Catastrophic Volcanic Eruptions: Causes and Mechanisms

One of the main natural disasters is explosive volcanic eruptions, often lasting 2–4 months. It is obvious that such eruptions of volcanoes cause simultaneous mass release of gas bubbles from the melts of their shallow peripheral chambers, which must lead to a sharp increase in the volume of material contained in them, i.e., to explosions. It is shown that the main prerequisite for an explosive eruption is a sharp decrease in the solubility of water in melts known from experimental data at pressures less than 1 kbar corresponding to a depth of 3.5 km (Shilobreeva et al., 1991). Therefore, rising water-saturated melts characteristic of suprasubduction (convergent) settings, automatically become supersaturated with water when they reach depths of 3–4 km, and are thus an explosive mixture that is ready to blow up at any moment. However, the release of gas bubble nuclei is a very energy-consuming process, and will not begin by itself. We believe that the trigger for a catastrophic explosion can be one of the earthquakes preceding the eruption, which resonates with self-oscillations in the peripheral chamber beneath the volcano. This greatly increases the power of the impulse and helps to overcome the energy barrier. It is shown that the necessary and sufficient conditions for the occurrence of a catastrophic eruption are: 1) the existence of a shallow chamber with a water-supersaturated magma melt; the presence of other volatiles (CO 2 , SO 3 etc.) does not play a significant role here; 2) the occurrence of a triggering earthquake that is in resonance with self-oscillations in this chamber; and 3) the presence of a continuous supply of the peripheral chamber beneath the active volcano with new melt portions, thus prolonging the eruption.