Monitoring and forecasting hazards from a slow growing lava dome using aerial imagery, tri-stereo Pleiades-1A/B imagery and PDC numerical simulation

Abstract

In December of 2017, a lava dome emerged at the Nevados de Chillan volcanic complex in the southern Andean volcanic zone, Chile, at the base of a summit crater excavated by explosions during two preceding years of unrest. This posed a number of potential hazards to the surrounding touristic region, so the eruption was carefully monitored. Structure from Motion techniques were used to generate DEMs from satellite and aerial images, from which several useful measurements could be made. Dome growth was characterised at an unprecedented resolution, allowing for the calculation of discharge rates and effusion rates in near real time. A simple model fit to the distance between the dome and crater rim predicted relatively accurately the arrival of the dome toe at the crater rim and the onset of dome collapse outside the crater. Simulations of the path and extent that potential pyroclastic density currents (PDC) generated by dome collapse would follow showed that PDC were not directly threatening populated areas. Over its life cycle as of August 2019, the dome growth was punctuated by frequent explosions, averaging around 30 per day, one of which generated a minor 600 m long PDC on 13 to 15 of July 2018. There appears to be a positive correlation between explosion frequency and lava dome growth rate suggesting that both explosive and effusive processes can coexist, operating at different timescales but responding to the same driving force. A positive correlation is apparent between dome growth rate and seismic activity such as the frequency of tremor and long-period earthquakes suggesting that these might be used as proxies to estimate effusion rate. Initial lava dome effusion rates of 1730 ± 110 m3/day in January 2018 declined to 100 ± 150 m3/day in June 2019. These growth rates are extremely slow when compared to other lava domes, about 300 to 600 times slower than the lava domes at Mt Unzen (1992) and Mt. St. Helens (1980).