https://doi.org/10.5194/nhess-2019-189 Preprint. Discussion started: 25 June 2019 c Author(s) 2019. CC BY 4.0 License. Processes culminating in the 2015 phreatic explosion at Lascar volcano, Chile, monitored by multiparametric data Ayleen Gaete1, Thomas R. Walter1, Stefan Bredemeyer1,2, Martin Zimmer1, Christian Kujawa1, Luis Franco3, Juan San Martin4, Claudia Bucarey Parra3 5 1 GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany 2 GEOMAR Helmholtz Centre for Ocean Research Kiel, 24148 Kiel, Germany 3 Observatorio Volcanológico de Los Andes del Sur (OVDAS), Servicio Nacional de Geología y Minería (SERNAGEOMIN), Temuco, Chile. 4 Physics Science Department, Universidad de la Frontera, Casilla 54-D, Temuco, Chile. 10 Correspondence to: Ayleen Gaete (
[email protected]) Abstract. Small steam-driven volcanic explosions are common at volcanoes worldwide but are rarely documented or monitored; therefore, these events still put residents and tourists at risk every year. Steam-driven explosions also occur frequently (once every 2-5 years on average) at Lascar volcano, Chile, where they are often spontaneous and lack any identifiable precursor activity. Here, for the first time at Lascar, we describe the processes culminating in such a sudden 15 volcanic explosion that occurred on October 30, 2015, which was thoroughly monitored by cameras, a seismic network, and gas (SO2 and CO2) and temperature sensors. Prior to the eruption, we retrospectively identified unrest manifesting as a gradual increase in the number of long-period (LP) seismic events in 2014, indicating an augmented level of activity at the volcano. Additionally, SO2 flux and thermal anomalies were detected before the eruption.