Image velocimetry (IV) methods for measuring river flow have gained significant attention, with growing interest in satellite imagery applications. Despite this potential, challenges exist in identifying surface features critical for IV at the coarser spatial resolutions of satellite imagery (1-3 m px-1), compared to near-field imagery (e.g. uncrewed aerial systems). Here we evaluate IV performance across resolutions ranging from 0.02 to 3 m px-1, examining the surface features required for successful Satellite IV (SIV). Results indicate that IV accuracy depends on scene characteristics, with high-contrast, well-distributed surface tracers essential at coarse resolutions. Using suitable scenes with spatial resolutions up to 3 m px-1, discharge estimates are comparable to both original-resolution results and reference data (+/- 5%). This study demonstrates the viability of SIV using 1 second image pairs and, provided that sufficient trackable surface features are present, highlights its potential to support river discharge monitoring, particularly in remote or ungauged regions.

Early warning systems (EWS) are essential for reducing loss of life during the event of glacial lake outburst floods (GLOFs). However, the efficacy of EWS is contingent on factors including warning dissemination and community response. Despite the crucial role of EWS, there remains a paucity of studies examining community experiences with GLOF EWS, which are imperative for improving existing systems. Using surveys, key informant interviews and focus groups, this study offers insights into warning dissemination (including sources and channels of communication) and evacuation during recent (in 2019 and 2023) GLOF events in Lunana, Bhutan. Our analysis showed that environmental cues, such as unusually loud river sounds and ground vibrations, were the main sources of initial warning during past GLOF events. Mobile phone calls from friends and family also emerged as common channels for disseminating both initial and subsequent warning messages. Participants described evacuation during recent events as challenging and uncoordinated, with some people lacking pre-prepared essential items and facing difficult conditions at evacuation sites, including exposure to extreme cold and limited shelter. We first recommend strengthening existing GLOF EWS, making it more community-based, and diversifying communication response channels and sources, particularly through resilient mobile phone-based communication. Second, we recommend enhancing people's resilience to future GLOFs by expanding existing advocacy programmes toward building people's response capability, including regular mock drills, evacuation preparedness training, and fit-for-purpose, co-designed shelters at evacuation sites.

Scientific exploration of the UK and Ireland's subsurface has made important contributions to scholarship and prosperity for people and the planet, including economic growth, sustainable use of natural resources, storage of greenhouse gases, and inspiring curiosity about the Earth beneath our feet. This article outlines a vision for an array of seismological instruments spanning the UK and Ireland, UKI Array, augmented by other types of geophysical sensors, to maximise the value offered by existing equipment pools. The mission is to research natural phenomena and structure in the deep and shallow Earth, to solve problems concerning hazards and resources, to connect scientists to schools and the broader public, and thus to inspire a new generation to learn about geophysics. The vision was created through a community driven process of engagement and participation. This paper describes the concept and design of the UKI-Array; a companion paper discusses related opportunities and potential applications.

Hazard and risk from glacial lake outburst floods (GLOFs) in Bhutan have traditionally been assessed with limited consideration of the downstream exposure and vulnerability associated with individual lakes. However, exposure and vulnerability are key components of risk, and when explicitly attributed to each lake, can provide a more robust basis for prioritising hazard investigations and mitigation efforts. We modelled hypothetical GLOF scenarios for all glacial lakes with an area greater than 0.05 km(2) and located within 1 km of a glacier terminus. We then determined GLOF risk by explicitly accounting for downstream impacts using depth-velocity outputs at each exposed element affected by the simulated GLOF from each lake, as well as the vulnerability of the affected community. Our study shows that approximately > 11 000 people, > 2500 buildings, > 250 km of road, > 400 bridges and similar to 20 km(2) of farmland are exposed to potential GLOF in Bhutan. We classified lake130 (Thorthormi Tsho) as a very high hazard glacial lake in Bhutan, five lakes as high hazard and 22 other lakes as moderate hazard. Among these high hazard glacial lakes, three of them: lake93 (Phudung Tsho), lake251, and lake278 (Wonney Tsho) were not recognised as being high hazard in previous studies. Five downstream local government administrative units (LGUs) were associated with very high GLOF risk, while eight others are associated with high GLOF risk. Five of these very high and high risk LGUs had not been previously documented as being at risk from GLOF. Our study underscores the significance of integrating potential inundation mapping and downstream exposure data to define high hazard glacial lakes. We recommend strengthening and expanding the existing GLOF preparedness and risk mitigation efforts in Bhutan, particularly in the LGUs, as having high GLOF risk identified in this study, to reduce potential future damage and loss.

