Fabian Thomas Walter

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Walter

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Fabian Thomas

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0000-0001-6952-2761

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Publications 1 - 10 of 36

Seismic Constraints on Damage Growth Within an Unstable Hanging Glacier
Chmiel, Malgorzata; Walter, Fabian Thomas; Pralong, Antoine; et al. (2023)
Geophysical Research Letters
Forecasting hanging glacier instabilities remain challenging as sensing technology focusing on the ice surface fails to detect englacial damage leading to large-scale failure. Here, we combine icequake cluster analysis with coda wave interferometry constraining damage growth on Switzerland's Eiger hanging glacier before a 15,000 m3 break-off event. The method focuses on icequake migration within clusters rather than previously proposed “event counting.” Results show that one cluster originated from the glacier front and migrated by 13.9(±1.2) m within 5 weeks before the break-off event. The corresponding crevasse extension separates unstable and stable ice masses. We use the measured source displacement for damage parametrization and find a 90% agreement between an analytical model based on damage mechanics and frontal flow velocities measured with an interferometric radar. Our analysis provides observational constraints for damage growth, which to date is primarily a theoretical concept for modeling englacial fractures.
Thinning leads to calving-style changes at Bowdoin Glacier, Greenland
van Dongen, Eef; Jouvet, Guillaume; Sugiyama, Shin; et al. (2021)
The Cryosphere
Ice mass loss from the Greenland ice sheet is the largest single contributor to sea level rise in the 21st century. The mass loss rate has accelerated in recent decades mainly due to thinning and retreat of its outlet glaciers. The diverse calving mechanisms responsible for tidewater glacier retreat are not fully understood yet. Since a tidewater glacier’s sensitivity to external forcings depends on its calving style, detailed insight into calving processes is necessary to improve projections of ice sheet mass loss by calving. As tidewater glaciers are mostly thinning, their calving styles are expected to change. Here, we study calving behaviour changes under a thinning regime at Bowdoin Glacier, north-western Greenland, by combining field and remote-sensing data from 2015 to 2019. Previous studies showed that major calving events in 2015 and 2017 were driven by hydro-fracturing and melt-undercutting. New observations from uncrewed aerial vehicle (UAV) imagery and a GPS network installed at the calving front in 2019 suggest ungrounding and buoyant calving have recently occurred as they show (1) increasing tidal modulation of vertical motion compared to previous years, (2) absence of a surface crevasse prior to calving, and (3) uplift and horizontal surface compression prior to calving. Furthermore, an inventory of calving events from 2015 to 2019 based on satellite imagery provides additional support for a change towards buoyant calving since it shows an increasing occurrence of calving events outside of the melt season. The observed change in calving style could lead to a possible retreat of the terminus, which has been stable since 2013. We therefore highlight the need for high-resolution monitoring to detect changing calving styles and numerical models that cover the full spectrum of calving mechanisms to improve projections of ice sheet mass loss by calving.
Observing avalanche dynamics with Distributed Acoustic Sensing
Fichtner, Andreas; Edme, Pascal; Paitz, Patrick; et al. (2021)
EGUsphere
Avalanche research requires comprehensive measurements of sudden and rapid snow mass movement that is hard to predict. Automatic cameras, radar and infrasound sensors provide valuable observations of avalanche structure and dynamic parameters, such as velocity. Recently, seismic sensors have also gained popularity, because they can monitor avalanche activity over larger spatial scales. Moreover, seismic signals elucidate rheological properties, which can be used to distinguish different types of avalanches and flow regimes. To date, however, seismic instrumentation in avalanche terrain is sparse. This limits the spatial resolution of avalanche details, needed to characterise flow regimes and maximise detection accuracy for avalanche warning. As an alternative to conventional seismic instrumentation, we propose Distributed Acoustic Sensing (DAS) to measure avalanche-induced ground motion. DAS is based on fibre-optic technology, which has previously been used already for environmental monitoring, e.g., of snow avalanches. Thanks to recent technological advances, modern DAS interrogators allow us to measure dynamic strain along a fibre-optic cable with unprecedented temporal and spatial resolution. It therefore becomes possible to record seismic signals along many kilometres of fibre-optic cables, with a spatial resolution of a few metres, thereby creating large arrays of seismic receivers. We test this approach at an avalanche test site in the Valleé de la Sionne, in the Swiss Alps, using an existing 700 m long fibre-optic cable that is permanently installed underground for the purpose of data transfer of other, independent avalanche measurements. During winter 2020/2021, we recorded numerous snow avalanches, including several which reached the valley bottom, travelling directly over the cable during runout. The DAS recordings show clear seismic signatures revealing individual flow surges and various phases/modes that may be associated with roll waves and avalanche arrest. We compare our observations to state-of-the-art radar and seismic measurements which ideally complement the DAS data. Our initial analysis highlights the suitability of DAS-based monitoring and research for avalanches and other hazardous granular flows. Moreover, the clear detectability of avalanche signals using existing fibre-optic infrastructure of telecommunication networks opens the opportunity for unrivalled warning capabilities in Alpine environments.
