Deep Valleys Research Articles

B-PO03-111 A NEW ELECTROPHYSIOLOGICAL TRIAD FOR ATRIAL FLUTTER CRITICAL ISTHMUS’ IDENTIFICATION AND LOCALIZATION

Atypical atrial flutter (AFL) is a supraventricular arrhythmia that can be treated with catheter ablation. However, the best approach is still to be defined and this strategy has suboptimal results. The Carto® electroanatomical mapping (EAM) version 7 displays a histogram of the local activation times (LAT) of the tachycardia cycle length (TCL), in addition to the activation and voltage maps. The study aimed to assess the ability of an electrophysiological triad to identify and localize the AFL’s critical isthmus. Retrospective and prospective analysis of a multicentric registry of individuals who underwent left AFL ablation during a 1-year period with Carto® EAM. All patients with non-left AFL, lack of high-density EAM, less than 2000 collected points or lack of mapping in any of the left atrium walls or structures were excluded. Ablation sites of arrhythmia termination were compared to an electrophysiological triad constituted by: areas of low-voltage (0.05 to 0.3mV), sites of deep histogram valleys (LAT-Valleys) with less than 20% density points relative to the highest density zone and a prolonged LAT-Valley duration that included 10% or more of the TCL. The longest LAT-Valley was designated as the primary valley, while additional valleys were named as secondary. We assessed 21 patients (9 patients retrospectively and 12 patients prospectively), 14 men with a median age 74 IQR 67-76 years). All patients presented with left AFL and 66% had a previous atrial fibrillation and/or flutter ablation. The median TCL and number collected points were 252 (220290) milliseconds and 3250 (IQR 24103900) points, respectively. All AFL presented with at least 1 LAT-Valley in the analysed histograms, which corresponded to heterogeneous low-voltage areas (0.05 to 0.3mV) and encompassed more than 10% of TCL. Seventeen of the 21 patients presented with a secondary LAT-Valley. All arrhythmias were effectively terminated after undergoing radiofrequency ablation in the primary or the secondary LAT-Valley location. An electrophysiological triad was able to identify the AFL critical isthmus in all patients. Further studies are needed to assess the usefulness of this algorithm to improve catheter ablation outcomes.

Plant adaptability in karst regions.

Karst ecosystems are formed by dissolution of soluble rocks, usually with conspicuous landscape features, such as sharp peaks, steep slopes and deep valleys. The plants in karst regions develop special adaptability. Here, we reviewed the research progresses on plant adaptability in karst regions, including drought, high temperature and light, high-calcium stresses responses and the strategies of water utilization for plants, soil nutrients impact, human interference and geographical traits on karst plants. Drought, high temperature and light change their physiological and morphological structures to adapt to karst environments. High-calcium and soil nutrients can transfer surplus nutrients to special parts of plants to avoid damage of high nutrient concentration. Therefore, karst plants can make better use of limited water. Human interference also affects geographical distribution of karst plants and their growing environment. All of these aspects may be analyzed to provide guidance and suggestions for related research on plant adaptability mechanisms.

Slope deformation, reservoir variation and meteorological data at the Khoko landslide, Enguri hydroelectric basin (Georgia), during 2016–2019

Abstract. The Greater Caucasus mountain belt is characterized by deep valleys, steep slopes and frequent seismic activity, the combination of which results in major landslide hazard. Along the eastern side of the Enguri water reservoir lies the active Khoko landslide, whose head scarp zone affects the important Jvari–Khaishi–Mestia road, one of the few connections with the interior of the Greater Caucasus. Here, we present a database of measurement time series taken over a period of 4 years (2016–2019) that enables us to compare slope deformation with meteorological factors and human-induced perturbations owing to variations in the water level of the reservoir. The monitoring system we used is composed of two digital extensometers, placed within two artificial trenches excavated across the landslide head scarp. The stations are also equipped with internal and near-ground surface thermometers. The dataset is integrated by daily measurements of rainfall and lake level. The monitoring system – the first installed in Georgia – was set up in the framework of a NATO-funded project, aimed at assessing different types of geohazards affecting the Enguri artificial reservoir and the related hydroelectrical plant. Our results indicate that the Khoko landslide displacements appear to be mainly controlled by variations in hydraulic load, in turn induced by lake level oscillations. Rainfall variations might also have contributed, though this is not always evident for all the studied period. The full databases are freely available online at the following DOI: https://doi.org/10.20366/unimib/unidata/SI384-2.0 (Tibaldi et al., 2020).

