Geological Survey of Estonia

Abstract Askja is a large central volcano in the Northern Volcanic Zone (NVZ) of Iceland which last erupted effusively in 1961 and subsequently experienced steady deflation from the 1970s until August 2021, when GPS and InSAR measurements confirmed that it had begun re‐inflating. A dense (1–2 km station spacing) network of broadband seismometers and nodes were deployed in the Askja caldera in response to this re‐inflation. Ambient noise tomography results reveal a shallow (2 km beneath the surface) low velocity zone underneath the center of uplift that we interpret to be a shallow magma storage region. This low velocity zone is also coincident with a region of positive (+3%) radial anisotropy, which contrasts with a radial anisotropy of −6% in the top 3–5 km of the crust elsewhere in the NVZ, likely due to pervasive vertically aligned fractures in the near surface caused by ongoing rifting. We interpret this significant change to be caused by the magma storage region being made up of horizontal sills. Effective media modeling was used to estimate a bulk sill aspect ratio of 0.2 and a melt fraction of 5%. This shallow melt zone is interpreted to be part of a two‐stage magma storage system with a deeper zone of melt (7 km beneath the surface) feeding the shallower one. This has significant implications for hazard because the shallow storage region can act as a source of either evolved or primitive melt, allowing for larger volume or potentially explosive eruptions.

Study region: Estonian-Latvian transboundary area Study focus: The primary aim of this study is to develop and apply a harmonized framework for assessing groundwater vulnerability and pollution risk in the Estonian-Latvian transboundary area. The DRASTIC and modified DRASTIC methods were employed to evaluate natural vulnerability, while DRASTIC-L and modified DRASTIC-L methods were used to integrate land use and assess pollution risk. Sensitivity analyses were conducted to identify the influence of key parameters, and results were validated using pollutant infiltration time calculations. This multi-method approach addresses the region's geological complexity and incorporates anthropogenic impacts to provide a comprehensive assessment. New hydrogeological insights for the region: The study reveals significant spatial variability in groundwater vulnerability, influenced by sediment composition, groundwater level, and land use. High-risk areas are predominantly located in regions with sandy sediments, shallow groundwater, and intensive agricultural activity, while zones with deeper groundwater and clay-rich sediments show greater natural protection. By integrating pollution risk mapping with traditional vulnerability assessments, the study highlights the critical role of anthropogenic pressures in shaping contamination risks. The findings underscore the importance of harmonized cross-border data collection and provide a replicable framework for sustainable transboundary groundwater management. These insights contribute to protecting water resources and ensuring the availability of safe drinking water for present and future generations.

Groundwater is a critical resource that supports ecosystems, agriculture, and drinking water supply, yet its sustainable management faces challenges, particularly in the transboundary regions. Collaborative approaches are needed to protect this shared resource, as pollution or overexploitation in one country can have significant consequences across borders. The Estonian-Latvian transboundary area is a good example of these challenges, with its reliance on both unconfined Quaternary aquifers, essential for ecosystems and rural communities, and confined first bedrock aquifers, critical for centralized water systems.This study develops a transboundary aquifer vulnerability assessment framework, integrating harmonized methodologies to evaluate natural vulnerability and pollution risk. The analysis uses the DRASTIC and modified DRASTIC index-based methods, combined with the DRASTIC-L approach, which incorporates land use data for a comprehensive evaluation of both natural and anthropogenic pressures. To improve the reliability of the assessment, pollutant travel time calculations were used to validate the findings.The results show high variability in aquifer vulnerability across the study area. The unconfined Quaternary aquifer is most vulnerable in regions with sandy sediments, shallow groundwater tables, and high recharge rates. The confined bedrock aquifers are covered with protective sediment layers, but their vulnerability varies depending on sediment thickness and hydraulic conductivity. Notably, discrepancies between Estonian and Latvian geological data were uncovered, as large polygons of well-protected areas often terminate abruptly at the border, highlighting inconsistencies in geological data between Estonia and Latvia.This framework emphasizes the importance of integrating natural vulnerability maps, pollution risk assessments, and harmonized methodologies developed for regional geological conditions. The study offers a scalable and adaptable solution for transboundary aquifer management by addressing data inconsistencies and fostering international cooperation.Integrating these insights into transboundary water management strategies can greatly improve decision-making by providing a more comprehensive understanding of groundwater vulnerability and pollution risks. Additionally, it helps to make groundwater systems more resilient to future challenges like climate change, land use changes, and increasing water demand. Ultimately, this approach supports the sustainable use and protection of shared groundwater resources, ensuring their availability and quality for current and future generations.

