Single-Station Seismo-Acoustic Monitoring of Nyiragongo's Lava Lake Activity (D.R. Congo)

Abstract

Since its last effusive eruption in 2002, Nyiragongo has been an open-vent volcano characterized by the world's largest persistent lava lake. This lava lake provides a unique opportunity to detect pressure change in the magmatic system by analyzing its level fluctuations. We demonstrate that this information is contained in the seismic and infrasound signals generated by the lava lake's activity. The continuous seismo-acoustic monitoring permits quantification of lava lake dynamics, which is analyzed retrospectively to identify periods of volcanic unrest. Synchronous, high-resolution satellite SAR (Synthetic Aperture Radar) images are used to constrain lava lake level by measuring the length of the SAR shadow cast by the rim of the pit crater where the lava lake is located. Seventy-two estimations of the lava lake level were obtained with this technique between August 2016 and November 2017. These sporadic measurements allow for a better interpretation of the continuous infrasound and seismic data recorded at the closest station (∼6 km from the crater). Jointly analyzed seismo-acoustic and SAR data reveal that slight changes in the spectral properties of the continuous cross-correlated low-frequency seismo-acoustic records (and not solely single events) can be used to track fluctuations of the lava lake level on a daily and hourly basis. We observe that drops of the lava lake and the appearance of significant long period (LP) "lava lake" events are a consequence of a probable deep lateral magma intrusion beneath Nyiragongo, which induces changes in its shallow plumbing system. In addition to contributing to understanding lava lake dynamics, this study highlights the potential to continuously monitor pressure fluctuations within the magmatic system using a single seismo-acoustic station located several kilometers from the vent.

Recent Activity of Nyiragongo (Democratic Republic of Congo): New Insights From Field Observations and Numerical Modeling

“…The application of the FFM to forecast volcanic eruptions is classically associated to rock failure (Boué et al, 2016;Kilburn, 2018;Kilburn & Voight, 1998;Vasseur et al, 2017). Despite existing correlations between seismic signals and lava lake level fluctuations reported at Nyiragongo (Barrière et al, 2018), we are aware that linking the elevation of the lava lake to rock failure is not straightforward. If the pressure is expected to reach a plateau in the years preceding flank eruptions (i.e., 1972-1977, 1995-2002, and in the next months to years ; Figures 2e and 3a), the induced stress is not expected to relax.…”

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

“…Conventionally, due to its high dynamic range the radar backscatter is expressed in decibels ( Over the last two decades, multiple studies have used SAR backscatter to observe volcanic eruptions (Table 1). These have included measurements of dome growth (e.g., Pallister et al, 2013;Wadge et al, 2011), mapping of fresh lavas (e.g., Arnold et al, 2017;Wadge et al, 2012), extracting lava lake heights (e.g., Barrière et al, 2018;Moore et al, 2019) and flow thicknesses (Arnold et al, 2017;Wadge et al, 2012) measured using radar shadows.…”

Towards Global Volcano Monitoring Using Multisensor Sentinel Missions and Artificial Intelligence: The MOUNTS Monitoring System

“…More advanced techniques track features in the radar image prior to geocoding (i.e., radar coordinates in range and azimuth) to quantify morphological changes. Tracking radar shadows, for example, has proven useful to detect crater deepening [23], infilling of valleys by pyroclastic flows [24], and lava lake level variations [61]. Tracking the position of specific reflectors on the other hand, has proven capable of quantifying volcanic dome growths [62].…”