Buried Valley Research Articles

A detailed investigation into the legacy of glacial readvances and ice-dammed lakes around Sellafield, West Cumbria: Implications for 3D modelling, hydrogeology and ground engineering

The glacial evolution of western Cumbria, England is reassessed following a comprehensive review of both published and extensive unpublished records from the Sellafield area, together with targeted fieldwork. The exercise scrutinises evidence for glacial readvances across former ice-dammed lakes, determining their occurrence, relative age, extent and legacy. It is concluded that the area was affected by at least two substantial glacial readvances following the maximum build-up of ice during the last, Late Devensian (Weichselian/Wisconsin) glaciation. The earlier Gosforth Oscillation involved locally sourced ice together with ice that circulated around the north of the Lake District into the Irish Sea basin whilst most of the region was substantially glaciated. The subsequent Fishgarth Wood Readvance involved ice flowing from the north, but when an ice centre positioned over the western Southern Uplands of Scotland had become dominant. Glacial oscillations across the coastal plain have resulted in a complex interdigitating sequence of sediments of contrasting permeability and physical properties, commonly preserved within buried valleys. The genesis of some thin units of clay-rich diamicton and pebbly clay previously interpreted as till is discussed in the light of ongoing debate concerning their possible glaciolacustrine origin.

Transport of nitrate-containing groundwater to coastal areas through buried tunnel valleys, Denmark

Nitrogen impact on the aquatic environment, including coastal areas, is too high in many countries worldwide, particularly in areas with intensive agriculture. Efficient mitigation initiatives demand that important pathways and the fate of nitrate in the hydrological cycle are known. In this study, we focus on groundwater nitrate contamination in two near-shore catchment areas in north-west Denmark. Groundwater in the area is mainly located in buried tunnel valleys, which are subsurface structures eroded by meltwater during Pleistocene glaciations in former glaciated areas. Groundwater samples from the aquifers inside the buried valleys reveal the presence of up to 120 mg/l nitrate down to 10 m below sea level and about 1 km down from the stream outlet towards the coast. We interpret the complex tunnel-valley infill to be responsible for the spatial heterogeneity of the groundwater geochemistry, where sandy geological windows create localised hydraulic pathways and complex redox structures. Groundwater and stream water chemistry in the study area clearly demonstrate the role of groundwater in nitrate transport within the catchment as well as the direct pathway to the coast bypassing the stream and riverine systems. Our results show that the buried tunnel valleys potentially contribute to submarine groundwater discharge and therefore could be responsible for a hitherto unaccounted input of nitrogen to the marine environment.

Drilling into a deep buried valley (ICDP DOVE): a 252 m long sediment succession from a glacial overdeepening in northwestern Switzerland

Abstract. The modern Alpine landscape and its foreland were strongly impacted by the numerous glacier advance and retreat cycles during the Middle-to-Late Pleistocene. Due to the overall erosive character of each glaciation cycle, however, direct traces of older glaciations tend to be poorly preserved within the formerly glaciated domains of the pan-Alpine area. Nevertheless, sediments of older glaciations may occur hidden under the modern surface in buried glacially overdeepened troughs that reach below the normal level of fluvial erosion (fluvial base level). These sedimentary archives, partly dating back to the Middle Pleistocene period, are of great scientific value for reconstructing the timing and extent of extensive Alpine glaciation, paleoclimate, and paleoenvironmental changes in the past and help to better understand ongoing and future changes in the pan-Alpine area. Therefore, the International Continental Scientific Drilling Program (ICDP) project DOVE (Drilling Overdeepened Alpine Valleys) targets several of these glacial overdeepened sedimentary basins to recover their sedimentary infills. In the frame of the DOVE project, a 252 m long drill core of unconsolidated Quaternary sediments was recovered in northern Switzerland from an over 300 m deep glacially overdeepened structure (“Basadingen Trough”) formed by the former Rhine Glacier lobe system. The recovered sedimentary succession was divided into three stratigraphic units on the basis of lithological and petrophysical characteristics. The lowest unit, deposited below the fluvial base level, consists of an over 200 m thick succession of glacial to (glacio)lacustrine sediments and contains remains of possibly two glaciation cycles. Overlying this lowermost succession, an ∼ 37 m thick fluvial-to-glaciofluvial gravel deposit occurs, which correlates to a locally outcropping Middle Pleistocene formation (“Buechberg Gravel Complex”). The sediment succession is capped by an ∼ 11 m thick diamictic succession interpreted as the subglacial till from the later extensive glaciation, including the regional glaciation during the Last Glacial Maximum. The recovered sediment succession thus supports the proposed multi-phase origin of trough formation and its infill.

