Evolution of Cotopaxi 2015 Eruption Revealed by Combined Geochemical and Seismic Observations

Authors: Silvana Hidalgo (presenter), Daniel Sierra, Benjamin Bernard, Escuela Politécnica Nacional; Jean Battaglia, Pablo Samaniego, Université Clermont Auvergne; Santiago Arellano, Chalmers University of TechnologyRené Parra, Universidad San Francisco de Quito; Peter Kelly, U.S. Geological Survey; Florian Dinger, Max-Planck Institut for Chemistry, University of Heidelberg; Charlotte Barrington, Nanyang Technological University

Characterization of volcanic unrests and eruptions through continuous geophysical and geochemical monitoring is critical in order to have a better understanding of sub-volcanic systems and to allow accurate threat assessment. We analyzed the seismic signals and SO2 emissions of Cotopaxi volcano between April and November 2015 to better understand the link between seismicity and outgassing. Transient events detected include Volcano-Tectonic (VT), Long-Period (LP) events and Explosion Quakes, but also Ice Quakes (IQ) with various spectral signatures related to the glacier covering the volcano summit. To identify the different types of recorded events, we looked for families of repeating events. We found 4 characteristic types of temporal evolutions during the unrest and eruptive activity. An increase in SO2 emissions was detected by scanning DOAS few weeks after the onset of seismic unrest. SO2 emissions, up to 5000 t/d, and seismic tremor were observed until August 13 when a swarm of volcano-tectonic earthquakes preceded the first hydromagmatic explosions, on August 14. BrO was also detected in the plume during the unrest but exhibited a significant increase since the onset of ash emissions. Airborne in-situ Multi-GAS measurements of CO2, SO2, and H2S revealed that the plume had a low CO2/SO2 molar ratio around 2.5 and that SO2 was the most abundant S-containing gas. Solar-FTIR measurements of the plume detected a SO2/HCl molar ratio of 5.8 ± 4.8 and 6.6 ± 3.0, before and after the explosions, respectively. All these geochemical signals suggest a shallow magmatic source of the emitted gases. Glass chemistry of the emitted ashes indicates a homogenous juvenile magma having suffered an intense S-exsolution and degassing. Since November 2015 all monitored parameters have shown a significant decrease. During Cotopaxi’s unrest and eruption, multi-parameter monitoring has proved to nicely track the sub-surface processes and helped the choice of eruption scenario.

Bio:

Silvana Hidalgo, Instituto Geofísico, Escuela Politécnica Nacional (Ecuador)

Silvana is a Doctor with 20 years of experience. She currently is Director of the Instituto Geofísico, Escuela Politécnica Nacional at Pichincha, Ecuador, where she is responsible of monitoring volcanic fluids.

Silvana is a member of IAVCEI and AGU.