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- Title
High‐Resolution InSAR Reveals Localized Pre‐Eruptive Deformation Inside the Crater of Agung Volcano, Indonesia.
- Authors
Bemelmans, M. J. W.; Biggs, J.; Poland, M.; Wookey, J.; Ebmeier, S. K.; Diefenbach, A. K.; Syahbana, D.
- Abstract
During a volcanic crisis, high‐rate, localized deformation can indicate magma close to the surface, with important implications for eruption forecasting. However, only a few such examples have been reported, because frequent, dense monitoring is needed. High‐resolution Synthetic Aperture Radar (SAR) is capable of achieving <1 m spatial resolution and sub‐weekly revisit times, but is under‐used. Here we use high‐resolution satellite SAR imagery from COSMO‐SkyMed, TerraSAR‐X, and Sentinel‐1 to detect intra‐crater uplift preceding the November 2017 onset of eruptive activity at Agung, Indonesia. Processing the SAR imagery with an up‐to‐date, accurate, high‐resolution digital elevation model was crucial for preventing aliasing of the deformation signal and for accurate georeferencing. We show that >15 cm of line‐of‐sight shortening occurred over a 400‐by‐400 m area on the crater floor in September‐October 2017, accompanying a deep seismic swarm and flank dyke intrusion. We attribute the deformation to the pressurization of a shallow (<200 m deep) hydrothermal system by the injection of magmatic gases and fluids. We also observe a second pulse of intra‐crater deformation of 3–5 cm within 4 days to 11 hr prior to the first phreatomagmatic eruption, which is consistent with interaction between the hydrothermal system and the ascending magma. This phreatomagmatic eruption created the central pathway used during the final stages of magma ascent. Our observations have important implications for understanding unrest and eruption forecasting, and demonstrate the potential of monitoring with high‐resolution SAR. Plain Language Summary: At volcanoes, the ground surface can move due to the activity of magma and associated fluids underground. This deformation is a warning sign that can be useful when forecasting volcanic eruptions, especially when the deformation area is small (less than 1–2 km2), indicating that magma or magmatic fluids are close to the surface (less than 1 km deep). High‐resolution satellites such as COSMO‐SkyMed can measure ground deformation several times per week with better than 1 m resolution and are thereby able to detect and monitor rapid small‐area deformation. We use high‐resolution elevation and radar satellite data to detect deformation on the crater floor of Mount Agung, Indonesia, occurring before the November 2017 eruption. We show that the crater floor moved toward the satellites by more than 15 cm in September‐October 2017, accompanying an earthquake swarm, caused by magma intruding into the flank of the volcano. In the 4 days leading up to the eruption, we see another 3–5 cm of deformation. A shallow body of magmatic fluids less than 200 m below the crater floor was probably responsible for this ground deformation. Our research shows the potential of monitoring volcanoes with high‐resolution radar satellites. Key Points: We analyze high‐resolution Interferometric Synthetic Aperture Radar data from before the November 2017 eruption of Agung, Indonesia, and find localized deformation∼15 cm of intra‐crater deformation occurred in September‐October, with another 3–5 cm in the 4–0.5 days before the first phreatomagmatic explosionMagmatic fluids emitted by a flank dyke pressurized the shallow (<200 m) hydrothermal system, causing precursory deformation
- Subjects
INDONESIA; VOLCANIC eruptions; SENTINEL-1 (Artificial satellite); VOLCANIC craters; VOLCANIC activity prediction; DIKES (Geology); SYNTHETIC aperture radar; DIGITAL elevation models; EARTHQUAKE swarms
- Publication
Journal of Geophysical Research. Solid Earth, 2023, Vol 128, Issue 5, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2022JB025669