Satellite Geodesy Reveals Shallow, Transient Magma Intrusions at Sotará Volcano, Colombia

Sotará, a little known andesitic-dacitic stratovolcano in southwestern Colombia, is an important site for investigating volcanism in the Andes because of its geological and tectonic settings. Although there are no recorded historical eruptions, the volcano exhibits geothermal activity, deformation, and volcano-tectonic seismicity. Its remote location and rugged terrain pose challenges for access and routine monitoring. The application of satellite geodesy, specifically continuous GNSS and DInSAR, has enabled effective monitoring of recent unrest episodes from 2013 to 2020. During these episodes, in 2017-18 and 2019-20, a subtle yet distinct volcanic deformation was observed. Initially, GNSS and DInSAR recorded about 1.5 cm of uplift prior to any increase in seismic activity. Subsequently, an increase in volcano-tectonic seismicity was followed by inflation detected by both GNSS and DInSAR, indicating an uplift around 2.5 cm. Modeling of observed deformation suggests the injection of small magma batches beneath the volcano. During the first episode, magma volumes ranged from 0.0003 to 0.0022 km3 at depths between 1.2 km and 3.9 km. In the second episode, volumes ranged between 0.0003 to 0.0017 km3 at similar depths. Despite this activity, neither episode culminated in an eruption, and both seismicity and deformation returned to background levels by February 2020.