British Geological Survey

Abstract Pyroclastic density currents (PDCs) are gravity currents that frequently form during explosive volcanic eruptions. These ground‐hugging density currents consist of high‐temperature mixtures of pyroclasts (e.g., ash, pumice), lithics, and gas. They have the potential to generate co‐PDC plumes, which detach from the underlying PDC as they buoyantly rise into the atmosphere. Co‐PDC plumes, composed of fine‐grained ash particles and hot gas, can reach heights of tens of kilometers, potentially dispersing large volumes of ash over continental scale areas, impacting the environment, and posing a risk to aviation. Owing to their formation mechanism, co‐PDCs have unique characteristics, such as fine particle sizes (e.g., <90 μm) and a high‐aspect ratio, irregular‐shaped, source geometry. Here, we consider how the release of ash into the atmosphere from a co‐PDC plume may differ to that from a typical Plinian eruption column, and the implications for operational modeling of the resulting ash cloud for the provision of advice to the aviation industry. We use the Numerical Atmospheric‐Dispersion Modelling Environment (NAME), which is used by the London Volcanic Ash Advisory Centre. We performed a sensitivity analysis to determine which co‐PDC source parameters are important for modeling the associated ash clouds. We show that variations in the source geometry, that is, the total area and aspect ratio, have a minor impact after the first ∼6 hr in the atmosphere.

The Indo-Gangetic Basin (IGB) is a large trans-boundary aquifer system encompassing the alluvial Indo-Gangetic Plain (IGP) as well as the southern parts of the Indus, Ganges and the Rajasthan Inland drainage basin, supporting a large agrarian population. In recent decades, expansion of groundwater irrigation through shallow-medium tubewells (70m) in the Rajasthan Inland drainage basin and the Indus basin and shallow-medium tubewells in the Ganges basin during this period. Post-2010, we show that groundwater levels have shifted from a declining trend to a more stable trend in the Ganges basin overall. Nevertheless, in the north-west Ganges basin, Indus basin and Rajasthan inland drainage basin, despite experiencing increased rainfall and an extended multi-annual wet anomaly, groundwater levels continue to decline post-2010. The rate of decline has stabilised in the Indus basin but continues to increase in Rajasthan Inland drainage basin. In the Central Ganges basin, the trend shifts from a declining trend pre-2010 to a positive trend with rising groundwater levels. Groundwater levels in south-western parts of the Ganges basin that were stable between 1998-2010 now show a rising trend. The Minor Irrigation Census indicates no significant increase in the number of shallow–medium and deep tubewells across the Indo-Gangetic Basin between 2014 and 2017. However, land use inventory data for 2014–2024 show an expansion of cropped area in the Rajasthan Inland Drainage and Indus basins, along with an overall increase in the area sown more than once across the IGB. These patterns suggest that changes in agricultural practices, crop types and cropping patterns across sub-basins are contributing to long-term groundwater trends and variability in the region. Our results reveal pronounced, scale-dependent heterogeneity in the response of the IGB to climatic, environmental and anthropogenic stressors.

Arctic rivers can act as a route for methane (CH4) to enter the atmosphere from landscapes impacted by ongoing permafrost thaw and climate warming. Thermokarst erosion and thaw induced mass-wasting are underway across the Arctic, increasing organic matter supply to river systems that could act as substrates for methanogenesis. In addition, warming of air and water temperatures could increase methanogenesis in analogy with responses seen in other aquatic, non-fluvial settings. Despite this recognition, the source, drivers and sensitivity of Arctic river CH4 emissions to geomorphic and climate change remain obscured.Here, we apply novel sampling methods and use radiocarbon and a multi-stable isotope approach to quantify CH4 emissions, age and source in Arctic rivers of the Mackenzie River Basin across two field campaigns in winter 2023 and summer 2024. Despite evidence for CH4 oxidation, we find that sediment-laden Arctic Rivers are hotspots of CH4 release, both downstream of sites of increased thaw-driven mass wasting and within large channels of the river delta. We find that river CH4 emissions increase by three times in the summer season compared to the winter, sustained by an aged, but higher quality organic matter substrate. A detailed reach-scale CH4 budget reveals a high apparent temperature sensitivity of river CH4 emissions that has not been recognized before, suggesting that ongoing warming, permafrost thaw and increased erosion will increase river CH4 emissions in the Arctic.

