Legacy mine wastes have accumulated over centuries in regions such as Benguet, Philippines, and Cornwall, United Kingdom. Inefficient historical processing left valuable metals in these materials, supporting their potential role in a circular economy through secondary resource recovery. However, elevated concentrations of toxic metals such as arsenic also pose long-term environmental risks. This dual character highlights the need to evaluate legacy mine wastes not only as potential secondary metal resources but also as sources of environmental liability.Studying legacy mine wastes presents several challenges. These materials are often highly heterogeneous, vary significantly across short spatial scales, and are often poorly documented in terms of their composition, emplacement, and subsequent alteration. Furthermore, intrusive investigations can disturb legacy wastes and mobilise toxic metals, while conventional methods such as drilling are costly, invasive, and limited in coverage. In contrast, geoelectrical techniques provide a non-invasive and cost-effective way to characterise the internal structure and hydrogeological behaviour of mine wastes over larger areas, and are therefore applied in this study to investigate legacy tailings at the Padcal–Philex mine in Benguet, Philippines, and at Wheal Maid (WM), as well as legacy waste rock deposits at Binner Downs (BD) in Cornwall, UK.At the Padcal–Philex site, several arrays of PRIME electrical resistivity monitoring equipment were installed along and across Benches 4 and 5 of Tailings Storage Facility 1 (TSF1) to characterise the hydrogeological behaviour of the tailings. Daily measurements collected between April 2023 and May 2024 demonstrate that electrical resistivity tomography (ERT) can effectively monitor moisture dynamics within the tailings during both monsoon and dry seasons, a key factor in assessing tailings stability and in planning future secondary resource recovery. Further data processing shows that ERT can distinguish between muddy and sandy tailings units, which have different average copper content, validated by auger sampling.At Wheal Maid, ERT surveys were conducted along multiple profiles in July 2024, May 2025, and September 2025 to investigate acid mine drainage (AMD) processes in the lower lagoon area. The resistivity models reveal zones of persistently low resistivity, interpreted as areas influenced by AMD within the lagoon. These low-resistivity zones may indicate seepage of AMD-rich water beneath the tailings and tailings dam, suggesting pathways for contaminant transport to the downstream River Carnon. At Binner Downs, ERT imaging successfully delineates the boundary between legacy waste rock and the original ground surface, improving understanding of waste distribution and thickness.Overall, these results demonstrate the value of geoelectrical techniques for investigating legacy mine wastes. By enhancing understanding of subsurface heterogeneity, moisture behaviour, and contaminant pathways, geoelectrical techniques provide a non-intrusive framework to support environmental risk assessment, remediation planning, and the evaluation of targeted reprocessing opportunities in legacy mining landscapes.

A key parameter influencing crop growth is the availability of water and its spatial distribution within agricultural soils. The strong electrical response associated with variations in water content means that electrical geophysical methods such as Electrical Resistivity Tomography ( ERT ) are ideally suited for studying soil moisture dynamics. While relative changes in electrical resistivity allow conclusions to be drawn on the temporal variability of soil moisture in the subsurface, they do not provide quantitative estimates of soil moisture. Laboratory measurements of soil moisture and electrical resistivity - together with the fitting of a model to these data (e.g. Waxman-Smits) - enable the estimation of soil moisture from ERT models. While this method is established, examples are limited for Alfisols in general, and from African sites in particular. We present laboratory data on agricultural Alfisols from three sites in southern Africa, to define relationships between electrical resistivity and volumetric water content. We fit the data to several widely used models, and utilise the novel application of Akaike’s Information Criterion to identify the best model for each dataset. In addition to identifying which model is most suitable for each site, our findings also allow us to make conclusions on whether a single or multiple models are required per site, or even whether heterogeneities make the utilisation of a model inadvisable. We then compare our results against complementary laboratory datasets to explain which soil physical parameters are the main causes of variability in electrical response at each site.

