Classifying the Infrasonic Fingerprints of a Dynamic Volcanic System: A Quantitative Comparison of Optical and Infrasound Records at Villarrica Volcano, Chile.

Abstract:

On March 3, 2015 Villarrica Volcano underwent an abrupt change in volcanic behavior that culminated in a large fire fountaining event lasting 30 minutes that prompted the evacuation of residents within 9 km from the vent. This paroxysm was the first in 30 years and changed summit morphology by temporarily capping the previously stable lava lake with volcanic material. After March 3, Villarrica exhibited a period of quiescence before reactivating with various levels of ash venting associated with strombolian style activity. Ten infrasound arrays, each comprising three pressure transducers, were deployed in January and February that recorded until mid June and serendipitously chronicled the awakening, paroxysm, and recovery to a more open vent system typical to Villarrica. Coincidentally, several optical datasets were gathered. Time lapse photography, provided by Proyecto Observacion Villarrica Internet (POVI), recorded vent activity at an interval of ~15 seconds with a 240 mm zoom lens at 16 km from the vent, starting December 2014 until March 12, 2015. Additionally, video footage of the vent was recorded at 30 frames per second (fps) with a 50 mm lensed surveillance camera between March 4 and June of 2015 at a distance of 16 km from the vent. The combined infrasound and image processing approach offers novel insight into the various acoustic signatures of a dynamic and violent volcanic system. Video parameters, including plume color, ascent rate, and duration of venting are synthesized as time series. These video metrics of vent activity are then quantitatively compared to the corresponding infrasound waveform. The result is the classification of several different infrasound modes of activity during the diverse eruptive sequence of Villarrica between January and June of 2015.