Mapping the susceptibility of rain-triggered lahars at Vulcano island (Italy) combining field characterization, geotechnical analysis, and numerical modelling

摘要

The characterization of triggering dynamics andremobilized volumes is crucial to the assessment of associated lahar hazards.We propose an innovative treatment of the cascading effect between tephrafallout and lahar hazards based on probabilistic modelling that alsoaccounts for a detailed description of source sediments. As an example, wehave estimated the volumes of tephra fallout deposit that could beremobilized by rainfall-triggered lahars in association with two eruptivescenarios that have characterized the activity of the La Fossa cone (Vulcano,Italy) in the last 1000?years: a long-lasting Vulcanian cycle and asubplinian eruption. The spatial distribution and volume of deposits thatcould potentially trigger lahars were analysed based on a combination oftephra fallout probabilistic modelling (with TEPHRA2), slope-stabilitymodelling (with TRIGRS), field observations, and geotechnical tests. Modelinput data were obtained from both geotechnical tests and field measurements(e.g. hydraulic conductivity, friction angle, cohesion, total unit weight ofthe soil, and saturated and residual water content). TRIGRS simulations show howshallow landsliding is an effective process for eroding pyroclastic depositson Vulcano. Nonetheless, the remobilized volumes and the deposit thicknessthreshold for lahar initiation strongly depend on slope angle, rainfallintensity, grain size, friction angle, hydraulic conductivity, and thecohesion of the source deposit.