Slope Gullies Research Articles

Controlling gully- and revegetation-induced dried soil layers across a slope–gully system

The introduction of exotic plants and improper management strategies with regard to plant species can change the soil-water balance of deep soils, which in turn results in the formation of a dried soil layer (DSL) within the soil profile. The Loess Plateau (LP) of China has a complex terrain; however, only a few studies have evaluated the effects of the gully-induced DSL patterns, especially in hilly and gully regions of the northern LP. In this study, we collected soil-water content data to a depth of 5 m at 40 sampling sites in a slope–gully system to investigate and characterize DSLs and their spatial patterns. Results show that the DSL indices vary greatly in different slope positions. The thickness of DSLs (DSLT) and quantitative index (QI) in the gully were significantly (p < 0.05) higher than those in the non-gully areas. The relative contribution of soil properties was higher than those of terrain factors in the gully, whereas the contribution of terrain factors was higher than those of soil properties under shrubland. Gullies contributed to the complex spatial DSL patterns in the slope–gully system. Partial least squares regression (PLSR) was used to detect the relative significance of 10 selected environmental factors that affect spatial DSL patterns. Variable importance in projection (VIP) demonstrated that soil properties, especially Clay and Silt content, significantly influenced the DSL formation depth (DSLFD), DSLT, and QI. Land-use and slope position were the most important factors that influenced the mean soil-water content (SWC) within DSLs (DSL-SWC), which exhibited the highest VIP values. PLSR models simulated DSL indices accurately in DSL-SWC; the values for variation in response (R2) and goodness of prediction (Q2) were 0.94 and 0.92, respectively. Therefore, our findings provide a helpful base reference for DSL management and reclamation of hill and gully regions of the LP.

Response of Soil Water Dynamics to Rainfall on A Collapsing Gully Slope: Based on Continuous Multi-Depth Measurements

Soil water conditions play an important role in the formation of a collapsing gully, but we are still at the early stages of understanding how the soil water changes on the slope after different rainfall events due to a lack of high-frequency continuous field observations. This study aimed to reveal the response of soil water dynamics to rainfall events for different slope aspects and positions based on continuous multi-depth observations of soil water on a typical collapsing gully slope from 2017 to 2019 in Wuhua County, Guangdong Province, China. The vegetation characteristics and soil properties were investigated, and the storage of soil water was also calculated. The results showed that the dynamics and storage of soil water varied with the slope aspect, slope position and vegetation cover. The response time of the soil water to intensive rainfall events on the sunny slope was shorter than that on the shady slope, while soil water storage in the sunny slope was significantly lower than in the shady slope (p &lt; 0.01). For the different slope positions, the soil water response time to the intensive rainfall events on the upper slope was shorter than that in the middle slope, while the soil water storage in the middle slope was significantly higher than on the upper slope. This was mainly due to the redistribution runoff from the upper slope to middle slope, delaying the process by which rainwater infiltrated into the soil layers. Moreover, vegetation significantly allayed the response of soil water dynamics to an intensive rainfall event but increased the storage of soil water, owing to the protection of soil surface from rain and conservation of high soil clay content. The bare area in the middle position of the sunny slope was speculated to be the potential source of the collapsing gully because it lacked the cover of vegetation. Our findings highlight the importance of soil water dynamics on the formation of a collapsing gully and provided valuable insights for the optimization of soil conservation and management practices for collapsing erosion.

Sublacustrine gravity-induced deposits: The diversity of external geometries and origins

