Lava delta deformation as a proxy for submarine slope instability

• Published in: Earth and planetary science letters 2018-04, Vol.488, p.46-58
• Main Authors: Di Traglia, Federico, Nolesini, Teresa, Solari, Lorenzo, Ciampalini, Andrea, Frodella, William, Steri, Damiano, Allotta, Benedetto, Rindi, Andrea, Marini, Lorenzo, Monni, Niccolò, Galardi, Emanuele, Casagli, Nicola
• Format: Article
• Language: English
• Subjects: InSAR; lava delta; limit equilibrium analysis; Stromboli volcano; submarine landslides; volcano deformation
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2018.01.038

•COSMO-SkyMED and SENTINEL-1 data reveal lava delta instability at Stromboli.•3D Limit Equilibrium Method analysis was based on new bathymetric data.•Higher unstable submarine slope comprises the lava delta and its surrounding areas.•Instability of the submarine slope is increased by lava delta accumulation.•Lava delta deformation reveals submarine landslide instability. The instability of lava deltas is a recurrent phenomenon affecting volcanic islands, which can potentially cause secondary events such as littoral explosions (due to interactions between hot lava and seawater) and tsunamis. It has been shown that Interferometric Synthetic Aperture Radar (InSAR) is a powerful technique to forecast the collapse of newly emplaced lava deltas. This work goes further, demonstrating that the monitoring of lava deltas is a successful strategy by which to observe the long-term deformation of subaerial–submarine landslide systems on unstable volcanic flanks. In this paper, displacement measurements derived from Synthetic Aperture Radar (SAR) imagery were used to detect lava delta instability at Stromboli volcano (Italy). Recent flank eruptions (2002–2003, 2007 and 2014) affected the Sciara del Fuoco (SdF) depression, created a “stacked” lava delta, which overlies a pre-existing scar produced by a submarine–subaerial tsunamigenic landslide that occurred on 30 December 2002. Space-borne X-band COSMO-SkyMED (CSK) and C-band SENTINEL-1A (SNT) SAR data collected between February 2010 and October 2016 were processed using the SqueeSAR algorithm. The obtained ground displacement maps revealed the differential ground motion of the lava delta in both CSK and SNT datasets, identifying a stable area (characterized by less than 2 mm/y in both datasets) within the northern sector of the SdF and an unstable area (characterized by velocity fields on the order of 30 mm/y and 160 mm/y in the CSK and SNT datasets, respectively) in the central sector of the SdF. The slope stability of the offshore part of the SdF, as reconstructed based on a recently performed multibeam bathymetric survey, was evaluated using a 3D Limit Equilibrium Method (LEM). In all the simulations, Factor of Safety (F) values between 0.9 and 1.1 always characterized the submarine slope between the coastline and −250 m a.s.l. The critical surfaces for all the search volumes corresponded to the 30 December 2002 landslide, which involved the lava delta and its surrounding areas. InSAR data provided the post-effusive