Lahars are a widespread phenomenon on Vulcano island (Italy), where many loose pyroclastic deposits provide a significant source of sediments. In this study we have estimated the volumes of tephra-fallout deposit that could be remobilized by rainfall-triggered lahars in association with two eruptive scenarios that have characterized the activity of La Fossa cone: a long-lasting Vulcanian cycle and a subplinian eruption. The spatial distribution and volume of tephra-fallout deposits that could potentially trigger lahars were analysed based on a combination of tephra-fallout probabilistic modelling (with TEPHRA2), slope stability modelling (with TRIGRS), field observations and geotechnical tests. Field characterization includes tephra-fallout primary deposits in the lahar initiation zones and lahar deposits both on the volcanic cone and in the ring plain. Model input data (hydraulic conductivity, friction angle, cohesion, total unit weight of the soil, saturated and residual water content) were obtained from both geotechnical tests and field measurements. In particular, hydraulic conductivity plays an important role on the stability of tephra-fallout deposits. Our parametric analysis has shown that the tephra-fallout critical thickness required to trigger a lahar for the considered rainfall event is between 20–25 cm for the Vulcanian scenario, and between 10–65 cm or
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Baumann et al. (2019) studied this question.