Tracking secondary lahar flow paths and characterizing pulses and surges using infrasound array networks at Volcán Fuego, Guatemala.

Abstract:

Lahars are one of the most impactful hazards at many volcanoes, including at Volcan Fuego (Guatemala). Due to their sudden onset, variations in initiation mechanisms (rainfall, eruption-induced, or spontaneous), and complex flow behavior, lahars remain a major challenge to those studying them. On 1 December 2018, a storm system at Volcan Fuego produced heavy rainfall and a subsequent lahar. This event was detected by permanent, telemetered seismo-acoustic stations along several of the river channels, particularly two stations located along the Las Lajas channel on the southeast side of the volcano. To establish the timing, duration, and speed of the lahar, cross-correlated lag times were calculated for the infrasound records within both the infrasound arrays and between the two different arrays. Through analysis of records at the two different arrays we determined the average speed of flow between two of the stations, located approximately 7.5km and 12km from the summit, to be 6.9 meters per second. Co-located seismic and acoustic signals are highly correlated and indicate at least 4 or 5 pulses/surges in the lahar with approximately 9-10 minute intervals between pulses. Flow speeds appeared to decrease from ~8.3m/s to ~6.3m/s over the course of the event. Observed pulses are reasonably explained by either variations in rainfall intensity or the erosion mechanism commonly seen in these lahars - both of which can influence sediment load. We argue that varying sediment load is reflected by clear fluctuations in infrasound and seismic power recorded at one of the stations. This particular event studied with infrasound provides insight into how lahars occur around Volcán Fuego. When compared with the seismic records, infrasound signal analysis reinforces the importance and utility of this technology to detect and track rain-triggered lahars, as well as quantify the hydrological and geomorphic parameters that characterize these types of flows. We believe geophysical monitoring is prudent in understanding lahar hazards, risk and impacts on human populations. Future studies of Volcán Fuego will focus on quantifying the occurrence of these events as rapid gravity mass movements.