Gilbert‐type deltas are sensitive recorders of short‐term base‐level changes, but the delta‐front record of a base‐level rise tends to be erased by fluvial erosion during a subsequent base‐level ...fall, which renders the bulk record of base‐level changes difficult to decipher from the delta‐front deposits. The present detailed study of three large Pleistocene Gilbert‐type deltas uplifted on the southern coast of the Gulf of Corinth, Greece, indicates a genetic link between the delta‐front morphodynamic responses to base‐level changes and the delta‐slope sedimentation processes. Sigmoidal delta‐brink architecture signifies a base‐level rise and is accompanied by a debrite‐dominated assemblage of delta foreset deposits, thought to form when the aggrading delta front stores sediment and undergoes discrete gravitational collapses. Oblique delta‐brink architecture tends to be accompanied by a turbidite‐dominated assemblage of foreset deposits, which are thought to form when the delta‐front accommodation decreases and the sediment carried by hyperpycnal effluent bypasses the front. This primary signal of the system response to base‐level changes combines further with the secondary ‘noise’ of delta autogenic variation and possible allogenic fluctuations in fluvial discharge due to regional climatic conditions. Nevertheless, the evidence suggests that the facies trends of delta foreset deposits may be used to decipher the delta ‘hidden’ record of base‐level changes obliterated by fluvial topset erosion. Early‐stage bayhead deltas may be an exception from the hypothetical model, because their narrow front tends to be swept by river floods irrespective of base‐level behaviour and their subaqueous slope deposits are thus mainly turbidites.
In order to estimate the rate of slope processes on the Moon, we studied the morphology and topographic configuration of 24 craters in the diameter range of 5–15 km. These craters are located in Mare ...Serenitatis, Mare Crisium, and Mare Fecunditatis, as well as in the continental terrain of Montes Apenninus. The craters were formed in three types of targets: (1) two-layered (continent, overlaid by a mare), (2) single-layered mare, and (3) single-layered continent. The topographic configuration was established for each crater, and the frequency–size distribution of overlapping craters on the walls and in the continuous ejecta zone was determined. The age of the craters was estimated (from 0.31 to 3.83 Gyr) based on the crater density in the ejecta zone. Comparing this density with the density on the walls allowed us to estimate the rate of slope processes. The rate of slope processes (
E
, mm/Myr) on the Moon is nonlinear and described by a power-law function
Е
= 4.39
А
–1.03
, where
А
is the age (Gyr). The estimated rates of slope processes in our study range from ~17 mm/Myr for the youngest crater to ~0.8 mm/Myr for the oldest crater. The studied craters represent stable landforms, and their configuration remains almost unchanged over billions of years. The target type has no significant influence on either the rate of slope processes or the changes in crater shape over time.
In the rich of archaeological sites dated from the late Palaeolithic to the Modern Period region of the Serteyka River, deposits of an extensive accumulative fan were studied in detail. In the lower ...sector of the present-day Serteyka River valley, the strict chronology and depositional conditions of an extensive accumulative fan deposits were studied in detail. An important part of the project has been also: a checking of usefulness of luminescence, radiocarbon and lead methods of dating in determination of the age of inorganic deposits accumulation The 14C, optically stimulated luminescence (OSL), and 210Pb dating methods were used to determine the fan's deposition age. Then, we discussed the depositional conditions of the accumulative fan by the textural, geochemical, and palaeoecological analysis.
The use of 14C and 210Pb methods of dating allows for elaboration of a reliable model of the evolution of slope processes occurring from the 2nd half of 17th c. AD to 2nd half of 19th c. AD (i.e. during the younger part of the Little Ice Age). It was a period of human induced deforestation, as confirmed by the first results of palaeobotanical analyses. In addition, four OSL dates have been obtained, but the acquired age significantly exceeded previous expectations. Three dates indicate the Neolithic period, and a chronological inversion of OSL dates can be seen. This may be due to incomplete bleaching of the sand grains during transport, which indicates that the material being transported had a relatively large volume. The lower deluvium of the accumulation fan is formed by the drainage of hydrated sediment (mudflows).
Summarizing, slope sediments can be extremely difficult material for absolute dating. This may be due to the redeposition of the material, the hiatuses in deposition and incomplete bleaching of quartz grains. In the case of 14C (AMS) dating, the dependence is on the presence of plant macroremains within the studied material. In the case of slope deposits, there is a very high probability of the redeposition of organic material. Lead dating, on the other hand, has a small chronological range. Moreover, the dating of inorganic sediments with this method poses many problems, including of a methodological nature. In the tested accumulative fan, as a result of insufficient grain whitening and the short chronological range of the 210Pb method, the 14C method was the main analysis determining the age of inorganic sediments.