Rising global temperatures are driving widespread mass loss across the Himalaya, threatening water security for ~ 800 million downstream residents. While proglacial lake expansion accelerates glacier mass loss, retreat trends remain highly heterogeneous and poorly understood. Here, we quantify monthly terminus position changes from 2017 to 2024 for 74 large Himalayan lake-terminating glaciers using high-resolution PlanetScope imagery. We identify a highly synchronous seasonal retreat pattern across the entire Himalayan arc, peaking in late summer, independent of regional precipitation regimes. This seasonal cycle correlates strongly with peak seasonal air temperatures. In contrast to this consistent seasonal cycle, the magnitude interannual retreat on individual glaciers is highly episodic and stochastic, exhibiting no distinct geographic gradient. We suggest that these interannual trajectories are governed by localised sensitivity to climate and velocity fluctuations, rather than baseline glacier size or topography. Our findings demonstrate that while broad trends can be applied at macro-scales, applying linear frontal retreat rates or constant calving values is not appropriate for modelling the evolution of individual lake-terminating glaciers. Thus, incorporating non-linear, episodic retreat into models is vital for forecasting future water supplies and the risks posed by expanding proglacial lakes in specific catchments.

Rapid atmospheric warming, especially at high altitude, leads to alpine mountain landscapes becoming more vulnerable to mass movements and consequently unstable. For example, decay of mountain permafrost contributes to rockfalls, landslides and debris flows; glaciers are retreating and losing mass at alarming rates, exposing unstable slopes that are more likely to fail; and meltwater, which collects in a growing number of glacial lakes, can pose an outburst flood hazard, putting communities and infrastructure downstream at risk of damage. Occurring now with increasing frequency, these natural phenomena often combine to create complex multi-hazard cascades that are more powerful and have a greater reach down-valley than a singular isolated event. Combined with increasing population and infrastructure and economic activity in high mountains, there is therefore increased vulnerability of society to natural hazards in high alpine mountains, as has been experienced in the Swiss Alps in 2025, with the collapse of the Birch Glacier and the destruction of the alpine village of Blatten. Here, we review the physical processes of this recent event, their impact on environment, people and economy, and consider what can be learned from them.

Modelling complex mass flow processes, such as glacial lake outburst floods (GLOFs), for hazard and risk assessments requires extensive data and computational resources. Researchers often rely on low-resolution, open-access datasets and parameters derived from plausibility due to the difficulty involved in conducting direct measurements. This results in considerable uncertainties in forward modelling, potentially limiting the accuracy and reliability of predictions. To determine the sensitivity of the model outputs stemming from input parameter uncertainties in the forward modelling, we selected 9 parameters relevant to GLOF modelling and performed a total of 84 simulations, each representing a unique GLOF scenario in the physically based r.avaflow model. Our results indicate that mass-movement-triggered moraine-dammed GLOF modelling outputs are notably sensitive to five parameters, which are, in order of importance: (1) volume of mass movement entering the lake, (2) DEM datasets, (3) origin of mass movement, (4) entrainment coefficient, and (5) basal friction angle. The GLOF output parameter resulting from the volume of mass movement entering the lake has the greatest coefficient of variation (CV) (47 %), while the internal friction angle had the lowest CV (0.4 %). For future GLOF modelling, we recommend carefully considering the output uncertainty stemming from the sensitive input parameters identified here, some of which cannot be constrained before a GLOF and which must be addressed using statistical approaches.

