Paroxysmal Events at Volcán de Fuego: Understanding the Signals

Abstract:

Volcán de Fuego, Guatemala, has been in an open vent state since 1999. Background activity is characterised by: 1) frequent strombolian explosions, both ash-poor and ash-rich, producing plumes reaching heights of ~1km with ejection of incandescent material to about 300 m; 2) low levels of acoustic and seismic tremor, which is often the result of prolonged degassing episodes or chugging (i.e. highly frequent and regular small explosions which occur one after another with little-to-no repose interval); 3) the intermittent generation of lava flows in the drainage channels to the west, south and east faces. In 2015, eruption intensified, as phases of low (background) levels of activity were increasingly interspersed with large paroxysmal eruptions. Since 1524, over 50 paroxysms at Fuego have reached VEI ≥ 2, with the largest eruptions VEI 4, which produced plumes up to 25km above sea level, pyroclastic flows capable of travelling over 11km, and large lava flows in the drainage channels.

Here, we analyse seismic and acoustic data to characterise and separate signals associated with background activity and paroxysms. We focus on paroxysmal activity during June and November 2018. Our analysis further combine remote sensing data (MODIS, SWIR and optical images) and ground-based visual observations to build up a holistic picture of the state of the volcano in the days and weeks preceding the paroxysms to diagnose the processes that led to the heightened activity, and understand the interplay between these signals. We investigate how these observations fit with models proposed for the triggering mechanism of paroxysms and compare these with past events at Fuego to show how the system has evolved. From these comparisons, we outline key observations which precede and thus indicate potential impending transition to paroxysmal activity.