Bedrock Relief Research Articles

Geologіcal structure of the lower terraces of the Prut valley іn the «Chernіvetsky gate dіstrіct» (accordіng to engіneerіng and geologіcal exploratіon data)

The article provides a detailed examination of the geological structure of Quaternary deposits at the bottom of the Prut River valley in the «Chernivtsi Gate» area based on engineering and geological survey data. The primary focus is on analyzing the structure and composition of geological formations, as well as studying geological processes and phenomena that influence the formation of the relief. During the research, materials from engineering and geological surveys were analyzed. This allowed for obtaining reliable information about the composition and physico-mechanical properties of the Quaternary deposits that form the bottom of the Prut River valley. The studies revealed significant variability in the thickness of the alluvium in the «Chernivtsi Gate» area, directly influenced by the relief of the river's bedrock. The relief of the Neogene clay surface shows significant irregularities that are not reflected on the surface of the valley. This indicates a complex erosional history of the valley, determined by both hydrological and tectonic factors. The results of the surveys provide important information for assessing the stability of the area, planning construction, and other engineering works. The conclusions of the study emphasize the need to consider geological conditions during the design and development of infrastructure in this region. Overall, the article makes a significant contribution to understanding the geological structure and processes that influence the formation of the relief at the bottom of the Prut River valley. Keywords: floodplaіn terraces, geologіcal sectіons, engіneerіng geology, «Chernіvetskі Vorota», Quaternary deposіts, stratіgraphy.

Modeling of geophysical derived parameters for groundwater potential zonation using GIS-based multi-criteria conceptual model

This study modeled geophysical derived parameters and multi-critically synthesized their themes based on geospatial and analytical hierarchy processes (AHP) approaches for groundwater potentiality prediction mapping. These methodologies were investigated in a typical hard rock geologic terrain, southwestern, Nigeria. Considering the spatially acquired 96 vertical electrical sounding (VES) data in the area, geoelectric sections revealing five subsurface layers including the topsoil, laterite, weathered layer, fractured basement and fresh basement rock were produced mindful of the 2-D resistivity structure subsurface imaging data interpreted results. The correlative results of the 2-D resistivity structure images and VES data interpretation results delineated major low resistivity vertical discontinuity typical of fractured zones characterized with width range of 25–40 m, while the depth vary from about 40 to > 60 m. Themes of groundwater potential conditioning factors (GPCFs), namely: regolith, bedrock relief, hydraulic head, coefficient of anisotropy, aquifer resistivity and aquifer thickness were prepared from the re-analyzed hydrogeological and geophysical data. The produced themes were appropriately weighted in the context of AHP data mining technique. The groundwater potential prediction index (GPPI) mathematical modeling equation for the area was established via applying the weight linear average algorithm involving the AHP weightage results. The synthesized results of the applied GPPI model equation on the GPCFs’ hydrogeologic themes give GPPI values in the range 1.59–3.65 for the study area. The geospatial modeling of the GPPI estimated values result produced groundwater potential prediction index map for the area. The produced GPPI model map zoned the area into low (1.59–2.30), medium (2.30–2.61), medium–high (2.61–3.02) and high (3.02–3.65) groundwater potential classes. The area analysis of the GPPI map indicates that more than 70% of the study area has ‘low to medium groundwater potential. The GPPI map result verification using reacting operating characteristics technique results gave 86% and 81% success and prediction rates, respectively. The findings of this study are useful to water managers and decision-makers for locating appropriate positions of new productive wells in the study area and other areas with similar geologic settings.

