Thomas R. Walter

Thomas R. Walter
Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum GFZ | GFZ · Department of Physics of the Earth

PhD

About

276
Publications
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5,446
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Publications

Publications (276)
Article
Full-text available
Understanding and constraining the source of geodetic deformation in volcanic areas is an important component of hazard assessment. Here, we analyse deformation and seismicity for one year before the March 2021 Fagradalsfjall eruption in Iceland. We generate a high-resolution catalogue of 39,500 earthquakes using optical cable recordings and develo...
Article
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Catastrophic lava dome collapse is considered an unpredictable volcanic hazard because the physical properties, stress conditions, and internal structure of lava domes are not well understood and can change rapidly through time. To explain the locations of dome instabilities at Merapi volcano, Indonesia, we combined geochemical and mineralogical an...
Article
Full-text available
Explosive eruptions at steep-sided volcanoes may develop with complex precursor activity occurring in a poorly-understood magma plumbing system so that timelines and possible interactions with the geologic surrounding are often unresolved. Here we investigate the episode prior to the energetic December 20, 2017 eruption at Bezymianny volcano, Kamch...
Article
Full-text available
Repeated Synthetic Aperture Radar (SAR) acquisitions can be utilized to produce measurements of ground deformations and associated geohazards, such as it can be used to detect signs of volcanic unrest. Existing time series algorithms like Permanent Scatterer (PS) analysis and Small Baseline Subset (SBAS) are computationally demanding and cannot be...
Conference Paper
Volcanoes often display pronounced faults and structural anisotropies. To better understand the structural evolution of volcano morphologies, we performed an unoccupied aircraft systems (UAS) survey of Mount Thorbjorn, an accessible volcanic edifice located on Reykjanes Peninsula, SW Iceland. The photogrammetric analysis yielded a 20 cm resolution...
Article
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Volcanoes are traditionally considered isolated with an activity that is mostly independent of the surrounding, with few eruptions only (< 2%) associated with a tectonic earthquake trigger. Evidence is now increasing that volcanoes forming clusters of eruptive centers may simultaneously erupt, show unrest, or even shut-down activity. Using infrared...
Preprint
Full-text available
One year of deformation and seismicity prior to a volcanic eruption in March 2021 at an oblique plate boundary in Iceland created a unique opportunity to study the interaction between upwelling magma and geothermal processes. We apply poroelastic modelling to explain satellite geodetic data showing three uplift and subsidence cycles at the Svartsen...
Article
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Dome-building volcanoes often develop by intrusion and extrusion, recurrent destabilization and sector collapses, and renewed volcanic growth inside the collapse embayment. However, details of the structural architecture affiliated with renewed volcanic activity and the influences of regional structures remain poorly understood. Here, we analyze th...
Article
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Ground subsidence caused by natural or anthropogenic processes affects major urban areas worldwide. Sinkhole formation and infrastructure fractures have intensified in the federal capital of Maceió (Alagoas, Brazil) since early 2018, forcing authorities to relocate affected residents and place buildings under demolition. In this study, we present a...
Article
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The eruption frequency of geysers can be studied easily on the surface. However, details of the internal structure including possible water and gas filled chambers feeding eruptions and the driving mechanisms often remain elusive. We used a multidisciplinary network of seismometers, video cameras, water pressure sensors and one tiltmeter to study t...
Article
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Strong explosive eruptions of volcanoes throw out mixtures of gases and ash from high-pressure underground reservoirs. Investigating these subsurface reservoirs may help to forecast and characterize an eruption. In this study, we compare seismic tomography results with remote sensing and petrology data to identify deep and subaerial manifestations...
Article
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Continued post-collapse volcanic activity can cause the rise of a new edifice. However, details of such edifice rebirth have not been documented yet. Here, we present 7-decade-long photogrammetric data for Bezymianny volcano, Kamchatka, showing its evolution after the 1956 sector collapse. Edifice rebirth started with two lava domes originating at...
Article
