Marine geologists at the British Geological Survey (BGS) have visualised what lies beneath the waves of Loch Lomond, revealing an image of the loch bed and various sedimentary features of the subsurface. 

Using seismic data, marine geoscientists at BGS have discovered a new sedimentary rock unit buried in deposits beneath the loch, giving new insights into its past glacial history.  

Much of the Scottish Highlands were covered by an extensive mountain ice cap 12 900 to 11 700 years ago, during the last period of cold climate (known as the Younger Dryas or the Loch Lomond Stadial).

Decades of onshore research have shown how past ice ages have shaped the landscape of Loch Lomond, including carving of the present-day loch itself and its surroundings through processes such as erosion and deposition. However, this new dataset provides an interpretation of the stratigraphy now buried beneath the loch.  

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BGS used multibeam bathymetry surveys to gather detailed information about the features on the loch bed. The data revealed a series of flat-topped and prograding features (or the growth of a river delta further out into the sea over time) and ancient glacial geomorphological features.

These features include drumlins, which are oval-shaped hills largely composed of glacial drift that form parallel to the direction of ice flow, and streamlined bedrock, created by glacial restructuring of hard beds that produces a collection of extended rock landforms, interpreted as showing the direction of the palaeo-ice advance.  

The Herald: 3D model of Southern and Central basins3D model of Southern and Central basins (Image: British Geological Survey)

Nicola Dakin, marine geoscientist at BGS, said: “It’s been incredibly exciting to have had the opportunity to interpret these datasets and present the loch surface and subsurface in a way we’ve never seen before.

"The seismic mapping and interpretation of the Inchmurrin Formation helps us understand past landscapes and geological events that are now buried under the loch bed. We are keen to undertake further research in and around the area, building on the seismostratigraphical framework that we observe in Loch Lomond.”

BGS geoscientists used seismic data to map the subsurface of the loch. Seismic data uses sound waves, which travel through buried layers of sediment, forming an acoustic image based on density variations between different sediment types.

The Herald: Interpretation of the stratigraphy now buried beneath the lochInterpretation of the stratigraphy now buried beneath the loch (Image: British Geological Survey)

Geoscientists interpreted the acoustic signature, linking sedimentary processes and depositional environments to past climatic cycles. This provided a framework to create an updated chronostratigraphy within the loch.

Work is continuing to build understanding of other lochs in the area.

The Loch Lomond dataset could enable BSG to offer insights into the extent and rates of landscape adjustment that accompanied the transition from glacial to non-glacial conditions.

BSG said such findings are of "global importance" when considering landscape stability and potential future geohazards in regions that are undergoing rapid deglaciation, such as around the European Alps, Himalayas and New Zealand’s Southern Alps.