Thermal, seismic and infrasound observations of persistent explosive activity and conduit dynamics at Santiaguito lava dome, Guatemala

In January 2003 we deployed a seismo-acoustic array along with thermal sensors to define the dynamics and source characteristics of persistent, intermittent explosive activity at the Santiaguito lava dome, Guatemala. Seismic and acoustic waveforms accompanying thermal transients (i.e. the thermal signature produced by the vertical ash plumes) allowed discrimination of 35 explosions from minor degassing events during the 15.5 h observation period. Characteristics of thermal transients along with elastic and thermal energy flux from the explosive ash emissions allowed for a standardized measurement of eruption intensity, duration, frequency and repose interval. Using the thermal data we calculated a range of minimum exit velocities of 16-76 m/s and convective rise rates of 9-26 m/s to heights of 100 and 600 m above the vent. Source depths for the explosions were calculated using the thermo-acoustic delay, indicating a source 100-620 m below the vent. The intensity of the explosions, based on thermal amplitude and proxies for elastic energy released is not dependent on repose interval or depth. The data support the notion for shear-induced fragmentation at the conduit walls due to stick-slip movement of the upper, degassed, part of the magma column as a source mechanism. Loci of explosion depths suggest that this operates within a 500 m thick dacite plug in the uppermost portion of the conduit.