Geophysical Approach for Groundwater Resource Assessment: A Case Study of Oda Community Akure, Southwestern Nigeria

The geophysical investigation for groundwater was carried out at Oda town, Akure south local government area of Ondo State. Fourteen (14) points were sounded using a Schlumberger array with AB/2 of 80 m and the resulting geoelectric parameters were used in the estimation of the aquifer layer parameters of the subsurface. The first layer resistivity value ranges from 29 to 164 Ωm and thickness ranges from 0.6 to 2.5 m. The second layer has a resistivity value ranging from 21-1361 Ωm with a thickness ranging from 1.5 m to 14.6 m. The third layer resistivity value is from 68 to 297 Ωm with thickness ranging from 4 m to 12.4 m. The fourth layer which is the deepest layer has a resistivity value ranging from 180 to 4364 Ωm with depth ranging from 4 m to 19.5 m. The parameters interpreted from the geoelectric data were used to generate the aquifer thickness and resistivity maps, with bedrock relief which were combined to produce the groundwater potential map of the area. These maps were used to characterise the study area into low to high groundwater potential zones. The southwestern and eastern parts were identified as productive groundwater potential zones. The result was validated by taking water column depth from eight existing hand-dug wells. A significant correlation was obtained between the groundwater potential model and the well water column. The surveyed area is generally suitable for hand-dug well aside from the north-eastern part where groundwater potential is low and water volume is observed.

Filling and drainage of a subglacial lake beneath the Flade Isblink ice cap, northeast Greenland

Abstract. The generation, transport, storage and drainage of meltwater play important roles in the Greenland Ice Sheet (GrIS) subglacial system. Active subglacial lakes, common features in Antarctica, have recently been detected beneath the GrIS and may impact ice sheet hydrology. Despite their potential importance, few repeat subglacial lake filling and drainage events have been identified in Greenland. Here we examine the surface elevation change of a collapse basin at the Flade Isblink ice cap, northeast Greenland, which formed due to sudden subglacial lake drainage in 2011. We estimate the subglacial lake volume evolution using multi-temporal ArcticDEM data and ICESat-2 altimetry data acquired between 2012 and 2021. Our long-term observations show that the subglacial lake was continuously filled by surface meltwater, with the basin surface rising by up to 55 m during 2012–2021, and we estimate 138.2 × 106 m3 of meltwater was transported into the subglacial lake between 2012 and 2017. A second rapid drainage event occurred in late August 2019, which induced an abrupt ice dynamic response. We find that the 2019 drainage released much less water than the 2011 event and conclude that multiple factors, such as the volume of water stored in the subglacial lake and bedrock relief, regulate the episodic filling and drainage of the lake. By comparing the surface meltwater production and the subglacial lake volume change, we find that only ∼ 64 % of the surface meltwater descended to the bed, suggesting potential processes such as meltwater refreezing and firn aquifer storage, which need to be further quantified.

Application of GIS-Based Frequency Ratio Model to Geoelectric Parameters for Groundwater Potential Zonation in a Basement Complex Terrain

This study applied a geographic information system (GIS) based frequency ratio (FR) model for groundwater potential assessment in a crystalline basement complex terrain, southwestern, Nigeria. The aim of the study is to investigate the proficiency of the model when applied to geo-electric parameters. Four geo-electrically derived groundwater potential conditioning factors (GPCFs) were used, namely; Aquifer resistivity (AQR), Aquifer thickness (AQT), Coefficient of anisotropy (COA), and Bedrock relief (BED). The well location inventories were partitioned randomly into 70% (45 wells) for model training and 30% (19 wells) for model testing. The frequency ratio model algorithm was used to synthesize the GPCFs to produce the groundwater potential index (GWPI). The estimated GWPI was processed in the GIS environment to produce a groundwater potential zonation map which enabled the demarcation of the study area into five potential zones. The produced FR-based model map was validated through the application of the area under the curve (AUC) approach and spatial attribute comparative scheme (SACS). The AUC validation approach for the FR model showed a 64% success rate and 61% for prediction rate. The quantitative SACS result, based on the well data analysis, established 63% agreement with the insitu well water column thickness map. Similarly, the result of the qualitative SACS established a 71% Agreement. The SACS analysis shows that the FR-based model is a good alternative for prediction of groundwater potential zones even when applied to GWCFs that are geo-electrically derived. Thus, the produced map could form part of decision-making mechanisms for groundwater exploitation and management in the area.