Our current knowledge of deep-water depositional systems is mainly built of extensive achievements obtained from marine basins. Although lacustrine basins are important oil & gas productive areas of the world, gravity-induced deposits in these basins are poorly understood in the literature when compared with those documented in marine basins. Based on new insights from 3D seismic data, this paper attempts to investigate the effect of the interaction between gravity-induced flows and lake-floor topography on the resulting external geometry of gravity-induced deposits in the Cretaceous Qingshankou and Nenjiang formations of the Songliao Basin (SLB).Eight different shapes of gravity-induced deposits were identified in the SLB, and which were in turn grouped into four distinct categories according to external shape, internal architecture and spatial assembly: (1) Channel-fan complexes; (2) Fan-form complexes; (3) Strip-form complexes; and (4) Pond-form complexes. Furthermore, fan-form complexes can be subdivided into four subcategories (isolated fan with compressional ridges, isolated fan without compressional ridges, mother-son fans and stacked fans). Strip-form complexes can be subdivided into two subcategories, including strip-form controlled by gully system and strip-form controlled by growth faults.Sediment transport mechanism (density flows or mass transport flows) and lake-floor topography together influence the pathways, runout distances, discharge places and internal characteristics of gravity induced deposits, which could ultimately influence external geometries of gravity-induced deposits in the SLB. Consequently, sublacustrine gravity-induced deposits does not exhibit classic fan-like geometry. Frequent and powerful hyperpycnal flows associated with flood events are fairly common, and develop channel-distal fan complexes. MTDs exhibit various external geometries, which are significantly affected by growth faults, slope gullies, gradient, and basin-floor irregularities. The new depositional model built from the SLB is vital to understanding the distribution of gravity-flow deposits in a sublacustrine slope.

Influences of revegetation mode on soil water dynamic in gully slope of the Chinese Loess hilly–gully region

Gully slope is one of the most active areas of soil erosion in small watershed of the Chinese Loess hilly–gully region. Although its soil erosion has been effectively controlled with the implementation of the “Grain-for-Green Program” in this region, the soil water storage and distribution have been also impacted. In particular, unreasonable revegetation model has aggravated the water shortage, which may in turn threaten the health of ecosystems. However, yet little is known about the effect mechanism of vegetation on soil water in the gully slope. In this study, we examined the relationship between two revegetation modes, including afforestation (i.e. black locust forest) and natural revegetation (i.e. the grassland), and soil water in a depth of 0–120 cm of the gully slope, during the rainy season. The results showed that the effect of the vegetation to the soil water was smaller than that of the precipitation. Furthermore, the response of soil water to the environmental factors was higher in afforestation vegetation due to its lower soil water content, resulting in higher space dependence for soil water, compared to the natural revegetation. The lower soil water content of the black locust forest was mainly caused by its higher recession rate, not its supply. The soil water was deficient for a long time, caused by afforestation, with a shallower formation depth of the dried soil layer and stronger desiccation degree. However, this deficient could not be effectively relieved until in wet year. In comparison with the ridge slope, the effect of vegetation to soil water in gully slope was stronger, with greater water consumption in afforestation vegetation and the higher water storage in natural revegetation. From the aspect of water resources conservation on the water scale, the natural revegetation was the optimal revegetation mode in the gully slope of the loess hilly region.

A preliminary investigation of gully edge effect on the distribution pattern of soil moisture across a permanent gully

Describing and mapping soil water content (SWC) distribution are required to understand and explain the hydrological phenomena at various spatial scales. Soil drought in the hilly and gully regions of Loess Plateau reduces agricultural production and plants biomass, which has attracted great attention but few studies associated it with the gullied terrain. To understand the SWC distribution pattern in the slope–gully system, we established a cross-section transect for SWC observation across a permanent gully and acquired 23 occasions of SWC data in the periods from October 2014 to September 2018. The standardized beta coefficient in stepwise multiple linear regression was employed to determine the strength of the effect of the selected variables (soil textural separates, soil depth, relative height, distance to the gully and saturated hydraulic conductivity) on SWS distribution. Spectral and cross-spectral analysis were performed on the time series of SWC to evaluate the cyclical behavior and the similarity for adjacent sites, respectively. The following results were obtained: First, the SWC distribution had a bilateral asymmetrical pattern across the gully, which constituted a specific and detailed content of spatial variability of SWC. Second, soil water storage in the slope–gully system was primarily affected by soil texture, meanwhile, the effect of distance to the gully was stronger than that of soil depth. Third, the SWC of the adjacent pair sites presented consistent periodic behavior. The cross-spectral analysis indicated a dissimilar pattern for soil layer of 0–60 cm and deep synchrony for the other depth layers. In conclusion, the gully edge effect aggravated the SWC status in the south bank and caused a bilateral asymmetrical pattern in the slope–gully system. These results improved our knowledge on the complicated distribution of SWC in the gullied region. Moreover, the results indicate that ignoring the nearby areas of a permanent gully in a catchment is inappropriate when investigating soil water resources.