Rockfalls are an efficient agent of landscape denudation and a crucial but poorly quantified component of the glacier debris supply cascade. Climate change is driving increased rockfall generation as rising air temperatures cause glacier thinning and thawing of permafrost. These processes alter rock slope stress profiles and thermal regimes, leading to greater sediment fluxes in cryospheric systems as landscapes adjust to ice-free conditions. We used repeat terrestrial laser scans combined with change detection during the summer of 2019 to quantify rockfall activity over a 0.7 km(2) rock wall area along the ablation zone lateral margins of the debris-covered Miage Glacier, Italy. We detected 2,581 rockfalls spanning eight orders of magnitude (10(-3)-10(4) m(3); median 0.021 m(3)) including an event of about 28 x 10(3) m(3) from a newly deglaciated slope. Large rockfalls (>= 10 m(3)) on lower, glacier-proximal slopes, whilst infrequent (<1% by count), achieved the most geomorphic work. Most (79%) rockfalls originated within <75 m above the glacier surface (mAG; representing 29% of the survey area); a boundary that corresponds with the Little Ice Age trimline. Some rockwalls exhibited a secondary zone of higher rockfall activity at about 125-150 mAG, revealing a second trimline with a millennial-scale signal of elevated rock damage possibly associated with ice surface dynamics during or immediately after the Younger Dryas Stadial. Modelled rockfall runout distances were determined in part by path topography: rockfalls originating from lower slopes travelled <100 m horizontally whilst those originating higher could travel up to 650 m, approaching the glacier centreline, reflecting a spatial differential in hillslope-glacier connectivity that will evolve concurrently with cryospheric degradation in the wider catchment. We show that detailed, short-term monitoring campaigns can yield novel and useful descriptions of mass movement fluxes and spatial patterns in alpine regions. Expanding our dataset by observing rock walls near the equilibrium line altitude could help bridge the longitudinal gap to existing high elevation inventories to provide a more unified picture of rockfall dynamics in deglaciating catchments.

Abstract. Modelling complex mass flow processes like glacial lake outburst floods (GLOFs) for hazard and risk assessments involves substantial data and computational resources, often leading researchers to use low-resolution, open-access data and parameters based on plausibility rather than direct measurement, which, although effective in back analysis, introduces significant uncertainties in forward modelling. To determine the sensitivity of the model outputs stemming from input parameter uncertainties in the forward modelling, we selected nine parameters relevant to GLOF modelling and performed a total of 78 simulations in the physically-based r.avaflow model. Our results indicate that GLOF modelling outputs are notably sensitive to six parameters, which are, in order of importance: 1) volume of mass movements entering lakes; 2) DEM datasets; 3) the origin of mass movements; 4) mesh size; 5) basal frictional angle; and 6) entrainment coefficient. The volume of mass movement impacting lakes has the greatest impact on GLOF output, with an average coefficient of variation (CV) = 47 %, while the internal friction angle had the least impact (CV=0.4 %). We recommend that future GLOF modelling should carefully consider the output uncertainty stemming from the sensitive input parameters identified here, some of which cannot be constrained before a GLOF and must be considered only statistically.

Glacial lake outburst floods (GLOFs) represent a major hazard and can result in significant loss of life. Globally, since 1990, the number and size of glacial lakes has grown rapidly along with downstream population, while socio-economic vulnerability has decreased. Nevertheless, contemporary exposure and vulnerability to GLOFs at the global scale has never been quantified. Here we show that 15 million people globally are exposed to impacts from potential GLOFs. Populations in High Mountains Asia (HMA) are the most exposed and on average live closest to glacial lakes with ~1 million people living within 10 km of a glacial lake. More than half of the globally exposed population are found in just four countries: India, Pakistan, Peru, and China. While HMA has the highest potential for GLOF impacts, we highlight the Andes as a region of concern, with similar potential for GLOF impacts to HMA but comparatively few published research studies.

