Formation Of Valleys Research Articles

Evaluating possible glacial modification in the Martian tropics near Gale crater using a new U-shaped valley metric

Growing evidence supports the case for glacial processes within the equatorial regions of Mars. However, few examples of modeling or numerical analysis exist to support this hypothesis. Here we apply an automated method on valleys near Gale crater to extract morphometric data and analyze formative processes responsible for their current expression. The V-index utilized is a new robust method that is an alternative to traditional valley parabolic curve fits. This approach more easily characterizes irregular valley cross sections and thus aids in distinguishing between glacial and nonglacial forms. We applied this method along with standard power law and quadratic curve fits on valley cross sections along a 2300 km extent of the Martian tropics near Gale crater. Both V-index and power law b fit values suggest that the majority of the valleys are U-shaped and possibly created through glacial erosive processes. Further, V-index and power law b values plotted against elevation show a positive trend with higher V-index (glaciated) values associated with higher elevation. This suggests that an equilibrium-line altitude (ELA) may have existed at the time of valley formation. The timing of the formation of these U-shaped valleys is poorly defined. However, our initial crater statistics conducted within the study area suggest a young ∼1.05 (±0.25) Ga relative ages of the valley floors. Equatorial glaciers that produced these and other related glacial forms may be as old as the Hesperian to Amazonian transition (∼3 Ga) but more intriguingly may be associated with Amazonian equatorward migration of the Martian cryosphere during more recent periods of high obliquity oscillations.

In Rare Opportunity, Researchers Observe Formation of Icelandic Valleys

In Rare Opportunity, Researchers Observe Formation of Icelandic Valleys

A Comparative Analysis of Enamel Surface Roughness Following Various Interproximal Reduction Techniques: An Examination Using Scanning Electron Microscopy and Atomic Force Microscopy.

Interproximal enamel reduction (IER) is a minimally invasive therapeutic procedure commonly used in orthodontics to address both functional and aesthetic issues. Its mechanical effects on enamel surfaces induce the formation of grooves, furrows, scratches, depressions, and valleys. The aim of this study was to assess the enamel surface roughness resulting after the application of currently available methods for interproximal reduction. Ninety freshly extracted human teeth were divided into six groups and subjected to the stripping procedure, using a different method for each group (diamond burs, abrasive strips of 90 μm, 60 μm, 40 μm, 15 μm, and abrasive discs). A single individual performed stripping according to the manufacturer's recommendations, involving interproximal reduction on one tooth's proximal face and leaving the other side untreated. Qualitative and quantitative assessment of the enamel surfaces was carried out using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM), obtaining 2D and volumetric 3D images of the enamel surface microstructure and nanostructure. The study found that diamond burs and abrasive strips of 60 μm and 90 μm increased enamel roughness due to intense de-structuring effects, while the 40 μm polisher had a gentler effect and 15 μm abrasive strips and polishing discs preserved enamel surface quality and removed natural wear traces.

Paleo-valley infills record landscape response to late-Quaternary glacial/interglacial climate oscillations in the French western Alps