Alpine rockwall erosion patterns follow elevation-dependent climate trajectories

Mountainous topography reflects an interplay between tectonic uplift, crustal strength, and climate-conditioned erosion cycles. During glaciations, glacial erosion increases bedrock relief, whereas during interglacials relief is lowered by rockwall erosion. Here, we show that paraglacial, frost cracking and permafrost processes jointly drive postglacial rockwall erosion in our research area. Field observations and modelling experiments demonstrate that all three processes are strongly conditioned by elevation. Our findings on catchment scale provide a potential multi-process explanation for the increase of rockwall erosion rates with elevation across the European Alps. As alpine basins warm during deglaciation, changing intensities and elevation-dependent interactions between periglacial and paraglacial processes result in elevational shifts in rockwall erosion patterns. Future climate warming will shift the intensity and elevation distribution of these processes, resulting in overall lower erosion rates across the Alps, but with more intensified erosion at the highest topography most sensitive to climate change.

Analysis of high-resolution aeromagnetic (HRAM) data of geological transition zones of southeastern part of Bauchi, N.E Nigeria

The study investigated the subsurface tectonic framework and structural disposition of the basement/sedimentary transition zone in the southeastern part of Bauchi, Northeastern Nigeria, to delineate the basal and lateral contacts and unravel some of the hydrogeological and engineering challenges in such areas. The method deployed involved analysis of high-resolution aeromagnetic (HRAM) data, through the application of several filtering techniques. The transformation techniques applied include reduction to pole, second vertical derivative techniques analytic signal, and Euler deconvolution. Euler depths result range of 1 to 200 m coincides with region where basement rocks outcrop on the surface while depth range between 0 and −800 m correspond to sedimentary terrain (Kerri-Kerri Fm.) or part of the area where the basement rocks are overlain by thick overburden sediments. The 2-D depth model around the transition zone showed high variability as it ranged from 0 to -500 m owing to the presence of basement highs and depressions. The basement highs are usually characterized by impermeable rocks with poor aquifer characteristics and are responsible for the failure of boreholes in these zones. The basement depressions, however, constitute good groundwater prospects depending on the hydrological properties of the sedimentary infill. The general orientation of lineaments in the area revealed NW-SE, NE-SW, and ENE-WSW, with minor N-S and E-W trends, suggesting a pan-African origin. The occurrence of lineaments in parts of the contact zones also contributes to the groundwater prospects. The erratic bedrock relief exhibited by the study area is also detrimental to foundation of pavement structures as it undermines their durability. Therefore, a detailed site investigation is crucial in such geological contact zones prior to the erection of structures. Additionally, vertical electrical soundings are recommended before borehole drilling to ascertain the suitability of these hydrogeologically complex zones.

The outlines of the bedrock relief and the Quaternary cover between the Estonian mainland and the islands of Muhu and Saaremaa in the West Estonian Archipelago

The outlines of the bedrock relief and the Quaternary cover between the Estonian mainland and the islands of Muhu and Saaremaa in the West Estonian Archipelago

ANTASed – An Updated Sediment Model for Antarctica

We compile existing seismic, gravity, radar and magnetic data, together with the subglacial bedrock relief from the BEDMACHINE project, to build the most detailed sediment model for Antarctica. We interpolate these data according to a tectonic map of Antarctica using a statistical kriging method. Our results reveal significant sediment accumulation in Antarctica with several types of sedimentary basins: parts of the Beacon Supergroup and more recent rifting basins. The basement relief closely resembles major geological and tectonic structures. The thickness of sediments has significant variations around the continent, and depends on the degree of crustal extension. West Antarctica has wide sedimentary basins: the Ross basin (thickness 2–6 km), the Filchner-Ronne basin (2–12 km) with continuations into East Antarctica, the Bentley Subglacial Trench and the Byrd basin (2–4 km). The deepest Filchner-Ronne basin has a complex structure with multi-layered sediments. East Antarctica is characterized by vast sedimentary basins such as the Pensacola-Pole (1–2 km), Coats Land (1–3 km), Dronning Maud Land (1–2 km), Vostok (2–7 km), Aurora (1–3 km), Astrolabe (2–4 km), Adventure (2–4 km), and Wilkes (1–4 km) basins, along with narrow deep rifts filled by sediments: JutulStraumen (1–2 km), Lambert (2–5 km), Scott, Denman, Vanderford and Totten (2–4 km) rifts. The average thickness of sediments for the whole continent is about 0.77 km. The new model, ANTASed, represents a significant improvement over CRUST 1.0 for Antarctica, and reveals new sedimentary basins. Differences between ANTASed and CRUST 1.0 reach +12/−3 km.