The Empress Group in Alberta, Canada

Basal gravel and sand mantling the bedrock floors of buried valleys throughout the Canadian Interior Plains, and conformably overlying proglacial lacustrine sediment, comprise the Empress Group. While previously conceptualized as stratigraphically equivalent deposits of preglacial rivers prior to the first and most extensive continental and montane glaciations, subsequent stratigraphic studies indicated that buried valley basal gravel must have been deposited between, or during, progressively more extensive continental glaciations and could not be stratigraphically equivalent throughout the buried valley network. However, in the general absence of formation-rank stratigraphic description of basal gravel units that might better inform the geologic history of the deposits, most workers simply consider Empress Group sediments time-transgressive. In this paper, we examine basal gravel at provincial and regional scales to understand its genesis and geologic history. At the provincial scale, we map basal gravel in three dimensions using a novel machine learning approach. At the regional scale, we formally define basal gravel formations at either end of the largest buried valley system in Alberta, which informs its glacial history and physiographic development and shows the importance of formation-rank stratigraphic description. Our results indicate that the buried valley network across Alberta is palimpsest in genesis and basal gravel units within it are chronostratigraphically intercalated between tills. We advocate that the Empress Group definition be extended across Alberta with modifications to improve its clarity and utility, and formally define the Old Fort, Unchaga, Ipiatik, and Winefred formations as part of the Empress Group.

Buried River Valleys of the Neogene and Early Quaternary in the Middle Volga Region, European Russia

Buried river valleys from the Neogene–Quaternary time are widespread throughout the Middle Volga region of the Russian Plain. They have been studied for a long period, since the 1940s, with the last major generalizations dating back to the 1980s. This paper presents new results based on GIS mapping using materials from the state geological study of the region in 1960–1970, 1984–1996 and 2000–2002. On the whole, the pattern of the buried valley network is close to the modern valley network of the region. During the Quaternary, the right-sided displacement of the valley incisions prevailed. The incisions of modern river valleys are located above the Neogene (pre-Akchagyl) incisions almost throughout the entire territory. The vertical displacement amplitude ranges from 30 to 200 m. The morphometric characteristics of the paleovalleys (the depth and width of the incisions, as well as the gradients of the bottoms of the paleovalleys) exceeded modern ones. The maximum values were typical for the middle Paleo-Volga valley: the width of the valley reached 10 km, the incision depth was−201.4 m below sea level and the bottom gradient was 0.9–5.0 m/km. The most important factor that influenced the position of paleovalleys and their morphological appearance was fluctuations in the level of the Caspian paleowaterbody. According to this study, the development of paleovalleys began in the Miocene and ended in the Early Quaternary. The alluvial–lacustrine type of sedimentation was predominant. The results of this work contribute to the study of the paleogeography of the Cenozoic of the southeast of the Russian Plain.

東京低地の埋没谷形状と地盤震動特性：上野-小岩測線での検討結果

To better understand how ground motion in the Tokyo Lowland is affected by the geological conditions in the shallow subsurface, we analyzed borehole logs and conducted microtremor observations along the Ueno-Koiwa survey line, which crosses the buried valley beneath the Tokyo Lowland. Remarkable peaks in the H/V spectra at ~1 Hz were found in the area of the lower buried terrace (buried flat surface 2), whereas the peaks at ~1 Hz are small in the area of the buried valley bottom with the thickest valley-filling post-Last Glacial Maximum (LGM) deposits. The sharp peaks around buried terrace 2 are generated by the large contrast in the physical properties of the soft, muddy post-LGM deposits and the underlying gravel bed, which suggests larger ground-motion amplification during an earthquake. The variation of the ground motion characteristics along the survey line obtained by microtremor observation is consistent with the distribution of seismic intensity during the 1923 Kanto Earthquake. It is, therefore, important to consider not only the thickness and physical properties of the post-LGM deposits during seismic hazard assessment, but also the total geological composition, including the Pleistocene strata below the post-LGM deposits.