Early-warning of landslide failure relies on understanding subsurface processes that drive slope destabilisation, including changes in moisture content or mechanical behaviour. Material heterogeneity in landslide systems causes spatiotemporal variation in these dynamic processes. There is therefore a need to develop methods that can detect and measure changes in the subsurface to inform landslide stability. Seismic monitoring can record information on the elastic behaviour of the ground in response to immediate and long-term processes, such as slope displacement and moisture variation. Here, we report on data acquired by a seismic network deployed at a slow-moving clay-rich landslide in North Yorkshire UK, representative of many landslides in clay-rich lowland slopes. The temporary network was operational for two years with the aim of understanding how the seismic response of the landslide varies between sensors deployed on parts of the landslide with distinctly different hydrogeological properties. We present an overview of the rationale and deployment procedure, as well as a preliminary assessment of data quality, event analysis, tilt observations, horizontal-to-vertical spectral ratio (H/V) ratio calculations, and ambient noise cross-correlation. We conclude that the moisture dynamics of the slope have a significant influence on observed data, and make further recommendations for the analysis of the dataset. Our study demonstrates the feasibility of analytical techniques using these data, promotes the unique dataset to foster further in-depth analysis, and encourages similar seismological deployments on active landslides.

Polders are coastal low-lying areas reclaimed on the sea mainly for agriculture. They are constantly drained by pumps, ditches and subsurface drains. In West-Flanders, Belgium they are composed of a shallow freshwater lens on top of denser saline groundwater. This freshwater lens is essential for crop growth but during dry periods, it can disappear and the saline groundwater can enter the root zone by capillary rise and endanger yield. To prevent this, farmers can use controlled drainage to raise the water table in their field during winter months to increase the freshwater lens thickness. To study the effectiveness of the technique, we monitored three fields with piezometers, resistivity sticks alongside field mapping using electromagnetic induction for three years. The resistivity sticks highlighted lithological differences, but also enabled us to monitor the fresh–saline water interface and the water table accurately. Controlled drainage retained additional rainfall during intense summer precipitation but little effect was observed on the fresh–saline water interface. Soil heterogeneity and past land use of the field seem to have a larger effect on the fresh–saline water interface. Despite the limited effect on the freshwater lens, the value of geophysical methods for monitoring its thickness for field-scale study was demonstrated.

Climate change is bringing hotter, drier summers and warmer, wetter winters, intensifying winter floods and causing larger seasonal variations in soil moisture. These shifts place increasing stress on levees – many of which were constructed decades or centuries ago – making their current performance challenging to assess. Levee performance depends on limiting water ingress, as increased seepage can trigger piping and slope failure, potentially leading to catastrophic breaches. Hydraulic conductivity strongly controls water ingress, but is challenging to measure directly and can change as the materials deteriorate. To investigate how environmental loading affects levee performance, a clay levee in northern England was monitored for four years every 48 hours using electrical resistivity tomography (ERT) – a geophysical technique sensitive to fluid changes – alongside environmental sensors (soil moisture, river stage, and meteorological data). Two zones showed clear responses to climatic and hydrological forcing: the foundation strata, where groundwater levels rose with river levels, and the active layer (upper ~1.5 m), which seasonally dried in summer and rewetted in winter. These zones may therefore be particularly vulnerable to future climatic extremes and flood events. Analysis of annual drying-front depths indicates that average summer desiccation depths could increase from ~0.6 m to >1 m in northern England by the late 21st century (UKCP18 data, RCP8.5). This enhanced desiccation may reduce their performance, especially in early autumn when open shrinkage cracks can act as seepage pathways during subsequent floods. Forward planning using geophysical methods will help guide remediation and mitigate the effects of potential failure in levees.

Moisture induced landslides in clay slopes are generally driven by heterogeneity in both saturation levels and material properties and their arising complex and dynamic interactions in the subsurface. The use of time-lapse geophysical imaging can illuminate four-dimensional subsurface moisture dynamics and geotechnical property changes at the slope-scale, thereby complementing conventional geotechnical point sampling and sensing, and geodetic observations of the ground surface. Here we consider: (1) the development of novel time-lapse geoelectrical, seismic and fibre-optic geophysical imaging technologies for landslide monitoring; (2) in-situ and laboratory derived petrophysical relationships to enable geotechnical information to be estimated from geophysical models; (3) surface topography determination and ground deformation tracking using geodetic observations; (4) coupled geophysical-hydrological modelling of slopes; (5) perspectives and recommendations for the incorporation of integrated geophysical-geodetic-geotechnical technologies into landslide early warning systems – illustrated using results from a number of long-term field observatories.

