Ground deformation before the 2015 eruptions of Cotopaxi volcano detected by InSAR

Abstract

Cotopaxi volcano started a period of volcanic unrest in April 2015 that led to a series of eruptions between August and November 2015. We use COSMO‐SkyMed Interferometric Synthetic Aperture Radar supported by continuous GPS observations spanning the period of 2014–2016 to obtain time‐dependent ground deformation data over Cotopaxi volcano related to the period of unrest and onset of eruptions. We find evidence of precursory deformation, with a maximum uplift on the western flank of 3.4 cm from April to August 2015. Deformation is explained by an inclined sheet intrusion located a few km southwest of the summit with an opening volume of 6.8 × 106 m3, extending from a depth of 12.1 km and shallowing to 5.5 km below the summit, that contributed to internal edifice growth. The temporal coincidence of deformation prior to the eruptions potentially suggests that short‐term eruptions at Cotopaxi are partly controlled by episodic edifice growth.

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

“…Pressures below 87 MPa (3.4 km) are able to explain the observed degassing as SO 2 , HCl, and HBr exsolution from magma requires low pressures (Baker & Alletti, ). Morales Rivera et al () proposed a source model based on deformation data that would be located between 5.5 and 12.1 km below the summit. This reservoir is in agreement with the pressures obtained for low‐silica glass.…”

“…This reservoir is in agreement with the pressures obtained for low‐silica glass. Two reservoir zones were imaged, indicating that magma could ascend from a reservoir zone as deep as 12–13 km (Morales Rivera et al, ) toward a shallower area at about 2‐ to 5‐km depth in order to start degassing.…”

“…Morales Rivera et al (2017) proposed that the deformation estimated using COSMO-SkyMed interferometric synthetic aperture radar and continuous GPS prior to the eruption is consistent with an opening volume of 6.8 × 10 6 m 3 . The modeled inclined sheet intrusion is located 7 km SSE of the crater.…”

“…The wide range of signals, with variable and sometimes similar spectral characteristics, makes the identification complex. For this reason, we did not use the preliminary catalog resulting from daily monitoring Morales Rivera et al, 2017;Mothes et al, 2017), which is mostly based on visual identification of waveforms at a single reference station and may unfortunately include significant numbers of misidentifications. Therefore, to identify the different types of events activated prior to and during the eruption, we chose an approach based on the automated with an STA/LTA (short-term amplitude/long-term amplitude) higher than 2.5 (black) and with a peak-to-peak amplitude higher than 1.65 μm/s (red).…”

Periodicity in the BrO/SO<sub>2</sub> molar ratios in the volcanic gas plume of Cotopaxi and its correlation with the Earth tides during the eruption in 2015

“…In this manuscript we retrieve the variation of the BrO/SO 2 20 molar ratios recorded by NOVAC during the 2015 period of unrest at Cotopaxi volcano (e.g. Bernard et al (2016), Gaunt et al (2016), Morales Rivera et al (2017) and examine a correlation between its variation and variations in the meteorological and geological conditions, including the calculated variations of the Earth tide-induced ground surface displacements.…”