Estimation of Aquifer Storativity Using 3D Geological Modeling and the Spatial Random Bagging Simulation Method: The Saskatchewan River Basin Case Study (Central Canada)

Hydrosystems in the Saskatchewan River Basin of the Canadian Prairies are subject to natural and socioeconomic pressures. Increasingly, these strong pressures are exacerbating problems of water resource accessibility and depletion. Unfortunately, the geometric heterogeneity of the aquifers and the presence of lithologically varied layers complicate groundwater flow studies, hydrodynamic characterization, and aquifer storativity calculations. Moreover, in recent hydrogeological studies, hydraulic conductivity has been the subject of much more research than storativity. It is in this context that the present research was conducted, to establish a 3D hydrostratigraphic model that highlights the geological (lithology, thickness, and depth) and hydrodynamic characteristics of the aquifer formations and proposes a new uncertainty framework for groundwater storage estimation. The general methodology is based on collecting and processing a very fragmentary and diverse multi-source database to develop the conceptual model. Data were harmonized and entered into a common database management system. A large quantity of geological information has been implemented in a 3D hydrostratigraphic model to establish the finest geometry of the SRB aquifers. Then, the different sources of uncertainty were controlled and considered in the modeling process by developing a randomized modeling system based on spatial random bagging simulation (SRBS). The results of the research show the following: Firstly, the distribution of aquifer levels is controlled by tectonic activity and erosion, which further suggests that most buried valleys on the Prairies have filled over time, likely during multiple glaciations in several depositional environments. Secondly, the geostatistical study allowed us to choose optimal interpolation variographic parameters. Finally, the final storativity maps of the different aquifer formations showed a huge potential of groundwater in SRB. The SRBS method allowed us to calculate the optimal storativity values for each mesh and to obtain a final storativity map for each formation. For example, for the Paskapoo Formation, the distribution grid of groundwater storage shows that the east part of the aquifer can store up to 5920 × 103 m3/voxel, whereas most areas of the west aquifer part can only store less than 750 × 103 m3/voxel. The maximum storativity was attributed to the Horseshoe Canyon Formation, which contains maximal geological reserves ranging from 107 to 111 × 109 m3. The main contribution of this research is the proposed 3D geological model with hydrogeological insights into the study area, as well as the use of a new statistical method to propagate the uncertainty over the modeling domain. The next step will focus on the hydrodynamic modeling of groundwater flow to better manage water resources in the Saskatchewan River Basin.

Implications on Gravity Anomaly Measurements Associated with Different Lithologies in Turkana South Subcounty

The use of gravity data has demonstrated capability for monitoring lithological changes on a large scale as a consequence of differentiating basement and sedimentary of buried valleys. Gravity anomalies are associated with lateral contrasts in density and therefore deformation by faulting or folding will be manifested if accompanied by lateral density changes, otherwise, the vice versa is true. The study’s objective is to evaluate the effectiveness of gravity method in establishing different lithologies in an area. The study has revealed that regional anomaly gravity map presents high anomalies in the Northern region in the NW-SE trend and low anomalies in the southern trend in NW-SE, while the residual anomaly gravity map shows different trends for the low and high gravity anomalies. The gravity anomalies are well interpreted in line with the lithologies of the study area rather than the deformation of the same lithologies. There are observed high values of gravity anomaly values (ranging from -880.2 to -501.2 g.u.) where there are eolian unconsolidated rocks overlying the basement compared to low gravity anomaly values (ranging from -1338.9 to -1088.7 g.u.) where the andesites, trachytes and phonolites overly the basement. The different regional gravity anomalies relate well with different rock densities in the study area along the line profile for radially averaged power spectrum. The gravity highs are noted in the eastern point and are associated with andesites, trachytes, basalts and igneous rocks, while the gravity lows are associated with sandstone, greywacke, arkose, and eolian unconsolidated rock. The utilization of the information from the Power spectrum analysis demonstrates that the depth to the deepest basement rock is 12.8 km which is in the eastern flank, while the shallowest to the basement of 1.1 km to the western flank.

