Analyzing Explosive Volcanic Deposits From Satellite‐Based Radar Backscatter, Volcán de Fuego, 2018. Issue 9 (23rd September 2021)

• Record Type: Journal Article
• Authors: Dualeh, E. W.; Ebmeier, S. K.; Wright, T. J.; Albino, F.; Naismith, A.; Biggs, J.; Ordoñez, P. A.; Boogher, R. M.; Roca, A.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 9(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-09-23
• Subjects: explosive volcanism -- SAR backscatter -- Fuego June 2018 Eruption; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2021JB022250
• Languages: English
• ISSNs: 2169-9313

Abstract

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 k m 2 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 k m 2, 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. Plain Language Summary: Volcanic eruptions cause changes to the Earth's surface that can be observed using satellite‐based radar instruments. Changes to the radar scattered back from the surface can be caused by new volcanic deposits or changes to the ground caused by an eruption. However, such signals are also affected by what was there before the eruption and variations in the satellite positions. Deposits from explosive eruptions are particularly hard to identify because they can affect radar signals in different ways. We use a high spatial and temporal resolution satellite radar dataset to identify different volcanic deposits from the June 2018 eruption of Volcán de Fuego, Guatemala. We were able to identify three types of volcanic deposit from radar backscatter: hot mixture of solid particle and gas (pyroclastic density currents), water saturated flow with solid particles (lahars), and ash. We observe backscatter changes over six drainage systems that were affected by pyroclastic density currents in June 2018. Combining our radar dataset with rainfall data, we identify nine periods of lahars in one drainage between June and October 2018. We describe what information and corrections are helpful to identify volcanic changes in backscatter and especially to monitor the progression of an explosive eruption. Key Points: Radar backscatter observed 3 pyroclastic density currents and 9 periods of lahar activity in a single drainage system between January and October 2018 Backscatter noise is reduced by up to 42% by using dense time series, which aids in the extraction of subtle signals in explosive deposits Backscatter corrections and understanding of pre‐eruption scattering properties are necessary for meaningful analysis of explosive deposits