INFLUENCE OF LITHOSTRATIGRAPHY ON THE RETROGRESSION OF UNCONSOLIDATED SEDIMENTARY COASTAL CLIFFS FROM A HIGH RESOLUTION, MULTI-SCALE AND MULTI-SOURCE ANALYSIS (ST. LAWRENCE ESTUARY, EASTERN CANADA)

This work investigates the controls and processes causing retrogression in unconsolidated coastal cliffs using terrestrial and airborne LiDAR surveys (2005, 2010 and 2013) and aerial photographs (1964-2012) at Pointe-au-Bouleau, on the north shore of the St. Lawrence Estuary, in Eastern Canada. The high lithostratigraphic variability of the sediment allowed for the identification of stratigraphic and lithological variables that explain the retreat dynamics of coastal cliffs. Space-for-time substitution, based on field observation and measurements, was also used to model how lithostratigraphy controls the evolution of emerged glacimarine coastal cliffs over decadal to centennial time scales. This case study presents new quantitative data that contributes to a better understanding of the role of sediment architecture, stratigraphy and geomorphology on present and future coastal evolution. The methodological approach includes the development of a new conceptual model suitable for identifying erosion hotspots on cliffed coastlines. The high-resolution methodology (< 5 cm) used herein demonstrates the need for further research using LiDAR data in order to quantify the processes involved in the dynamics of coastal cliffs.