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Rapid, multichannel monitoring of fumaroles on Volcán Colima, Mexico, provides new insight into the time‐scales and magnitudes of fumarole temperature variation. Temperatures in five fumaroles, all located along a single fracture cutting the summit lava dome of the volcano, were monitored at 20‐min intervals between May 1991 and May 1992. Measurements were made using a programmable data logger deployed near the fumarole field, and data were radiotelemetered to a nearby volcano observatory at regular intervals. Mean fumarole temperatures varied between 350°C and 550°C. Statistical analysis of these time series shows that significant diurnal variation occurs in each fumarole. Magnitudes of these daily fluctuations are generally between 25°C and 50°C, although larger‐amplitude variations occur, especially in cooler fumaroles. Simultaneous monitoring of atmospheric pressure at the fumaroles indicates that these variations in temperature are inversely correlated with barometric pressure. These observations indicate that fumarole temperatures respond to atmospheric forcing. A numerical model developed to explore the dependence of fumarole temperature on mass flow demonstrates that many aspects of observed temperature variation are accounted for by mass flow variation, resulting from small changes in barometric pressure. The relationship between mass flow and fumarole temperature is nonlinear: the response of fumarole temperatures to a given change in mass flow is greatest in fumaroles with low mass flow (and cool temperatures). The nature of this dependence is little affected by fumarole geometry for the cases considered. Continuous measurement of fumarole temperatures may be an effective means of monitoring local mass flow on volcanoes. At Volcán Colima, average temperatures changed by less than 100°C during the 1‐year sampling period. During and immediately following effusive activity, changes in degassing were abrupt and inconsistent along the length of the fracture. Following this period, temperatures decreased gradually, and there was a higher degree of correlation between fumaroles. The method described here represents a substantial improvement over traditional fumarole‐monitoring techniques because subtle variation can be quickly identified using standard statistical techniques, and the method provides regular information about thermal activity on a volcano, minimizing the hazards normally associated with the collection of these data on a regular basis.

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Journal of Geophysical Research: Solid Earth, v. 98, issue B11, p. 19713-19722

Copyright 1993 by the American Geophysical Union.