Hydrothermal Eruptions: Mechanisms and Implications for Prediction

Abstract

Hydrothermal eruptions are common in both exploited and unexploited geothermal systems. They vary in scale and frequency over several orders of magnitude. Not all hydrothermal eruptions are the same - at least 5 different mechanisms can be postulated, covering a wide range of preeruption physical conditions. At one extreme hydrothermal eruptions might require super-lithostatic fluid pressures to initiate. These would be reasonably easy to detect, and therefore predict given a sufficient number of monitor drillholes. At the other extreme, hydrothermal eruptions can start from a fiee water surface with no excess confining pressures. The occurrence of that type of eruption is more difficult to monitor for and predict. Potentially any hydrothermal system with boiling springs could generate a hydrothermal eruption. However, very large eruptions probably require some special geological event and so are rare.