Capturing Glacier-Wide Cryoseismicity With Distributed Acoustic Sensing
Walter, Fabian Thomas; Paitz, Patrick; Fichtner, Andreas; et al. (2021)
EGUsphere
Over the past 1-2 decades, seismological measurements have provided new and unique insights into glacier and ice sheet dynamics. At the same time, sensor coverage is typically limited in harsh glacial environments with littile or no access. Turning kilometer-long fiber optic cables placed on the Earth’s surface into thousands of seismic sensors, Distributed Acoustic Sensing (DAS) may overcome the limitation of sensor coverage in the cryosphere. First DAS applications on the Greenland and Antarctic ice sheets and on Alpine glacier ice have highlighted the technique’s superiority. Signals of natural and man-made seismic sources can be resolved with an unrivaled level of detail. This offers glaciologists new perspectives to interpret their seismograms in terms of ice structure, basal boundary conditions and source locations. However, previous studies employed only relatively small network scales with a point-like borehole deployment or < 1 km cable aperture at the ice surface. Here we present a DAS installation, which aims to cover the majority of an Alpine glacier catchment: For one month in summer 2020 we deployed a 9 km long fiber optic cable on Rhonegletscher, Switzerland, and gathered continuous DAS data. The cable followed the glacier’s central flow line starting in the lowest kilometer of the ablation zone and extending well into the accumulation area. Even for a relatively small mountain glacier such as Rhonegletscher, cable deployment was a considerable logistical challenge. However, initial data analysis illustrates the benefit compared to conventional cryoseismological instrumentation: DAS measurements capture ground deformation over many octaves, including typical high-frequency englacial sources (10s to 100s of Hz) related to crevasse formation and basal sliding as well as long period signals (10s to 100s of seconds) of ice deformation. Depending on the presence of a snow cover, DAS records contain strong environmental noise (wind, meltwater flow, precipitation) and thus exhibit lower signal-to-noise ratios compared to conventional on-ice seismic installations. This is nevertheless outweighed by the advantage of monitoring ground unrest and ice deformation of nearly an entire glacier. We present a first compilation of signal and noise records and discuss future directions to leverage DAS data sets in glaciological research.
Immediate Ice Stream and Shear Margin Response to Calving at Sermeq Kujalleq in Kangia, Greenland
Wehrlé , Adrien; Rousseau , Hugo; Lüthi , Martin P.; et al. (2025)
Geophysical Research Letters
The sensitivity of Greenland outlet glaciers to short-term flow disturbances lacks observations to be well constrained in numerical models. Specifically, sudden gigaton-scale calving events regularly occurring at major Greenland outlet glaciers like Sermeq Kujalleq in Kangia (SKK; also known as Jakobshavn Isbræ) are known to perturb background ice flow in complex ways. Here, we present high-rate terrestrial radar observations and show an immediate step-wise acceleration of SKK ice stream up to 11 km from its terminus, one of the longest immediate calving responses so far reported in Greenland. Focusing on SKK's shear margins, we detected large instantaneous increases in deformation rates in its most crevassed section, which, together with the along-flow response, provide evidence for strong lateral and longitudinal coupling of the ice stream. Using a simplified theoretical framework, we show that the loss of lateral drag due to calving is a key component of such a widespread calving response.
Monitoring Glacier Dynamics with a Low-Cost Integrated GNSS-Seismic Platform
Soja, Benedikt; Walter, Fabian Thomas; Binder, Daniel; et al. (2025)
Monitoring glacier dynamics across multiple timescales is essential for advancing our understanding of cryospheric responses to climate change. To address this challenge, the HERMIT project (High-Altitude and Polar Research through Integrated GNSS and Seismic Technology), supported by the Swiss Polar Institute, is developing a compact and affordable platform that integrates Global Navigation Satellite System (GNSS) and seismic sensors for deployment in high-altitude and polar environments. The HERMIT system combines millimeter-precision GNSS positioning with three-component seismic measurements in a modular package designed for harsh conditions. By relying on affordable yet highly performant components, HERMIT seeks to enable denser and more versatile monitoring networks, with applications ranging from glacier dynamics to paraglacial slope stability. This contribution presents the development of the platform and first results from a 2025 field campaign on the Rhone Glacier (Switzerland), where ten HERMIT stations were installed to examine the temporal and spatial interactions between basal sliding and subglacial hydrology during the melt season.
Calving-driven fjord dynamics resolved by seafloor fibre sensing
Gräff, Dominik; Lipovsky, Bradley Paul; Vieli, Andreas; et al. (2025)
Nature