The importance of topography in the occurrence of glacial valleys in Belarus

The relief of the ice-sheet bed predetermines the location of the valleys both in vast regions and in local, relatively limited areas. The influence of the relief in a large region on the formation of valleys occurs in lowland, more dissected northern and western regions of Belarus. Here, the bedrock relief plays a key role in appearance the hollow-like Vidzovsky, Polotsk and Surazh glacial erosion depressions and in isolation of the elevations separating them. The distribution of these largest forms of glacial erosion is associated with the regional picture of the glacial ice flow in topographic depressions, increased erosion of the ice bed, which developed under the glacial streams and lobes of the Scandinavian ice sheet. The degree and character of the relief dissection, the size, surface slope and orientation of the depressions, river paleo-valleys, elevations, and escarps had a leading role in the location of valleys in local, relatively limited areas. Their significance for the formation of valleys was to determine the local picture of the glacial flow and the areas where stresses were concentrated at the bed and glacial erosion intensified. The formation of tunnel valleys was possible in depressions and in the dissected relief of the glacial bed, which contributed to the accumulation of meltwater, the formation of subglacial lakes, as well as the concentration of meltwater in the subglacial channels.

Geoelectric Investigation of the Groundwater Potential of the Federal Housing Estate, Eastern Part of Ado-Ekiti, Southwestern Nigeria

This study aimed at evaluating the potential for groundwater development in the eastern part of Ado-Ekiti, Southwestern Nigeria using Vertical Electrical Sounding (VES). Data were acquired with ABEM SAS 300 and processed through partial curve matching techniques and assisted with 1-D forward modelling. Geoelectric parameters were determined from the VES interpreted result. Seven (7) different VES type curves (H, A, HA, KH, HK, QH and HKH) indicating inhomogeneity of the subsurface layer beneath the study area were observed. Weathered layer resistivity map having values ranging from 3.2 – 272 Ωm, overburden thickness of value vary between 0 and 28m and bedrock relief values range from 360 – 480 m were delineated. It was estimated from the result that the northwestern and southeastern part which constituted about 15%of the study area possess high groundwater potential while the remaining 85% of the study area exhibit low/moderate potentials for yielding substantial water. Hence, the groundwater potential rating of the area was considered generally low.Keywords- Geoelectric, Groundwater potential, Overburden thickness, Vertical Electrical Sounding

Updated Antarctic crustal model

We use seismic data together with a subglacial bedrock relief from the BEDMAP2 database to obtain a new three-layer model of the consolidated (crystalline) crust of Antarctica that locally improves the global seismic crustal model CRUST1.0. We collect suitable data for constructing crustal layers, analyse them and build maps of the crustal layer thickness and seismic velocities. We use the subglacial relief according to a tectonic configuration and then interpolate data using a statistical kriging method. The P-wave velocity information from old seismic profiles have been supplemented with the new shear-wave velocity models. We adjust the thickness of crustal layers by multiplying a total crustal thickness by a percentage ratio of each individual layer at each point. Our results reveal large variations in seismic velocities between different crustal blocks forming Antarctica. The most pronounced differences exist between East and West Antarctica. In East Antarctica, a high P-wave velocity (vP > 7 km/s) layer in the lower crust is absent. The P-wave velocity in the lower crust changes from 6.1 km/s beneath the Lambert Rift to 6.9 km/s beneath the Wilkes Basin. In West Antarctica, a thick mafic lower crust is characterized by large P-wave velocities, ranging from 7.0 km/s under the Ross Sea to 7.3 km/s under the Byrd Basin. In contrast, velocities in the lower crust beneath the Transantarctic and Ellsworth-Whitmore Mountains are ~6.8 km/s. The P-wave velocities in the upper crust in East Antarctica are within the range 5.5–6.4 km/s. The upper crust of West Antarctica is characterized by the P-wave velocities of 5.6–6.3 km/s. The P-wave velocities in the middle crust vary within 5.9–6.6 km/s in East Antarctica and within 6.3–6.5 km/s in West Antarctica. A low-velocity layer (5.8–5.9 km/s) is detected at depth of ~20–25 km beneath the Princes Elizabeth Land.

