Slope Stability in a Multi-Hazard Eruption Scenario (Santorini, Greece)

Under the European FP7 SNOWBALL project (2014–2017), the island of Santorini was used as a case study to validate a procedure to assess the possible multiple cascading effects caused by volcanic eruptions. From January 2011 to April 2012, the area was affected by low to moderate (Mw <3.2) seismic shaking, which caused concern regarding a possible volcanic eruption that ultimately failed to materialize. Assuming the worst-case scenario of a sub-Plinian eruption, this study provides insights into the approach adopted by the SNOWBALL project to identify the most critical areas (hot spots) for slope stability. Geological field surveys, thematic maps, and geomorphological data on aerial photos and landform interpretation were adopted to assess the static susceptibility. The eruption scenario is related to two different phenomena: a pre-eruption earthquake (Mw 5.2) and the subsequent ash fallout deposition following the prevailing winds. Landslide susceptibility in seismic conditions was assessed through the HAZUS approach and the estimate of Newmark displacements (u), while the critical areas for ash fallout mobilization were assessed adopting empirical relationships. The findings are summarized in a scenario map reporting the most critical areas and the infrastructures most vulnerable to such phenomena.