EFFECT OF MIG WELDING PROCESS PARAMETERS ON EROSION AND CORROSION BEHAVIOR OF ASTM A106 GRADE-B PIPE WELDMENTS

Evaluating the integrity of the welded pipes used for fluid transportation in processing industries demands certain investigations on the erosion and corrosion behavior under various environmental conditions. ASTM A106 Grade-B pipes are butt welded using an automated MIG welding setup to obtain the optimum output response such as Reinforcement Form Factor (W1), Penetration Shape Factor (W2), and Tensile Strength (W3) in the weldments. The slurry erosion test is conducted on the weldment surface by varying the velocity and erodent concentration in acidic (0.1M H2SO[Formula: see text] and alkaline (3.5%[Formula: see text]wt. NaCl) conditions. Correspondingly, the samples are subjected to electrochemical corrosion test in 0.1[Formula: see text]M H2SO4 and 3.5% wt. NaCl solutions. The SEM investigations carried out on the eroded weldment surface show glimpses of erosion mechanisms such as shallow and deep ploughing, oxide cracks, ridges and valleys, scale formation at some areas attributing to sulphide deposition. The corrosion that occurred on the weldment surface tested under acidic conditions is relatively high compared to the alkaline conditions. The reinforcement form factor is the most preferable weld bead characteristic to obtain better erosion and corrosion resistant weldments in the investigated pipe material.

Analysis of the possibility of switching to agroforestry in Zselic

Agroforestry solutions offer better use of disadvantaged agricultural land. Steep slopes and the constant risk of game damage are not conducive to agriculture. On slopes, the cost of machine operating hours is higher than on plane areas, and machines also wear out faster due to higher loads. Varied topography, steep slopes and deep valleys characterize the examined Zselic hills. There is typical forest management on the steep slopes that results in higher opportunity for game damage in the agricultural areas surrounded by forests. There are steep slopes under agriculture cultivation too that involve high operating costs. In our article, we examined whether the actual steep areas under current agricultural cultivation (slope> 12%) are large enough to consider switching to agroforestry. We have found that a quarter of all agricultural areas included in the examination is located on steep slopes, where it is worth considering switching to game damage-resistant agroforestry.

Comparative study of bridge configurations for dynamic analysis

A bridge is a physical structure which carries roadway, pathway or a railway etc over the obstacles like a water body example a river, deep valley, a rail or a road. Today the bridges are diversified into Cable stayed bridge, Suspension Bridge, Arch Bridge, Box Girder Bridge, Solid Slab Bridge, Arch Bridge, Movable Bridge, Truss Bridge, Cantilever Bridge etc. The bridge design varies by many factors such as aesthetic appearance, its usage or functionality of the bridge, anchorage, terrain and topography where the bridge to be constructed, and economic factors or funds etc.The main objective of analyzing and design of bridges is to find the internal stresses, deflections, shear force, moments, deformation by the action of various loads and load effects. In the present context a cable stayed bridge, T-beam bridge and a truss bridge each of span 80 m is considered by modeling and analysis of the corresponding bridges subjected to dynamic load conditions by using SAP 2000.The deflections in the girder bridge are very less when compared to truss bridge and cable stayed bridge. The durability and reliability of girder bridge is high. The cable stayed bridge and truss bridge are susceptible for environmental effects like they are prone to corrosion.

Sampling stable amorphous tantalum states from energy landscape

Amorphous pure metals are important for technological applications and provide a simple system for the study of fundamental science. Through detailed analysis of the microscopic structure of vapor-deposited Ta film, we reveal the presence of various micro-regions with distinct packings of different atomic clusters. These results suggest that high-throughput production of atomic cluster packing can be generated during the packing of vaporized atoms on a large depositing substrate, allowing sampling the energy landscape of the system in an extended range. The proper packing of atomic clusters favoring glass formation and corresponding to stable amorphous states located in the deep valley of energy landscape can be arrested, finally giving rise to the formation of amorphous Ta states that can hardly be obtained by traditional liquid-quenching methods.