Reconstructing mountainous landscape evolution throughout the Quaternary is challenging because of the poor long-term preservation of geomorphic records in a context of rapid surface dynamics and topographic rejuvenation. The Quaternary geomorphic evolution of the western European Alps has been strongly controlled by climatic oscillations between glacial and interglacial periods. Significant erosion and sediment remobilization during these glacial/interglacial cycles have left very few sedimentary archives to quantify the surface dynamics and paleo-environmental conditions within the mountain belt over the last hundreds of thousands of years. Alpine valleys within the periglacial zone are potential candidates to target long-term geological archives, since they may contain alluvial deposits that have been preserved from subsequent glaciations. In the Drac valley (French western Alps), three generations of paleo-valleys are preserved, each of which was filled with alluvial and lacustrine sediments in response to glacial damming downstream. The valleys were incised during subsequent times of glacial retreat, leading to the formation of epigenetic valleys. Detailed 3D mapping of the paleo-valleys was carried out using photogrammetric models to constrain their geometry. Mapping was combined with luminescence dating of alluvial deposits to reconstruct the temporal evolution of the Drac valley. This chronological framework, together with additional data from the literature, allowed us to quantitatively constrain the complex alluvial dynamics along the Drac river during the last ca. 230 ka. Poly-phased alluvial deposition occurred in the most recent paleo-valley between ca. 90 and 20 ka (i.e., from late MIS 5 to MIS 2) in a context of global climate cooling and major Alpine glaciation. Sediment infilling of the intermediate paleo-valley is dated at around 130 ka; i.e., during the late-glacial phase of the penultimate glaciation, at the abrupt warming transition between MIS 6 and MIS 5. Finally, the oldest paleo-valley was filled around 230 ka (during a sub-stage of MIS 7) probably in a cooling and glacial context. The overall alluviation pattern and chronology of the study area highlight the asynchronous and partially contrasting glacial dynamics between the different glacier systems (i.e., Drac, Bonne and Romanche/Isère glaciers) within the Ecrins-Pelvoux massif of the French western Alps.

Formation of fluvial xenolandscapes of Martian valleys and channels


 
 
 Contemporary concepts of Martian Valley formation and the current state of their study are examined. Three-dimensional modeling was conducted using the examples of two regions on Mars, the Lani Chaos Region and Kasei Vallis, to determine and map the main morphological features typical of Martian valleys as a basis for identifying xenolandscapes. The xenaxiomatic author’s concept was applied as a means of investigating xenolandscape diversity on the surface of Earth-like planets, in this case, Mars. The xenaxiomatic concept is the result of incorporating and utilizing traditional knowledge of the differentiation and application of axioms of cognition. Specialized for xenoplanetological use, this integrative cognitive tool is a variant of an axiomatic approach. The main essence of this approach, in the case of distinguishing xenolandscapes, lies in developing a unified scheme for searching for corresponding xenolandscape elements that are axiomatically elementary fragments of the planet’s surface, followed by their classification and xenolandscape interpretation. Scientific awareness has been achieved by filling it with all available information from various natural sciences related to xenoplanetology and subsequent exploratory xenolandscape interpretation and synthetic cartographic representation of characteristic, typical local xenolandscape formations on Mars (part of the Kasei Vallis valley). These depicted objects are extra-rank, meaning they have not yet been ranked in terms of xenolandscape formations but are uniformly formed due to the synergy of influences and interactions of different forces, yet genetically stemming from the same xenolandscape-forming factors of material and energy-field xenonature. A mechanism for the formation of modern Martian valleys is proposed through the influx of heat flow and impact events. Exploratory xenolandscape studies, with their positions verified by this conducted research in terms of theoretical, methodological, and methodical content, have become an unexpected benchmark for the effectiveness of similar theoretical and methodological components of classical landscape science, with which the research capabilities of landscape science can and should be compared.
 
 

Morphostructural aspects of the sandstone karst in Northeastern Brazil: Example from Serra da Capivara – PI

This work analyses morphostructural aspects and their influence on the development of the karst reliefof Serra da Capivara (State of Piauí, northeastern Brazil). For this purpose, structural data derived from lineamentextraction, sedimentary bed geometry, karstification degree of the layer, and analysis of the karst morphologywere performed. Structural lineament data showed a NE-SW orientation trend, coinciding with the orientationof the Transbrasiliano Lineament. The reactivation of the brittle structures can be related to the orientation, scarpretreat, direction, and incision of the main valleys. From the analysis of the fracture array (NE-SW) and beddingplanes, we suggest that the fracture connectivity of these structures resulted in conduit formation, which evolvedto form subterranean galleries. Thus, the expansion of the karst system led to the formation of valleys, which aresituated in higher deformed zones, such as fold hinges. These valleys currently constitute the most advancedstage of karstification, with the development of the tributary drainages as the most recent stage. The structuraldirections show a NE-SW trend, represented by larger valleys, and subordinated to this, an NW-SE trend, whereheadwaters of low-order channels are located.

