Deep-sea deposits of the Stromboli 30 December 2002 landslide.

Stromboli is a 3000-m-high island-arc volcano rising to 900 m above sea level. It is the most active volcano of the Aeolian archipelago in the Tyrrhenian Sea (Italy). In the last 13 ka, four large-volume (1-km3) flank collapses have shaped the northwestern flank [Sciara del Fuoco (SdF)] of the volcano with the potential to cause hazardous tsunamis. In addition, smaller volume, more frequent partial collapses of the SdF have been shown to be tsunami-generating events. One such partial collapse occurred on 30 December 2002. The resulting landslide generated a 10-m-high tsunami that impacted the island. Multibeam bathymetry, side-scan sonar, and seabed visual observations reveal that 25-30 × 106 m3 of sediments were deposited on the offshore from the SdF landslide. Samples have led to the recognition of a proximal coarse-grained landslide deposit on the volcano slope and a distal, cogenetic, sandy turbidite 24 km from the Stromboli shoreline. The proximal landslide deposit consists of two contiguous facies: (1) a chaotic, coarse-grained deposit and (2) a sand facies that develops laterally with and over the coarse-grained deposits. Distally, a capping 2- to 3-cm-thick sand layer, not present in a prelandslide September 2002 core, represents the finer-grained turbidite equivalent to the proximal deposits. Characteristics of the SdF landslide deposits suggest that they derive from cohesionless, sandy matrix density flows. A range of density flow transitions, based principally on particle concentration and grain-size partitioning of cohesionless parent flows, can be identified in the proximal and distal deposits of this relatively small-scale landslide event on Stromboli.