Mesofauna at the Soil-Scree Interface in a Deep Karst Environment

The community patterns of Collembola (Hexapoda) were studied at two sites along a microclimatically inversed scree slope in a deep karst valley in the Western Carpathians, Slovakia, in warm and cold periods of the year, respectively. Significantly lower average temperatures in the scree profile were noted at the gorge bottom in both periods, meaning that the site in the lower part of the scree, near the bank of creek, was considerably colder and wetter compared to the warmer and drier site at upper part of the scree slope. Relatively high diversity of Collembola was observed at two fieldwork scree sites, where cold-adapted species, considered climatic relicts, showed considerable abundance. The gorge bottom, with a cold and wet microclimate and high carbon content even in the deeper MSS horizons, provided suitable environmental conditions for numerous psychrophilic and subterranean species. Ecological groups such as trogloxenes and subtroglophiles showed decreasing trends of abundance with depth, in contrast to eutroglophiles and a troglobiont showing an opposite distributional pattern at scree sites in both periods. Our study documented that in terms of soil and subterranean mesofauna, colluvial screes of deep karst gorges represent (1) a transition zone between the surface and the deep subterranean environment, and (2) important climate change refugia.

Surface morphology characterization of unidirectional carbon fibre reinforced plastic machined by peripheral milling

This paper aims to characterise surface morphology and 3D roughness parameters of unidirectional carbon fibre reinforced plastic (UD-CFRP) milled at 0°, 45°, 90°, and 135° fibre orientation angles (FOAs). Side milling experiments are conducted on UD-CFRP laminates. Surface damage forms and texture direction of milled surface are analysed. Spatial frequency of defects on CFRP surface is quantitatively determined using radially averaged 2D PSD. The kinematic-dynamic surface topography is reconstructed considering feed, runout and vibration, then the ideal roughness parameters, Sa, Sq, Ssk, and Sku are calculated and compared with the measured ones, finally the material factor-induced roughness components are quantified. Results show that CFRP surface has no regular feed marks. The frequency of fibre breakage or surface defects is greater than tooth passing frequency. FOAs sorted by their average Sa in descending order is 135°>90°>45°>0°, where surface defects contribute 93.9%, 77.1%, 73.2%, 72.2% of the total roughness respectively, which suggests that surface defects show a more important role than tool kinematics and vibration in formation of milled surface. The negative Skewness (Ssk < 0) and high Kurtosis (Sku = 4.0–11.5) of milled surface signify porosity and the presence of many anomalous deep valleys in milled surface, respectively.

A new electrophysiological triad for atrial flutter critical isthmus identification and localization

Abstract Funding Acknowledgements Type of funding sources: None. Introduction In a previous retrospective study it was demonstrated that an electrophysiological triad was able to identify critical isthmus in atrial flutter (AFL) patients. This triad is based in the Carto® electroanatomical mapping (EAM) version 7, which displays a histogram of the local activation times (LAT) of the tachycardia cycle length (TCL), in addition to the activation and voltage maps. This study aimed to prospectively assess the ability of an electrophysiological triad to identify and localize the AFL’s critical isthmus. Methods Prospective analysis of a unicentric registry of individuals who underwent left AFL ablation with Carto® EAM. All patients with non-left AFL, lack of high-density EAM, less than 2000 collected points or lack of mapping in any of the left atrium walls or structures were excluded. Ablation sites of arrhythmia termination were compared to an electrophysiological triad constituted by: areas of low-voltage (0.05 to 0.3mV), sites of deep histogram valleys (LAT-Valleys) with less than 20% density points relative to the highest density zone and a prolonged LAT-Valley duration that included 10% or more of the TCL. The longest LAT-Valley was designated as the primary valley, while additional valleys were named as secondary. Results A total of 12 patients (9 men, median age 72 IQR 67-75 years) were included. All patients presented with left AFL and 67% had a previous atrial fibrillation and/or flutter ablation. The median TCL and number collected points were 250 (230─290) milliseconds and 3150 (IQR 2340─3870) points, respectively. All AFL presented with at least 1 LAT-Valley in the analysed histograms, which corresponded to heterogeneous low-voltage areas (0.05 to 0.3mV) and encompassed more than 10% of TCL. Eleven of the 12 patients presented with at least 1 secondary LAT-Valley. All arrhythmias were effectively terminated after undergoing radiofrequency ablation in the primary or the secondary LAT-Valley location. Conclusion In a prospective analysis, an electrophysiological triad was able to identify the AFL critical isthmus in all patients. Further studies are needed to assess the usefulness of this algorithm to improve catheter ablation outcomes.