Groundwater potential evaluation using geoelectrical and analytical hierarchy process modeling techniques in Akure-Owode, southwestern Nigeria

The complexity and heterogeneity of hydrological conditions in Akure-Owode of southwestern Precambrian basement complex of Nigeria largely control the availability of groundwater supplies in the area. Akure-Owode, being one of the four hydrogeological provinces in Sub-Saharan Africa is worst hit by poor access to continuous supply of groundwater resource throughout the year. Analytical hierarchy process (AHP) modeling technique in conjunction with geo-electric measurements was employed to unravel subsurface complexities and groundwater potential zones in the study area. Geophysical-derived groundwater potential conditioning criteria, namely bedrock relief (B), resistivity (R) and aquifer thickness (T) were synthesized by AHP pairwise comparison weighting and ranking technique to generate groundwater potential indices (GPIs) of the area. Raster-weighted overlay analysis were performed on the GPIs to obtain groundwater potential model (GPM) of the study area. The produced GPM was binned into low, medium and high groundwater potential prediction zones. The performance evaluation of the groundwater potential model using the spatial locations of prolific boreholes and hand-dug wells in the area indicates 80% success rate. Emerging from the vertical electrical sounding curve analysis, weathered (unconfined) and weathered/fractured (unconfined) aquifer types were identified in the area. Hence, the developed groundwater potential map in this study can be harnessed for optimal groundwater resource management of Akure-Owode area.

Vulnerability assessment of an aquifer in the basement complex terrain of Nigeria using ‘LAHBUD’ model

We integrated hydrogeological and hydrogeophysical parameters to evaluate aquifer vulnerability to contamination in a basement complex terrain in Nigeria. Aeromagnetic and Shuttle Radar Topography Mission (SRTM) data were used to generate the composite lineament density map. Lithology information was obtained from the existing geological map, while land-use and land-use changes were derived from the Landsat 8 imagery. We also acquired 216 vertical electrical soundings (VES) to estimate the geoelectric parameters including depth to aquifer, hydraulic conductivity, and bedrock relief maps. The information obtained from geoelectric parameters, lithology, lineament density, and land use were used as the parameters in assessing the aquifer vulnerability using multi-criteria decision analysis (MCDA) in the context of the analytical hierarchy process (AHP). The assigned weights for the various aquifer vulnerability indices are 0.4569, 0.2482, 0.1469, 0.0775, 0.0402 and 0.0303 respectively for lithology (L), depth to aquifer (A), hydraulic conductivity (H), bedrock relief (B), land-use (U) and lineament density (D). These values were normalized and used in establishing a consistency ratio of 6.94%, which is lower than 10% (recommended limit). The MCDA was used to develop the aquifer vulnerability (‘LAHBUD’) model which was used to classify the study area into very low, low, moderate, high, and very high aquifer vulnerability zones. Geochemical parameters obtained from water samples were used to validate the ‘LAHBUD’ model, and gave 81% agreement in predicting the risk level of possible contaminant influence with the conceptual model, and thus confirm the reliability of the model adopted for this study.

