|Villarica eruption March 3, 2015.|
AP Photo/Aton Chile
Villarrica has a persistent lava lake in the bottom of a summit crater. It is ~40 m diameter, and in the early 2000's, it ranged from about 20-100 m below the summit crater rim. In 2004, abundances of gases were measured by Shinohara and Witter, and found to consist of H2O, CO2 and SO2. The gas emissions were the same in the continuous emissions as in lava spattering events, suggesting that the degassing occurs at very shallow levels and that the lava spattering is caused by the bursting of bubbles formed under equilibrium conditions in the magma.
In 2000, in response to a regional seismic event, the eruption of a small volume of lava apparently plugged the conduit (Ortiz et al., 2003) on September 22. On October 5 and 8, a series of explosions reopened the conduit. Ortiz et al. found that the frequency of the harmonic tremor caused a shift in the peak frequency of the tremor from 1 Hz (open conduit) to 2 Hz (closed conduit). (Aside: This is interesting because it is the opposite of normal pipe behavior for which open pipe frequencies are twice the closed pipe frequencies.)
In a textural and geophysical study conducted over a 10-day period in 2004, Gurioli et al (2008) found two types of pyroclasts: scoria and "golden pumice." They have identical glass compositions, but different textures, and the authors concluded that they underwent different histories in the conduit. They interpreted the golden pumice as rising in the expanding inner part of the eruptive jet, and the scoria as forming the outer portion of the jet. The scoria was entrained during passage of fresh material (that became the golden pumice) through older material in the upper portion of the conduit.
Shinohara and Witter, Geophysical Research Letters, 32(20), L20308, 5 pages, 2005
Ortiz, et al., Journal of Volcanology and Geothermal Research, 128 (1-3), pp. 247-259, 2003.
Gurioli, et al., Journal of Geophysical Research: Solid Earth, 113(B8), B08206, 2008.