Widespread glacial erosion on the Scandinavian passive margin

AbstractThe topography in Scandinavia features enigmatic high-elevation low-relief plateau regions dissected by deep valleys and fjords. These plateau regions have long been interpreted as relict landforms of a preglacial origin, whereas recent studies suggest they have been modified significantly by glacial and periglacial denudation. We used late Pliocene–Quaternary source-to-sink analyses to untangle this scientific conundrum. We compared glacier-derived offshore sediment volumes with estimates of erosion in onshore valleys and fjords and on the inner shelf. Our results suggest that onshore valley and fjord erosion falls 61%–66% short of the offshore sink volume. Erosion on the inner shelf cannot accommodate this mismatch, implying that the entire Scandinavian landscape and adjacent shelf have experienced significant glacial erosion.

Unloading depth of rock masses and its relations with river downcutting in deep valleys in Southwest China

Intense and deep unloading is a common manifestation of rock masses in deep valley in Southwest China. In this work, we investigated the evolution of four main rivers and the characteristics of the unloading cracks in rock masses in the river valleys, and we studied the relations of the tensile unloading fractures of rock masses with the downcutting of rivers based on the investigation results on the unloading crack features of 33 hydropower stations in the study area. The Lancang River, Jinsha River, Dadu River and Yalong River in the study area had downcut of 250–660 m, 120–430 m, 400–670 m and 350–460 m, respectively, since the Quaternary. The unloading and the redistributed stress of valley caused by the river downcutting had important effects on the unloading fracture of rock masses. The maximum strong and weak tensile unloading fracture depths of the rock masses exceeded 160 m and 230 m, respectively, in these valleys. The unloading depths of the rock masses increased with increasing river level elevations and the heights of the river valleys and varied within a certain range. In a certain valley, the unloading depth increased with the elevation of the rock masses. An empirical method was proposed in this work for roughly estimating the strong and weak tensile unloading depths of a rock masses. • The maximum strong unloading depths of the rock masses exceeded 160 m in deep valley Southwest China. • The unloading depths of the rock mass increased with river level elevation, valley height and elevation of rock mass. • An empirical method was proposed in this work to roughly estimate the strong and weak unloading depths.

Oceanic crustal structures and temporal variations of magmatic budget during seafloor spreading in the East Sub-basin of the South China Sea

Following magma-poor continental rifting, the South China Sea (SCS) experienced seafloor spreading from ~33 Ma to ~15 Ma with an intervening southward ridge jump at ~25 Ma, generating the oceanic East, Northwest and Southwest Sub-basins. However, the magmatic processes during spreading remain poorly known owing to the lack of oceanic crustal images. Here we present a composite profile comprising three seismic lines that run from the northern continent-ocean transition (COT) to the extinct spreading center of the East Sub-basin to reveal the crustal structures. In the northernmost oceanic portion, the first oceanic crust featuring rough basement with numerous faults, and diffuse and weak Moho reflector, is only 3.9–4.5 km thick, implying relatively low magmatic budget and protracted tectonic extension continued from the magma-poor continental rifting to initial spreading. From the northern COT ocean-ward to the abandoned ridge where the jump event occurred, the basement becomes smooth with subdued faults. The Moho reflector tends to be continuous and strong, and the igneous crust gradually becomes thick (locally up to 8.4 km), suggesting considerably increasing magmatic budget during the early spreading stage. However, in the central portion spanning from the abandoned ridge to the extinct spreading axis, the basement becomes rough with crustal faults again. And the crust gradually becomes thin, to only 3.7 km at the extinct spreading center where a deep median valley is still visible, though severely altered by post-spreading volcanism, implying decreasing magmatic budget and increasing tectonic extension during the late spreading stage. Therefore, the crustal structure variations in the East Sub-basin reflects a prominent increasing to decreasing change of magmatic budget during spreading with the peak around the intervening ridge jump. Thin, tectonized crust and deep median valley around the extinct spreading center further support slow seafloor spreading during the last spreading stage of the SCS which ended at ~15–16 Ma, and also suggest that magma contribution from the Hainan mantle plume might be very limited if any.