Overdeepenings in the Swiss plateau: U-shaped geometries underlain by inner gorges

We investigated the mechanisms leading to the formation of tunnel valleys in the Swiss foreland near Bern. We proceeded through producing 3D maps of the bedrock topography based on drillhole information and a new gravimetric survey combined with modelling. In this context, the combination of information about the densities of the sedimentary fill and of the bedrock, together with published borehole data and the results of gravity surveys along 11 profiles across the valleys, served as input for the application of our 3D gravity modelling software referred to as PRISMA. This ultimately allowed us to model the gravity effect of the Quaternary fill of the overdeepenings and to produce cross-sectional geometries of these troughs. The results show that 2–3 km upstream of the city of Bern, the overdeepenings are approximately 3 km wide. They are characterized by steep to oversteepened lateral flanks and a wide flat base, which we consider as a U-shaped cross-sectional geometry. There, the maximum residual gravity anomaly ranges between − 3 to − 4 mGal for the Aare valley, which is the main overdeepening of the region. Modelling shows that this corresponds to a depression, which reaches a depth of c. 300 m a.s.l. Farther downstream approaching Bern, the erosional trough narrows by c. 1 km, and the base gets shallower by c. 100 m as revealed by drillings. This is supported by the results of our gravity surveys, which disclose a lower maximum gravity effect of c. − 0.8 to − 1.3 mGal. Interestingly, in the Bern city area, these shallow troughs with maximum gravity anomalies ranging from − 1.4 to − 1.8 mGal are underlain by one or multiple inner gorges, which are at least 100 m deep (based on drilling information) and only a few tens of meters wide (disclosed by gravity modelling). At the downstream end of the Bern area, we observe that the trough widens from 2 km at the northern border of Bern to c. 4 km approximately 2 km farther downstream, while the bottom still reaches c. 300 to 200 m a.s.l. Our gravity survey implies that this change is associated with an increase in the maximum residual anomaly, reaching values of − 2.5 mGal. Interestingly, the overdeepening’s cross-sectional geometry in this area has steeply dipping flanks converging to a narrow base, which we consider as V-shaped. We attribute this shape to erosion by water either underneath or at the snout of a glacier, forming a gorge. This narrow bedrock depression was subsequently widened by glacial carving. In this context, strong glacial erosion upstream of the Bern area appears to have overprinted these traces. In contrast, beneath the city of Bern and farther downstream these V-shaped features have been preserved. Available chronological data suggest that the formation of this gorge occurred prior to MIS 8 and possibly during the aftermath of one of the largest glaciations when large fluxes of meltwater resulted in the fluvial carving into the bedrock.

Simplified Genomic Data Revealing the Decline of Aleuritopteris grevilleoides Population Accompanied by the Uplift of Dry-Hot Valley in Yunnan, China.

Understanding the evolutionary history of endangered species is crucial for identifying the main reasons for species endangerment in the past and predicting the changing trends and evolutionary directions of their future distribution. In order to study the impact of environmental changes caused by deep valley incision after the uplift of the Qinghai-Tibet Plateau on endangered species, we collected 23 samples belonging to four populations of Aleuritopteris grevilleoides, an endangered fern endemic to the dry-hot valleys (DHV) of Yunnan. Single-nucleotide variation sites (SNPs) were obtained by the genotyping-by-sequencing (GBS) method, and approximately 8085 SNP loci were identified. Through the reconstruction and analysis of genetic diversity, population structure, population dynamics, evolution time, and ancestral geographical distribution, combined with geological historical events such as the formation of dry-hot valleys, this study explores the formation history, current situation, reasons for endangerment and scientifically sound measures for the protection of A. grevilleoides. In our study, A. grevilleoides had low genetic diversity (Obs_Het = 0.16, Exp_Het = 0.32, Pi = 0.33) and a high inbreeding coefficient (Fis = 0.45). The differentiation events were 0.18 Mya, 0.16 Mya, and 0.11 Mya in the A. grevilleoides and may have been related to the formation of terraces within the dry-hot valleys. The history of population dynamics results shows that the diversion of the river resulted in a small amount of gene flow between the two clades, accompanied by a rapid increase in the population at 0.8 Mya. After that, the effective population sizes of A. grevilleoides began to contract continuously due to topographic changes resulting from the continuous expansion of dry-hot valleys. In conclusion, we found that the environmental changes caused by geological events might be the main reason for the changing population size of A. grevilleoides.

