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In December 2018, the Anak Krakatau volcano was destroyed in a cascade of eruptions following a flank destabilization. A tsunami triggered by these events devastated coastal areas and caused loss of lives, highlighting the importance of better understanding destabilization processes and possible structural weaknesses. Satellite remote sensing data provided by Planet Labs, Pleiades, and TerraSAR-X allow us to monitor volcanic evolution stages at high temporal resolution and to catalog events for the period 2018-2023. We aim to identify possible zones of structural weakness in the newly forming volcanic building, that may pose risks in future development, by focusing on activity patterns like surface degassing and sealing processes. Posteruptive degassing, observed in the crater lake and on the western shore of the island highlights an off-centered activity. Several periods of coverage and reoccurrence of the surficial degassing pattern by tephra and ashes are observed until June 2020, when a lava flow largely covered and effectively sealed the open degassing surface. A second lava flow covers all of the original open degassing surfaces and degassing now exclusively occurs on the eastern margin of the new lava flow. The alternate layering of tephra and lava flows, acting as inclined sealing planes, indicates the possibility of a critical evolution where pressurization and hydrothermal alteration effects of the lateral gas flow might create future zones of structural weakness. We suggest a close monitoring and cataloging of Krakatau’s structural evolution, and investigation of the gas-rock interactions to assess their potential to create future sliding planes., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The morphology of Askja caldera walls demonstrates features related to slope instability and permafrost variations that can be linked to each other. However, the causal link between mass wasting and cryosphere in active volcanic environments is poorly understood. Factors of permafrost degradation and associated slope instability at Askja may involve volcanic heat flow and atmospheric temperature increase. To investigate long-term morphological changes related to slope processes and permafrost activity, we performed photogrammetric processing and comparative analysis of archive aerial, recent Pleiades satellite, and drone data. We extracted DEMs and orthophotographs covering the period of 1970-2022 and revealed evidence of slope instability, previous mass wasting occurring on different scales, and permafrost degradation. The high-resolution multitemporal data allowed recognition of such surface features as emerging tensile cracks and multiple thermokarst sinkholes. Our photogrammetric dataset was complemented with SAR and infrared data processing, and historical ground-based photographs analysis. Our results show that landslides are common at Askja caldera, and considering the identified morphological features, a new mass wasting event can occur at any time. We outline unstable areas at the caldera walls and discuss the relevance of permafrost and instability that may have contributed to the Askja 2014 rockslide avalanche. We suggest that slope instability at Askja poses significant hazards and requires constant remote sensing and on-site monitoring., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Here we present a photogrammetric dataset on the 2018-2019 eruption episode at Shiveluch Volcano, one of the most active volcanoes in Kamchatka Peninsula. The data were acquired by optical sensors and complemented by thermal sensors. The optical satellite images were tri-stereo panchromatic 1-m resolution imagery acquired on 18 July 2018 with Pléiades satellite PHR1B sensor. We processed the data in Erdas Imagine 2015 v15.1. For the relative orientation of the images, 37 tie points were calculated automatically with further manual correction, and for the interior and exterior orientation, Rational Polynomial Coefficients block adjustment, which is a transformation between pixels to latitude, longitude, and height information, was automatically employed. After the image orientation, we obtained a photogrammetric model with a total root mean square error (RMSE) of 0.2 m. By using the Enhanced Automatic Terrain Extraction module (eATE) with normalized cross correlation algorithm as implemented in the Erdas Imagine software, we were able to extract a 2 m resolution point cloud (PC) referenced to the WGS84 coordinate system UTM57 zone. This PC was filtered with the CloudCompare v2.9.1 noise filter and then manually cleaned with the CloudCompare segmentation tool. As strong volcanic steam emissions caused a large gap in the PC at the NE part of the dome, we used a 5 m resolution DEM constructed from TanDEM-X data to fill the gap and obtain the missing topography. TanDEM-X is a bistatic SAR mission, formed by adding a second, almost identical spacecraft, to TerraSAR-X. Therefore, it allows the acquisition of two simultaneous SAR imageries over the same area, eliminating possible temporal decorrelations between them and maintaining a normal baseline between 250 and 500 m, which is suitable for SAR interferometry for DEM generation. We used the interferometric module in ENVI SARscape to build the interferogram, perform the unwrapping step and finally convert it into height information using forward transformation from radar to geographic coordinates. The RMSE of the generated DEM is evaluated based on the coherence value, i.e. quality of the interferogram, and is estimated to be approximately 5 m.

