Problems and progress in volcanology

Abstract

Summary Volcanoes are, and always have been, concentrated chiefly along continental edges and within ocean basins. Volcanism is most nearly continuous in orogenic belts, other than those of Alpine-Himalayan type, and in the oceans; it is intermittent and short-lived adjoining orogenic belts and ceases for vey long periods only in continetal nuclei. More information is needed concerning the shapes and depths of volcanic reservoirs. Wedging, stoping and fluxing rather than explosive churning are the chief means by which vents are opened. The source and maintenance of heat are largely unsolved problems, but much of the requisite thermal energy probably comes from ascending juvenile gases. Among the factors that control volcanic behaviour one of the chief is the rate of vesiculation; magma composition, degree of crystallization, retrograde boiling and depth of magma chambers appear to be relatively unimportant. The origin of the water vapour given off by volcanoes remains in dispute, but in certain kinds of eruptions groundwater plays an important part. Many calderas and volcano-tectonic depressions owe their formation chiefly to large-scale subterranean migration of magma. methods of prediction are being improved; seismic and tilt measurements now offer the most reliable information, but magnetic and electric methods merit further trial.