High-magnitude mass flows can have a pervasive geomorphological legacy, yet the shortterm response of valley floors to such intense disturbances is poorly known and poses significant observational challenges in unstable landscapes. We combined satellite remote sensing, numerical modeling, and field observations to reconstruct the short-term geomorphological response of river channels directly affected by the 7 February 2021 ice-rock avalanche-debris flow in Chamoli district, Uttarakhand, India. The flow deposited 10.4 & PLUSMN; 1.6 Mm3 of sediment within the first 30 km and in places reset the channel floor to a zero-state condition, requiring complete fluvial re-establishment. In the 12 months post-event, 7.0 & PLUSMN; 1.5 Mm3 (67.2%) of the deposit volume was removed along a 30-km-long domain and the median erosion rate was 2.3 & PLUSMN; 1.1 m a-1. Most sediment was removed by pre-monsoon and monsoon river flows, which conveyed bedload waves traveling at 0.1-0.3 km day-1 and sustained order-of-magnitude increases in suspended sediment concentrations as far as 85 km from the event source. Our findings characterize a high-mountain fluvial cascade with a short relaxation time and high resilience to a high-magnitude geomorphological perturbation. This system response has wider implications, notably for water quality and downstream hydropower projects, which may be disrupted by elevated bedload and suspended sediment transport.

The frequency of large supraglacial landslides (rock avalanches) occurring in glacial environments is thought to be increasing due to feedbacks with climate warming and permafrost degradation. However, it is difficult to (i) test this; (ii) establish cause-effect relationships; and (iii) determine associated lag-times, due to both temporal and spatial biases in detection rates. Here we applied the Google Earth Engine supraglacial debris input detector (GERALDINE) to Glacier Bay National Park & Preserve (GLBA), Alaska. We find that the number of rock ava-lanches (RAs) has previously been underestimated by 53 %, with a bias in past detections towards large area RAs. In total, GLBA experienced 69 RAs during 1984-2020, with the highest frequency in the last three years. Of these, 58 % were deposited into the accumulation zone and then sequestered into the ice within two years. RA sources clustered spatially at high elevations and around certain peaks and ridges, predominantly at the boundary of modelled permafrost likelihood. They also clustered temporally, occurring mainly between May and September when air temperatures were high enough to initiate rock-permafrost degradation mechanisms. There was a chronic background debris supply from RAs, with at least one RA occurring in all but nine years; however, a debris rich period during 2012-2016 was driven by three large RAs delivering 44 % of all (1984-2020) debris (by area). Comparable investigation of slope-failures in other remote currently glaciated regions is lacking. If RA rates are similar elsewhere, especially the bias towards emplacement onto/into accumulation zones, their contribution to glacial sediment budgets has been globally underestimated.

Deglaciation due to atmospheric warming has led to the formation and expansion of numerous glacial lakes, especially in the eastern Himalaya. Many of these glacial lakes are susceptible to glacial lake outburst floods (GLOFs), which can cause far-reaching impacts on downstream infrastructure and livelihoods. This study is a comprehensive assessment of GLOF susceptibility, hazard, exposure, vulnerability, and risk for four potentially dangerous glacial lakes (Bechung Tsho, Raphstreng Tsho, Thorthomi Tsho, and Lugge Tsho) located in the Lunana glacier complex of the Phochu basin in Bhutan. Exposure and risk assessments were based on modelled GLOF hydrodynamics, infrastructure data, population and housing census data. Among the four glacial lakes, Thorthormi Tsho and Lugge Tsho are relatively more susceptible to outburst floods than Raphstreng Tsho and Bechung Tsho. Outflow flood volumes from these lakes range between 6 x 105 and 3 x 108 m3 which can potentially impact over 16,000 people, two hydropower projects, numerous other infrastructures, and agricul-tural land up to 150 km downstream of the lakes. The GLOF exposed elements are largely in Punakha and Wangdue Phodrang districts, which are located 90 and 100 km downstream of the Lunana glacier complex respectively. Among 17 subdistrict blocks within the basin, one (Lunana) lies in a very high GLOF risk area, while 9 others are in the high GLOF risk zone. The study highlights the importance of multi-source data in improving the knowledge of downstream GLOF risk and serves as a base for improving GLOF risk reduction strategies in high mountain regions.