PLACER DEPOSITS OF DIAMONDS AND THEIR FORMATION CONDITIONS

This article reviews information from published papers and studies by the authors about placer diamond deposits. Original data were obtained in result of field and laboratory-analytical work carried out in various countries of Africa and South America. The main types of placer diamond deposits – fluvial, fluvioglacial, eolian, and man-made – have been considered and characterized. The main attention is given to fluvial continental placers, which are the most diverse, well-studied and have the greatest industrial importance. Primary, secondary and mixed deposits are distinguished according to the method of feeding; short, moderate and long transport deposits – according to the distance of the diamond-bearing material movement. It is noted that although the short transport placers (deluvial-proluvial and beds of short watercourses) have not industrial value, they are very informative for the searching for root sources. It is important to reliably diagnose these deposits by lithological-facies and mineralogical features during prospecting works. The concepts about the conditions for the formation of diamond placers in various landscape and geological conditions are developed and clarified. Alluvial-proluvial-lacustrine and proluvial-lacustrine types of placers studied in Yakutia and Brazil are characterized in detail. Their characteristic feature is that their productive strata, being re-deposited products of crustal weathering, themselves underwent a hypergenic change at the place of occurrence, which significantly masks the primary conditions of formation. Continental alluvial redeposition and long transport placers, as well as marine, yield the most high-quality expensive diamonds, the average value of which can reach $300–400 per carat. Often, such placers are formed due to the erosion of ancient Proterozoic placers, which belong to the category of fossils. The article summarizes the genetic and morphological types of diamond placers in the form of a principle diagram of the distribution of sedimentary reservoirs of kimberlite minerals. The landscape-dynamic zones of sedimentation are highlighted. A classification scheme of sedimentary reservoirs containing diamond placers has been developed. Continental, transitional and marine environments are distinguished, with further detalization of sedimentation environments – peneplain, alluvial-lacustrine accumulative plain, alluvial-deltaic plain and shelf zones of sea basins. It is shown that the formation of valley placers, their internal structure, thickness, granulometric composition and diamond content of alluvium are influenced by the dynamic phases of the formation of annual valleys. Visualization of the mutual relationship of different morpho-genetic types of placer diamond deposits is given.

Understanding the formation of surface relief gratings in azopolymers: A combined molecular dynamics and experimental study.

The formation of surface relief gratings in thin azopolymeric films is investigated using atomistic molecular dynamics simulations and compared to experimental results for the specific case of poly-disperse-orange3-methyl-methacrylate. For this purpose, the film is illuminated with a light pattern of alternating bright and dark stripes in both cases. The simulations use a molecular mechanics switching potential to explicitly describe the photoisomerization dynamics between the E and Z isomers of the azo-units and take into account the orientation of the transition dipole moment with respect to the light polarization. Local heating and elevation of the illuminated regions with the subsequent movement of molecules into the neighboring dark regions are observed. This leads to the formation of valleys in the bright areas after re-cooling and is independent of the polarization direction. To verify these observations experimentally, the azopolymer film is illuminated with bright stripes of varying width using a spatial light modulator. Atomic force microscopy images confirm that the elevated areas correspond to the previously dark areas. In the experiment, the polarization of the incident light makes only a small difference since tiny grain-like structures form in the valleys only when the polarization is parallel to the stripes.