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Vulcanian explosions are hazardous and are often spontaneous and direct observations are therefore challenging. Ebeko is an active volcano on Paramushir Island, northern Kuril Islands, showing characteristic Vulcanian-type activity. In 2019, we started a comprehensive survey using a combination of field station records and repeated unoccupied aircr...
Article
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Imaging growing lava domes has remained a great challenge in volcanology due to their inaccessibility and the severe hazard of collapse or explosion. Changes in surface movement, temperature, or lava viscosity are considered crucial data for hazard assessments at active lava domes and thus valuable study targets. Here, we present results from a ser...
Conference Paper
Geysers are hot springs whose frequency of water eruptions remain poorly understood. We setup a local broadband seismic network for one year at Strokkur geyser, Iceland, and developed an unprecedented catalog of 73,466 eruptions. We detected 50,135 single eruptions, but find that the geyser is also characterized by sets of up to six eruptions in qu...
Article
Full-text available
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 identifi...
Article
Full-text available
Geysers are hot springs whose frequency of water eruptions remain poorly understood. We setup a local broadband seismic network for one year at Strokkur geyser, Iceland, and developed an unprecedented catalog of 73,466 eruptions. We detected 50,135 single eruptions, but find that the geyser is also characterized by sets of up to six eruptions in qu...
Article
Full-text available
Flank instability and sector collapses, which pose major threats, are common on volcanic islands. On 22 Dec 2018, a sector collapse event occurred at Anak Krakatau volcano in the Sunda Strait, triggering a deadly tsunami. Here we use multiparametric ground-based and space-borne data to show that prior to its collapse, the volcano exhibited an eleva...
Article
In addition to enabling the physical processes of volcanic systems to be better understood, seismology has been also used to infer the complexity of magma pathways and plumbing systems in steep-sided andesitic and stratovolcanoes. However, in these volcanic environments, the application of seismic location methods is particularly challenging and sy...
Article
Full-text available
Enclosed topographic depressions are characteristic of karst landscapes on Earth. The developmental relationship between depression types, such as sinkholes (dolines) and uvalas, has been the subject of debate, mainly because the long developmental timescales in classical limestone karst settings impede direct observation. Here we characterize the...
Article
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Most of the world’s 1500 active volcanoes are not instrumentally monitored, resulting in deadly eruptions which can occur without observation of precursory activity. The new Sentinel missions are now providing freely available imagery with unprecedented spatial and temporal resolutions, with payloads allowing for a comprehensive monitoring of volca...
Article
Full-text available
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 identifi...
Article
Full-text available
Lava domes grow by extrusions and intrusions of viscous magma often initiating from a central volcanic vent, and they are frequently defining the source region of hazardous explosive eruptions and pyroclastic density currents. Thus, close monitoring of dome building processes is crucial, but often limited to low data resolution, hazardous access, a...
Article
Full-text available
During eruptive activity of andesitic stratovolcanoes, the extrusion of lava domes, their collapse and intermittent explosions are common volcanic hazards. Many lava domes grow in a preferred direction, in turn affecting the direction of lava flows and pyroclastic density currents. Access to active lava domes is difficult and hazardous, so detailed...
Article
Calderas represent morphological depressions several kilometers in diameter, and the unloaded crustal stresses they produce can form rapidly (e.g. Pinatubo, 1990) or slowly (e.g. Hawaii, 2018). Active calderas are known as sites of persistent magma intrusions, and yet the dynamics of their shallow plumbing system is not well constrained. We use sca...
Article
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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...
Conference Paper
Volcanoes are complex systems where multiple phases such as an edifice with cracks, fluids like water and magma and gases interact. Ruptures of solid rock as well as magma movement or bubble formation/ collapse are thought to produce seismic signals and announce or accompany a volcanic eruption. As seismic networks on volcanoes are mostly sparse, a...
Article
The existence of a causal link between large earthquakes and volcanic unrest is widely accepted. Recent observations have also revealed counterintuitive negative responses of volcanoes to large earthquakes, including decreased gas emissions and subsidence in volcanic areas. In order to explore the mechanisms that could simultaneously explain both t...
Article
