Long-Term Analysis of Infrasound at Villarrica Volcano and the Eruption of March 3, 2015

Abstract:

For the last 30 years Villarrica volcano has shown persistent degassing and mild strombolian activity taking place at the lava lake located inside its crater. This activity exhibited changes in the magnitud of the strombolian explosions, levels of the lava lake, and gas emission rates. In February 2014, a six-component infrasound array was installed 8 km to the NW of the summit in order to acquire a long-term record of the acoustics associated with the explosive activity originated at Villarrica’s crater. Visual observations from the crater rim and acoustic data show that in 2014 the activity at Villarrica was relatively low and began to increase at the beginning of February 2015. Between January and early March of 2015 four complementary three-component infrasound arrays were deployed between 4 and 9 km from the crater. Villarrica volcano erupted on March 3rd, 2015, exhibiting a >1000 m high lava fountain, scoria flows, snow-ice avalanches and lahars, among other phenomena. The eruption was preceded by 25 minutes of strombolian explosions that gradually increased in magnitud and frequency until they turned into the lava fountain. The data collected with the infrasound arrays are used to identify changes in explosive activity as well as the flow of at least three lahars. Analysis of the amplitude, number of events, waveform and frequency content of the acoustic signal show small and/or short (hours to days) variations in the persistent explosive activity of Villarrica’s lava lake during 2014. The short (~27 days) increased level of activity and subsequent eruption may be interpreted as the result of a relatively gas-rich magma intruding into the upper plumbing system.