Current Status, Problems and Prospects of Conservation of Meadow Steppes in the Nizhny Novgorod Region

The meadow steppe of the Nizhny Novgorod region is an endangered ecosystem, which is associated with a significant part of the biological diversity in the region. It covers now not more than 1.5% of the former area. At the same time, the steppes are inhabited by more than 100 wildlife species listed in the regional Red Book. Using GIS methods we have developed a technique that allowed us to identify about 14,000 potential steppe sites. In 2013-14, according to obtained data an inventory of steppes was carried out. About 50% of the potential sites identified with use of GIS methods were surveyed. Almost all the areas with a high probability of steppe ecosystems remained were examined. At least 90% of remained meadow steppes have been discovered. In order to monitor the steppe ecosystems, 29 most significant sites were reexamined in 2019. A total of 136 slopes of ravines and gullies with a total area of 9732 hectares were identified, where plant communities with the dominance of steppe species are represented. The land areas ranged from 1.4 ha to 454 ha, and the share of steppe associations ranged from 0.1% to 80%. Changes in the species composition and number of steppe plants in the region are characterized. About 15% of the area of the Nizhny Novgorod meadow steppes are protected as 8 natural monuments of regional significance, another 20% are on lands that are reserved by the regional government as the regional protected areas. It is planned to increase the share of the preserved steppe areas, which have legal protection, to 85% of their area. The trend of factors leading to degradation of steppe ecosystems and recognising as limiting for steppe wildlife species is analyzed. It is proposed to implement a program of restoration of pasture cattle breeding to solve the problem of the meadow steppe ecosystem conservation in the Nnizhny Novgorod region.

Structural-morphological and sedimentary features of forearc slope off Miyagi, NE Japan: implications for development of forearc basins and plumbing systems

Multibeam (MB) and subbottom profile (SBP) data along the forearc slope off Miyagi, Japan, are combined to investigate structural-morphological and sedimentary structures along the forearc slope of the Japan Trench subduction zone. In addition to dip-oriented slope gullies, the MB data image a nearly dip-perpendicular slope trough bounded by a fault scarp landward of the trench-slope break. Seaward of the trench-slope break, the subbottom mostly contains normal faults that dip in opposite directions. The SBP data show not only unconformity and sliding surfaces, but also underfilled (forearc trough) and filled structures that may reflect the most recent forearc subsidence and basin filling. We propose these forearc trough and associated filling structures may indicate the earliest developments of modern isolated basins. Thus, a model of forearc basin development from slope gully to slope trough, isolated basins and forearc basin, transferred by active structures, could be proposed. Observed seafloor liquefaction in the SBP data may represent a near-surface seep structure of a plumbing system that enables hydrosphere-mantle fluid migration plausibly activated by earthquake cycles.

Dynamic Changes in Surface Damage Induced by High‐Intensity Mining of Shallow, Thick Coal Seams in Gully Areas

This study proposes a novel approach to study the mechanism of mining and dynamic changes in surface subsidence and geological hazard‐prone regions caused by shallow, thick coal seam mining in gully areas. This approach combines field observation, three‐dimensional modeling, numerical simulation, and theoretical analysis based on the conditions of the Chuancao Gedan coal mine. The in situ stress field of coalbeds is influenced by the gully terrain. Shear stress becomes concentrated on the surface, causing geological disasters such as landslides and collapse of gully slopes. High‐intensity mining activities increase the concentration and are more likely to cause such geological disasters. The influence area and severity vary dynamically with the expansion of the excavation area. With the continuous expansion of coal seam mining, the amplification ratio η (the ratio of the maximum impact range of surface subsidence and the mined‐out area) first increased to 3.35, then decreased, and finally reached a constant value of 2.1. The principle of road line selection is proposed based on an analysis of surface subsidence and gully slope stability on the goaf edge. The principle of subsection reinforcement of the gully slope under the dynamic influence of coal seam mining is also determined.