Buynevich, I.V.; Tõnisson, H.; Pupienis, D.; Jarmalavičius, D.; Rosentau, A.; Bitinas, A.; Davydov, O.V.; Kont, A.; Vilumaa, K.; Suursaar, Ü.; Savarese, M., Luik, K.; Kadurin, S.V., and Suuroja, S., 2024. High-resolution sampling and rapid image-based assessment of dark opaque fractions in coastal sands. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 778-782. Charlotte (North Carolina), ISSN 0749-0208. Dark opaque constituents (mafic and heavy minerals, dark bioclastic fragments, disseminated organics) occur in varying amounts and combinations in beach and dune sands, with heavy-mineral concentrations (HMCs) punctuating quartz-dominated siliciclastic lithosomes. Typically occurring in trace amounts (<3-5%), heavy minerals provide important information about sediment source, regional transport pathways, and (paleo-)energy conditions, as well as produce strong reflections in georadar images when concentrated (>10%). Often comprising thin laminae (1–2 mm), HMCs present challenges for sampling, with traditional point-counts and heavy-mineral separation being extremely time-consuming. To address this issue, we present examples of simple grayscale-based field and micrograph analyses of samples from beach and coastal dune sites in the United States (Florida, New Jersey), the Baltic Sea (Estonia and Lithuania), and the Black Sea (Ukraine). Macrophotographs of exposures and trench walls show patterns of color intensity using image-processing freeware (e.g., Image J). Inverse grayscale (IG) values (white: IG=0; black: IG=255) along random profiles through outcrop or mounted grain photos help in readily distinguishing very dark minerals (magnetite, ilmenite, biotite, etc.; IG>240) from those with mid-range hues (feldspars, bioclastics, dark garnets; IG∼100–150) and near-clear translucent grains (fractured garnets, quartz; IG∼10–20), all on a white background. Once standardized for lighting, magnification, and granulometrically adjusted screen capture coverage, areal grayscale plots (histograms) aid in quantitative assessment of the relative “dark” fraction, with quartz-rich sand yielding low average color-intensity values (compared to even moderate HMCs (IG>60). Because denser mineralogical components often occur in the finer sand fraction, such analysis provides a conservative estimate of their relative contribution. Our approach has the potential to complement traditional sedimentological and geophysical (e.g., georadar) datasets with independent compositional metrics.

The potential expansion of an oil shale quarry near environmentally protected Lake Uljaste in northern Estonia has ignited a public discourse on its potential impact on the lake's water level. This study, conducted between 2021 and 2023, aimed to elucidate the hydrogeological dynamics of the area, understand the functioning of groundwater flow systems, and predict the consequences of quarry expansion on the lake's water balance over the next 15 years.Lake Uljaste is a small (area of 0,64 km2) closed-basin lake with an average depth of 3,4 m. As the lake does not have any channelized surface water inflow or outflow, most of the water budget components have to be estimated indirectly. For this purpose, two water balance models were developed, incorporating hydrological/meteorological and stable isotope data, respectively, serving as inputs for a transient groundwater model.In addition, several different methods were applied including geophysical mapping, coring surveys, monitoring well construction, electrometry, and groundwater/surface water monitoring to characterize the local geological conditions and groundwater-surface water interaction. Seismo-acoustic profiling provided insights into the depth of lake bottom sediments, while electrical conductivity and isotopic composition of surface water and groundwater aided in conceptualizing the local groundwater flow system.The study revealed that, the lake water balance is mainly controlled by precipitation and evaporation and is very sensitive to changes in climatic conditions. Despite the fact, that the amount of direct groundwater inflow is small, the groundwater level beneath the lake significantly influences its water level. Predictions from the groundwater model indicate a notable lake level decline due to the potential water abstraction of the planned quarry. Thus, without preventive measures against groundwater level decline beneath the lake, the expansion of the quarry to its planned position would result in a significant decline in lake water level leading probably to severe environmental problems.Several uncertainties remain regarding the conceptual understanding of the lake water balance and catchment hydrology which need to be addressed to improve the existing models. The most important of these concerns need for a more precise determination of hydrodynamic properties of the lake bottom sediments, which are needed to estimate the subsurface outflow from the lake. In addition, the installation of a weather station for characterizing the microclimatic conditions near the lake and refining of the stable isotope mass-balance model through improved characterization of vertical and horizontal mixing in the lake, are needed for more accurate water balance calculations. These refinements are crucial for assessing the extent of lake water seepage into the groundwater, a vital parameter for groundwater modeling and an important pre-requisite for sustainable groundwater resource management in the area.&amp;#160;

Sandy beaches high in recreation value make up 16% of the over 4000 km long shoreline of Estonia. The shore processes associated with climate change have remarkably accelerated over recent decades. Many sandy shores have suffered from strong erosion, including an excellent former beach at Valgeranna. The jetties, which were built in the 1860s to protect the navigation channel of Port Pärnu from clogging, have prevented natural sediment transport along the coast from south to north. At the same time, the sandy beach in Pärnu is expanding, and part of the sand accumulates with strong storms also in between the jetties, reducing the width of the shipping channel. The channel needs regular dredging, but, so far, the dredged sediment has been taken far away to the open sea and accumulated on the seabed. The current paper addresses the possibilities of using that sand for beach restoration in destructed and eroded areas. An overview of the applied methods and measurements during field studies is given. The results of modelling the processes of wave activity and sediment transport are discussed. The recycling of shore sediments is an important measure in sustainable coastal zone management. Different options and scenarios are analysed in order to find the most reasonable ways to bring sand back onto beaches and stabilize natural processes. Support from the state by working out respective laws and regulations would be motivating as well.