Small-scale slope instability on the submarine flanks of insular volcanoes: the case-study of the Sciara del Fuoco slope (Stromboli)

Abstract

Small-scale landslides affecting insular and coastal volcanoes are a relevant geohazard for the surrounding infrastructures and communities, because they can directly impact them or generate local but devastating tsunamis, as demonstrated by several historical accounts. Here, a review of such landslides and associated predisposing/triggering mechanisms is presented, with particular reference to the submarine volcanic flanks. We take into account, as a case study, the instability phenomena occurring on the Sciara del Fuoco (SdF, hereafter), a 2-km wide subaerial-submarine collapse scar filled by volcaniclastic products, which form the NW flank of the Stromboli volcano. Because of its steepness (> 30°) and the high amount of loose volcanic material funneled from the summit crater towards the sea, the submarine part of the SdF is prone to instability phenomena recurring at different spatial and temporal scale. Particularly, landsides with a volume of some millions of cubic meters, as the 2002 tsunamigenic landslide, can repeatedly affect the submarine slope. Based on the integration of 11 years (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013) of morpho-bathymetric monitoring of the SdF with geotechnical characterization of volcaniclastic and lava flow materials, stability analyses of the subaerial and submarine slope and previous literature studies, we analyze the role of different triggering mechanisms in controlling the occurrence and size of submarine slope failures at the SdF, such as dykes intrusion as occurred in 2002 or the emplacement of a large delta as occurred in 2007.

Submarine and Subaerial Morphological Changes Associated with the 2014 Eruption at Stromboli Island

“…Regardless, the estimated volume of the E1 slope failure is two order magnitude larger than any instability processes occurred since the emplacement of the 2007 lava delta, and it also affected the more stable part of the delta according to the previous bathymetric surveys [26]. Such findings support our inference that triggering mechanisms for this larger slope failure are likely different from those common involved in the "ordinary" readjustment of the submarine slope, such as the loading of the 2014 lava flows on the submarine slope or the seismic activity associated with the 2014 eruptive event.…”

“…The DEMs used to constrain seafloor changes associated with the August-November 2014 eruption were collected in February 2013 and January 2016, respectively (Figure 3). Despite the time gap before and after the eruption, our 20 years' experience on submarine monitoring of the SdF has evidenced that the main morphological changes occur during eruptive crisis or increased period of Strombolian activity, while the "ordinary" evolution of the slope is limited to small readjustments of the shallowest part of the SdF [20,[24][25][26].…”

“…The tsunami waves related to the 2002 submarine and subaerial landslides severely impacted the Stromboli coastline with a maximum runup of 10 m [21], evidencing the high hazard associated with similar events that have repeatedly occurred also during the previous century [22,23]. Since then, SdF slopes have been carefully monitored through repeated topographic surveys for their submarine [24][25][26] and subaerial part [27]. These surveys are part of a more complex monitoring network including: ground-based thermal infrared data [3]; infrasonic monitoring [28], seismic network [29], borehole strainmeters [10], dilatometric sensors [30], ground tiltmeters [31], plume and soil gas geochemical monitoring [32,33], two ground-based interferometric synthetic aperture radar sites [34] and satellite thermal monitoring [35].…”

Offshore Geological Hazards: Charting the Course of Progress and Future Directions

“…Despite the high tsunamigenic potential associated with these large-scale events, their hazard is relatively low because they have recurrence times on the order of thousands of years. In contrast, small-and medium-sized slope instabilities affecting active volcanic flanks are more hazardous because they have markedly shorter recurrence times and are able to generate local but devastating tsunamis [220,221]. One of the best examples is recognizable at Stromboli Island, where five tsunamigenic landslides over just the last century have been reconstructed [222].…”

Editorial: Flank dynamics, sector collapses, lahars, and rockfalls: analysis, monitoring, and modelling of small to large scale volcanic slope instability

“…The four papers belonging to this Special Issue present an updated general overview of the progress in volcanic slope instability analysis, monitoring, and modelling from multi-disciplinary efforts, from slope to edifice and regional scale. The topics discussed range from the geological/ volcanological evolution of a Quaternary silicic volcanic complex (Shiribetsu) in Japan (Goto et al 2020), the analysis of two very famous case studies for tsunamigenic landslides at Stromboli (Italy; Casalbore et al 2020) and Ritter island (Papua Nuova Guinea, Karstens et al 2020), to studies of grain-size distribution and sedimentological features of volcaniclastic mass flows (Makris et al 2020).…”