Constraints on eruption processes and event masses for the 2016–2017 eruption of Bogoslof volcano, Alaska, through evaluation of IASI satellite SO2 masses and complementary datasets

Abstract

Bogoslof volcano, Alaska, experienced at least 70 explosive eruptions between 12 December 2016 and 31 August 2017. Due to its remote location and limited local monitoring network, this eruption was monitored and characterized primarily using remote geophysical and satellite techniques. SO 2 emissions from Bogoslof were persistently detected by the Infrared Atmospheric Sounding Interferometer (IASI) satellite sensors. Of Bogoslof's 70 explosive events, 50% produced measurable SO 2 masses ranging from 0.1 to 21.5 kt, with a median and standard deviation of 0.7 ± 4.0 kt SO 2 , respectively. Here, we compare IASI-derived SO 2 masses from Bogoslof events to complementary geophysical datasets to provide insights into eruption source processes, namely the degree of seawater scrubbing of water-soluble SO 2 and variations in magma flux. Correlations with the number of lightning strokes and infrasound energy are expected to indicate magma-flux as a controlling process, while correlations with infrasound frequency index are expected to indicate variations in vent-water content as a controlling factor. These comparisons suggest that the measured SO 2 masses are primarily a function of eruption magnitude (degassed magma mass) and that scrubbing of SO 2 emissions by vent seawater may have exerted a minor effect on the observed SO 2 masses. SO 2 masses were combined with petrologic constraints on melt inclusion and matrix glass S concentrations to calculate degassed magma masses and volumes. The cumulative SO 2-derived degassed magma mass and estimated volume (dense-rock equivalent) for the full Bogoslof eruption were found to be 2.8 × 10 10 kg and 9.3 × 10 6 m 3 , respectively. When individual event masses are compared against event masses calculated using an empirical plume-height method, a strong correlation is found (R 2 = 0.83), with better than order-of-magnitude agreement in most cases. These estimates of eruption masses provide useful information on the magnitude, behavior, and associated hazards of the 2016-2017 eruption, and potentially future unrest at Bogoslof volcano.

Seismo-acoustic evidence for vent drying during shallow submarine eruptions at Bogoslof volcano, Alaska

“…VASR* then varies irregularly during the eruption from 0.00068-0.0078 Pa/μm/s, and is higher than the January 31 eruption, mostly because of the very high acoustic amplitudes. The eruption also produced an ashpoor plume to 6.1 km, 0.7 kt of SO 2 , and 21 lightning strokes (Lopez et al 2019;Schneider et al 2019;Van Eaton et al 2019). WorldView-2 satellite imagery from this period (Fig.…”

“…A trend from low to high VASR* for long duration events also suggests an increase in acoustic efficiency as the vent dried out. These findings are valuable for understanding eruptive processes and hazards because the extent of water involvement strongly affects the atmospheric transport of ash and SO 2 Lopez et al 2019), and production of volcanic lightning . Our results are also consistent with recent studies that illustrate care should be taken when extrapolating plume height or mass eruption rate from seismic and acoustic frequency content, duration, and amplitude.…”

“…More detailed satellite-based observations and interpretation are available in separate manuscripts, such as Waythomas et al (2019) and Schneider et al (2019). Details on satellite-derived SO 2 and lightning observations are available in Lopez et al (2019) and Van Eaton et al (2019), respectively.…”

“…Ash was only detected previously from event 23 on January 18. Above-average SO 2 was also detected (3.6 kt compared to an average of 2 kt) (Lopez et al 2019). Figure 6a displays the seismo-acoustic waveforms, spectrograms, FI, and VASR* for 2.5 h surrounding a typical eruption during the 2016-2017 eruption sequence, February 20, 2017 (event 36).…”

“…Sufficient water in the eruption mixture could potentially enhance scrubbing of SO 2 (Symonds et al 2001) and early fallout of volcanic ash as accretionary lapilli (Van Eaton et al 2015). Preliminary satellite-based observations indicate the 2016-2017 Bogoslof eruption was relatively SO 2and water-rich for most events (Lopez et al 2019;Schneider et al 2019). Therefore, information on the location of the vent with respect to sea level and related shallow water eruption processes is key to understanding the eruption and associated geophysical observations.…”