Analyzing Explosive Volcanic Deposits From Satellite‐Based Radar Backscatter, Volcán de Fuego, 2018

Abstract

Satellite radar backscatter has the potential to provide useful information about the progression of volcanic eruptions when optical, ground‐based, or radar phase‐based measurements are limited. However, backscatter changes are complex and challenging to interpret: explosive deposits produce different signals depending on pre‐existing ground cover, radar parameters and eruption characteristics. We use high temporal‐ and spatial‐resolution backscatter imagery to examine the emplacement and alteration of pyroclastic density currents (PDCs), lahar and ash deposits from the June 2018 eruption of Volcán de Fuego, Guatemala, using observatory reports and rainfall gauge data to ground truth our observations. We use a temporally dense time series of backscatter data to reduce noise and extract deposit areas. We observe backscatter changes in six drainages, the largest deposit was 11.9‐km‐long that altered an area of 6.3 normalknormalm2 and had a thickness of 10.5 ±2 m in the lower sections as estimated from radar shadows. The 3 June eruption also produced backscatter signal over an area of 40 normalknormalm2, consistent with reported ashfall. We use transient patterns in backscatter time series to identify nine periods of high lahar activity in a single drainage system between June and October 2018. We find that the characterization of subtle backscatter signals associated with explosive eruptions are best observed with (1) radiometric terrain calibration, (2) speckle correction, and (3) consideration of pre‐existing scattering properties. Our observations demonstrate that SAR backscatter can capture the emplacement and subsequent alteration of a range of explosive deposits, allowing the progression of an explosive eruption to be monitored.

Mapping Areas Impacted by Volcanic Flows During an Eruption Using Synthetic Aperture Radar and Optical Imagery

“…The ΔdB signal for volcanic flow deposits, either PDCs or lava flow, is about two times higher in HV than in HH polarization. The results are comparable to other studies of PDCs mapped from SAR backscattering intensity changes at Montserrat volcano (Wadge et al, 2011), Merapi volcano in Indonesia (Solikhin et al, 2015) and Volcán de Fuego in Guatemala (Dualeh et al, 2021), which allowed us to develop "ΔdB signature fields" for volcanic flows (Figure 9). Their interpretation is that when deposits go from dry to wet, the radar penetration decreases and has more interactions with near-surface scatterers thus increasing the return signal towards the satellite.…”

“…SAR data, on the other hand, compensate for these limitations with all-weather and all-day imaging capabilities. SAR and optical data have been applied to fast-moving volcanic flows in other studies, either individually (Wadge et al, 2002(Wadge et al, , 2011Terunuma et al, 2005;Thouret et al, 2010;Solikhin et al, 2012;Bignami et al, 2013;Arnold et al, 2018;Krippner et al, 2018;Pallister et al, 2019;Valade et al, 2019;Dualeh et al, 2021) or in combination (e.g., Solikhin et al, 2015;McAlpin et al, 2013), but the context of emergency mapping has rarely been a focus. In this paper, we use the case studies of the 2015 eruptions from Volcán de Colima in Mexico and Volcán Calbuco in Chile (Figure 1) to calibrate detection thresholds of different types of fast-moving volcanic flows from optical and SAR imagery.…”

High‐Resolution InSAR Reveals Localized Pre‐Eruptive Deformation Inside the Crater of Agung Volcano, Indonesia

“…These areas are affected by signal overlay caused by the steep crater walls and only very small perpendicular baseline (≤25 m) interferograms are coherent in the signal overlay affected areas. On 25 November 2017, magmatic eruptions covered the crater floor in lava, making continued displacement analysis with InSAR impossible due to loss of coherence (Dietterich et al., 2012; Dualeh et al., 2021; Zebker et al., 1996).…”

Deposit‐Derived Block‐and‐Ash Flows: The Hazard Posed by Perched Temporary Tephra Accumulations on Volcanoes; 2018 Fuego Disaster, Guatemala

“…The 3 June 2018 eruption was the largest eruption of the current eruptive phase, with an estimated total ejected volume of 0.04 ± 0.01 km 3 dense rock equivalent (Pardini et al., 2019), although this estimate may be an overestimate if it includes recycling of stored, previously erupted tephra. The volume of new PDC deposits in the Las Lajas valley has been estimated to be 0.02–0.03 km 3 (Naismith et al., 2019) and 0.01–0.02 km 3 (Albino et al., 2020), with thicknesses of up to 10.5 ± 2 m (Dualeh et al., 2021).…”