Suchergebnisse

Abstract. Central Georgia is an area strongly affected by earthquake and landslide hazards. On 29 April 1991 a major earthquake (Mw  =  7.0) struck the Racha region in Georgia, followed by aftershocks and significant afterslip. The same region was hit by another major event (Mw  =  6.0) on 7 September 2009. The aim of the study reported here was to utilize interferometric synthetic aperture radar (InSAR) data to improve knowledge about the spatial pattern of deformation due to the 2009 earthquake. There were no actual earthquake observations by InSAR in Georgia. We considered all available SAR data images from different space agencies. However, due to the long wavelength and the frequent acquisitions, only the multi-temporal ALOS L-band SAR data allowed us to produce interferograms spanning the 2009 earthquake. We detected a local uplift around 10 cm (along the line-of-sight propagation) in the interferogram near the earthquake's epicenter, whereas evidence of surface ruptures could not be found in the field along the active thrust fault. We simulated a deformation signal which could be created by the 2009 Racha earthquake on the basis of local seismic records and by using an elastic dislocation model. We compared our modeled fault surface of the September 2009 with the April 1991 Racha earthquake fault surfaces and identify the same fault or a sub-parallel fault of the same system as the origin. The patch that was active in 2009 is just adjacent to the 1991 patch, indicating a possible mainly westward propagation direction, with important implications for future earthquake hazards.

Abstract. Lava domes are subjected to structural weakening that can lead to
gravitational collapse and produce pyroclastic flows that may travel up to
several kilometers from a volcano's summit. At Merapi volcano, Indonesia,
pyroclastic flows are a major hazard, frequently causing high numbers of
casualties. After the Volcanic Explosivity Index 4 eruption in 2010, a new lava dome developed on
Merapi volcano and was structurally destabilized by six steam-driven
explosions between 2012 and 2014. Previous studies revealed that the
explosions produced elongated open fissures and a delineated block in the
southern dome sector. Here, we investigated the geomorphology, structures,
thermal fingerprint, alteration mapping and hazard potential of the Merapi
lava dome by using drone-based geomorphologic data and forward-looking
thermal infrared images. The block on the southern dome of Merapi is
delineated by a horseshoe-shaped structure with a maximum depth of 8 m and it
is located on the unbuttressed southern steep flank. We identify intense
thermal, fumarole and hydrothermal alteration activities along this
horseshoe-shaped structure. We conjecture that hydrothermal alteration may
weaken the horseshoe-shaped structure, which then may develop into a failure
plane that can lead to gravitational collapse. To test this instability
hypothesis, we calculated the factor of safety and ran a numerical model of
block-and-ash flow using Titan2D. Results of the factor of safety analysis
confirm that intense rainfall events may reduce the internal friction and
thus
gradually destabilize the dome. The titan2D model suggests that a
hypothetical gravitational collapse of the delineated unstable dome sector
may travel southward for up to 4 km. This study highlights the
relevance of gradual structural weakening of lava domes, which can influence
the development fumaroles and hydrothermal alteration activities of cooling
lava domes for years after initial emplacement.

Abstract. Tsunamis caused by large volcanic eruptions and flanks collapsing into the
sea are major hazards for nearby coastal regions. They often occur with
little precursory activity and are thus challenging to detect in a timely
manner. This makes the pre-emptive identification of volcanoes prone to
causing tsunamis particularly important, as it allows for better hazard
assessment and denser monitoring in these areas. Here, we present a
catalogue of potentially tsunamigenic volcanoes in Southeast Asia and rank
these volcanoes by their tsunami hazard. The ranking is based on a
multicriteria decision analysis (MCDA) composed of five individually
weighted factors impacting flank stability and tsunami hazard. The data are sourced from geological databases, remote sensing data, historical volcano-induced tsunami records, and our topographic analyses, mainly considering the eruptive and tsunami history, elevation relative to the distance from the sea, flank steepness, hydrothermal alteration, and vegetation coverage. Out of 131 analysed volcanoes, we found 19 with particularly high
tsunamigenic hazard potential in Indonesia (Anak Krakatau, Batu Tara,
Iliwerung, Gamalama, Sangeang Api, Karangetang, Sirung, Wetar, Nila, Ruang,
Serua) and Papua New Guinea (Kadovar, Ritter Island, Rabaul, Manam, Langila, Ulawun, Bam) but also in the Philippines (Didicas). While some of these volcanoes, such as Anak Krakatau, are well known for their deadly tsunamis, many others on this list are lesser known and monitored. We further performed tsunami travel time modelling on these high-hazard volcanoes, which indicates that future events could affect large coastal areas in a short time. This highlights the importance of individual tsunami hazard assessment for these volcanoes, the importance of dedicated volcanological monitoring, and the need for increased preparedness on the potentially affected coasts.

