Thermal techniques for characterizing magma body geometries

Abstract

The surface heat flux distribution resulting from emplaced magma bodies can be used to help characterize the magma source. Closed-form analytical solutions for the conduction heat transfer from various idealized magma geometries (dikes, sills, and spheres) are obtained using either the Schwarz-Christoffel transformation theorem (dikes and sills) or the ‘method of images’ with superposition (spheres). Comparison of these analytically determined heat flux distributions with field data from active geothermal areas at Yellowstone, Avachinsky volcano, Kilauea Iki, and the Coso geothermal area indicates that these fields may be conduction dominant, at least over certain depths. The comparison for Yellowstone implies that a sharp thermal boundary exists at a depth of approximately 1 km; this supports the suggestion by Morgan et al., (1977) that a strong hydrothermal zone exists at about that depth. The comparison for Avachinsky indicates that a spherical magma chamber exists at approximately 4·8 km depth; this is in close agreement with estimates by Fedotov et al., (1976) for a spherical magma chamber at 5 km depth. The comparison for Kilauea Iki indicates that the edge of the buried molten lava lense was 210 – 216 m from the center of the lake in 1975; this result is in good agreement with several independent geophysical measurements.