Groundwater is a resilient resource that is vital for local water supplies and maintaining baseflow in rivers and streams, particularly during low flow periods. Due to global climate change, the occurrence of meteorological drought is increasing in both frequency and severity, causing or amplifying water scarcity events even in areas considered water rich, like Scotland. While groundwater is generally more resilient to drought than surface water sources, the specific impacts on the resilience of the resource is influenced by local hydrogeology, geography, and climate. To evaluate differences in groundwater response between sites and assess vulnerability and resilience at varying timescales, it is important have standardised parameters to evaluate.The Standardised Groundwater Index (SGI) is a normalisation procedure that can be applied to groundwater level data from observation boreholes to compare drought response more easily between locations. To standardise groundwater data, typical methods use a specific probability distribution which is unlikely to represent variability over large, diverse regions across different seasons or empirical probabilities requiring large sample sizes. Here, in the transformation to standardised units, probability distributions are optimised using Akaike Information Criterion (AIC) to select the most appropriate distribution for each season at each location. Incorporating model fit statistics for each time and site reduces uncertainty in calculations, particularly at the tails of the distribution which is vital for drought studies.Groundwater storage and memory is evaluated across 33 sites in Scotland through the autocorrelation function of the SGI time series and correlated with Standardised Precipitation Evapotranspiration Index (SPEI) to evaluate the time scale of groundwater drought propagation at each location and better characterise storage properties for aquifers of different lithologies and dominant flow types (e.g. intergranular, fractured). Autocorrelation lengths of less than 5 months are common in the fractured flow systems compared to lag periods of 9 months or greater in more highly transmissive aquifers likely dominated by intergranular flow.Hierarchical cluster analysis of the SGI time series provides an added line of evidence to the differential response between hydrogeological units and to identify areas where local changes in geology, structure, or surface water connections could be influencing groundwater response. Characterisation of the groundwater drought response can reveal areas of greater groundwater resilience and provide water managers better metrics to assess the spatiotemporal controls of groundwater drought propagation, along with modelling the timing and magnitude of seasonal groundwater minima.

The Strathmore Basin is an extensive Silurian-Devonian basin which spans the entire width of Scotland. This basin has had a long and complex tectonic history, including periods of significant volcanic activity, faulting, basin folding, and several movements along the basin-bounding Highland Boundary Fault. Today, the basin is largely covered by substantial glacial deposits; bedrock exposure is limited.Some areas of the basin were last mapped in the 1880’s (i.e., before aerial photography, and nearly a century before the theory of plate tectonics). Progressive mapping of adjacent map sheets up to the 1970’s has led to mismatches at sheet boundaries, significant inconsistencies in structural interpretation, and irregularities in stratigraphic relationships. Addressing these legacy issues in geological maps is critical for ensuring suitability for 21st century applications; these data are used to inform the management of the regional aquifer within the Devonian sandstones, and for evaluation of potential geothermal energy resources.A novel basin-wide approach has been taken to revise the geological mapping to improve map quality and consistency across the Strathmore Basin. This has involved a range of techniques, including digital terrane analysis, targeted field visits, the integration of published geochronological data, and the compilation of basin-wide datasets of over 4,000 structural measurements and more than 20,000 observation points from multiple BGS data sources. This approach has allowed for a new large-scale structural interpretation of the fold and fault systems, particularly related to the Highland Boundary Fault, as well as a new understanding of key stratigraphic markers and a more coherent representation of the geology across the basin. This approach highlights the value of using both modern and historic datasets, and crucially, revisiting targeted outcrops in the field.As traditional survey styles become less affordable, and the need for seamless maps more acute, regional approaches provide an important methodology, helping to maximise the value of existing data and targeting areas for new data collection. Understanding these strengths and limitations is essential for the future of resurvey, especially in countries such as the UK with a long surveying history and high demand for accurate and consistent geological information to manage energy, water, and mineral resources.

Tropical Andean glaciers provide an important flux of freshwater to communities living both in high-altitude Cordillera and population centres downstream in countries such as Peru and Bolivia. Glacier recession threatens the sustainability of these water resources, and accurate modelling of future glacier behaviour is required to manage water stress in the region. These models must capture all processes contributing significantly to overall glacier mass budgets. Here we examine supraglacial pond and ice cliff development on three clean-ice glaciers in the Cordillera Vilcanota, Peru and their overall contribution to glacier mass balance. Whilst such features are common and well-studied on debris-covered glaciers, their development on debris-free glaciers has not been examined in detail. We use high-resolution contemporary and historical satellite imagery and repeat drone surveys to examine surface structure and geometry change over three glaciers during 1977–2024. We show how cliff and pond formation is driven by aspect-dependent surface melt of crevasse walls. These features act as ice loss hotspots, which enhance glacier net mass loss by ∼10% despite accounting for