The densely populated neighborhoods of Pinheiro, Bebedouro, Mutange, Bom Parto and Levada in the Municipality of Maceió (Brazil) are suffering serious geological instability. Fractures, on both buildings and roads, have intensified since the beginning of 2018 and some of the areas were evacuated, due to safety reasons, by the local authorities during the second half of 2019. The preliminary investigation conducted by the Brazilian Geological Service (Serviço Geologico do Brazil - CPRM), suggested that the direct cause of the instability is connected to the salt mining activities carried out on near the cost of the Mundaú Lagoon. In this study we use radar interferomtery (InSAR) and 2D geomechanical modelling to characterize almost 16 years of continuous deformation in Municipality of Maceió (Brazil). We exploited the full potential of the well-known Multi Temporal Interferometry techniques (MTI) based on Advanced Synthetic Aperture Radar Differential Interferometry (A-DInSAR) and processed all available historical and currently operational SAR missions: the C-band ASAR ENVISAT, the L-band ALOS-1 POLSAR, L-band ALOS-2 POLSAR and C-band Sentinel-1 missions. The results show clear main deformation field over the neighborhood of Pinheiro with concentric pattern to the shore and increasing deformation intensity up to 25cm per year from 2003 to 2019. A minor deformation area is detected also south of the lagoon corresponding to the neighborhood of Bom Parto and Levada. A 2D geomechanical modelling of salt-cavern stability using Distinct Elements is developed to derive the relationship between the detected deformations and the salt mining activities. As a general conclusion, our study shows how MTI analysis is very efficient and reliable tool for emergency management purposes. Especially after the launch of the Sentinel-1 mission, which provides an acquisition in single pass every 12 days, we are able to detect when a surface displacement commence and monitor the deformation progress and status in time.

The combined effects of climate change and human land use activities are increasing the occurrence of extreme events, such as floods and landslides worldwide. Between mid-March and the beginning of April 2019, almost the whole Iran was affected by intense record rainfall leading to widespread flash flooding. Starting in the northern province of Golestan and moving to the South and the West of the country, heavy rains have poured on 28 out of the 31 provinces. Approximately, 1900 cities and villages across the country were damaged with half a million people displaced at the peak of the disaster. The intense rainfall not only caused more than 140 rivers to burst their banks, but also triggered thousands of landslides. The presented work makes use of high resolution - spatial and temporal - optical and radar satellite remote sensing with the goal of performing large-area and at the same time detailed spatiotemporal analysis of landslide occurrence related to the main hydro-meteorological triggering events. Besides detection of rainfall and flood triggered landslides, pre- and post-failure landslide evolution has been analyzed including the first observed onset of landslide activation in February 2019 resulting from already increased precipitation in late fall and winter of 2018/19. Large-area landslide detection has been performed in a semi-automated way using time series of optical Planet Scope and Sentinel-2A/B data. For assessing the kinematics of pre- and post-failure slope motions, radar remote sensing based image correlation and differential interferometric synthetic aperture radar (DInSAR) methods have been applied using Sentinel-1A/B data. The obtained satellite remote sensing based results have been evaluated by field surveys conducted in cooperation between the GFZ Potsdam and the Forest, Range and Watershed Management Organization of Iran (FRWM) being responsible for landslide hazard and risk assessment as well as the design and implementation of mitigation measures. In this context, emphasis has been put on the potential of multi-sensor satellite remote sensing for improving large-area process monitoring and understanding, especially in relation to extreme triggering events of so far unprecedented magnitude which are likely to occur more frequently in the future because of ongoing climate change.