

“This strengthens the need for a thorough site investigation and characterisation prior to any nearshore infrastructure project commencing in the future.”

Co-author and marine geoscientist, John Howe of the Scottish Association for Marine Science, adds: “This study illustrates some of the amazing processes that shape our seabed.

“The seas around the UK are mostly hidden to us but with sonar technologies we are able to visualise the seafloor and examine features such as these underwater landslides. The more we explore our local water, the more surprises we can uncover.”

The research is available to view free until 31 July 2020 in the journal Geomorphology.