Evaluation of groundwater potential zones using integrated geophysical approach in Obun-Ewi, Ondo East local government, Southwestern Nigeria

Obun-Ewi area is underlain by the Precambrian Basement Complex rocks of Southwestern Nigeria. The area suffers from a shortage of freshwater and the main source of water is rainwater. Groundwater provides an alternative solution to face the gap between water demand and available water in this area. Groundwater study involving the application of a very low frequency electromagnetic (VLF-EM) survey and vertical electrical sounding (VES) was carried out in parts of Obun-Ewi area Ondo State, Nigeria to evaluate the groundwater potential of the study area. ABEM WADI equipment was used to establish six (6) VLF-EM traverses with a station interval of 10 m. The inversion of the real component data of VLF-EM into 2D pseudo-sections was generated using Karous-Hjelt software. Linear features assumed to be minor fractures/conductors inferred from the filtered real pseudo-sections helped in choosing twenty-three (23) vertical electrical sounding points that were further probed using DDR-3 resistivity equipment. The Schlumberger electrode configuration was employed with half-current electrode separation (AB/2) ranging from 1 to 100 m. The partial curve matching technique was used to interpret the VES data quantitatively. The geoelectric parameters (depths and resistivities) were used to produce the geoelectric sections, isoresistivity map, isopach maps of the weathered layer and overburden, longitudinal unit conductance map and bedrock relief map of Obun-Ewi, Ondo town. The results obtained from the geoelectric sections revealed three subsurface geologic layers, namely: the topsoil, weathered layer (comprises of clay/sandy clay and laterite), and fractured basement/fresh bedrock. The topsoil resistivity varied from 56 to 1222 Ωm, and depth ranged from 0.5 to 1.8 m. The weathered layer resistivity values ranged from 16 to 1168 Ωm; while the thickness varied from 0.7 to 6.2 m. The overburden thickness varied between 1.6 and 7.2 m. The delineated weathered and fractured basement columns constituted the aquifer units. The composite groundwater potential map generated demarcated the study area into good, moderate and poor groundwater potential zones. The groundwater potential map revealed that about 69.6% of the study area fell within the poor groundwater potential rating, about 21.7% constituted the moderate groundwater potential rating while the remaining 8.7% constituted high groundwater potential rating. The study concluded that the groundwater potential of Obun-Ewi, Ondo town is generally poor, with areas around central South (around VES 9) and far Northern part of the study area (around VES 21) has good groundwater potential, suitable for siting boreholes.

Seismic Imaging of the Mesozoic Bedrock Relief and Geological Structure under Quaternary Sediment Cover: The Bolmin Syncline (SW Holy Cross Mountains, Poland)

The clear and detailed images of geological structures that can be obtained by seismic methods are one of the main drivers of their popularity in geological research. The quality of final geophysical images and models relies strongly on the amount of data that goes into them. Analysing several complementary seismic datasets allow an improved interpretation. Responding to this challenge, this article proposed an optimal combination of geophysical methods for near-surface applications. Multi-channel analysis of surface waves, first-arrival travel-time tomography, and ground-penetrating radar were the key supports for standard reflection seismic imaging. Ease of use and fast and cheap acquisition are some of the advantages of the mentioned methods. Considering that all recorded wave fields required minimal additional processing while offering a significant improvement in the final stack, it was worth the extra effort. Thanks to that, the better-estimated velocity filed allowed high quality images to be obtained up to 200 m. The Mesozoic bedrock was a distinct and very strong reflector in the resulting reflection seismic imaging. There was also a clearly visible depression of the horizon corresponding to erosion or a structure (syncline). Deeper, it was possible to track two or even four detachments of faulting origin.

Eocene Origin of Owens Valley, California

Bedrock (U-Th)/He data reveal an Eocene exhumation difference greater than four kilometers athwart Owens Valley, California near the Alabama Hills. This difference is localized at the eastern fault-bound edge of the valley between the Owens Valley Fault and the Inyo-White Mountains Fault. Time-temperature modeling of published data reveal a major phase of tectonic activity from 55 to 50 Ma that was of a magnitude equivalent to the total modern bedrock relief of Owens Valley. Exhumation was likely accommodated by one or both of the Owens Valley and Inyo-White Mountains faults, requiring an Eocene structural origin of Owens Valley 30 to 40 million years earlier than previously estimated. This analysis highlights the importance of constraining the initial and boundary conditions of geologic models and exemplifies that this task becomes increasingly difficult deeper in geologic time.

