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

Abstract

Sotará is a little-known andesitic-dacitic stratovolcano in southwestern Colombia. Although there are no recorded historical eruptions, the volcano shows clear evidence of 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 unrest in this hard-to-reach area. During 2017–2018 and 2019–2020, a subtle yet distinct volcanic deformation was observed by GNSS and InSAR. Initially, about 1.5 cm of uplift was observed prior to any increase in seismic activity. Subsequently, an increase in volcano-tectonic seismicity was followed by additional uplift of around 2.5 cm. Modeling of the observed deformation suggests the injection of small magma batches beneath the volcano: 0.0003─0.0022 km3 at depths of 1.2─3.9 km in 2017–2018, and 0.0003─0.0017 km3 at similar depths in 2019–2020. Neither episode culminated in an eruption, and both seismicity and deformation returned to background levels by February 2020. The observed unrest patterns offer empirical constraints on the behavior of shallow magmatic systems in the Northern Andes, an area that remains less well represented in volcano deformation data sets. The small magma volumes and limited uplift reflect episodic magma replenishment in a long-dormant volcanic system, consistent with models of tectonically modulated magma ascent along the Andean margin. These findings strengthen regional comparisons with better-studied Andean volcanoes (e.g., Sabancaya or Nevado del Ruiz), helping to build a more unified understanding of arc volcanism and magma plumbing systems.