Long, episodic awakening of volcanoes: The case of Chiles-Potrerillos, Ecuador

Volcanoes that have been dormant for tens of thousands of years often have a long warm-up time before eruption onset.   Magma and fluid migration are obstructed by closed fractures at depth, a sealed hydrothermal lens, and conduit blockage, all of which work against magma emplacement.  Our first significant activity at Chiles-Potrerillos was a Mw 5.5 earthquake, followed by an intense seismic swarm in October 2014.   Uplift occurred, perhaps in concert with movement on local faults.  Subsequently, lulls in activity and little deformation or changes in the hydrothermal springs assuaged our concerns.  Then, more seismic swarms registered in 2018-19, 2022-24, and in late 2025.  Commonly, 2000-4000 VT events are registered each day.  Overall seismic production is ~1.5 million events.    While most events are VTs and are less than Mw= 1, numerous events fall into the 3-4 Mw category and are felt.  Deformation detected by GPS and InSAR (Sentinel-1 and TerraSAR-X) exceeds 40 mm/yr and now involves the southern flank of Chiles volcano, as well as a rectangular zone 20 km to the SE, called Potrerillos, where several domes are located.  Overall, and significantly, the deformation has presented strong, then lower rates of uplift, but values are rarely negative.  Surface manifestations at hot springs have remained unchanged over the past 12 years.  While we believe that magma is probably stressing the system, the seals of the hydrothermal system remain intact, which impedes the onset of explosions, strong exsolution of magmatic gases, and overall increased heat flow.  We anticipate that before an eruption onset, deformation will become more abrupt and concentrated, with or without increased seismicity, since much of the country rock is already fractured.