Interactions between melting ice and a warming ocean drive the present-day retreat of tidewater glaciers of Greenland, with consequences for both sea level rise and the global climate system. Controlling glacier frontal ablation, these ice–ocean interactions involve chains of small-scale processes that link glacier calving—the detachment of icebergs—and submarine melt to the broader fjord dynamics. However, understanding these processes remains limited, in large part due to the challenge of making targeted observations in hazardous environments near calving fronts with sufficient temporal and spatial resolution. Here we show that iceberg calving can act as a submarine melt amplifier through excitation of transient internal waves. Our observations are based on front-proximal submarine fibre sensing of the iceberg calving process chain. In this chain, calving initiates with persistent ice fracturing that coalesces into iceberg detachment, which in turn excites local tsunamis, internal gravity waves and transient currents at the ice front before the icebergs eventually decay into fragments. Our observations show previously unknown pathways in which tidewater glaciers interact with a warming ocean and help close the ice front ablation budget, which current models struggle to do. These insights provide new process-scale understanding pertinent to retreating tidewater glaciers around the globe.
Toward automatic avalanche detection with Distributed-Acoustic-Sensing leveraging telecommunication infrastructure
Edme, Pascal; Paitz, Patrick; Fichtner, Andreas; et al. (2024)
EGUsphere
Snow avalanches pose significant threats in alpine regions, leading to considerable human and economic losses. The ability to promptly identify the locations and timing of avalanche events is essential for effective prediction and risk mitigation. Conventional automatic avalanche detection systems typically rely on radars and/or seismo-acoustic sensors. While these systems operate successfully regardless of weather conditions, their coverage is often confined to a single slope or a small catchment (distances < 3 km). In our study, we demonstrate the feasibility of detecting snow avalanches using Distributed Acoustic Sensing (DAS) through existing fiber-optic telecommunication cables. Our pilot experiment, conducted over the 2021/2022 winter, involved a 10km long fiber-optic dark cable running parallel to the Flüelapass road in the eastern Swiss Alps close to Davos. The DAS data reveal distinct evidence of numerous dry- and wet-snow avalanches, even when they do not reach the cable, as confirmed photographically. We show that avalanches can be distinguished from other signals (e.g., vehicle traffic) using a frequency-dependent STA/LTA attribute, enabling their detection with high spatiotemporal resolution. These findings pave the way for cost-effective and near-real-time avalanche monitoring over extensive distances, leveraging existing fiber-optic infrastructure.
Brief communication: An autonomous UAV for catchment-wide monitoring of a debris flow torrent
Walter, Fabian Thomas; Hodel, Elias; Mannerfelt, Erik S.; et al. (2022)
Natural Hazards and Earth System Sciences
Debris flows threaten communities in mountain regions worldwide. Combining modern photogrammetric processing with autonomous unoccupied aerial vehicle (UAV) flights at sub-weekly intervals allows mapping of sediment dynamics in a debris flow catchment. This provides important information for sediment disposition that pre-conditions the catchment for debris flow occurrence. At the Illgraben debris flow catchment in Switzerland, our autonomous UAV launched nearly 50 times in the snow-free periods in 2019-2021 with typical flight intervals of 2-4 d, producing 350-400 images every flight. The observed terrain changes resulting from debris flows exhibit preferred locations of erosion and deposition, including memory effects as previously deposited material is preferentially removed during subsequent debris flows. Such data are critical for the validation of geomorphological process models. Given the remote terrain, the mapped short-term erosion and deposition structures are difficult to obtain with conventional measurements. The proposed method thus fills an observational gap, which ground-based monitoring and satellite-based remote sensing cannot fill as a result of limited access, reaction time, spatial resolution, or involved costs.
In-situ Measurements of Stick-Slip Motion at the Bed of an Alpine Glacier
Gräff, Dominik; Walter, Fabian Thomas (2018)
Until recently, observations of sudden frictional processes at the bed of glaciers were limited to monitoring form the glacier surface. We study these processes causing stick-slip motion with a new approach that was applied the first time in a field campaign in summer 2018: We carried out the first in-situ measurements of an active seismogenic fault at a bi- material interface beneath a glacier. Enabled by guided hot water drilling, we targeted borehole experiments to specific glacier bed regions where spatially limited microseismic stick-slip sliding happens and combine them with the recordings of a high-densitiy network of seismometers at the glacier surface. From the various measurements we can determine the subglacial water- and thus pore pressure evolution and its effect on the fault stability. Futhermore the in-situ borehole measurements enable us to study material properties such as the till and ice characteristics within the stick-slip asperities and compare them to off-site reference measurements in seimically non-active regions of the glacier bed. Finally from acceleration, ice deformation measurements, and borehole camera videos from the glacier bed, we can estimate the amount of aseismic and co-seismic sliding, which cannot be obtained remotely from the ice surface. Summed up, with our in-situ measurements of an seismogenically active strike-slip fault beneath an alpine glacier, we open a unique posibility for studying seismogenic stick-slip motion at a bi-material interface in a natural environment.

Publications 1 - 10 of 36

Fabian Thomas Walter

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