• Anak Krakatau's 2018 eruption and tsunami were preceded by a decade of subtle ground movement detectable by satellite radar.
• Researchers used InSAR data to identify a slow landslide-like movement of the volcano's flank, with acceleration before the collapse.
• Real-time InSAR monitoring could revolutionize volcanic hazard prediction, especially in areas lacking ground-based GPS.

In 2018, the Anak Krakatau volcano in Indonesia erupted, triggering a devastating tsunami that resulted in over 400 fatalities. A new study published in AGU reveals that the collapse of the volcano's southwestern flank, which caused the tsunami, was preceded by years of subtle, unnoticed ground movement. Researchers from Penn State analyzed over a decade of satellite radar data using Interferometric Synthetic Aperture Radar (InSAR) to uncover these hidden movements. The findings suggest that the volcanic collapse was not a sudden event but rather a slow landslide, with the mountain's flank gradually shifting over many years.

• What: Analysis of satellite data reveals precursory ground movement of Anak Krakatau volcano before the 2018 tsunami.
• Who: Researchers from Penn State University, including Young Cheol Kim and Christelle Wauthier, are the key individuals involved in the study.
• When: The ground movement occurred from 2006 to 2018, with significant acceleration just months before the eruption.
• Where: The event occurred at the Anak Krakatau volcano in Indonesia.

The study's findings highlight the potential of InSAR technology to monitor volcanic activity and predict future eruptions. By analyzing satellite data, researchers were able to identify subtle ground movements that preceded the 2018 Anak Krakatau eruption and tsunami. This information could be crucial for preventing future disasters, especially in regions where traditional monitoring tools are not feasible. The ability to detect acceleration in slip could serve as an early warning sign of potential volcanic collapse. The use of high-performance computing, like Penn State's Roar computer cluster, was essential in processing the vast amount of data required for this study.

the detachment fault experienced approximately 15 meters (roughly 50 feet) of slip from 2006 to 2018 with acceleration and deceleration periods, and a notable acceleration prior to the 2018 collapse.

the whole chunk of the volcano that collapsed was already moving—like a slow landslide. And so, it’s very important to be able to look at the temporal evolution of that deformation, because if you have an acceleration, it can lead to a collapse.

If you have a sudden acceleration of slip, it might be the sign that you will have a collapse happening. Whether it’s this volcano or others susceptible to collapse worldwide, if you don’t have ground-based data in real time, maybe having near-real-time InSAR processing can help researchers be on the lookout for any significant acceleration in slip.

This study shows, unfortunately retrospectively, that we could forecast it if we had this remote sensing data set to get the surface deformation.

The study of Anak Krakatau's 2018 eruption underscores the value of satellite monitoring for predicting volcanic disasters. By analyzing InSAR data, researchers identified precursory ground movements that could have served as a warning sign. Real-time InSAR monitoring holds promise for improving volcanic hazard prediction, especially in regions lacking ground-based instruments. While the findings are retrospective, they offer valuable insights for future volcanic monitoring efforts and disaster preparedness.