VOLCANO-HYDROLOGIC INTERACTION AT MASAYA VOLCANO, NICARAGUA

Volcanic eruptions can be caused by movement of magma, by interaction of magma with groundwater, or by a combination of the two. Fumarolic gases are a surface manifestation of the magma-groundwater interaction and can be used to study variations in both the magmatic and hydrologic systems. Continuous monitoring of fumarolic gas temperature at Masaya, Telica and Cerro Negro volcanoes in Nicaragua, and at Cotopaxi volcano in Ecuador, reveal that at background state these temperatures are a reflection of atmospheric and hydrological variations, but during volcanic activity the characteristic signal changes.

We have recorded fumarole temperature, rainfall, self-potential, seismicity, atmospheric temperature and atmospheric pressure every five minutes since May 2006. We found that fumarole temperatures 3.5km from the active vent at Masaya volcano increased rapidly and cyclically by up to 5°C during volcanic activity. These variations show a clear relationship with volcanism, but rainfall also has a noticeable effect. Current models do not address this level of detail, or emphasize the effect of the local groundwater system. Using the TOUGH2 modeling code I have begun to recreate the system at Masaya and have found that permeability, pore pressure and fumarolic gas interaction with groundwater can have a strong effect on fumarolic temperatures. Continued collection and analysis of temperature measurements therefore helps to improve understanding of volcanic systems and their interaction with hydrologic systems, potentially aiding in forecasting eruptive activity.