Tectonic impact on Pleistocene and Holocene erosional patterns in a formerly glaciated intra-plate area

Deep-seated faults have for a long time been thought to have had an influence on the formation of valleys both in the subsurface and in the present-day terrain in and around former glaciated areas. To systematically investigate if, and if so, how faults may have impacted on the erosional patterns during the Pleistocene and the Holocene in Denmark, three separate vector datasets of mapped buried valleys, topographic valleys, and deep-seated faults have been compared with respect to orientations. Several correlations in the datasets were found. Correlations between tunnel valleys and deep-seated faults suggest that structural weaknesses along faults within the sedimentary succession may have altered the hydraulic properties of the sedimentary strata and thereby have created biased erosion patterns beneath the ice sheets. Correlations between deep-seated faults and erosional valleys in the modern landscape point to active tectonics enabling the erosion to mirror the tectonic framework in the present-day topography. We propose a model that invokes the mechanism of glacially triggered faulting in all of the Danish area, intermittently impacting on erosion. The erosion during the Quaternary seem to have favoured old and well-established patterns, and areas over active faults appear to represent zones more susceptible to erosion. Our findings suggest that recurrent impact on erosion patterns from glacially triggered faulting can be expected in and around former glaciated areas during the Pleistocene and the Holocene.

Seismic microzonation of a region with complex surficial geology based on different site classification approaches

A seismic microzonation study was conducted to refine the seismic hazard model for the city of Saguenay, Canada. The Quaternary geology underlying Saguenay shows complex glacial and post-glacial stratigraphy with a number of buried valleys filled with fluvioglacial and glaciomarine sediments. High impedance contrast between rock formations and surficial sediments is prone to seismic amplification. To evaluate their applicability, advantages and limitations in capturing the geological specificity of the study area, four site classification methods were applied: the current National Building Code of Canada (NBCC) and Eurocode 8, both mainly based on the average shear-wave velocity for the surficial sediments (VS,avg) and for the top 30 m (VS,30); a method based on the fundamental site period (T0); and a hybrid method based on the combination of VS,30, T0 and VS,avg. The study specifically aimed to evaluate the importance of the site classification parameters on the resulting microzonation maps. VS,30 is capable to present the geological and geotechnical site conditions, however, the results may be further improved by considering Vs,avg in shallow and T0 in thick layers of soil sediments as secondary parameters. The T0 method gives also satisfactory results with T0 showing a better correlation to Vs,30 than to Vs,avg. The versatile hybrid method may be challenging to apply in certain cases with its nine different site categories and parameters.

A comparison of 2D inversion of RMT and 1D weighted joint inversion of ground-based and helicopter-borne electromagnetic data

A Pleistocene buried valley, the Cuxhaven Valley, located in Northern Germany, is extensively studied by three different electromagnetic methods. In order to enhance the resolution of the very shallow subsurface structures, the radiomagnetotelluric (RMT) measurements were conducted on the buried valley in addition to the helicopter-borne electromagnetic (HEM) and transient electromagnetic (TEM) data, which were available from the study area along the same profile. First, the RMT soundings are interpreted using the conventional 1D and 2D inversion algorithms. The RMT interpreted models inferred two-layer structure of the subsurface up to a depth of 30 m, which comprises a resistive layer at the top. Available lithological data is used for correlating the resistivity values derived from the 2D inversion of the RMT data with the subsurface formation. Subsequently, a 1D weighted joint inversion algorithm is utilized to interpret these three data sets jointly. The 2D interpreted models of RMT soundings are compared with the 1D weighted joint interpreted models of RMT, HEM, and TEM soundings.