Modern status of diversity of soil mesofauna communities in meadow-steppe areas of Northern Podillia

Meadow-steppe vegetation was much more abundant in the past and covered large areas. However, nowadays, only small refugia of such vegetation remain due to the intensification of agriculture and significant anthropogenic transformations. These refugia, found on the slopes of hills and gullies, are of high scientific value with regard to the conservation of soil invertebrates’ microhabitats. This study is the first one conducted with the purpose to investigate invertebrate mesofauna diversity in meadow-steppe areas of Northern Podillia. Soil invertebrates that belong to 40 families from six classes of three phyla are the object of our research. They are an essential component of terrestrial ecosystems due to their regulative role in the topsoil. Soil invertebrates are functionally divided into different groups, but our special attention was given to “ecosystem engineers”, 13 species of Formicidae in particular, which are the organisms that significantly influence the soil by their activity. In addition, ants selectively affect the distribution of both autotrophs and heterotrophs. Formicidae alter or create micro-habitats and regulate the ability of other species to use the resources. The study presents structural and functional organization of soil invertebrate communities as well as indicators of their taxonomic diversity and dynamic density. The material was collected during 2018 field season in two relic meadow-steppe areas of the Holohoro-Voroniatsky hills of Podillia (Makitra and Bila Mts.) and analyzed according to the standard methods. In the structural and functional organization of invertebrate communities (trophic groups), phytophages prevail by their diversity (39 taxa), and zoophages predominate by dynamic density (up to 70 % of numbers of collected material). Formicidae are the eudominant part among the latter. High taxonomic diversity (93 invertebrate taxa: 62 species, 11 genera, and 20 fami­lies) as well as dynamic density and dominance structure of ground litter fauna communities in meadow-steppe areas of Northern Podillia indicate their significant role in the functioning of particular ecosystems (e.g., such steppe species as Blaps halophila Fischer von Waldheim, 1822 , Myrmica deplanata Emery, 1921 , Tapinoma erraticum (Latreille, 1798 , etc.).

New data on the spider fauna (Araneae) of the Penza Region (Russia)

Arachnological research in the Penza Region was conducted in the 1980s and in the mid-2000s only. Initially, a list of 112 species was published and spider distribution within five types of habitats throughout the region was analyzed (Pyatin, 1988). Later on, spiders were studied in four segments of the Privolzhskaya Lesostep Nature Reserve and the species lists for each segment were compiled (Polchaninova, 2008, 2015a, b, 2020). In total, 273 spider species of 23 families were recorded from the reserve. The segments are located in four administrative districts of the region. The present paper provides an annotated list of 71 spider species recorded for the first time from the Lunino District. The material was collected by pitfall trapping in 2004 and 2005 in five habitats in the Nature Monument Solontsovaya Steppe: meadow steppe on the chernozem soil on a gentle slope (33 species), steppe on the clayey soil on a steep gully slope (33 species), steppe on the solonetz soil on a gentle slope (43 species), sand and clay quarry (28 species), and bank of a pond (29 species). The most abundant was the spider assemblage of the meadow steppe (736 individuals) dominated by Pardosa fulvipes (62 % of total spiders collected in the habitat). Other spider assemblages were less abundant (minimum 243 individuals on the pond bank and maximum 324 individuals in the solonetz steppe), and their dominance structure was more uniform. The dominant complexes consisted of Gnaphosa lugibris, Haplodrassus signifier and Xerolycosa miniata in the clayey steppe (53 % of total spiders in the habitat), X. miniata, P. fulvipes, P. palustris, and P. agrestis in the solonetz steppe (60 %), X. miniata and P. fulvipes in the quarry (57 %), and P. fulvipes, P. palustris, and Diplostуla concolor on the pond bank (63.5 %). Thus, Pardosa fulvipes and Xerolycosa miniata were the most numerous species at the study site. A high abundance of both species was also observed in the Borok segment of the Privolzhskaya Lesostep Nature Reserve, which suggests similarity of ecological conditions in the grassland habitats of both localities. One species, Mastigusa arietina, is new to the Penza Region. Taking into account 40 species recorded by М. Pyatin (1988) but absent from our collection, the spider fauna of the Penza Region numbers 313 species of 27 families.