Highly densed BCN nanofiber core with MoS2 shell for enhanced hydrogen evolution reaction and supercapacitance applications

Boron carbon nitrogen (BCN) nanofibers was synthesized using chemical vapor deposition (CVD) followed by depositing molybdenum disulfide (MoS2) forming a core–shell structure. This core–shell nanocomposite was directly grown on carbon paper to form working electrode, where it displayed excellent energy storage ability as well as hydrogen evolution reaction (HER) catalytic activity. We believe that during the shell deposition, it effectively etched the inert basal plane of MoS2, leading to the formation of entrenched valleys and to the further increasing of the active edge sites. Coupled with high surface area and high density BCN nanofibers core, the MoS2/BCN nanofiber catalyst demonstrated a very low overpotential of 85 mV in acidic media at a current density of 10 mA cm−2 for HER. In addition, the optimally tuned MoS2/BCN nanofiber also showed superior electrochemical performance as a supercapacitor with higher specific capacitance of 446.3 A g−1 at current density of 0.25 A g−1. Overall, this excellent catalytic activity is found to be due to their abundant active sites and fast ion transfer capability.

Exploring electronic and valley properties of single-layer SMSiN2 (M = Mo, W): a first-principles study on two-dimensional Janus materials.

In this study, we employ first-principles calculations to explore the electronic and valleytronic properties of single-layer (SL) SMSiN2 (M = Mo, W), which are two-dimensional Janus materials with strong spin-orbit coupling. Our findings indicate that SL SMoSiN2/SWSiN2 possess a direct/indirect band gap, where the valence band maximum is situated at the K/K' point, giving rise to the formation of degenerate valleys. When considering spin-orbit coupling, SMoSiN2 and SWSiN2 demonstrate intriguing valley spin splitting in their valleys, with a maximum splitting of up to 0.14/0.39 eV in the valence bands. By implementing magnetic doping with V and Cr, we provide a demonstration that valley polarization could be realized in SL SMSiN2. Moreover, the findings reveal high carrier mobility in SL SMSiN2, notably in SWSiN2, where hole carriers can achieve a remarkable mobility of up to 7.98 × 103 cm2 V-1 s-1 along the zigzag direction. Furthermore, our observations suggest that strain can be effectively utilized to manipulate the character and magnitude of the band gap, as well as the valley spin splitting in these materials.

Early to middle Miocene ice sheet dynamics in the westernmost Ross Sea (Antarctica): Regional correlations

The present-day morpho-stratigraphy of the Ross Sea is the result of Cenozoic tectonic and cryospheric events, and constitutes a key record of Antarctica's cryospheric evolution. An enduring problem in interpreting this record in a broader regional context is that the correlation between eastern and western Ross Sea stratigraphy has remained uncertain due to the limited number of drill sites. We correlate the glacial-related features observed on a dense network of seismic reflection profiles in McMurdo Sound with those identified in the Nordenskjöld and Drygalski Basins, as well as the basins farther east in the central Ross Sea. We present an improved correlation of the regional patterns of early to middle Miocene ice-sheet variance across the Ross Sea constrained by new evaluation of seismic facies and age models from one site recovered by the Antarctic Drilling Project (ANDRILL) in the southwestern most part of McMurdo Sound. We also integrate this correlation with the recently published seismic framework in the central Ross Sea. The formation of U-shaped valleys during the early Miocene in McMurdo Sound, together with prograding sedimentary wedges in the western-most basins, and the central Ross Sea, suggest two major phases of overall advance of a marine-terminating ice sheet between ~18 Ma and ~17.4 Ma. Widespread formation of turbiditic channel-levee systems in McMurdo Sound and rapid sediment deposition in Nordernskjöld Basin point to subsequent ice-sheet retreat between ~17.4 Ma and ~15.8 Ma, coinciding with the onset of the Miocene Climate Optimum (MCO; ~17–14.5 Ma). However, the carving of troughs and formation of irregular morphologic features suggest that an extensive ice sheet still remained along the western Ross margin at ~17.4 Ma and a brief episode of ice-sheet advance occurred at ~16.8 Ma in the earliest interval of the MCO. Subsequent marine-based ice sheet advance during the Middle Miocene Climate Transition (MMCT, ~14.0–13.8 Ma) is indicated by widespread erosional features. Our results reconcile the semi-continouous seismic and drill core stratigraphy of the offshore Ross Sea continental shelf with inferences of ice sheet dynamics from continuous far-field deep sea and sea level records, as well as the highly discontinous (and heavily debated) onshore records of pre-MMCT glaciation and aridification of the Transantarctic Mountains at 14 Ma. • Core-log-seismic correlation allows regional correlation of the Ross Sea record • 2 major advances of marine-terminating ice sheet occurred between 18 and 17.4 Ma • Ice sheet retreated at the onset of the Miocene Climate Optimum • Short-term ice-sheet advance occurred at ~16.8 Ma • Widespread marine-based ice sheet correlates to the Miocene Climate Transition

