TRIGGERING OF VOLCANIC-ERUPTIONS

Although earthquakes and volcanic eruptions are each manifestations of large-scale tectonic plate and mantle motions, it is usually thought that the occurrences of these events are not directly related. There h ave been some studies, however, in which triggering of volcanic erupti ons by earthquakes (remote from the volcano) has been proposed(1,2), T he 1992 Landers (southern California) earthquake caused triggered seis micity at very large distances(3), including the magmatically active(4 ) Long Valley caldera region which also experienced a significant coin cident deformation transient(5), Motivated by this demonstration of th e ability of a distant earthquake to disturb a volcanic system, and th e earlier studies of specific cases of eruption triggering, we examine here the historical record of eruptions and earthquakes to see if the re are indeed significantly more eruptions immediately following large earthquakes. We find that within a day or two of large earthquakes th ere are many more eruptions within a range of 750 km than would otherw ise be expected. Additionally, it is well known(6) that volcanoes sepa rated by hundreds of kilometres frequently erupt in unison; the charac teristics of such eruption pairs are also consistent with the hypothes is that the second eruption is triggered by earthquakes associated wit h the first.