Coastal western Scotland lies directly under the core of the modern North Atlantic winter storm track, yet long winter-sensitive terrestrial archives of storminess are rare. We present a new 2,500-year (~600 BCE–1981 CE), high-resolution speleothem record from a sea cave on the Isle of Islay, a uniquely winter-dominated site that captures past changes in storm activity, moisture pathways, and North Atlantic hydroclimate. This multiproxy record, comprising stable isotopes (δ¹⁸O, δ¹³C) and marine aerosol-related elements (Na, S), reflects the combined influence of Atlantic westerlies, sea-spray transport, and seasonal recharge.Islay δ¹⁸O and δ¹³C reflect changes in the pathway and hydrological processing of Atlantic winter moisture. Lower values occur during intervals with enhanced effective recharge and stronger Atlantic influence, such as the Roman and Medieval Warm Periods. In contrast, higher values reflect reduced recharge and colder circulation regimes during the Dark Age Cold Period and Little Ice Age. Sodium concentrations rise during these cold intervals, indicating enhanced sea-spray delivery and intensified winter storminess, while sulphur reflects mixed sea-salt and non-sea-salt marine aerosol inputs.Comparison with Greenland ice core data shows that Islay Na covaries with Greenland Na⁺, and that major volcanic events (e.g., 1257 CE) produce synchronous S maximum in both regions. These teleconnected responses demonstrate that coastal Scotland and Greenland share common winter storm generation processes and Arctic–Atlantic moisture variability. This study provides the first long-term speleothem–ice-core teleconnection framework for reconstructing North Atlantic winter storm-track behaviour over the past 2,500 years.

Geomagnetic jerks are the fastest variations we observe in secular variation (SV) of the internal geomagnetic field. They have been deemed spatiotemporally unpredictable, and thus make it difficult to forecast magnetic field changes. Recent core surface flow-inversions of satellite SV data show that pulses in modelled azimuthal flow acceleration are contemporaneous with localised low latitude jerks observed in the Atlantic and Pacific from 2000—2024.In order to explore to what extent such pulses might be responsible for observed geomagnetic jerks, we simulate them with synthetic flow models. We use a Fisher–Von Mises probability distribution to spatially define the pulse, which ensures that its spherical harmonic expansion in terms of poloidal and toroidal spherical harmonic coefficients converges. To recover a dynamic flow, we add uncorrelated noise to these toroidal and poloidal acceleration coefficients. After this, we obtain SV from flow acceleration using the diffusionless induction equation, investigating a variety of background flows and core-surface magnetic field structures with our flow-acceleration pulse. Finally, we plot the expected SV at the Earth’s surface.We successfully generate geomagnetic jerks, similar to those observed by CHAMP in the Atlantic in 2003.5 and 2007, and Swarm in the Pacific in 2017 and 2020. This pulse-like simulator for low-latitude jerks is in agreement with results from numerical dynamo simulations, which suggest that jerks originate from Alfvén wave packets emitted from the inner-outer core boundary. Our results further suggest that there is no need for waves longitudinally propagating along the outer core surface for jerks to occur.

Abstract This study investigates the effects of geomagnetically induced currents (GIC) on New Zealand's electrical infrastructure via an intentional ground injection of direct current (DC) from a high voltage DC converter station. GIC manifests as quasi‐DC currents within power systems, potentially causing transformer saturation, increased reactive power demand, elevated harmonics, and transformer overloading. In January 2023, with support from Transpower, we utilized New Zealand's high voltage DC link to inject current directly into the ground at Haywards substation in Wellington, North island. This allowed us to monitor the effects of half‐cycle saturation of two 216 MVA, 220/110 kV autotransformers. Over 9 days, six injection tests were conducted, each lasting between one and 2 hours, with peak ground injection current reaching approximately 621 A, corresponding to 35 A measured to flow through one of the transformers on site. The saturation threshold of the transformer was measured to be around 20 A. Analysis of power quality measurements revealed a clear correlation between even total harmonic distortion and DC current, along with corresponding increases in acoustic sound and vibration levels. There was strong agreement between differential magnetometer (DMM) and transformer measurements of DC current. Variations in very low frequency radio harmonic observations were correlated with temporal variations in ground current. These findings provide valuable insights into the impact of GICs on in‐service equipment and inform grid operators on potential mitigation strategies.

Abstract Soft cliffed coasts are particularly vulnerable to erosion and their retreat depends on environmental, geological and geomechanical factors. In this work, we use a mathematical modeling approach to understand effects of future global sea level rise on these coasts over multiple centuries. We develop a simple mass conservation model, equating material eroded from a cliff to the sediment required for foreshore adaptation to sea level rise. The model considers geological differences between cliff and beach sediment, variable and uncertain rates of sea level rise, and the complex inland topography a cliff may erode through. The model is solved analytically, and long‐term behaviors discussed, including conditions for an equilibrium recession rate or a change in coastal typology. Methods for obtaining estimates of model parameters are detailed and an application of the depth of closure concept to multi‐century timescales proposed. The model is applied to the Holderness coast, United Kingdom. It predicts an acceleration of cliff retreat due to rising sea levels over the next centuries, though local topographical features may cause temporary deceleration. No long‐term equilibrium behavior is identified. The study also estimates that vulnerable locations along this coast will experience a change in coastal typology within the next few hundred years. These findings highlight the importance of inland topography in determining an eroding cliffed coast's resilience to sea level rise. We propose that the relative sea level rise corresponding to typology change should be used as an indicator of cliff resilience to sea level rise, instead of current cliff height.