Sedimentary processes and seabed morphology of the Southwest Greenland margin

Bathymetric and seismic data from the Southwest Greenland margin have been used to provide an integrated shelf-to-basin overview of the margin architecture between 57° N and 64° N. A variety of glacially formed morphologic features, contour current-related erosion and sedimentary deposits, and evidence of downslope sediment transport via canyons, channels and gullies is found here. The study area is characterized by two major canyons bordering Fylla Bank in the northern part and a narrow shelf and steep slope to the south, where erosion due to strong boundary currents occur down to c. 3000 m water depth. The narrow shelf area appears to be an intra-ice stream area, and numerous channels and gullies on the upper slope point to hyperpycnal melt water release from a stable or retreating wide ice front. Further southward, the shelf is widening and the morphology indicates dominance of former ice stream activity. This difference in glaciation style may reflect the different bedrock types. Sedimentary and morphologic characteristics of the Fylla Bank canyons and some of the slope gullies and channels point to actual cascading of dense winter water or hyperpycnal melt water flow from the shelf. Deep-water channels at the base of the slope evidence transport of Greenland-derived sediment to the central Labrador Sea basin and buried channels further west indicate a former contribution to the Northwest Atlantic Mid-Ocean Channel (NAMOC) system. However, in contrast to widespread turbidite channels on the present seabed bordering NAMOC to the west, east of NAMOC contourite deposits have largely covered the deep-water tributary turbidite channels originating from the Greenland margin.

Temporal variations in soil erodibility indicators of vegetation-restored steep gully slopes on the Loess Plateau of China

Near soil-surface characteristics change considerably with vegetation growth during one growing season, and thus likely induce the temporal variations in soil erodibility indicators. This study was performed to investigate the temporal variations in soil erodibility indicators under different vegetation-restored gully slope lands on the Loess Plateau of China. Soil erodibility indicators included the K factor, mean weight diameter (MWD), mean number of drop impacts (MND), saturated conductivity (Ks), cohesion (Coh), penetration resistance (PR), and one comprehensive soil erodibility index (CSEI). One slope cropland (as the control) and seven vegetation-restored gully slope lands were selected to measure soil erodibility indicators for seven times from April 23 to October 10, 2018. Near soil-surface characteristics were also measured to explain the temporal variations in soil erodibility indicators. The results showed that the temporal variations in soil erodibility indicators of different vegetation lands were similar. The K factor fluctuated considerably, while the MWD, MND, Ks, Coh, and PR gradually increased over time. However, all erodibility indicators of the control cropland fluctuated over time with no distinctive trend. The CSEI of all sites fluctuated significantly over time. Compared to the control cropland, the mean K factors of different vegetation lands decreased by 2%–24%, but the mean values of MWD, MND, Ks, Coh, and PR increased by 108%–217%, 152%–343%, 94%–306%, 73%–175%, and 30%–199%, respectively. Consequently, the mean CSEI of different vegetation lands was reduced by 41% to 86%. The temporal variations in soil erodibility indicators were closely related to the seasonal changes in root mass density. Bothriochloa ischaemum (Linn.) Keng was considered the most effective restoration community to reduce soil erodibility of steep gully slope lands. The results contribute to improving the eco-environment on the Chinese Loess Plateau.

ХАРАКТЕРИСТИКА ЧИСЕЛЬНОСТІ ТА ПРОСТОРОВОГО РОЗПОДІЛУ ПОПУЛЯЦІЙ ЗЕЛЕНОЇ ЯЩІРКИ (Lacerta viridis Laurenti, 1768) НА ТЕРИТОРІЇ НПП «ДНІСТРОВСЬКИЙ КАНЬЙОН»