TBM-spoil characterization and utilization at the Follo Line project

The potential use of surplus materials commonly considered as waste has been investigated by the project “Geomaterials in the Circular Economy” (GEOreCIRC). TBM spoil is one of the materials which were assessed, based on data from the Follo Line tunnel project in Oslo, Norway. For this tunnel, four TBMs were used simultaneously and the tunnel generated almost 9 million metric tonnes of spoil. The excavated TBM spoil was used to establish a building platform for a new district in the Oslo municipality, by filling a 30 m deep valley. An extensive campaign of laboratory testing, field measurements and monitoring was conducted for the deposit. The geotechnical properties, such as grain size distribution, grain shape, brittleness, density, permeability and friction angle were determined. The optimal water content for compaction and maximum dry density were determined using the Standard Proctor test. Field measurements included plate load tests and nuclear density gauge (Troxler), with several measurements for each layer of the deposit. In addition, the spoil was analysed for a wide range of possible contaminants associated with natural rock minerals and machinery used in the tunnelling process. The results show that the level of contamination is low, and related to background levels from the bedrock itself, with levels below specified threshold values for contaminated soil according to Norwegian regulations.

A Historical Earthquake-Induced Landslide Damming Event at the Qiaojia Reach of the Jinsha River, SE Tibetan Plateau: Implication for the Seismic Hazard of the Xiaojiang Fault

In bedrock mountainous areas where active faults and deep river valleys interact, earthquake-induced landslides can be used to explore local seismic hazards. The intersection of the highly active Xiaojiang Fault and the Jinsha River and its main tributaries in southwest China is a site of abundant earthquake-induced landslides. We found some boulders inappropriately scattered on the east bank of the Qiaojia reach of the Jinsha River, where the Qiaojia Segment of the Xiaojiang Fault passes through. We investigated the lithology and topography nearby and confirmed its source area, as well as the existence of a landslide damming event in the field. A high-resolution Digital Surface Model (DSM) generated from Unmanned Aerial Vehicle (UAV) images was used to analyze its characteristics and calculate its parameters. Optically Stimulated Luminescence (OSL) and 14C dating methods on the related dammed lake sand shows the age of the landslide, which is not later than 878 AD. The characteristics of large size with limited depositional extent, spatial relevance between the landslide and Xiaojiang Fault, and temporal-coincidence of the landslide with 624 AD earthquake support the seismic origin of this landslide. Moreover, the 624 AD earthquake was reanalyzed for its magnitude and macro-epicenter based on the coseismic displacement of the Heishui River floodplain. It was calculated to be Mw7.7 or Ms7.9 and relocated to the Qiaojia area. No M ≥ 7 earthquakes have occurred on the Qiaojia Segment for nearly 1,400 years since 624 AD. The elapsed time is close to the average recurrence interval of large earthquakes on the Qiaojia Segment. Therefore, the seismic hazard of the Qiaojia area should be considered in the future.

Tectonic activity level evaluation using geomorphic indices in the Shekarab Mountains, Eastern Iran

In order to evaluate the level of tectonic activities in the Shekarab Mountains, several geomorphic indices such as stream length gradient index (SL), valley floor width to valley height ratio (Vf), hypsometric curve (Hc), hypsometric integral (Hi), drainage basin shape (Bs), and relative tectonic activity (Iat) were calculated. Vf values show fastest uplift, deepest valleys, and highest river incision are associated with the basin 24. The high values of SL in the range of 900 to 3250 on the high resistance rocks related to the western basins indicate that the western part of the Shekarab Mountains has had recent tectonic activities. Moreover, distribution of high Hc and Hi values are related to the highest tectonic activity in the western and northeastern basins. Accordingly, the study area was divided into four subareas based on Iat values, which are the following: class 1, very high relative tectonic activity (10.17%); class 2, high relative tectonic activity (11.77%); class 3, moderate relative tectonic activity (29.96%); and class 4, low relative tectonic activity (48.10%). It can be concluded from the Iat values that different parts of the study area had undergone unequal uplift and tectonic activities in the NE-SW direction are showing the highest uplift rate, which is in consistency with the present time compression direction in the Shekarab Mountains.

The value of climate responses of individual trees to detect areas of climate-change refugia, a tree-ring study in the Brazilian seasonally dry tropical forests

