Magmatic Pathways and Structures

A problem in studies of magmatic degassing is that physicochemical changes occurring in the edifice of active volcanoes (e.g., gas scrubbing by shallow hydrothermal systems) can "mask" changes occurring at depth. Preliminary multi-parameter studies on the influence of well developed hydrothermal systems on geophysical measurements have raised important questions that we are continuing to investigate. Most important among these is whether we can separate the effect on the observed geophysical signals of variations in the hydrothermal system from that of new intruding magma. We are expanding upon this work with static (Bouguer gravity surveys) and comparative dynamic (repeated gravity/deformation) studies at Poás and Kawah Ijen volcanoes, which are notable for their extremely well developed hydrothermal systems and very large hyperacid crater lakes. In order to better characterise the distribution and depth of hydrothermal systems on active volcanoes (where well data is normally not available), we are integrating CO₂ soil gas concentrations, self-potential and resistivity geoelectrical data with signal analysis algorithms. I plan to initiate similar investigations at other crater lake volcanoes such as Copahue (Argentina), El Chichon (Mexico) and Kelud (Indonesia).

Studies of this type (e.g., Masaya, Kilauea) are also allowing us to map shallow substructures (e.g., buried faults and fractures) as well as locate shallow hydrothermal systems that show no visible surface expression. Future work at Masaya will expand upon this with precise delineation of a large ring fault structure within the caldera. However, as all potential field (gravity, magnetism, electrical) solutions are inherently non-unique, it is only by incorporating a wide variety of independent data sets (e.g., petrological and direct measurements of volatile contents, GPS and satellite radar interferometry), that we may hope to better constrain 3D models of the magma systems and thus identify the trigger mechanisms of volcanic eruptions (e.g., Sierra Negra volcano, Galapagos).