Subaqueous landslides associated with historical road improvements in steep glaciated terrain, Loch Lomond, western Scotland

Abstract

Shorelines in steep glaciated terrain are focal points for development and can provide important natural corridors for transport (e.g. road, rail). However, the steep subaqueous slopes at nearshore sites present challenging ground conditions, and only in recent decades has the acquisition of continuous high-resolution bathymetric datasets become available to inform investigations. This study investigates a site in Loch Lomond, Scotland, where a reported displacement of 15 000 m 3 of rock fill occurred prior to completion and stabilization of an embankment for the A82 road, during improvement work undertaken in the 1980s. We revisit the area using new multibeam swath bathymetry, shallow sub-bottom seismic data and geomorphological mapping, as well as borehole logs from the original ground investigation. The bathymetric and seismic data provide strong evidence for older subaqueous landslide activity at the site. The data indicate that embankment construction was also associated with occurrence of subaqueous landslides, incorporating a total volume of up to 95 000 m 3 . The research demonstrates the value of nearshore geophysical datasets in steep glaciated terrain, both for understanding geomorphological response to past shoreline modifications and as part of investigations where future developments (e.g. transport, energy infrastructure) are planned.