Hydrological processes in mountainous watersheds, and how soil, bedrock, and plants interact are still poorly understood. Through a dense network of soil moisture and temperature sensors, high resolution electrical resistivity tomography monitoring, and weather data we assess the above and below-ground processes driving the hydrological response of a hillslope during snowmelt and summer monsoon. The monitoring transect covers different bedrock and vegetation types, with a steep upper part characterized by shallow bedrock and covered by pine trees, and a gentle lower part underlain by colluvium and covered mostly by grass and veratrum. Coupling the monitoring data with a simplified hydrological model, we observe several important hydrological processes that show how variations in bedrock and vegetation type change subsurface flow patterns, allowing us to answer how subsurface flow pathways differ between shallow and deep bedrock units, and to assess the interactions between vegetation, bedrock types and subsurface flow dynamics. While on the steep section, characterized by thin soil and shallow bedrock, we observe mostly shallow and rapid lateral flow, on the gentle slope underlain by colluvium vertical flow is prevailing. Timelapse resistivity patterns indicate that for shallow bedrock, fractures and tree roots may provide preferential flow pathways into deeper bedrock units during snowmelt, which may provide means to mitigate summer drought conditions. Shading of the trees seems to further mitigate drought conditions by limiting evaporation of summer monsoon rainfall, leading to less drying of the shallow soil layer. In the lower, gentle part of the profile snowmelt is contributing to vertical flow recharging the aquifer, while in the summer upwelling groundwater is providing moisture to sustain plant growth. These observations show that variations in bedrock and vegetation pose a strong control on hillslope hydrology, creating spatially complex flow patterns. These results highlight the spatial heterogeneity of hydrological processes in mountainous watersheds, which need to be understood to predict how watersheds respond to disturbances.

Disused coal tips formed by waste materials from coal mining activities can become unstable over time. Landslides or avalanches of coal waste can occur, especially during heavy rainfall or by other environmental factors, leading to significant safety hazards for nearby residents and infrastructure. The Welsh Government Coal Tip Safety Taskforce has recently identified over 2,500 disused coal tips in Wales potentially posing a risk, following a significant landslip in Tylorstown after the 2020 storms. Ongoing climate change further destabilises these legacies of past mining activities, posing great challenges to land management and hazard remediation, as instability within the coal tip can be invisible to surface surveys and inspections.Wattstown in the Rhondda Cynon Taf County Borough was identified as a preferred location for deploying long-term 4D geoelectrical monitoring, with the aim of observing the moisture dynamics between a heavily vegetated basin area upslope of the coal tip (where a previous landslip has occurred) and the downslope tip materials. A BGS-designed Proactive Infrastructure Monitoring & Evaluation (PRIME) system has been deployed here to characterise this site using eight 32-electrode arrays. PRIME is a low-cost, low-power, non-invasive 4D geo-electrical imaging technology designed for near-real-time infrastructure monitoring. The eight ERT sensor arrays are arranged so that four arrays form two long 2D survey lines to monitor the main slope in directions perpendicular to each other, while a further five arrays cover the landslip region in a 3D configuration, in which one of the arrays is common between the linear and the grid configuration. A full daily measurement schedule allowing for ground motion tracking has been implemented since Mid-2023. Measured data is transferred daily to the BGS servers, and system diagnostics reports are automatically generated to confirm the recent monitoring status and performance of the PRIME system.The baseline resistivity model shows a lower resistivity layer with a variable thickness of 0 - 5 m covering the whole monitored area. This layer is interpreted as spoils that have been deposited and subsequently reprofiled. Our observation also matches with the presence of high clay contents found in the hand-augered soil. Below the reprofiled spoils resistivity values increase significantly, likely to be underlying bedrock that is composed of sandstone with interbedded layers of coal and silt.Time-lapse inversion revealed the influence of effective precipitation on the moisture dynamics of the coal tip. Several anomalies were observed within the gradually decreasing resistivity distribution in the near-surface. Along the line perpendicular to the slope, larger low-resistivity features are observed in both the ditches that run parallel to the slope. This could be the result of preferential infiltration in these areas and the ponding of surface water. In the rotational landslip area, PRIME monitoring data has identified what is potentially a preferential flow path from 5 m to 10 m below ground level.Through continuous monitoring of the disused coal tip, the PRIME system demonstrated its capability for enhanced coal tip assessment, detecting critical hydrogeological processes through minimally-invasive subsurface imaging. Ongoing work aims to establish in-situ petrophysical relationships.

