RECENT DYKE-INDUCED LARGE-SCALE BLOCK MOVEMENT AT MOUNT-ETNA AND POTENTIAL SLOPE FAILURE

HERE we report the results of a geodetic survey undertaken on Mount Etna between 1981 and 1988. Observed horizontal ground movements in the vicinity of the Valle del Bove caldera, demonstrate that dyke emplacement during 1983 and 1985 resulted in the 2.8-m eastward displacement of a block of western caldera rim. A history of past instability and collapse along the rim is indicated by the presence of large back-rotated blocks of prehistoric volcanics1. Furthermore, the unusually linear form of the present western rim indicates past slope failure along north-south aligned surfaces, and therefore that dyke-induced collapse may have been an important agent in caldera enlargement. We suggest a self-sustaining mechanism, whereby the stress regime generated as a consequence of the caldera's existence, results in the repeated injection of north-south orientated dykes adjacent to the western rim2,3. Dilation associated with magma intrusion leads in turn to periodic phases of slope instability and failure of the cliff wall, causing a progressive westward migration of the western rim. © 1990 Nature Publishing Group.