Abstract
Viscous magma flow in a fissure capable of changing its width is analyzed to understand magma transport in various tectonic conditions. The analysis predicts that the fissure widens only when the magma pressure of the chamber plus twice the tensile stress component normal to the fissure is positive. The effect of the tectonic stress is simulated by use of a simple model of magma plumbing system. For a moderate stress range, magma that has accumulated in the chamber first fills space in a widening fissure and then extrudes out of the surface. When the stress is compressional and strong enough to suppress the effect of accumulation, the fissure cannot open. When the stress is extensional and exceeds a critical value, the fissure widens up to an ultimate finite width with magma kept in it. Recent eruptions in eastern Izu peninsula and Izu-Oshima volcano are interpreted in relation to the difference of the local stress condition.