Arctic regions are under immense pressure from a continuously warming climate. During the winter and shoulder seasons, recently deglaciated sediments are particularly sensitive to human-induced warming. Understanding the physical mechanisms and processes that determine soil liquid moisture availability contributes to the way we conceptualize and understand the development and functioning of terrestrial Arctic ecosystems. However, harsh weather and logistical constraints limit opportunities to directly observe subsurface processes year-round; hence automated and uninterrupted strategies of monitoring the coupled heat and water movement in soils are essential. Geoelectrical monitoring using electrical resistivity tomography (ERT) has proven to be an effective method to capture soil moisture distribution in time and space. ERT instrumentation has been adapted for year-round operation in high-latitude weather conditions. We installed two geoelectrical monitoring stations on the forefield of a retreating glacier in Svalbard, consisting of semi-permanent surface ERT arrays and co-located soil sensors, which track seasonal changes in soil electrical resistivity, moisture, and temperature in 3D. One of the stations observes recently exposed sediments (5–10 years since deglaciation), whilst the other covers more established sediments (50–60 years since deglaciation). We obtained a 1-year continuous measurement record (October 2021–September 2022), which produced 4D images of soil freeze–thaw transitions with unprecedented detail, allowing us to calculate the velocity of the thawing front in 3D. At its peak, this was found to be 1 m d−1 for the older sediments and 0.4 m d−1 for the younger sediments. Records of soil moisture and thermal regime obtained by sensors help define the conditions under which snowmelt takes place. Our data reveal that the freeze–thaw shoulder period, during which the surface soils experienced the zero-curtain effect, lasted 23 d at the site closer to the glacier but only 6 d for the older sediments. Furthermore, we used unsupervised clustering to classify areas of the soil volume according to their electrical resistivity coefficient of variance, which enables us to understand spatial variations in susceptibility to water-phase transition. Novel insights into soil moisture dynamics throughout the spring melt will help parameterize models of biological activity to build a more predictive understanding of newly emerging terrestrial landscapes and their impact on carbon and nutrient cycling.

This study underscores the need for subsurface imaging and monitoring techniques to offer timely information on railway embankment condition and to contribute to the decision-making processes needed to minimise the risks of catastrophic slope failure. We investigate electrical resistivity tomography (ERT) as a means of providing railway earthwork asset condition assessment information through the deployment of a bespoke ERT monitoring system (PRIME – the Proactive Infrastructure Monitoring and Evaluation system), which has been specifically developed for geotechnical monitoring applications.We focus on two test sites, Botley and Withy Beds, which are situated on mainline railway embankments in the UK near Southampton and London respectively. Both embankments have long histories of slope instability and are constructed from London Clay (a high plasticity clay widely associated with ground deformation problems). Long-term ERT monitoring infrastructure has been deployed across both sites to enable imaging of subsurface heterogeneity and to monitor subsurface moisture content variations. At Botley a grid of electrodes extending from the embankment shoulder to toe, over an area of ~20 by 30 m, was deployed to enable time-lapse 3D imaging of a progressive rotational failure at the site, whilst at Withy Beds a line of electrodes was deployed along the embankment toe to enable time-lapse 2D imaging for a ~300m length of susceptible embankment. Manual geodetic (total station and LiDAR) monitoring of the slope geometry and electrode positions, and conventional geotechnical monitoring using temperature, soil moisture and matric suction sensors have also been used at the sites to validate the results of the ERT monitoring. In additional, laboratory petrophysical testing of samples from the sites has been used to establish relationships between resistivity, moisture content and matric suction.More than three-years of ERT monitoring data have been collected from the sites. Initial analyses of the results have shown strong correlations between the conventional geotechnical monitoring results and ERT derived estimates of soil moisture. At the site scale, a remarkably clear low-resistivity layer can be seen in the middle embankment segment of Botley, which suggests a high clay content and likely limited hydraulic permeability. The properties of this layer, in conjunction with time-lapse ERT observations made during periods of heavy rainfall, have revealed the hydrological functioning of the slope and the strong influence of evapotranspiration associated with clusters of mature trees. On the other hand, the Withy Beds embankment shows less intense drying and wetting patterns, even though noticeable fluctuations in resistivity suggest the presence of localised zones of moisture build-up. The sandy sections at the Withy Beds site are consistently dry even after rainfall, which permits water to seep into the clay layer beneath. On the other hand, the clay lands have higher moisture content and exhibit summertime surface drying.In this study we have provided unprecedented insights, in terms of ERT monitoring duration and spatiotemporal resolution, into the structure and moisture dynamics of mainline railway embankments. ERT has been demonstrated as novel means of providing operationally relevant condition monitoring information to support the management of vulnerable railway earthworks associated with complex ground conditions.