The nearly complete coverage of the U.S. Atlantic continental slope and rise by multibeam bathymetry and backscatter imagery provides an opportunity to reevaluate the distribution of submarine ...landslides along the margin and reassess the controls on their formation. Landslides can be divided into two categories based on their source areas: those sourced in submarine canyons and those sourced on the open continental slope and rise. Landslide distribution is in part controlled by the Quaternary history of the margin. They cover 33% of the continental slope and rise of the glacially influenced New England margin, 16% of the sea floor offshore of the fluvially dominated Middle Atlantic margin, and 13% of the sea floor south of Cape Hatteras. The headwall scarps of open-slope sourced landslides occur mostly on the lower slope and upper rise while they occur mostly on the upper slope in the canyon-sourced ones. The deposits from both landslide categories are generally thin (mostly 20–40 m thick) and comprised primarily of Quaternary material, but the volumes of the open-slope sourced landslide deposits can be larger (1–392 km
3) than the canyon-sourced ones (1–10 km
3). The largest failures are located seaward of shelf-edge deltas along the southern New England margin and near salt domes that breach the sea floor south of Cape Hatteras. The spatial distribution of landslides indicates that earthquakes associated with rebound of the glaciated part of the margin or earthquakes associated with salt domes were probably the primary triggering mechanism although other processes may have pre-conditioned sediments for failure. The largest failures and those that have the potential to generate the largest tsunamis are the open-slope sourced landslides.
Despite over a century of investigations into gullies and gully erosion, the characterization and categorization of gullies and the varied definitions, nomenclatures and terminology used has caused ...some confusion in understanding and communicating the relationships of gully forms and processes around the world. We firstly review the gully literature and highlight how a lack of consistency in gully definition and characterization prevents unifying theory from being developed within this important field of research, since it is often unclear whether different landscape features being discussed are comparable. We propose that conventionally employed qualitative planform and cross‐sectional characteristics of gullies alone are inadequate to define gully types, yet both these features remain central to most modern gully descriptions. We discuss the need to revise and augment these basic characteristics with clearly defined morphogenetic attributes such as landscape context, soil material characteristics, erosion processes, hydrological integrity, modes of development, and head/side‐wall morphology for an effective, practicable, generic gully classification scheme. Central to a gully classification scheme is the need for a clear definition of what a gully is – and is not – for which geomorphological criteria are proposed to differentiate a ‘gully’ from other ‘incisional land surface forms’. This gully definition hinges largely on the identification of a retreating head scarp and the internal erosion by mass‐movement and other sidewall slope erosion processes, coupled with the transport of the soil materials from the gully void. By defining a gully and synthesizing descriptions of gully ‘types’ from the literature and our own experience, we propose key morphogenetic attributes of gullies necessary to form a framework for a systematic gully classification scheme. An initial, eclectic classification framework is presented as both a summation and a synthesis of the literature review, and as a progenitor to a dynamic generic classification scheme that is proposed in a follow‐up article.
From reviewing the gully erosion literature for definitions, terminology, and categorization we conclude that a systematic classification of gullies is necessary to overcome the apparent disorder. Thus, we propose key morphogenetic attributes of gullies to form a framework for a generic gully classification scheme. An initial classification framework is presented as both a summation and a synthesis of the literature, and as a progenitor to a dynamic classification scheme that is proposed in a follow up article.
Results are presented from an isopycnic coordinate model of ocean circulation in the Amundsen Sea, focusing on the delivery of Circumpolar Deep Water (CDW) to the inner continental shelf around Pine ...Island Bay. The warmest waters to reach this region are channeled through a submarine trough, accessed via bathymetric irregularities along the shelf break. Temporal variability in the influx of CDW is related to regional wind forcing. Easterly winds over the shelf edge change to westerlies when the Amundsen Sea Low migrates west and south in winter/spring. This drives seasonal on‐shelf flow, while inter‐annual changes in the wind forcing lead to inflow variability on a decadal timescale. A modelled period of warming following low CDW influx in the late 1980's and early 1990's coincides with a period of observed thinning and acceleration of Pine Island Glacier.