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.

CHANGES OF THE RADIATION CHARACTERISTICS OF SURFACE OF TUNGSTEN AS A RESULT OF INFLUENCE OF HELIUM ION BEAMS

The change in the radiation characteristics of the surface of tungsten was studied. Helium ions beams with energies of 0.12 and 4 MeV were used. Curves of ionization and damage are got on length of free run of ions of helium. The change the radiation characteristics of the surface of tungsten was studied. In the case of treatment with a beam of helium ions with energies of 0.12 MeV an increase in the hardness of the tungsten surface was found. Bubbles development has been studied. The appearance of tungsten tendrils around the bubbles, the formation of hills and valleys was considered.

Influence of the thermal сonditions within the bed of the last ice sheet on the distribution of glacial valleys of the Belarusian Poozerie area

Within the bed of the Poozerie (Weichselian) ice sheet, which occupied the northern part of Belarus at the maximum stage and at the beginning of degradation, three concentric thermal zones were identified according to geological and geomorphological criteria: the outer zone of basal frozen ice, the zone of discontinuous frozen bed, the inner zone of the thawed bed. Comparison of glacial valleys with thermal zoning shows that their distribution and formation closely related to thermal conditions. During the Poozerie (Weichselian) ice sheet advance into the northern region of Belarus, thermal zoning affected geological denudation processes. This led to local erosion and valleys in the outer zone of basal frozen ice, large-scale manifestation of glacial excavation and squeesing out and the formation of lobate glacial depressions, large radial valleys and subglacial lakes in the inner zone of the thawed bed and along its outer border with the zone of discontinuous frozen bed. The formation of large tunnel valleys became possible at the stage of degradation of the ice sheet (Vitebsk phase), after the melted glacial waters of subglacial dammed lakes found an outlet into the marginal zone through an intermittent frozen bed and were released as a result of catastrophic floods through separate channels, which were deepened, widened and formed tunnel valleys.

On the influence of varying the crystallographic texture of alumina CVD coatings on cutting performance in steel turning

Understanding the mechanisms at the tool/chip interface during metal cutting is crucial in the production of almost every metallic component used in engineering applications. It is critical to have rapid, durable, and reliable machining processes. This work contributes to the understanding of mechanisms occurring on the tool in the secondary shear zone, and it is focusing on the tool side of the contact. Crystallographic textured Chemical Vapor Deposited (CVD) α-Al2O3 coated cutting tools are dominating the steel turning area, as they show an increased performance compared to coatings with randomly oriented grains. In this study, we investigate the effect of three different CVD α-Al2O3 textures on the initial rake crater behavior. This was done using a turning test designed to generate crater wear only in the alumina layer, which was deposited onto an inner Ti(C,N) layer, which in turn was deposited on a cemented carbide insert. With this approach, the influence of the underlying coating layer and substrate was reduced. Pre- and post-machining characterization of the different contact areas on the surfaces of the three textured CVD α-Al2O3 coatings, (0001)(0001), (011‾2) and (112‾0), was performed using scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) and energy dispersive X-ray spectroscopy (XEDS). Plastic deformation, micro-rupture, abrasion and chemical reactions with the workpiece material are all identified as mechanisms involved in crater formation during turning. For the (0001)-textured coating, the observed low wear-rate is attributed to homogeneous basal-slip dominating plastic deformation, while for the (011‾2) and (112‾0) textures the main deformation mechanisms are attributed to heterogeneous plastic deformation, causing micro-rupture and abrasion, leading to higher wear-rates. The effect of a larger coating grain size is mainly seen as the formation of wider ridges and valleys, while the effect on wear rate was limited.