A low‐dimensional model of bedrock weathering and lateral flow coevolution in hillslopes: 2. Controls on weathering and permeability profiles, drainage hydraulics, and solute export pathways

AbstractThe advance of a chemical weathering front into the bedrock of a hillslope is often limited by the rate weathering products that can be carried away, maintaining chemical disequilibrium. If the weathering front is within the saturated zone, groundwater flow downslope may affect the rate of transport and weathering—however, weathering also modifies the rock permeability and the subsurface potential gradient that drives lateral groundwater flow. This feedback may help explain why there tends to be neither “runaway weathering” to great depth nor exposed bedrock covering much of the earth and may provide a mechanism for weathering front advance to keep pace with incision of adjacent streams into bedrock. This is the second of a two‐part paper exploring the coevolution of bedrock weathering and lateral flow in hillslopes using a simple low‐dimensional model based on hydraulic groundwater theory. Here, we show how a simplified kinetic model of 1‐D rock weathering can be extended to consider lateral flow in a 2‐D hillslope. Exact and approximate analytical solutions for the location and thickness of weathering within the hillslope are obtained for a number of cases. A location for the weathering front can be found such that lateral flow is able to export weathering products at the rate required to keep pace with stream incision at steady state. Three pathways of solute export are identified: “diffusing up,” where solutes diffuse up and away from the weathering front into the laterally flowing aquifer; “draining down,” where solutes are advected primarily downward into the unweathered bedrock; and “draining along,” where solutes travel laterally within the weathering zone. For each pathway, a different subsurface topography and overall relief of unweathered bedrock within the hillslope is needed to remove solutes at steady state. The relief each pathway requires depends on the rate of stream incision raised to a different power, such that at a given incision rate, one pathway requires minimal relief and, therefore, likely determines the steady‐state hillslope profile.

MicroGravity mapping for King Abdulaziz University campus: imaging subsurface

A gravity survey was undertaken to cover the King Abdulaziz University’s campus (~ 8 km2) as a pilot project funded from Deanship of Scientific Research (DSR). In the current study, 408 gravity stations were collected using the Scintrex CG5 gravimeter and a DGPS system, covering the whole university’ campus. The aim of this survey is to produce the first microgravity map for the King Abdulaziz University campus and image the subsurface conditions which help in the future constructions. Gravity surveys are carried out for 16 days, nights, and weekends when the campus has less traffic noise. Data were processed using conventional gravity data reduction technique, and then microgravity map for the campus was generated. Data were subject to geophysical filters such as edged detection (e.g., horizontal gradient) and depth estimation (e.g., Euler deconvolution, and 3D inversion) to image the subsurface conditions. Results indicate that bedrock relief surface is located at about 150 m. Some cracks/fractures were traced/detected underneath the surface in various directions. The results also indicate that the university campus is located on high-density rock zones, giving more stability to buildings.

The trends in the main thalweg path of selected reaches of the Middle Vistula River, and their relationships to the geological structure of river channel zone

Abstract Research carried out by the authors’ team in the valleys of many rivers in the Polish Lowlands has shown that the contemporary morphodynamics of channel zones is highly influenced by protrusions of erosion-resistant sub-alluvial bedrock. The article presents the results of analysis of two reaches of the Middle Vistula: near Solec nad Wisłą (km 330-340) and Gołąb (km 382-388), where such protrusions have been found. At each of them, two series of bathymetric measurements were carried out during medium and low water levels in the river channel. The measurements were made using hydrographic sets integrated with a GNSS receiver. The first series of measurements was carried out in July 2004, and the second one in September 2016. In parallel with the bathymetric surveys, low-altitude aerial photographs were taken in 2016 to document the morphology of the channel zone and the condition of the river engineering structures. A comparison of the obtained bathymetric maps shows a high correspondence between the thalweg line from 2004 and that observed twelve years later. This phenomenon proves the significance of the bedrock relief beneath the modern alluvial deposits for the water flow process in the channel. The relief causes the flow to concentrate in specific zones so strongly that it contributes to the damage of river engineering structures that put limits on the channel processes. This trend of concentrating the main thalweg is also accompanied by the diversity of depositional environments of river channel facies, identified along the studied reaches.