Debris Avalanches and Cryptodomes Offshore Vesuvius (Italy): Consequences on the Natural Environment
by
Alfonsa Milia
IAMC, CNR
Coauthors: A. Raspini, M.M. Torrente

One of the most important natural catastrophic events is the episodical huge sector collapse of volcanoes. Such slope failures produce high velocity debris avalanches that can move for distances exceeding 10 km. Oversteepening of the flank causes by cryptodome intrusion is one of the more common invoked triggering factor for flank collapses. Sometimes, as in 1980 on Mount St. Helens, such flank collapses can trigger the explosive eruption of rising magma column, suddenly depressurized by decapitation of the volcano. Several historic breached crater eruptions have resulted in fatalities, many from tsunamis produced by debris avalanches entering the sea from coastal volcanoes. Vesuvius, located in southern Italy close to the continental shelf of Naples Bay, is an active volcano that grew within the breached crater of Monte Somma. The interpretation of core data and high-resolution seismic profiles offshore of Somma-Vesuvius documents interlayered volcanic and marine units in the Late Quaternary succession. Two thick debris avalanche deposits were identified and mapped on the continental shelf. The identification of cryptodomes and two debris avalanches originating from Somma-Vesuvius are fundamental evidences of two flank collapses in the volcano history. Probably shallow intrusions (cryptodomes) steepened the south side of the Monte Somma causing it to be unstable and catastrophic landslides gave rise to the breached crater of Monte Somma and a chaotic landscape that extended into Naples Bay. In particular, the younger debris avalanche has a volume of approximately 1 km3 and is linked to the 3.5 ka Avellino plinian eruption. The products of the Avellino eruption cover an areas of approximately 2000 km all around the volcano and destroyed the Ancient Bronze Age settlements belonging to the facies of Palma Campania.

Date received: June 13, 2005

Copyright © 2005 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caqy-03.