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Logo: Institut für Photogrammetrie und Geoinformatik/Leibniz Universität Hannover
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Radarpaper in Nature Communications veröffentlicht

Precursor signals prior to Anak Krakatoa fatal eruption

On 22 December 2018, Anak Krakatau, an Indonesian island volcano collapsed its flank and triggered a deadly tsunami. Although the Anak Krakatau volcano was known to be active, individual observed anomalous signals were not interpreted as precursory to a volcanic eruption. Mahmud Haghshenas Haghighi and Mahdi Motagh, two researchers from the Institute of Photogrammetry and GeoInformation at the Leibniz University of Hannover, co-authored a new study published in the journal Nature Communications1. This comprehensive study employed ground-based and space-borne data to investigate the precursory activities of the Anak Krakatau volcano. Satellite data provided significant insight into the details of the precursory events.

Radar data acquired by Copernicus Sentinel-1 mission, highly penetrating through clouds and volcanic emissions, allowed delineating the outline of the volcanic island. The results indicated little variations in the first six months of the year 2018, but a raise in the island surface area during the six months prior to the collapse in December 2018. An increase in thermal activities evident in MODIS and Sentinel-2 satellite data also confirmed the start of a new activity period six months before the collapse. 

Deformation mapping in different geometries of the Sentinel-1 Radar data showed one-third of the island area had been creeping throughout a year before the failure with periods of accelerations corresponded to volcanic activities. Satellite thermal data revealed the increase in the volcanic activities within a few hours that lead up to the slope failure followed by volcanic eruptions. Ground-based seismic and infrasound instruments captured the landslide and eruption signals with a high temporal resolution. Shortly after the collapse, Sentinel-1 data helped outline the new perimeter of the island. 

Furthermore, a comparison of high-resolution Radar images from the German TerraSAR-X mission shows the details of morphological changes following the sector collapse, material deposition, and subsequent erosion. The finding of this study provided a detailed picture of volcanic activities before the Anak Krakatau eruption. They have important implications for a better understanding of volcanic hazards and the development of early detection technologies at other volcanoes around the globe.

¹: Walter, T. R., Haghighi, M. H., Schneider, F. M., Coppola, D., Motagh, M., et al. (2019). Complex hazard cascade culminating in the Anak Krakatau sector collapse. Nature Communications, 10(1), 1-11.
Link to the paper: https://www.nature.com/articles/s41467-019-12284-5

Figure 1 (upper): Deformation analysis using Sentinel-1 Radar data showed the spatial pattern of deformation and its acceleration corresponding to volcanic activities.

Figure 2 (lower): TerraSAR-X revealed morphological changes by sector collapse, material deposition, and subsequent erosion.