DEPOSITS OF THE ~5000 Y B.P. SCIARA DEL FUOCO TSUNAMI, STROMBOLI VOLCANO, ITALY

Recently, the role of sector collapse in the generation of catastrophic volcanigenic tsunami has become well understood. The ~5000 y b.p. tsunami generated by the sector collapse that formed the modern Sciara del Fuoco on the island volcano Stromboli (Aeolian Islands, Italy) likely affected the entire perimeter of the coastline, but the deposits of this event are mostly buried by more recent volcanic products or have been eroded. A breccia comprising subrounded to rounded lava clasts that crops out at 15 m a.s.l. near Malpassedu is interpreted as beach material that was redeposited by the advancing wave during run-up. Disorganized, nongraded, nonbedded, clast-supported breccias of subangular to angular lava blocks cropping out above 100 m a.s.l. at the same location are interpreted as a debris flow deposit generated when intense return flow of the tsunami wave remobilized colluvial material covering the steep slopes.

The location of these deposits matches the model calculation for maximum wave amplitude by Tinti et al. (2000). Convergence of the wave fronts refracted around the island in both directions produced a wave with an amplitude of at least 50 m, based on a conservative estimate of the volume of the triggering landslide. Whereas the identification and modeling of paleotsunami events is typically based on the observation of the sedimentary deposits of the tsunami run up, return flow may be equally or more important in controlling patterns of sedimentation. This work demonstrates the value of theoretical modeling of catastrophic events. Identification of the landslide potential of island and coastal volcanoes can lead to the calculation of the associated tsunami risk and therefore should become a priority of the scientific community and civil agencies.

Tinti, S., Bortolucci, E. & Romagnoli, C., 2000. Jour. Volc. Geotherm. Res. 96: 103-128.