Time-lapse gravity monitoring at Cotopaxi volcano, Ecuador: A glimpse inside a restless colossus

Cotopaxi, a glacier-clad stratovolcano located in Ecuador, showed signs of unrest in April 2015, which ramped up until August 14, 2015, with the advent of phreatomagmatic explosions. Time-lapse gravity measurements started at Cotopaxi volcano in June 2015. Minor gravity changes were detected prior to eruptive activity, however, the largest gravity variations at Cotopaxi were measured between October 2015 and March 2016, as other geophysical parameters reached background levels. Inverse modelling using GPS data pointed towards a deep intrusion prior to eruptive activity, while inverse modelling of post-eruptive gravity data fit with changes in the hydrothermal system. A deep magmatic source intruded between April and August 2015, leading to measured deformation and seismicity, while an inferred shallow source rose from depth and interacted with the hydrothermal system, causing the phreatomagmatic activity. Hydrothermal fluids were pushed from a deep aquifer into a shallow perched aquifer, and caused time-lapse gravity variations.