Reliable information about the species composition of the fauna, way of life, abundance, distribution, and breeding features is not only the initial data for in-depth zoological, evolutionary and ecological research, but also the source for nature conservation activity based on the analysis of the state of wildlife resources.&#x0D; The European green lizard (Lacerta viridis Laurenti, 1768; Reptilia, Squamata) is one of the most vulnerable species of reptiles in the domestic herpetofauna. Therefore, it is the object of ecological research aimed at studying population structure, biotopic distribution, including within the protected natural areas and areas that are undergoing significant anthropogenic transformation.&#x0D; The work is based on field studies conducted in April August 2018 and data from the regular phenological observations of the Dniester Canyon National Nature Park.&#x0D; The current status of the European green lizard population (Lacerta viridis Laurenti, 1768) within the territory of Dniester Canyon National Nature Park has been investigated. The abundance and spatial distribution of the species populations in different biotopes have been studiedon the basis of long-term phenological observations according to the program of the Chronicle of Nature of the National Nature Park and the authors’ research. The data of the species occurrence on the territory of the Park for the last six years is given. The abundance of the European green lizard populations under different biotopical conditions and the main factors influencing the studied parameters have been analyzed.&#x0D; The European green lizard has been found to be a stenotopic species that favors only 2-3 biotopes, so it is highly vulnerable due to distortion of specific stations. Besides, L. viridis is the dominant species of reptiles on the Dniester slopes, its tributaries, streams, gullies and ravines.&#x0D; The biotopes inhabited by this species can be grouped into three main types:&#x0D; 1) slopes of hills and ravines with thick-growing grassand bushes of hawthorn and dog rose (settlement density 30-50 inhabitants/km);&#x0D; 2) areas related to broad-leaved forests and mixed forests glades, outskirts of forests, forest roads (20-50 inhabitants/km);&#x0D; 3) steep slopes of gullies, steep bank slopes with limestone outcrops with herbaceous and shrubby vegetation (6-11 inhabitants/km).&#x0D; The spatial distribution of L. viridis communities in the region is predominantly aggregative and exists in several different forms, which is related to the configuration of favorable plots, the nutritive base and interspecies relationships.

Przemiany wybranych form rzeźby terenu województwa łódzkiego w ostatnim stuleciu

The paper presents changes in the relief of the Łodź Voivodeship over the past 100 years. In view of a shortage of data, only a few cases of changes to aeolian landforms and to selected forms appearing on the slopes of gullies and other young erosional cuts were described. The transformation of aeolian relief in the last 100 years was associated with the formation of small, initial aeolian hillocks and with the transformation by wind of older late-glacial dunes. The changes to gullies involved rapid transformation of their slope profiles under the influence of soil cultivation and comprised from 2.18 to 51.4% of the gullies’ slopes. As in the case of the dunes, the transformation of the relief both of former Neoholocene gullies, and of young, small, but permanent erosional forms originated on the slopes took place. Relief analysis of aeolian landforms and features occurring on the slopes was preceded by consideration of the vulnerability of the Łodź Voivodeship area to aeolian activity and slope processes.

Assessment of the Erosion Stability of Slopes in Terms of Digression and the Degree of Overgrowth

Agroecological systems of slopes experience stress due to constant dynamic movements, especially on the slopes of high steepness. We have formulated the idea of critical levels in the dynamic process of slope agroecological systems, which is subsequently considered as an indicator of sustainability. When analyzing the dynamic processes on the slopes, we identified the digression of the slope surface under the influence of erosion processes as a critical one. The object of research is the erosion slopes of ravines and gullies in the forest-steppe conditions of the Volga upland. The purpose of the study is to develop parameters for assessing the stability of erosion slopes based on the results of research and analysis of literature sources. Results and discussion. It is proposed to refer to the dynamics changes not only in species composition, but also changes in the degree of degradation in terms of overgrowth of slope areas, allowing to establish the processes of secondary succession as the destruction of the slope surface. According to our concept the changes of species diversity on the erosion slopes may be accompanied by the appearance of alien plants in consequence of the stability, biological diversity and protective functions of the protective forest plantations loss. The number of species may increase, but the erosion slope gradually loses its stability. Quantitative assessment of the degree of overgrowth in terms of undergrowth and their qualitative characteristics give an idea of compliance of the forest conditions on the slope with environmental requirements for self-seeding tree species. It is found that the number of self-seeding on the slopes with increasing stage of digression naturally decreases. The number of self-seeding, compared with seedlings, 2-4 times less, regardless of the degree of digression of the slope. On the control and on the site of stage I of digression, the number of shoots of self-seeding clearly differ, which affects the incidence rate. In other areas, the occurrence is 53 -100%, which confirms the uneven of overgrowing of the slope area.