Forests worldwide are facing increasingly frequent climate extremes due to global warming. The negative effects of climate change on tropical forests have been extensively reported by both permanent plots and tree-ring studies that targeted forest's responses to climate. While they focus mostly on community and population levels, the effects of landscape heterogeneity on trees’ sensitivity to climate is often not accounted for, overlooking the diverse responses of individual trees to climate variation. We tested the hypotheses that trees may differ in sensitivity to climate and that some microenvironmental conditions may exert the role of climate-change refugia. We built the first tree-ring chronology of Amburana cearensis trees sampled across a Seasonally Dry Tropical Forest (SDTF) in Brazil. We ensure a robust tree-ring dating using dendrochronological methods and 14C dating of trees inhabiting various conditions characterized here through the seasonality of the local Normalized Difference Vegetation Index. At the population level, the standard tree-ring chronology suggests that tree growth depends on rainfall and temperature, leading to a common conclusion that drier and warmer conditions would impact interannual tree growth in the tropics. However, the cluster analyses revealed groups of individual trees with distinct growth sensitivities to climate. The most sensitive trees were the individuals located in the highly seasonal vegetation of the epikarst, in contrast to the complacent trees (non-sensitive to regular interannual climate variability) inhabiting the less-seasonal vegetation in the deep soil epikarst and valley. Based on these groups of trees, we built two mean chronologies and assessed their climate-growth relationships. In accordance with the individual analysis, the tree-ring chronology of complacent trees showed no association with wet season precipitation and only moderate association with temperature. The areas supporting these complacent trees of A. cearensis in the less seasonal vegetation correspond to a quarter of the entire sampling site. The climate buffering capacity of these refugia may only be compromised in years of climate extremes when all sampled trees share low growth rates during years with anomalous low rainfall and high temperature. Assessing individual’s climate sensitivity is therefore paramount for a comprehensive understanding of the heterogeneous responses of tropical forests to climate change. The hidden individual tree responses in the population can help identify priority areas of management in a rapidly changing environment.

Monitoring and Assessment for the Susceptibility of Landslide Changes After the 2017 Ms 7.0 Jiuzhaigou Earthquake Using the Remote Sensing Technology

Monitoring the change of post-seismic landslides could provide valuable information for geological disaster treatment. The 2017 Jiuzhaigou Ms 7.0 earthquake has triggered a large number of landslides in the Jiuzhaigou United Nations Educational, Scientific and Cultural Organization (UNESCO) Natural Heritage site, which provides a unique opportunity for monitoring the spatio-temporal characteristics and exploring the impact factors of post-seismic landslides change. In this study, the spatio-temporal characteristics of landslides and their post-seismic changes are analyzed using multi-source, multi-temporal, and multi-scale remote sensing data combining with the field study. The Support Vector Machine classification, visual interpretation, field investigation, and Geographic Information System technology are employed to extract landslides and analyze their spatial distribution patterns. Moreover, the Certainty Factor method is used to explore the susceptibility of landslides and to find key impact factors. Our results show that the net increase area of landslide is 1.2 km2 until September 27th, 2019, which are induced by the expansion of coseismic landslide, the post-seismic landslide, and the expansion of vegetation degradation. Moreover, the area expansion of the coseismic and post-seismic landslides is mainly related to the increase of debris flow induced by the post-seismic torrential rainfalls. The highest net increase rate of post-seismic landslide change does not distribute on the regions with the highest density of coseismic landslides. The susceptibility of post-seismic landslide change is greatly influenced by slope, altitude, aspect, peak ground acceleration fault, and strata. It is higher in the coseismic landslide area with low susceptibility. This study also suggests that the potential landslides will most likely occur in the unstable slope region affected by the additional driving force. Therefore, great attention should be paid to identify and prevent the potential landslides on unstable slopes in addition to treatments of the sliding slopes. This study provides a good example for the monitoring and assessment of post-seismic landslides in mountainous regions with a steep slope and deep valley.

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.

Study of the in situ stress field in a deep valley and its influence on rock slope stability in Southwest China

The in situ stress field in valley areas is an important factor to consider in the construction of hydropower projects in southwest China. Due to intense tectonic movement, the action of gravity, and rapid river erosion, the resulting stress has a complex distribution and a large magnitude. The availability of stress measurements is insufficient to provide adequate understanding of the regional stress state. In this research, inversion analysis for the in situ stress field of a valley in the upper reaches of the Lancang River is carried out by using stepwise regression analysis and the FLAC3D numerical simulation, and the temporal and spatial distribution characteristics of the in situ stress are obtained. Based on those results, the influence of stress unloading effects on slope stability is discussed. The results show that the formation of the modern in situ stress field is the comprehensive result of interactions among gravity, tectonic movement, and river erosion. The reliability of the inverse result can be increased by improving the mesh density of the calculated model and considering multistep river erosion. Under the influence of the unloading effects, tensile fractures were formed and the rock mass loosened near the slope surface. With the presence of bedding dipping into the slope, toppling failure was triggered by the unloading rebound that mainly occurred in the stress relaxation zone.