Abstract
We present a benchmark study aimed at identifying the most effective modeling approach for tsunami generation, propagation, and hazard in an active volcanic context, such as the island of Stromboli (Italy). We take as a reference scenario the 2002 landslide-generated tsunami event at Stromboli simulated to assess the relative sensitivity of numerical predictions to the landslide and the wave models, with our analysis limited to the submarine landslide case. Two numerical codes, at different levels of approximation, have been compared in this study: the NHWAVE three-dimensional non-hydrostatic model in sigma-coordinates and the Multilayer-HySEA model. In particular, different instances of Multilayer-HySEA with one or more vertical discretization layers, in hydrostatic and non-hydrostatic formulation and with different landslide models have been tested. Model results have been compared for the maximum runup along the shores of Stromboli village, and the waveform sampled at four proximal sites (two of them corresponding to the locations of the monitoring gauges, offshore the Sciara del Fuoco). Both rigid and deformable (granular) submarine landslide models, with volumes ranging from 7 to 25 million of cubic meters, have been used to trigger the water waves, with different physical descriptions of the mass movement. Close to the source, the maximum surface elevation and the resulting runup at the Stromboli village shores obtained with hydrostatic and non-hydrostatic models are similar. However, hydrostatic models overestimate (with respect to non-hydrostatic ones) the amplitude of the initial positive wave crest, whose height increases with the distance. Moreover, as expected, results indicate significant differences between the waveforms produced by the different models at proximal locations. The accurate modeling of near-field waveforms is particularly critical at Stromboli in the perspective of using the installed proximal sea-level gauges, together with numerical simulations, to characterize tsunami source in an early-warning system. We show that the use of non-hydrostatic models, coupled with a multilayer approach, allows a better description of the waveforms. However, the source description remains the most sensitive (and uncertain) aspect of the modeling. We finally show that non-hydrostatic models, such as Multilayer-HySEA, solved on accelerated GPU architectures, exhibit the optimal trade-off between accuracy and computational requirements, at least for the envisaged problem size and for what concerns the proximal wave field of tsunamis generated by volcano landslides. Their application and future developments are opening new avenues to tsunami early warning at Stromboli.
Highlights
The generation of large tsunamis is a relatively rare phenomenon at volcanic islands on a decadal scale (Latter, 1981; Béget, 2000; Tinti et al, 2003a), but it represents a remarkable risk, in reason of the catastrophic impact it may have along the nearby coasts (Auker et al, 2013; Paris et al, 2013; Paris, 2015)
We present a synthetic benchmark study aimed at quantifying the impact of different physical and numerical approximations on the resulting waveforms and tsunami inundation patterns at Stromboli, and identifying the most effective trade-off between computational cost and model accuracy
We have presented a synthetic benchmark study aimed at quantifying the impact of different physical and numerical approximations on the resulting waveforms and tsunami inundation patterns at Stromboli, and identifying the most effective trade-off between computational cost and model accuracy
Summary
The generation of large tsunamis is a relatively rare phenomenon at volcanic islands on a decadal scale (Latter, 1981; Béget, 2000; Tinti et al, 2003a), but it represents a remarkable risk, in reason of the catastrophic impact it may have along the nearby coasts (Auker et al, 2013; Paris et al, 2013; Paris, 2015). Rapid pyroclastic avalanches are a special type of subaerial mass flow composed of air and hot pyroclastic particles (ash, lapilli, and blocks produced during explosive eruptions) They are peculiar of volcanic settings and differ from other subaerial landslide by their generation mechanism, which can be associated with the collapse of eruptive jets and/or lava domes, or by the impulsive directional ejection of pyroclasts (Branney and Kokelaar, 2002). They are characterized by an initially higher momentum, finer granulometry, and higher temperature, facilitating the built-up of pore pressure (Roche et al, 2011; Lube et al, 2020). The tsunamigenic capacity of pyroclastic avalanches is still only partially understood (De Lange et al, 2001; Freundt, 2003; Walder, 2003; Watts and Waythomas, 2003; Bougouin et al, 2020)
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