Despite numerous efforts to properly differentiate between contourites and other deep‐water deposits in cores and outcrops, reliable diagnostic criteria are still lacking. The co‐occurrence of ...downslope and along‐slope sedimentary processes makes it particularly difficult to differentiate these relatively homogeneous deposits. The main aim of this paper is to identify differences in deep‐water sediments based on Principal Component Analysis of grain size and geochemistry, sedimentary facies, and reinforced by microfacies and ichnofacies. The sediments studied were obtained from two International Ocean Drilling Program Expedition 339 sites in mounded and sheeted drifts in the Gulf of Cadiz. The statistical approach led to the discernment of hemipelagites, silty contourites, sandy contourites, bottom current reworked sands, fine‐grained turbidites and debrites over a range of depositional and physiographic elements. These elements are linked to contourite drifts, the drift‐channel transition, the contourite channel and distal upper slope. When bottom currents or gravity‐driven flows are not the dominant depositional process, marine productivity and continental input settling forms the main depositional mechanism in deep‐water environments. This is reflected by a high variability of the first principal component in hemipelagic deposits. The stacked principal component variability of these deposits evidences that the contourite drift and the adjacent contourite channel were influenced by the interrelation of hemipelagic, gravitational and bottom current induced depositional processes. This interrelation questions the paradigm that a drift is made up solely of muddy sediments. The interrelation of sedimentary processes is a consequence of the precession‐driven changes in the intensity of the Mediterranean Outflow Water related to Mediterranean climate variability, which are punctuated by millennial‐scale variability. Associated vertical and lateral shifts of the Mediterranean Outflow Water, and therefore of its interface with the East North Atlantic Central Water, controlled sediment input and favoured turbulent sediment transport in the middle slope. During the interglacial precession maxima/insolation minima, a more vigorous upper core of the Mediterranean Outflow Water and the enhanced impact of the East North Atlantic Central Water – Mediterranean Outflow Water interface allowed for the development of the sandier contourite deposits.
Using the particle flow code (PFC), this work analyses the kinetic features of a landslide which occurred on May 5, 2018 in Mabian, Leshan City, Sichuan Province, China. The analysis is based on ...geological field investigations and unmanned aerial vehicle (UAV) images. The micro-strength parameters corresponding to the macroscopic characteristics of landslide rock materials are inverted by the method of the support vector machine (SVM) and PFC coupling. Coupled with digital elevation model (DEM), a PFC
3D
numerical model of this landslide is constructed, and the slope failure process is simulated. In the kinetic analysis, the landslide velocity, displacement, and energy features are taken into account. The results show that the initial stage of a landslide begins with the acceleration of the overall movement, followed by the debris flow deceleration movement. Its total movement duration is about 32 s, of which the main sliding time is about 16 s. The maximum velocity of the landslide mass is 10.2 m/s, and the maximum displacement is 120 m. The kinetic energy of the landslide dominates in the acceleration stage, and the collision and friction energy dissipation dominate in the deceleration phase. The simulation results are in good agreement with the real landslide characteristics and the video interpretation of the landslide motion process. This work could provide a new way to study related landslides as well as a theoretical reference for the quantitative risk assessment and disaster prevention and mitigation of landslides in the area.
Detailed palaeogeographical studies of the accumulative fan in the Serteyka River valley in W Russia and underlying biogenic deposits were carried out. The base of a representative core of biogenic ...sediments in the distal zone is dated to 1291 BC, while its top to 1631 AD. In this paper, palynological, plant macrofossils, Chironomide and Cladocera, geochemical, geochronological and sedimentological analysis were performed. Four phases of biogenic deposition were distinguished by pollen and geochemical analyses. Two of them coincide with the climatic fluctuation during Medieval Climate Anomaly and Little Ice Age. During the formation of the fan, overbank deposits were accumulated also, indicating numerous and intense floods, which are in line with the trend observed for other sites in this region. The accumulative fan is formed by lower, middle and upper deluvia and agricultural diamicton in its top. All units have specific sedimentological and geochemical features as well as low admixture of plant macrofossils. The beginning of the formation of this relief form dates back to the second half of the 17th century AD, and the end of the accumulation falls on the second half of the 18th century AD. Our work suggests that natural conditions had an impact on the formation and development of studied accumulative fan, however, the decisive factor causing the intensification of the slope processes were related with deforestation resulted from strong human impact, which was marked in palynological and macrofossils analyses (e.g. increase in the contribution of plants macrofossils related to agriculture).
This paper presents a novel approach (Y-slope) to simulate entire slope failure processes, from initiation, transport to deposition. The algorithm is implemented in a combined finite-discrete element ...method code. Absorbing boundary conditions are implemented to improve computational efficiency for the initial stress state equilibrium. Strength reduction methods, considering both tensile and shear failure modes, are implemented to evaluate the slope stability, where the safety factor and critical failure surface are automatically obtained. The energy dissipation mechanism, due to blocks’ friction and collision, is incorporated to accurately simulate the block kinematics during the post-failure stage. The accuracy and robustness of Y-slope are validated by numerical tests, and the failure mechanism and failure progress of a homogeneous and jointed rock slope are presented. Results indicate that Y-slope can not only evaluate the slope stability state (e.g., safety factor and critical failure surface), but also simulate the entire failure process (e.g., slope deformation, failure surface evolution, block transport and deposition). In addition, the critical role of existing discontinuities on the slope stability and failure mechanism are also highlighted. This work proposes a promising tool in understanding the failure mechanism and assessing the potential risk by predicting the entire failure process of rock slopes.
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