Meander chute cutoff at an alluvial river facilitated by gypsum sinkholes

Collapse sinkholes are common in areas where gypsum strata underlie rock that is incompetent to bridge the cavities created by the groundwater dissolution of gypsum. On floodplains these can be obscured due to fill by overbank deposits, and channels tend to migrate towards larger enclosed depressions. This study utilises GIS to analyse the influence exerted by small collapse sinkholes on the channel dynamics of the alluvial River Ure, UK. At Ripon Loop, a large compound meander bend, sinkhole area and channel dynamics have been tracked over >160 years from multiple datasets, including historic maps, aerial imagery, lidar and a Structure-from-Motion photogrammetry dataset acquired for this study. This indicated two distinct populations, firstly long-lived, constant-sized sinkholes and secondly dynamically growing holes aligned with the contact of bedrock and unconsolidated materials of a buried valley at depth where artesian water saturated with sulphate enters the latter. Frequent overbank flows of the River Ure across the neck of the bend have interacted with sinkholes, e.g. by deposition of bedload in the down-valley end of the holes and localised headward incision on the opposite side due to the relatively high gradient between holes and the downstream limb. The location of holes has conditioned the incision of small shallow channels over at least 7 years, before cutoff occurred over several floods in 2019. Initially overbank flow traversed the neck via the chain of sinkholes before widening and deepening of the channel captured all the surface flow of the River Ure, resulting in the mobilisation of more than 20,000 m3 of sediment. Allogenic influences on fluvial systems in relation to meander dynamics are often neglected and this study is the first to link floodplain sinkholes with detailed mechanisms of a chute cutoff, hereby indicating a potential feedback to sinkhole dissolution processes.

Estimation using multiple-point statistics

In the last two decades, several geostatistical simulation techniques have appeared that allow taking into account complex structural information, by quantifying a multiple-point statistical (MPS) model. The higher-order statistics are typically informed from a training image, sample model, or geological exposure. Such MPS models can represent the subsurface and are then used to simulate subsurface models with high(er) order of realism than is possible using, for example, the widely used 2-point statistical models (such as sequential Gaussian simulation).All available methods dealing with MPS models are simulation methods, that can be used to generate multiple realizations of the underlying statistical model conditioned to hard and, to some extent, soft data. Such realizations can be very useful but are also computationally expensive to obtain. Here we consider the case when the end-user may not be interested in the set of produced realizations themselves, but rather in parameter-wise marginal statistical properties of a single model parameter derived from the simulated realizations. To obtain these, one would typically generate a larger number of independent realizations, and then compute some marginal statistics of these.Here we propose an MPS estimation algorithm, a variant of the widely used sequential simulation algorithm, that can be used to directly compute and store parameter-wise conditional statistics. This allows for a potentially faster and more accurate estimation than using sequential simulation. The method is demonstrated on both ENESIM- and SNESIM-type MPS algorithms and results compared using both sequential simulation and estimation. As an example, the method is applied for estimating the existence of near-surface buried valley systems in Kasted, Denmark.

Subsurface profiling of buried valleys in central alps (northern Italy) using HVSR single-station passive seismic

Active and passive seismic techniques permit to draw images of relevant buried morphologies in mountainous areas. Here we apply the Horizontal-to-Vertical Spectral Ratio (HVSR) passive seismic technique to draw the shape of a buried valley in the core of the Italian Central Alps, at the confluence among the fault-controlled Valtellina, Valchiavenna and Lake Como depressions (“Colico knot”). Twenty-three single-station, ambient-noise measurements were acquired and the site-specific fundamental frequency f0 was obtained by computing the HVSR in the 0.5 Hz to 5 Hz frequency band.Shear wave velocity (Vs)-versus-depth profiles were computed from the inversion of the HVSR curves, under the assumption of a 1D structure. To limit uncertainty, the results were calibrated by comparison with data from two sources: 1) HVSR profiles acquired in a comparable setting in Valtellina, at a site where estimates of Vs for the seismic basement and cover sediments were available; 2) borehole logs which crossed the sediments above the metamorphic bedrock at the Colico knot site. Independent data were used to constrain the best fit of the experimental HVSR peaks at the Colico knot site, in terms of frequency f0 and HVSR amplitude, thus retrieving information about Vs variations related to the bedrock versus sediments unconformity.A SW-NE elongated buried trough, as deep as 150 m below sea-level and up to 2 km wide was drawn from the present-day Adda valley to the Lake Como depression to the South. The morphology of this abandoned and buried course of the Adda river is controlled by active deep-seated gravitational slope deformation along the adjacent mountain slope. The valley was abandoned before the Last Glacial Maximum (latest Pleistocene), plausibly owing to narrowing and uplift induced by deep-seated slope deformation. In fact, the LGM Adda glacier reshaped the valley slopes and the bedrock watershed that separates at present the post-Glacial Adda river course from the paleo-Adda trough.