Between 2000 and 2020, the potential for glacial lake outburst floods (GLOFs) and the exposure and vulnerability of downstream populations to them, have changed across the globe. The impact of these changes on the danger posed by GLOFs, as well as the relative importance of each factor, remains contentious, making the implementation of appropriate management and risk reduction strategies challenging. Here we show that globally, since 2000, the number of people exposed to GLOF impacts has increased by 3.2 million (27% increase), to a total of 15 million people as of 2020. The largest increase in GLOF danger occurred across the Andes, while only nine countries experienced a decrease in GLOF danger, most notably in Nepal and Kyrgyzstan. Importantly, contrary to the notion presented in current research, we find the changes in the threat from GLOFs have not been universally driven by either lake change, exposed population, or vulnerability; instead, the primary driver varies both at regional- and national-scales. Further, we show that vulnerability to GLOF impacts has declined almost everywhere, but this decline has been insufficient to offset the combined growth in the number and area of glacial lakes and downstream exposure. We highlight the Andes as a global hotspot for high, and rapidly increasing, contemporary GLOF danger, and suggest the region be targeted for further research. Critically, we show that mitigating GLOF impacts will require bespoke solutions depending on the relative impact of lake conditions, exposure and vulnerability on changing GLOF danger.

Shallow landslides are a major natural hazard in the UK, causing more than £10M of economic losses annually and posing clear threats to life. Rainfall is an essential control on shallow landslide risk, but network operators currently use generic ‘on-off’ warnings based on localised rainfall intensity and duration, giving no strategic information about where the hazard is highest or evolving the quickest for any particular rainfall event. A new procedure has been developed to automatically evaluate the stability of slopes across regional scales in response to spatially and temporally variable rainfall events, quantified by rainfall radar data updated every 5 minutes. A physically based programme, TRIGRS, was used to assess the factor of safety (FS) of slopes in response to spatially variable rainfall radar data. The dynamic FS maps produced provide early warning and informed decision-making for the management of regional to national-scale infrastructures. Sensitivity analyses were performed to investigate the effect of the soil thickness, shear strength parameters, hydraulic parameters, and antecedent rainfall on the FS during a known landslide-causing rainfall event in Glen Croe, western Scotland. The results specifically highlight the slope where the failure occurred as a high-hazard area 1.0 hour before the event. The dynamic FS maps were particularly sensitive to soil thickness, the saturated hydraulic diffusivity and Gardner’s unsaturated conductivity, suggesting that more effort should be put into improving network-scale datasets of these parameters. Ultimately, the ability developed here to account for near-real-time spatial variabilities in rainfall data and slope responses measured through the relative change in FS values provides a potentially transformative new tool for network operators to proactively mitigate the impacts of specific storms as they develop.

Our study looks at how to use the landform called “molard” as a marker of permafrost degradation in arctic, sub-arctic and mountain environments. Molards in permafrost terrains are mound of loose debris that derive from the degradation of blocks of ice-rich sediments mobilised by a landslide. Such molards cannot form without ground ice, which cements the source material, allowing it to behave like solid during transport. Once the ground ice has thawed, its cementing action is lost, inducing collapse of the material into molards. We reconstruct the permafrost, geological, geographical settings of more than 50 landslides characterised by molards, compiling data available in the literature. We apply quantitative terrain analysis using high-resolution DEMs to describe, quantify and compare their topographic characteristics, morphometry, dynamics, and molards distribution and density. Our results show that landslides with molards can occur in terrains characterised by various permafrost distribution, from continuous to isolated. These landslides show a variety of morphological and morphometric characteristics, source materials often composed of loose debris or rheologically weak bedrock, and their molard distribution reflects the dynamics of the landslide. In this study, we show that molards are an indicator landform of permafrost degradation under different permafrost, geomorphological and geological conditions, and that they can be used to decipher landslide dynamics in cold environments. Acknowledgements: This study is funded by the Agence Nationale de la Recherche in the framework of the project ANR-19-CE01-0010 PERMOLARDS

On 22 March 2021, an approximately 50 Mm3 icerock avalanche occurred from 6500 m a.s.l. in the Sedongpu basin, southeastern Tibet. The avalanche transformed into a highly mobile mass flow which temporarily blocked the Yarlung Tsangpo river. The avalanche flow lasted ∼ 5 min and produced substantial geomorphological reworking. This event, and previous ones from the basin, occurred concurrently with, or shortly after, positive seasonal air temperature anomalies. The occurrence of future large mass flows from the basin cannot be ruled out, and their impacts must be carefully considered given implications for sustainable hydropower and associated socioeconomic development in the region.

