The ongoing activity of Mount St. Helens provides an opportunity to study the infrasonic wavefield produced by an active, silica-rich volcano. In late October 2004, as a pilot experiment for the Acoustic Surveillance for Hazardous Eruptions (ASHE) project, we deployed two infrasound arrays, each co-located with a broadband seismometer and weather station, to continuously record seismo-acoustic signals from Mount St. Helens. The nearest array, Coldwater, was deployed on the northern flank of the volcano, ∼13 km from the summit. The second array, Sacajawea, was deployed ∼250 km east of the volcano, at a distance where stratospherically ducted acoustic waves may be expected during the winter. This paper presents an overview of the experimental setup, and preliminary results from this unique data set. Eruptions on January 16th 2005 and March 9th 2005 produced strong infrasonic signals. The aseismic January 16th eruption signal lasted ∼9.4 min beginning at ∼11:20:44 01/16/05 UTC, while the March 9th eruption signal lasted ∼52.8 min beginning at ∼01:26:17 03/09/05 UTC, with the main steam and ash venting stage probably lasting ∼7.2 min. The March 9th signal was an order of magnitude larger than the January 16th signal, and was clearly recorded 250 km east at the Sacajawea array. Infrasonic expressions of long period (LP) seismic events (‘drumbeats’) have also been intermittently observed, and are recorded as acoustic waves mimicking the waveform and temporal sequence of their seismic counterparts. These acoustic observations provide important constraints for source models of long period events and eruptions.

Data are from the 4-element Coldwater array (CDWR, MSH2*) at Mount St Helens from November 1-16, 2004 and March 9, 2005 from 1 - 2:30 UTC.

The Coldwater (CDWR) array was located 13 km from the summit of Mount St Helens (backazimuth of 153 degrees) and consisted of four MB2000 (DASE/Tekelec) broadband aneroid microbarometers arranged in a centered triangle with an aperture of ~100 m  and porous hose wind noise suppression. The data were sampled at 40 Hz and have a flat response from 0.01 to 17 Hz. We refer the reader to Matoza et al (2007) for details on the array setup, eruption, and infrasound data analysis. 

Matoza, R. S., Hedlin, M. A., & Garcés, M. A. (2007). An infrasound array study of Mount St. Helens. Journal of Volcanology and Geothermal Research, 160(3-4), 249-262.

Data were uploaded to Dryad by Robin S. Matoza and Alexandra M. Iezzi, University of California Santa Barbara. 

Response has been removed from the SAC files and the waveforms are in Pascals [Pa]. 

X, Y pairs with array geometry relative to bay centre in km:
MSH21: [-0.0082572, 0.00016988]
MSH22: [0.042908, 0.014625]
MSH23: [0.015917, -0.050269]
MSH24: [-0.050568, 0.035474]