We explore the performance of distributed acoustic sensing (DAS) for crosswell seismic imaging at a shallow geothermal project in an abandoned mine. The UK Geoenergy Observatory (UKGEOS) research facility in Glasgow has repurposed an abandoned coal mine below the city with the goal to investigate the heat storage and heat recovery potential of flooded mines. Originally for distributed temperature sensing purposes, UKGEOS installed fiber-optic cables in boreholes less than 100 m deep passing through the mined coal seams now targeted for heat survey prior to heat pump installation to obtain a baseline velocity acquire data simultaneously with DAS and a colocated

Urban geothermal solutions to heating and cooling have developed slowly in the UK, partly due to limited understanding of subsurface heat flow regimes and how stored heat might be sustainably governed within heterogeneous aquifers. Understanding heat flow through various aquifers is the goal of the SmartRes project, in which heat flow trials will be conducted in a number of sites. To provide context for heat flow experiments in a fractured chalk aquifer, geophysical surveys were acquired at Trumplett’s Farm, a groundwater abstraction and monitoring site near Reading (Berkshire, UK). Here, groundwater flow is primarily within a fracture network, likely in an active zone within the upper 10 m of the saturated chalk. Seismic surveys recorded energy generated with an impact source at surface geophones (24 cabled GEODE, and 20 nodal Smart-Solo, geophones) and hydrophone strings, deployed to 100 m depth in boreholes drilled at the site. Smart-Solo nodes were deployed in a ~10 x 5 m grid at the site, with cabled geophones occupying lines between adjacent boreholes, with geophone intervals of up to 2 m. Nodal geophones recorded passively throughout the 3-day deployment and will be analysed using ambient noise correlation to evaluate anisotropy. The remaining data has been used for preliminary analysis with MASW (Multichannel Analysis of Surface Waves), P-wave refraction velocities, and vertical seismic profiles (VSPs). MASW analyses suggest shear wave velocity (Vs) ranges from 250-600 m/s in the uppermost 1.5 m, but estimates are challenging given poor dispersion imaging of the fundamental mode. Different source-receiver offsets were tested to eliminate mode superposition, but the best dispersion curves are observed for zero-offset shots. Data were processed in a commercially available software with relatively limited freedom to adjust inversion parameters, hence further analysis will use the MuLTI code to undertake a constrained Monte Carlo inversion approach. The deeper structure of the chalk was characterised in VSPs, indicating reflective P-wave horizons at 52 and 69 m depth, separating material with interval velocities of ~2100 m/s, ~2500 m/s and 3000 m/s. Observing these reflections required aggressive frequency-wavenumber filtering to suppress direct waves in the water column. Electrical resistivity tomography (ERT) surveys were conducted using the BGS PRIME ERT system to optimise array configuration for long-term monitoring. The reconnaissance survey included in-hole, borehole-to-surface, and surface ERT at 1 m intervals, employing C1P1-C2P2 bipole-bipole and dipole-dipole arrays around the site. Preliminary ERT inversion revealed low resistivity zones within the top 1.5 – 2 m across the site and mapped a potential south-dipping high resistivity structure. A longer ERT survey spread is planned to better reveal hydrodynamic interactions at deeper depths. This initial insight will be refined with a fibre-optic distributed acoustic sensing deployment at the Trumplett’s site and an optimised repeat of the BGS PRIME ERT array. These will be synchronous with a thermal response test at the Trumplett’s site monitored with distributed temperature sensing. Keywords: Seismic analysis, ERT, geothermal investigation, fractured aquifer, aquifer thermal energy storage

