Volcanic plumbing systems

Abstract

Report of a meeting held by the Volcanic Studies Group at the Open University on 7 December 1991. This research seminar, targeted principally at postgraduates and senior undergraduates, was convened with the object of reviewing current ideas on the functioning and form of volcanic and sub-volcanic plumbing systems. The seminar was topical, with the recent activity at Mount Pinatubo not only serving to keep volcanoes and volcanology in the public eye, but also providing a timely reminder, in human terms, of the importance of understanding the mechanisms which operate within and beneath volcanoes. Increased knowledge in this area can lead only to the more accurate prediction of volcanic events, and consequently to the more effective execution of mitigation policies and reduced risk at the world’s 700 or so currently active volcanoes. The first two speakers concerned themselves primarily with the application of physical parameters measured at the surface. R. S. J. Sparks (University of Bristol) presented a simple physical model designed to interpret observations of lava eruptions in terms of changing eruption conditions. The model assumes that magma overpressure is proportional to erupted volume which is in turn directly related to the effusion rate. These relationships were used, together with field observations, to monitor factors controlling variations in lava effusion rate. Application of the model to three well documented eruptions demonstrated that variations in magma flow rate during the course of an eruption may be explained by changes in magma overpressure, modified at times by additional factors including magma solidification