Publisher's version (útgefin grein) ; Meaningful forecasting of the atmospheric concentration and ground accumulation of volcanic ash during explo-sive eruptions requires detailed knowledge of the eruption source parameters. However, due to the large uncer-tainties in observations and limitations of current models used to make inferences from these, monitoring anongoing eruption and quantifying the mass eruption rate in real-time is a considerable challenge. Within theEU supersite project"FutureVolc", an integrated approach has been applied to develop a quasi-autonomousmulti-parameter system, denoted"REFIR", for monitoring volcanic eruptions in Iceland and assessing the erup-tion massflow rate by inverting the plume height information and taking account of these uncertainties. REFIRhas the capability to ingest and process streaming plume-height data provided by a multitude of ground basedsensors, including C–and X-band radars and web-cam based plume height tracking systems. These observationaldata are used with a suite of plume models that also consider the current wind and other atmospheric conditions,providing statistically assessed best estimates of plume height and mass eruption rate. Provided instrumentaldata is available, near real-time estimates are obtained (the delay corresponding to the scan rate of data-providing instruments, presently of the order of minutes). Using the Hekla 2000, and Eyjafjallajökull 2010 erup-tions in Iceland, the potential of REFIR is demonstrated and discussed through application to three scenarios. Thesystem has been developed to provide maximumflexibility. A setup script assists the user in adapting to localconditions, allowing implementation of REFIR for any volcanic eruption site worldwide. REFIR is designed to beeasily upgradable, allowing future extension of monitoring networks, learning from new events, and incorpora-tion of new technologies and model improvements. This article gives an overview of the basic structure, modelsimplemented, functionalities and the computational techniques of REFIR. ; The development of REFIR has been part of the FUTUREVOLC supersite project and was funded by the European Union's Seventh Programme for research, technological development and demonstration under grant agreement No 308377. TD's work was also funded by the project EVER-EST, as part of the EU's Horizon 2020 research and innovation programme under grant agreement no 674907. ; Peer Reviewed

Abstract. Small steam-driven volcanic explosions are common at volcanoes worldwide but are rarely documented or monitored; therefore, these events still put residents and tourists at risk every year. Steam-driven explosions also occur frequently (once every 2–5 years on average) at Lascar volcano, Chile, where they are often spontaneous and lack any identifiable precursor
activity. Here, for the first time at Lascar, we describe the processes
culminating in such a sudden volcanic explosion that occurred on 30 October 2015, which was thoroughly monitored by cameras, a seismic network, and gas and temperature sensors. Prior to the eruption, we retrospectively identified unrest manifesting as a
gradual increase in the number of long-period (LP) seismic events in 2014,
indicating an enhanced level of activity at the volcano. Additionally,
sulfur dioxide (SO2) flux and thermal anomalies were detected before the eruption. Then, our weather station reported a precipitation event, followed by an increase in steaming and a sudden volcanic explosion at Lascar. The multidisciplinary data exhibited short-term variations associated with the explosion, including (1) an abrupt eruption onset that was seismically
identified in the 1–10 Hz frequency band, (2) the detection of a 1.7 km high white-gray eruption column in camera images, and (3) a pronounced spike in SO2 emission rates reaching 55 kg s−1 during the main pulse of the eruption as measured by a mini-differential optical absorption spectroscopy (DOAS) scanner. Continuous carbon dioxide (CO2) and temperature measurements conducted at a fumarole on the southern rim of the Lascar crater revealed a pronounced change in the trend of the relationship between the CO2 mixing ratio and the gas outlet temperature; we speculate that this change was associated with the prior precipitation event. An increased thermal anomaly inside the active crater as observed in Sentinel-2 images and drone overflights performed after the steam-driven explosion revealed the presence of a ∼50 m long fracture truncating the floor of the active crater, which coincides well with the location of the thermal anomaly. This study presents the chronology of events culminating in a steam-driven explosion but also demonstrates that phreatic explosions are difficult to predict, even if the volcano is thoroughly monitored; these findings emphasize why ascending to the summits of Lascar and similar volcanoes is hazardous, particularly after considerable precipitation.

Abstract. Lava flow simulations help to better understand volcanic hazards and may assist emergency preparedness at active volcanoes. We demonstrate that at Fogo Volcano, Cabo Verde, such simulations can explain the 2014–2015 lava flow crisis and therefore provide a valuable base to better prepare for the next inevitable eruption. We conducted topographic mapping in the field and a satellite-based remote sensing analysis. We produced the first topographic model of the 2014–2015 lava flow from combined terrestrial laser scanner (TLS) and photogrammetric data. This high-resolution topographic information facilitates lava flow volume estimates of 43.7 ± 5.2 × 106 m3 from the vertical difference between pre- and posteruptive topographies. Both the pre-eruptive and updated digital elevation models (DEMs) serve as the fundamental input data for lava flow simulations using the well-established DOWNFLOW algorithm. Based on thousands of simulations, we assess the lava flow hazard before and after the 2014–2015 eruption. We find that, although the lava flow hazard has changed significantly, it remains high at the locations of two villages that were destroyed during this eruption. This result is of particular importance as villagers have already started to rebuild the settlements. We also analysed satellite radar imagery acquired by the German TerraSAR-X (TSX) satellite to map lava flow emplacement over time. We obtain the lava flow boundaries every 6 to 11 days during the eruption, which assists the interpretation and evaluation of the lava flow model performance. Our results highlight the fact that lava flow hazards change as a result of modifications of the local topography due to lava flow emplacement. This implies the need for up-to-date topographic information in order to assess lava flow hazards. We also emphasize that areas that were once overrun by lava flows are not necessarily safer, even if local lava flow thicknesses exceed the average lava flow thickness. Our observations will be important for the next eruption of Fogo Volcano and have implications for future lava flow crises and disaster response efforts at basaltic volcanoes elsewhere in the world.