Catastrophic mass flows originating from the mountain cryosphere can cause widespread loss of life, destruction of property, and significant geomorphological reworking along flow paths. Based on in-situ field investigations, high-resolution satellite imagery, digital elevation models (DEMs), seismic records, and meteorological data, we present the process reconstruction, triggering mechanism, and downstream implications of a 50 Mm3 ice-rock avalanche and mass flow that originated from 6500 m asl of the Sedongpu basin in southeastern Tibet on 22 March 2021.The avalanche transformed into a highly mobile mass flow which temporarily blocked the Yarlung Tsangpo river. The avalanche flow lasted ~5 minutes and produced substantial geomorphological reworking. This event, and previous ones from the basin (a total of ~50 Mm3 on October 2017 and into 2018 occurring close to the 2021 ice-rock avalanche source region, and the detachment of the low-angle tongue of Sedongpu Glacier in two separate events with a total of ~130 Mm3 on 17/18 October and 29 October 2018), occurred concurrently with, or shortly after periods characterized by record positive air temperature anomalies, which may have contributed to instability of the mountain cryosphere. The occurrence of future large mass flows from the basin under anthropogenic warming cannot be ruled out, and their likelihood and impacts must be carefully considered given potential risks to life and implications for sustainable hydropower and associated socioeconomic development along the Brahmaputra.

Blue ice is found in areas of Antarctica where katabatic winds, focussed by steep surface slopes or by topography around nunataks, cause enhanced surface ablation. This process draws up deeper, older ice to the ice sheet surface, often bringing with it englacial sediment. Prevailing theories for dynamically stable moraine surfaces in East Antarctica suggest that: (i) it is this material, once concentrated, that forms blue-ice moraines (BIM), (ii) that the moraine formation can be dated using cosmogenic isotope approaches, and that, (iii) since we expect an increase in exposure age moving away from the ice margin towards bedrock, dating across the moraine can be used to constrain ice-sheet history. To test this lateral accretion model for BIM formation we visited Patriot, Marble and Independence Hills in the southern Heritage Range, West Antarctica. Detailed field surveys of surface form, sediment and moraine dynamics were combined with geophysical surveys of the englacial structure of the moraines and cosmogenic nuclide analysis of surface clasts. Results suggest sediment is supplied mainly by basal entrainment, supplemented by debris-covered valley glaciers transferring material onto the ice sheet surface, direct deposition from rock-fall and slope processes from nunataks. We find that once sediment coalesces in BIM, significant reworking occurs through differential ablation, slope and periglacial processes. We bring these processes together in a conceptual model, concluding that many BIM in West Antarctica are dynamic and, whilst they persist through glacial cycles, they do not always neatly record ice sheet retreat patterns since linear distance from the ice margin does not always relate to increased clast exposure age. Understanding the dynamic processes involved in moraine formation is critical to the effective interpretation of the typically large scatter of cosmogenic nuclide exposure ages, opening a deep window into the million-year history of the West Antarctic Ice Sheet.

Rapid shallow landslides are a significant hillslope erosion mechanism and limited understanding of their initiation and development results in persistent risk to infrastructure. Here, we analyse the slope above the strategic A83 Rest and be Thankful road in the west of Scotland. An inventory of 70 landslides (2003–2020) shows three types of shallow landslide, debris flows, creep deformation, and debris falls. Debris flows dominate and account for 5,350 m3 (98%) of shallow-landslide source volume across the site. We use novel time-lapse vector tracking to detect and quantify slope instabilities, whilst seismometers demonstrate the potential for live detection and location of debris flows. Using on-slope rainfall data, we show that shallow-landslides are typically triggered by abrupt changes in the rainfall trend, characterised by high-intensity, long duration rainstorms, sometimes part of larger seasonal rainfall changes. We derive empirical antecedent precipitation (>62 mm) and intensity-duration (>10 h) thresholds over which shallow-landslides occur. Analysis shows the new thresholds are more effective at raising hazard alerts than the current management plan. The low-cost sensors provide vital notification of increasing hazard, the initiation of movement, and final failure. This approach offers considerable advances to support operational decision-making for infrastructure threatened by complex slope hazards.