Volume balance of frontally confined submarine landslides - a case study of the Ana Slide, Eivissa Channel, western Mediterranean Sea

Submarine landslides can cause devastating tsunamis and inundate surrounding coastal areas or directly compromise offshore infrastructure. A landslides’ ability to generate a tsunami is expressed as the tsunamigenic potential controlled, amongst other parameters, by the amount of landslide material mobilized during failure. The Ana Slide, located in the Eivissa Channel on the Balearic Promontory, western Mediterranean Sea, developed as a frontally confined landslide. This means that the mobilized mass is frontally buttressed against unaffected strata. Unique to the Ana Slide is that it is completely covered by high-resolution 2D, 3D reflection seismic and bathymetric data. Steady hemipelagic sedimentation prevailed in the study area way before the occurrence of the Ana Slide. Strata outside the perimeter of the Ana Slide shows predictable thicknesses that can be interpolated from outside to inside the landslide.

Within this study, we reconstruct the pre-failure seafloor morphology of the Ana Slide. We use a published GIS-tool for the source area and facilitate predictive sedimentary thicknesses as an interpretational basis for the sink area. These methods allow the actual volume of mobilized landslide material from the evacuational source into the accumulational sink area to be determined. In addition, we can calculate the ratio between actually mobilized landslide and affected material that was not directly involved in the landslide motion. Results of the volume balance calculation expose that the Ana Slide represents a “closed system” landslide because all evacuated landslide material from the source area has completely accumulated within the sink area with an uncertainty of < 5%.

Based on a detailed kinematic analysis previously performed for the Ana Slide, we show that the volume of actually mobilized landslide material is significantly smaller than that of the affected material that was not directly involved in the landslide motion. We show that mobilized landslide material can affect strata to significant depths beneath the deposit, while being relatively thin itself. This could potentially lead to erroneous or excessive landslide volume estimations. Our findings may therefore be critical for tsunamigenic potential assessment and geological hazard predictions.