Volcanic eruption prediction: Magma chamber physics from gravity and deformation measurements

One of the greatest remaining problems in modern volcanology is the process by which volcanic eruptions are triggered. It is generally accepted that e ruptions are preceded by magma intrusion [Sigurdsson and Sparks, 1978]. The degree of interaction between previously ponded magma in a chamber and new ly intruded magma determines the nature and rate of eruption and also the c hemistry of erupted lavas and shallow dykes. Here, we investigate the physi cs of this interaction. Volcano monitoring at its most effective is a syner gy between basic science and risk assessment, while hazard mitigation depen ds on reliable interpretation of eruption precursors. The simple and much u sed Mogi model relates ground deformation (Delta h) to changes in magma cha mber volume. Gravity changes (Delta g) combined with ground deformation Pro vide information on magma chamber mass changes. Our new models predict how the Delta g/Delta h gradient will evolve as a volcano develops from a state of dormancy through unrest into a state of explosive activity. Thus by sim ultaneous measurement of deformation and gravity at a few key stations, mag ma chamber processes can be identified prior to the onset of conventional e ruption precursors.