Robust and timely assessment of the condition of geotechnical infrastructure assets (e.g. cuttings, embankments, dams) is essential for cost effective maintenance and engineering interventions to prevent failure events. Infrastructure slopes (in transportation, utilities and water management) are experiencing increasingly high levels of failure and require considerable resources to maintain; in the order of hundreds of millions of pounds per year in the UK alone. The issue of accelerating asset deterioration is being exacerbated by the greater prevalence of extreme weather events. Conventional monitoring techniques are still dominated by surface observations, which provide infrequent information and deliver very few insights into subsurface deterioration processes which typically precede surface expressions of deterioration. Here we describe the development of novel geoelectrical imaging technology to monitor and assess the internal condition of infrastructure slopes in four-dimensions. In particular, we outline a workflow in which time-lapse geophysical models are used to inform estimates of soil moisture and suction distributions, and we consider the challenges associated with the deployment of geophysical monitoring systems on operational geotechnical assets. Examples are given from long-term field experiments on transportation and water management earthworks. We propose that novel geophysical monitoring complements more traditional forms of asset assessment to significantly enhance the resilience of safety critical infrastructure through improved subsurface information provision and decision support.

This study demonstrates that machine learning from seismograms, obtained from commonly deployed seismometers, can identify the early stages of slope failure in the field. Landslide hazards negatively impact the economy and public through disruption, damage of infrastructure and even loss of life. Triggering factors leading to landslides are broadly understood, typically associated with rainfall, geological conditions and steep topography. However, early warning at slope scale of an imminent landslide is more challenging. Through semi-supervised learning for seismic event detection from continuous seismic recordings over a period of about 10 years, we demonstrate that timely landslide induced displacement prediction is possible, providing the basis for landslide early warning systems. Our proposed methodology detects and characterises seismic precursors to landslide events making use of seismic recordings near an active slow moving earth slide-flow using a semi-supervised Siamese network. This data driven methodology identifies increase in microseismicity, and the change in the frequency spectrum of that microseismicity which identify key stages prior to a failure: ‘rest’, ‘precursor’ and ‘active’. Due to the semi-supervised nature of Siamese networks, the methodology is adaptable to discovering new types of distinct events, making it an ideal solution for precursor detection at new sites.

This review examines the application of the geophysical methods for Transportation Infrastructure Slope Monitoring (TISM). In contrast to existing works, which address geophysical methods for natural landslide monitoring, this study focuses on their application to infrastructure assets. It addresses the key aspects regarding the geophysical methods most employed, the subsurface properties revealed, and the design of monitoring systems, including sensor deployment. It evaluates the benefits and challenges associated with each geophysical approach, explores the potential for integrating geophysical techniques with other methods, and identifies the emerging technologies. Geophysical techniques such as Electrical Resistivity Tomography (ERT), Multichannel Analysis of Surface Waves (MASW), and Fiber Optic Cable (FOC) have proven effective in monitoring slope stability and detecting subsurface features, including soil moisture dynamics, slip surfaces, and material heterogeneity. Both temporary and permanent monitoring setups have been used, with increasing interest in real-time monitoring solutions. The integration of advanced technologies like Distributed Acoustic Sensing (DAS), UAV-mounted sensors, and artificial intelligence (AI) promises to enhance the resolution, accessibility, and predictive capabilities of slope monitoring systems. The review concludes with recommendations for future research, emphasizing the need for integrated monitoring frameworks that combine geophysical data with real-time analysis to improve the safety and efficiency of transportation infrastructure management.

