RECENT MORPHOLOGICAL CHANGES INDUCED BY SUBMARINE LANDSLIDES ON THE NICE CONTINENTAL SLOPE
Presented by Ms. Maelle KELNER on 23 Sep 2013 from 17:15 to 19:15
Type: Poster presentation
Session: Poster session
Time series bathymetric data acquired between 1991 and 2011 have been used to evaluate the recent morphological evolution of Nice upper continental slope (SE France, Ligurian Sea).This area is affected by a large number of submarine landslides. Frequency, size and impact of small size failure are not well-known and difficult to detect using classical tools.However it lead to regressive motion of continental slope, to the deposition of high-frequency turbidites in the basins and could generate local tsunami. Cartographic analysis was made to identify individual scarps, slope variations and shelfbreak location. Then DEM comparisons were performed for each time interval, using ArcGIS “Raster calculator”. It provided the specific background to locate and to quantify morphological changes over the last 20yrs at shallow water depths (0-200m).Shelfbreak migrations toward the coastline up to 60m following retrogressive scarp and chute incision is visible over time periods of 7-8 years where the continental shelf is >170m large. Sediment remobilizations on the upper slope are fast and significant; failure scars with volumes > 25000 m3 can appear, or scars with volumes ~150 000 m3 can disappear of the seafloor in less than 8 years. Between 1991 and 2011, alternation between periods of low morphological changes and periods of active failure events with significant volumes is clearly found. Erosion volumes can be multiplied by 10 during periods of enhanced landslide activity (1999-2006). The triggering processes are still questioned for this landslide activity variation. On the basis of local seismic data, hydrogeological analysis and chirp sismic cross sections, we try to define mechanisms on a few years period.All these observations and quantifications reveal that failure processes can be quite active and significant over very short periods of time (<7years). This whole study is a next step in term of current stability evaluation of the Nice submarine slope.