Geomorphology of Gullies at Thomas Lee Inlet, Devon Island, Canadian High Arctic

AbstractSlopes in and around Thomas Lee Inlet (Devon Island, Nunavut, Canada) are eroded by means of gullying, yet the driving factors, such as the nature of the substrate and availability of different sources for water, influencing gully morphology remain poorly understood. Here we investigate the factors that contribute to gully formation using a combination of satellite mapping, field observations and statistical analysis of morphological data. In total, 161 gullies were mapped within the 126 km2 study area. Factors linked to gullies, such as the nature of its substrate and the presence of glaciers, were integrated into a spatial geodatabase. A Factor Analysis of Mixed Data performed on the geodatabase was used to discriminate which factors may influence gully geometry. Our results show that the type of geological formation has a strong impact on gully slope. In addition, supplemental sources of water are often found near alcoves of the steep, longer and mature gullies, and levees often form in their aprons. Immature debris flow‐like gullies were dryer and found on short and variable (from steep to gentle) slopes. This detailed study of the rocky and arid Thomas Lee Inlet plateaus and slopes provides the first insight into gullied slopes as a hydrological component connecting upland units to downslope in this area.

Into the deep: A coarse-grained carbonate turbidite valley and canyon in ultra-deep carbonate setting

New high-resolution multibeam mapping images detail the southern part of Exuma Sound (Southeastern Bahamas), and its unchartered transition area to the deep abyssal plain of the Western North Atlantic, bounded by the Bahama Escarpment extending between San Salvador Island and Samana Cay. The transition area is locally referred to as Exuma Plateau. The newly established map reveals the detailed and complex morphology of a giant valley draining a long-lived carbonate platform from its upper slope down to the abyssal plain. This giant valley extends parallel to the slope of Long Island, Conception Island, and Rum Cay. It starts with a perched system flowing on top of a lower Cretaceous drowned main carbonate platform. The valley shows low sinuosity and is characterized by several bends and flow constrictions related to the presence of the small relict isolated platforms that kept alive longer than the main platform before drowning and merging tributaries. Turbidite levees on either side of the valley witness the pathway of multiple gravity flows, generated by upper slope over steepening around Exuma Sound through carbonate offbank transport, some of them locally >15°, and resulting slumping. In addition, additional periplatform sediments are transported to the main valley through numerous secondary slope gullies and several kilometre-long tributaries, draining the upper slopes of cays and islands surrounding Exuma Plateau. Some of them form knickpoints indicating surincision of the main Exuma Valley which is consistent with an important lateral supply of the main Exuma Valley. Prior to reaching the abyssal plain, the main valley abruptly evolves into a deep canyon, 5 km in width at its origin and as much as 10 km wide when it meets the abyssal plain, through two major knickpoints named “chutes” with outsized height exceeding several hundred of meters in height. Both chutes are associated with plunge pools, as deep as 200-m. In the deepest pools, the flows generate a hydraulic jump and resulting sediment accumulation. When the canyon opens to the San Salvador abyssal plain, the narrow, deep, and strong flows release significant volume of coarse-grained calcareous sediments in numerous turbidite layers interbedded with fine mixed siliciclastic and carbonate sediments transported by the Western Boundary Undercurrent (WBUC) along the Bahama Escarpment. Carbonate gravity flows exiting the canyon decelerate at the abyssal plain level and construct a several-kilometre-wide coarse-grained deep-sea turbidite system with well-developed lobe-shape levees, partially modified by the flow of strong contour-currents along the Bahama Escarpment.

Profile distribution of soil moisture in the gully on the northern Loess Plateau, China

