Linking ground-based data and satellite monitoring to understand the last two decades of eruptive activity at Sangay volcano, Ecuador

Abstract

Sangay is one of the most active volcanoes in Ecuador, as it has been almost continuously erupting at least since the 17th century. However, because of its remote location and low associated risk to human population, little is known about its eruptions. Here we summarize Sangay's volcanic activity from January 2001 to May 2020, based on ground-based data, satellite-derived observations, and chemical analysis of its erupted products. During the analyzed period, Sangay's activity changed from continuous to episodic, as revealed by seismic, thermal and ash emission data. We identified three main eruptive periods: the first, from 2001 to 2013, extruded a cumulative volume of 100±50 million m 3 of lava through long-lived activity;the second emitted 54±27 million m 3 in four short-lived episodes, which occurred once every year from 2015 to 2018; and finally, a third period since 2019, which has continuous but fluctuating intensity, and shows a significant increase of the extruded lava volume (172±86 million m 3 until 31 May 2020). Our results show a marked change in the eruption frequency and a significant increase in average discharge rate over time, although surface activity remained similar, with lava flows, small explosions, and ash venting.We propose that three magmatic processes acted to explain the observed changes: between 2001 and 2013 the long-living low intensity eruptions were promoted by buoyancy, while since 2019 similar but more intense activity was triggered by mass injections. In contrast, the episodic activity in between probably resulted from volatile exsolution due to crystallization (second boiling). Transitions between these three regimes are presumably the result of varying mass inflow rates. Our results provide insights into eruptive style transitions commonly observed at volcanoes of intermediate composition, such as Sangay, over a time scale of several years.

Forecasting and communicating the dispersion and fallout of ash during volcanic eruptions: lessons from the September 20, 2020 eruptive pulse at Sangay volcano, Ecuador

“…No correlation or pattern is observed with the distance from the vent. We note that the composition of the September 20, 2020 ash samples fall within the compositional field of the Sangay III edifice (Monzier et al, 1999) but is more mafic than the composition analyzed from the recent decades (Monzier et al, 1999;Vasconez et al, 2022) (Figure 9). We chose the samples SAN-20-25 and SAGA-20A to perform an exploratory componentry analysis (Supplementary Material S5).…”

“…Unfortunately, due to frequent power and transmission outages likely due to repeated ash fallout, SAGA did not record the September 20, 2020 eruptive pulse. The study by Vasconez et al (2022) found that a broadband seismic sensor with low anthropogenic noise levels located 67 km to the north-northeast (PUYO, Figure 1B) generally had fewer outages than SAGA and was a suitable alternative for identifying high-magnitude explosive activity from Sangay. Frequency-filtered RSAM (Real-time Seismic Amplitude Measurement) is computed in 1-min windows at the IG-EPN for PUYO seismic records in the 0.6-1.2 Hz band (raw seismic records and filtered RSAM data for September 20, 2020 are available in Supplementary Material S1).…”

“…500-1100 m above the crater). SAGA-20A was analyzed for major elements in a previous study and was approximately 1.3 wt% higher in SiO 2 (Vasconez et al, 2022). Based on optical characteristics and morphology observed with the binocular microscope, four main classes of components were identified in the ash samples (Figure 10A): 1) Dark colored juvenile fragments are black to brown, glassy, translucent to opaque, massive to vesicular, various shapes (blocky, subrounded, irregular); 2) Light-colored juvenile fragments are light gray, glassy, translucent, massive, blocky to sub-rounded; 3) Accidental material is variously colored (mostly red, dark gray, white), dull, opaque, variously shaped (blocky, sub-rounded, irregular); 4) Free crystals are white (plagioclase) and green (pyroxene), shiny, translucent and blocky.…”

“…Nonetheless, some efforts have been carried out to obtain meaningful information on its eruptive dynamics (Johnson et al, 2003;Lees and Ruiz, 2008;Ruiz et al, 2017). Recently, ground-based and satellite instruments have been combined to increase the monitoring capability at Sangay (Vasconez et al, 2022), but eruption source parameters (ESPs), generally constrained by detailed field and remote sensing studies, are still lacking.…”

“…According to Vasconez et al (2022), since 2003 Sangay has been semi-continuously active with mostly low-intensity ash emissions (<3.5 km above the crater) and short-runout lava flows (1-3 km long). Its most recent eruptive period began on May 7, 2019 and is still ongoing as of July 2022.…”