A geotechnical stratigraphy for the shallow subsurface in the Southern Central Graben, North Sea

The Integration of conventional 3D seismic data with high-resolution 2D seismic data and cone penetration test (CPT) data from geotechnical jack-up foundation reports has enabled a new late Quaternary geotechnical stratigraphy for the Southern Danish Central Graben area in the North Sea. The shallow subsurface has been subdivided into geotechnical units based on seismic appearance and soil behaviour type. The lateral thickness and geotechnical property variations have been mapped and associated with the existing stratigraphies from adjacent areas in the German and British sectors. The geotechnical variations have also been related to geomorphological features in the subsurface that are a result of the changing glacial conditions over the last 120.000 years. Particularly, buried valleys produce unpredictable geotechnical conditions that require additional evaluation and possibly borehole investigations as well as CPTs. The study synthesizes data from multiple geotechnical surveys and extrapolates the local knowledge from the different sites, providing a better regional understanding of the geology and the geotechnical behaviour of the shallow subsurface. • A geotechnical stratigraphy based on seismics and CPT data. • Correlation of seismic facies and geotechnical property distributions. • Regional stratigraphic input to improve risk assessment in offshore construction. • Geotechnical data improves geological evolution models.

The Origin of Terraces in Buried Valleys in the Northwest of the East European Plain

Abstract —The paper considers the origin of terraces that often complicate the slopes of abnormally deep buried valleys in the northwest of the East European Plain. The Izborsk–Maly valley (Pskov Region, Russia), which is half filled with Quaternary sediments, was chosen as the object of study. Since the upper part of the valley remains unfilled, it is possible to study in detail both geologic and geomorphologic structures of its terraced slopes being of particular interest in the context of the origin of buried valleys and the role of substrate in it. The four denudation-terrace levels that have been identified on the slopes of the Izborsk–Maly valley at absolute elevations of 53, 56–58, 70–72, and 75–77 m formed during the destruction of the preglacial karst landscape under the influence of Pleistocene glaciations. The formation of the terraces was probably linked with several stages of overdeepening of the valley and its expansion by the glacial erosion processes, which corresponded to at least two stages of the ice sheet advance in this area. The last stage may have been the beginning of the Late Valdai (Weichselian) glaciation or the activation of the edge of an ice sheet during its Luga phase (~15.7 cal kyr BP). Results of the study suggest that the Izborsk–Maly valley formed in subglacial conditions. The degree of glacial erosion was determined primarily by the coherence of Devonian carbonate-terrigenous rocks hosting the valley and the degree of the area transformation by karst processes. The cirque shape of slopes is the evidence of karst processes expression in pre-glacial time. Analysis of literature data shows that the origin of denudation terraces in the buried valleys in the northwest of the East European Plain has been paid little attention. The obtained data contribute to the study of this problem and provide insights into the origin of buried valleys.

Последствия техногенного погребения рек в городах (на примере Москвы)

This article reviews the consequences of man-made burial of river valleys in urban areas. Deep analysis of above-mentioned sources enabled to reveal the consequences of river system destruction in urban areas, located on platforms. Backfilling of the river valleys leads to the following negative changes: surface runoff increases by 200-280%, sediment load increases up to 60-90 m 3 per year by 1 km 2 , suffusion and land subsidence begin to develop within man-made buried valleys (2-3 mm per year). Subsurface flow changes cause progressive groundwater flooding and growing level of water mineralization. Total dissolved solids index grows, these waters become aggressive which results in drainage destruction and damaging of urban infrastructure, such as pipelines and sewerage. Destruction of urban river system leads sharp to the environmental issues: small rivers (including storm drain) accumulate various pollutants and deplete flora and fauna. Karst processes were activated in Moscow a few years after backfilling of the river valleys due to subsurface flow changes.