Groundwater seepage is a key driver of theater-headed valley formation in limestone

Abstract Groundwater seepage leads to the formation of theater-headed valleys (THVs) in unconsolidated sediments. In bedrock, the role of groundwater in THV development remains disputed. Here, we integrate field and remote-sensing observations from Gnejna Valley (Maltese Islands) with numerical modeling to demonstrate that groundwater seepage can be the main driver of THV formation in jointed limestone overlying clays. The inferred erosion mechanisms entail (1) widening of joints and fractures by fluid pressure and dissolution and (2) creeping of an underlying clay layer, which lead to slope failure at the valley head and its upslope retreat. The latter is slower than the removal of the talus by creep and sliding on the valley bed. The location and width of THVs are controlled by the location of the master fault and the extent of the damage zone, respectively. The variability of seepage across the fault zone determines the shape of the valley head, with an exponential decrease in seepage away from the fault giving rise to a theater-shaped head that best matches that of Gnejna Valley. Our model may explain the formation of THVs by groundwater in jointed, strong-over-weak chemical sedimentary lithologies, particularly in arid terrestrial settings.

Применение морфометрического анализа для оценки рельефа Юго-Западного Прибайкалья

The results of the South Western Baikal region relief morphometric analysis in the aspect of reconstructing its development history are presented. Maps of different-order (from the 6th to the 2nd) basic surfaces, and those of the basic surfaces’ differences, were compiled. The statistical coefficients of the basic surfaces’ differences in the studied territory are calculated. The obtained results enable estimating the intensity of neotectonic movements during the Quaternary period. It was revealed that during the this time of relief formation, the amplitude of neotectonic movements was more than 1100 m, with average values of 278 m. Relatively stable (upper reaches of the Bolshaya Bystraya River the southwestern tip of Lake Baikal) and active surface areas (upper reaches of Malaya Bystraya River, middle ones of Bolshaya Bystraya river, watershed surface of the Pokhabikha and Slyudyanka as well as the western tip of the Bystrinskaya basin) were identified. The maximum values of negative and positive movements were noted during the formation of river valleys of the fifth and fourth orders. A decrease in the intensity of neotectonic movements is noted from the time of formation of older to younger surfaces.

Constraining the formation of paleolake inlet valleys across crater rims

Impact crater lakes with an inlet valley were common on Mars during past epochs. However, it has not been established exactly how impact craters with initially high-standing rims were breached by an inlet. We investigated four potential mechanisms for inlet valley breach formation: (1) rim erosion, (2) depositional rim burial, (3) drainage head erosion, and (4) overflow. We used remote sensing measurements to assess the relative likelihood of these mechanisms for 39 crater paleolake inlet systems, keeping in mind that either a single mechanism or multiple mechanisms may have occurred. Our findings indicate that crater degradation associated with (1) rim erosion and/or (2) depositional rim burial played an important role in establishing connections between exterior fluvial systems and crater interiors, especially during the late Noachian - early Hesperian valley network era. Isolated fluvial valleys, interpreted to post-date the main valley network era, breached craters in a wider range of degradation states compared to valley network-fed craters. Interestingly, in many cases, these younger systems accomplished a comparable magnitude of fluvial erosion via drainage head erosion and across crater rims as the valley network inlets, despite differences in broader landscape dissection. This finding suggests fluvial activity was able to accomplish comparable geomorphic work during later periods of Mars' history, at least locally. Our catalog of analyzed paleolakes includes Jezero crater, and so our work provides broader context for in situ rover analyses at this site.