Gully is a typical geographical unit and a key component of the slope–gully system on the northern Loess Plateau. Understanding the distribution of soil moisture in gullies aids water resource regulation and ecological restoration. To investigate temporal–spatial variability of soil moisture, we measured values of soil water content (SWC) within 0–500 cm by using a neutron probe on 19 occasions from October 2014 to July 2017 in the gully and bank of a developed gully in Liudaogou catchment of Shenmu County. Results showed that the values of space–averaged soil water storage (SWS) in the gully were significantly (P < 0.01) higher than those in the bank. Soil clay content (SCC) and topography (including site elevation and distance from the gully head) were the most important factors affecting SWS of 0–500 cm in the gully. Topography can indirectly control SWS by redistribution of rainfall and soil properties. SWS and SCC rose with increasing distance from the gully head to the outlet. SWS in the gully exhibited strong temporal stability, and two time–stable sites around the middle section can be used to represent mean SWS within 500 cm depth in the gully. The gully sidewall significantly (P < 0.05) aggravated drought of soils in the bank between 150 and 250 cm from the gully edge. Gullies make the temporal–spatial patterns of soil moisture complex in slope–gully system. These results were expected to improve understanding of soil moisture distribution in the gully region and aid vegetative restoration of the northern Loess Plateau.

Geological and oceanographic controls on seabed fluid escape structures in the northern Zhongjiannan Basin, South China Sea

Mega-pockmarks, which can reach a few kilometers in width and a few hundred meters in depth, and associated fluid escape features in the Northern Zhongjiannan Basin, South China Sea, have received much attention in the recent years, due to their large variety of morphologies and sizes. In this work, an integrated interpretation of detailed multibeam bathymetry, conventional multi-channel seismic reflection and seismic oceanography sections covering the northern Zhongjiannan Basin, South China Sea, are used to image the seafloor morphology, the subsurface geology and the water column, in order to better understand the geological and oceanographic controls on the formation and evolution of the widespread fluid escape features in this region. Regional uplift and volcanism took place in this area near the Palaeogene–Neogene boundary and, during the Neogene–Quaternary post-rift thermal subsidence period, differential subsidence and diapirism deformed the overlying kilometer-scale successions. Mainly after the Miocene, focused flow of fluids originated at depth occurred along gas pipes, polygonal faults, tapered reflectors and faults into the shallow sediments, resulting in intense fluid blowouts and complex fluid escape structures on the seafloor. Our results show that elongated pockmarks, pockmark gullies and gullies in the northern slope are generally controlled by underlying buried channels and gullies. However, pockmark gullies and gullies in the southern slope are controlled by gravity sliding/slumping, along with crescent pockmarks developing parallel to water depth contours. To varying degrees, intense fluid escape activities associated with mud diapirism and gas escape in the study area resulted in mud extrusion and the formation of mud volcanoes, complex seabed morphologies and irregular pockmarks. Mega-pockmarks, collapse structures and blind valleys have formed at the apexes of tectonic uplifts related to volcanism and above basement highs, which suggests that these processes played a role in creating pathways for fluid escape. Bottom currents associated with the South China Sea Western Boundary Current, imaged here for the first time with the seismic oceanographic method, mainly flow to the south, and erode the seafloor, making pockmark walls and slopes of gullies and channels in the north steeper than those in the south. Some fluid escape structures, such as the mega-pockmarks and pockmark gullies, are buried by sediment transported by the bottom currents. Turbidity currents flowing downslope along the long pockmark gullies also erode the seafloor and make the NW slopes of the mud volcanoes less steep than those in the SE. Eddies imaged by the seismic sections may also play a role in transporting sediment to the deep sea in this area. Some of the reported fluid escape structures are still active, as indicated by the fluid pathways that reach the seafloor and plumes in the water column imaged by the seismic sections.

Periglacial complexes and the deductive evidence of ‘wet’-flows at the Hale impact crater, Mars

Abstract The Hale impact crater is a large complex crater ( c. 150 × c. 125 km) in the southern hemisphere of Mars. Recurring slope lineae have been observed on its central-peak slopes, as have relatively youthful gully-like landforms; the latter are observed adjacent to or in the midst of the former, as well as on all of the rim-material slopes. Three of the gullied slopes on the northern-rim materials exhibit landscape features that, on Earth, are synonymous with wet periglaciation, i.e. landscape modification by the freeze–thaw cycling of water. These features include: (1) gelifluction-like lobes; (2) patches of surface polygonization, possibly underlain by ice wedges and formed by thermal-contraction cracking; and (3) shallow, rimless and polygonized basins morphologically akin to terrestrial alases. Here, we use the spatial association of the gully-like landforms together with the putatively wet periglacial assemblages or complexes to deduce and ascribe, albeit indirectly, a wet origin to the former.