Bent incised valley formed in uplifting shelf facing subduction margin: case study off the eastern coast of the Boso Peninsula, central Japan

Abstract The Boso Peninsula is located in central Japan near the junction of the subduction boundary of three tectonic plates. A forearc basin has been developing there since 3 Ma and has been uplifting since 1 Ma. The basal surface of the Holocene deposits in the offshore area was investigated based on a seismic survey and is very similar to the adjacent land areas (the Iioka Plateau, the Kujukuri Plain and the Kazusa Hills). The basal surface in the Kujukuri Plain and its corresponding offshore area contains many incised valleys. Most of them extend southeastward, parallel to the direction from the hinterland to the ocean, but one incised valley (Kujukuri-oki Buried Valley) lies perpendicular to the others. A buried terrace is located SE of the valley and along the area where mudstone (of the Kiwada Formation) is distributed. The present observations indicate that differential erosion formed the terrace, after which the valley bent to follow the terrace. The rivers tend to be perpendicular to the strike of the sediment in the forearc basin owing to tectonic movement. Thus, the valley must have been incised into the underlying strata with a perpendicular strike and may have become bent in uplifting forearc basins.

Морфология погребенных долин ленского золотоносного района и связанные с ней особенности строения аллювиальных россыпей

In this article were summarized data of exploration work conducted in the valleys of the Lena gold-bearing area, starting from the early stages of exploration (1910–1920s) and ending with the 1990s, including large-scale production plans. the drainage system of the area inherits the faults that were formed in the late jurassic – early cretaceous. buried valleys inherit their position during several erosion cycles: in the same reaches the position and width of valleys of different ages remains approximately the same, but in the bottoms of valleys of different ages large transformations are observed. in the formation of the morphology of the buried valley of the Lena gold-bearing area, the leading role belongs to river channel processes. Stable position of the river valleys determines the inherited position of the placers, as a rule, they are located within the contours of the modern valleys or their bottoms, or are slightly shifted to terrace staircases. Inherited are also morphodynamic types of channels, however, in cases of displacement of the valleys to areas with different lithological and tectonic conditions, morphological structure of valleys and alluvial deposits also change. This leads to formation of beads-like widening of the valleys and steps in their longitudinal profiles. Specific examples of such changes are illustrated from the large valleys of the rivers vacha and bodaybo. Three types of buried erosional terraces were considered that alternate along the length of valleys and determine specific position of the placers. a significant influence of the major tributaries to the structure of placers was found that is expressed in the presence of a transverse to the axis of the valley of the gold-bearing layers and sudden changes of elevation values of their beds. the established regularities are relevant to other mining areas and may have great practical importance in prospecting and exploration of mineral deposits.

Current challenges of underground water resources research in volcanic areas of the Armenian highlands (case study: mount Aragats)

From the hydro-geological perspective the territory of the Central Volcanic Highlands of Armenia is a highly elevated area which mainly belongs to the hydrodynamic zone of intense underground flow.
 Our systematic and planned research aimed at studying groundwater in the Central Volcanic Highlands of Armenia covers the following regions: Mount Aragats, Gegham, Vardenis and Syunik Volcanic Highlands, the Ararat, Shirak and Sevan valleys, the Lori Volcanic Plateau etc.
 In the Armenian Highlands, along the periphery of Mount Aragats, the purpose of the conducted studies was to determine the possibilities of applying the vertical electrical sounding (VES) method for mapping the basement relief of water-resistant rocks and identifying the aquifers.
 In general, the lava of Armenian volcanic highlands is characterized by the formation and accumulation of two main types of underground runoff: concentrated and distributed. Concentrated runoff is a concentrated underground stream formed in the buried valleys and moves in a certain direction along a paleo-relief. Distributed runoff is a relatively dispersed underground stream formed in the buried watershed between paleo-valleys and moving in their direction. It feeds the concentrated runoff.
 Based on the hydro-geophysical studies, the main conclusions on distribution and exploitation of groundwater across certain volcanic regions of the Central Volcanic Highlands of Armenia are presented. Mount Aragats, where electrical exploration surveys took place using the VES method, is presented as a case study. Hydro-geophysical studies made it possible to analyze certain drainage basins of the rock massif in order to allow a more detailed “dissection” of the groundwater runoff.
 As a result, a summary map of the paleo-relief was compiled. The map shows the distribution of the underground runoff of the volcanic massif of Mount Aragats which forms an important basis for conducting hydrogeological initiatives aimed at solving the problem of fresh water shortage at the national level.