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Fissure eruptions are associated with lava fountains which often show complex distinct venting activity in pulsating form, and the development of characteristic morphological features such as scoria or spatter cones. Most morphological studies are based on observations of old structures and are not related to direct observations and systematic reco...
Article
The summit region of steep volcanoes hosting lava domes often displays rapid geomorphologic and structural changes, which are important for monitoring the source region of hazards. Explosive crater excavation is often followed by new lava-dome growth, which is one of the most dynamic morphometric changes that may occur at volcanoes. However, detail...
Article
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The fall of hydrological base-level is long established as a driver of geomorphological change in both fluvial and karst systems, but few natural occurrences occur on timescales suitable for direct observation. Here we document the spatiotemporal development of fluvial and karstic landforms along the eastern coast of the hypersaline Dead Sea (at Gh...
Article
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Meaningful forecasting of the atmospheric concentration and ground accumulation of volcanic ash during explosive eruptions requires detailed knowledge of the eruption source parameters. However, due to the large uncertainties in observations and limitations of current models used to make inferences from these, monitoring an ongoing eruption and qua...
Article
Long-term and wide-area geodetic observations may allow identifying distinct postseismic deformation processes following large earthquakes, and thus can reveal fault behaviorand permit quantifying complexities in lithospheric rheology. In this paper, the first 7 years of GPS (Global Positioning System) displacement data following the 2008 Mw7.9 Wen...
Article
Full-text available
The growth of lava domes may cause gradual oversteepening and can lead to gravitational instability and eventual collapse to 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 involving high numbers of casualties. After the VEI 4...
Conference Paper
Full-text available
https://meetingorganizer.copernicus.org/EGU2018/EGU2018-10558.pdf Monitoring the growth of a lava flow field is of interest in densely populated areas where flows threaten roads, houses, other infrastructure and life. Monitoring usually relies on satellite data, ground-based GPS data and modelling of lava flows although they are also accompanied b...
Conference Paper
https://meetingorganizer.copernicus.org/EGU2018/EGU2018-9235.pdf Geothermally active systems are known to produce not only seismic events but also long-lasting, emergent signals referred to as tremor. Boiling in such a system is thought to be a viable generation mechanism for tremor that was adapted in other environments such as glaciers or volcan...
Article
Small-scale geomorphological changes that are associated with the formation, development, and activity of volcanic craters and eruptive vents are often challenging to characterize, as they may occur slowly over time, can be spatially localized, and difficult, or dangerous, to access. Using high-spatial and high-temporal resolution synthetic apertur...
Article
Geysers are local hydrothermal vents with periodic gas bubble driven explosions at the surface. Little is known, however, on the control on distribution, the dynamics and the geometry of the conduits of geysers. To better understand the link between the deep and surface expression at the Geysir geothermal field, Iceland, a detailed analysis of the...
Conference Paper
Full-text available
An effusive eruption in 2014/15 created a 85 km2 large lava flow field in a remote location in the Icelandic highlands. The lava flows did not threaten any settlements or paved roads but they were nevertheless interdisciplinarily monitored in detail. Images from satellites and aircraft, ground based video monitoring, GPS and seismic recordings allo...
Article
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Volcanoes commonly inflate or deflate during episodes of unrest or eruption. Continuum mechanics models that assume linear elastic deformation of the Earth’s crust are routinely used to invert the observed ground motions. The source(s) of deformation in such models are generally interpreted in terms of magma bodies or pathways, and thus form a basi...
Article
Dome building activity is common at many volcanoes and due to the gravitational instability, a dome represents one of the most hazardous volcanic phenomena. Shallow volcanic processes as well as rheological and structural changes of the dome affecting the fluid transport have been linked to transitions in eruptive activity. Also, hydrothermal alter...
Article
Dome-building volcanoes undergo rapid and profound topographic changes that are important to quantify for the purposes of hazard assessment. However, as hazardous lava domes often develop on high-altitude volcanoes that exhibit steep-sided topography, it is challenging to obtain direct field access and thus to analyze these morphological and struct...