Multibeam bathymetry investigations of mass movements in Lake Le Bourget (NW Alps, France) using a portable platform

Abstract

Here we report on a recent survey undertaken on Lake Le Bourget (NW Alps, France) using a multibeam echosounder mounted on a portable and shallow-draft platform. The 3.6 × 2.8 m survey platform can be transported from one lake to another and deployed within a few hours. Its shallow draft allows surveying in areas as shallow as 3 m, while the multibeam echosounder allows maximum sounding depths of 500 m. The collected data have allowed identifying two main areas of the lake affected by mass movements. In the northwest sector of the lake, a large mass wasting deposit of 1.8 km2 is found at the base of a very steep slope. This large deposit may be correlated with a major late-glacial mass-wasting event that triggered a seiche in Lake Le Bourget. To the north of this deposit a mass-wasting deposit is interpreted to have been caused by the AD 1822 earthquake. In the southeast sector of the lake, many lobes and a large mass wasting deposit are reported for the first time. The presence of gas-rich sediments in this area has prevented acoustic penetration and thus their identification during previous seismic surveys. The occurrence of mass movements is correlated with interflow deposition zones. In addition to the mass movements, a series of collapse craters are identified in the northern sector of the lake. These collapse craters are located near the head scars of an incipient slide. Considering that earthquakes are common in the region and can cause liquefaction within the lake sediments, there is a possibility that this incipient slide may further develop and eventually generate a massive (> 107 m3) slide. © Springer Science + Business Media B.V. 2010.