The dynamics of moisture content in cover systems constructed on mining wastes were monitored at the pilot scale using 2D autonomous, remote, and non-invasive time-lapse electrical resistivity tomography combined with conventional point sensors. A methodology was proposed to process the daily hydrogeophysical datasets from 23 m-long instrumented sections of covers with capillary barrier effects (CCBEs) designed to act as oxygen barriers, and covers with low saturated hydraulic conductivity layers (LSHCCs) designed to limit the water infiltration rate. Hydrogeophysical monitoring suggested that CCBEs were able to maintain high degrees of saturation in the moisture-retaining layer throughout the one-year monitoring period, which would make it an efficient oxygen barrier. Larger spatio-temporal changes in moisture content were observed in LSHCCs and most of the low hydraulic conductivity layers remained below 85% saturation, which was attributed to the combined effect of low precipitation, rapid vegetation development, and water percolation through the cover. The methodology proposed in this pilot-scale "proof-of-concept" study allowed the hydrogeological behavior of the cover systems to be monitored in the 23 m-long instrumented sections using continuous geoelectrical data, which demonstrated that this innovative monitoring technique could be useful for geochemical and geotechnical monitoring programs in large-scale mining waste storage facilities.

The rising demand for critical metals presents a major economic opportunity for mineral-rich countries. For a sustainable transition to a low-carbon future, it is essential to minimise impacts of mineral resource development to the environment, ecosystems, and societies of these nations. Although there has been considerable progress in the social aspects of the mining sector, environmental metrics are not showing comparable improvement. The Philippines exemplifies this challenge as a country that aims to conserve its exceptional biodiversity to maximise ecosystem services while expanding mining activities for economic growth, in a geographical setting with high mineral potential and vulnerability to natural hazards and climate change. Similar to many mining areas, environmental baselines are mostly non-existent, compounded by a legacy of mining impacts despite an established policy framework. We review issues associated with large- and small-scale mining and identify underlying research challenges and opportunities in the Philippines. Potential environmental research pathways include (i) innovative approaches for catchment scale characterisation and identification of contaminant sources; (ii) quantifying and predicting contaminant transport; (iii) deployment of flexible monitoring devices for larger-scale water quality monitoring programmes; (iv) tailings dam monitoring and management; and (v) resource assessment and metal recovery in ores and tailings. By integrating geomorphological tools with geochemical data, as well as 2D/3D numerical modelling techniques, it becomes possible to predict and understand the behaviour and fate of contaminants across different spatial and temporal scales. The development of cost-effective water quality assessment devices and protocols can help overcome logistical challenges in monitoring a wider range of hydrological conditions. Advanced applications of remote sensing, combined with machine learning, and geophysical monitoring systems provide new opportunities to detect mining footprints and observe change in tailings dams more effectively. Potential impacts of mine wastes can be further minimised by exploring innovative technologies such as the use of metal-accumulating native plant species and environmentally safe solvents to reprocess modern and legacy tailings. Insights from these pathways will enable the realisation of a more sustainable mining future, through the incorporation of findings into existing and future governmental and small- and large-scale mining policy and practice. This will lead to sustainable development for society, particularly in nations that are well positioned to benefit from sustainable mineral resource development.

Many landslides can cause significant damage to infrastructure, property, and human life. To study landslide structure and processes, geophysical techniques are most productive when employed in combination with other survey and monitoring tools, such as intrusive sampling. Here, the integration of electrical resistivity tomography (ERT) and seismic refraction tomography (SRT) methods is used to assess landslides in Thungsong district, Nakhon Si Thammarat, the south of Thailand, where is a hilly and seasons of prolonged rainfall region. The 2D cross-plot analysis of P-wave velocity and resistivity values obtained by these two methods is introduced to identify potential landslide-prone zones in this region. The results of the 2D cross-plot model reveal detailed image of the subsurface conditions, highlighting areas of low P-wave velocity (lower than 600 m/s) and low resistivity (lower than 600 Ωm). These areas are indicative of weak zone and are potential to be sliding materials. Moreover, an intrusive sampling data from boreholes is also used for the calibration and validation geophysical data with geological data. This can improve the accuracy of landslide assessment and develop effective mitigation strategies to reduce the risk of landslides in this area. In addition of the 2D cross-plot, the volume of sliding material is also determined from the difference of the surface and slipping plane elevations. The volume calculation of sliding material is roughly 33447.76 m3. This approach provides a preliminary tool for landslide studies and monitoring landslides in this region, thus enabling an improved understanding of slope failure processes in this context, and the basis of a landslide mitigation strategy in the future.