Regressive Erosion Research Articles

The Xerias Window near Argos (Peloponnesus) - an example of a regional geological structure of interregional importance

The Argolic-Arcadian border range is built up by rocks of the Tripolitza and the Pindos Zones. Its tectonic architecture is deeply exposed in the area of the Xerias Window. Key structures are worked out in this article. The nappe-shaped superposition of the Tripolitza Zone by the Pindos Zone is obvious in the frame of the Xerias Window. The vergence of the key structures of the latter varies everywhere between W and SW, which proves a relative transport of the Pindos Zone as a whole in that direction. After finishing the nappe transport both Pindos and Tripolitza Zone experienced further, collective deformations, which are brought in a probable chronological order. Round about since Upper Miocene, the compressive stress of the Hellenides was followed by young extensional tectonics, which continues until today. Its influence on the development of the window and on the forming of its frame is described. The most important faults that can be related to the spreading tectonics are called within this investigation as Xerias Faults. Finally, the impacts of the strong regressive erosion, of the numerous landslides, and of the widespread slope waste both on exposing and on covering the tectonic elements are regarded.

Assessing regressive erosion effects: Unveiling riverside land use land cover changes post hydroelectric project construction

In Ecuador, the Coca Codo Sinclair Hydroelectric Project (CCSHP) provides 34 % of the country's energy demand. However, since its inauguration in 2016, regressive erosion in the Coca River has accelerated, causing the collapse of the San Rafael waterfall in 2020 and damage to oil and electricity infrastructure. This study aimed to assess the effects of regressive erosion along the Coca River through changes in land use and land cover (LULC) to identify the impact of CCSHP operations on migration, deposition, and river channel erosion during 2017–2021. The methodology includes: i) Creation of cloud-free mosaics with Sentinel-2 satellite imagery; ii) LULC classification LULC classification post-operation of the CCSHP (2017), before (2019) and after (2021) the San Rafael waterfall collapse, using the Random Forest algorithm; iii) Estimation of variations in the fluvial dynamics of the Coca River. The results showed that between 2017 and 2019, the extent of water bodies and bare soil increased by 258.58 ha (25 %) and 5195.45 ha (71 %), respectively. Meanwhile, between 2019 and 2021, the extent of sand deposits increased by 387.71 ha (42 %). These changes reflect an acceleration of regressive erosion since the construction and implementation of the CCSHP, information that can be used as an initial tool to analyze the impact of hydropower in the upper Amazon and strengthen environmental protection and risk management policies.

Major fluvial erosion and a 500‐Mt sediment pulse triggered by lava‐dam failure, Río Coca, Ecuador

AbstractThe failure of a 144‐m‐high lava‐dam waterfall on the Río Coca, Ecuador, in February 2020 initiated a catastrophic watershed reset—regressive erosion upstream and a massive sediment pulse downstream—as the river evolves towards a new equilibrium grade. The evolution of this river corridor after a sudden base‐level fall embodies the “complex response” concepts long understood through laboratory experiments, numerical modelling and smaller‐scale field studies, but that have not been observed in the field before on this scale. This paper presents geomorphic and geotechnical data to characterize the evolution of the Río Coca since 2020. In the three years after the lava‐dam failure, the erosion front migrated almost 13 km upstream along the mainstem river and triggered secondary headcuts that began migrating up tributaries. Erosion of the mainstem and tributary valleys generated a sediment pulse estimated to be 277 million m3 and ~500 million tonnes (Mt) over three years, depositing sediment tens of meters thick over tens of kilometres downstream from the former waterfall. This sediment pulse is one of the largest in modern times, comparable to the annual sediment load of a major continent‐draining river but with orders‐of‐magnitude greater sediment yield. Geomorphic adjustment of the Río Coca represents a highly unusual natural disaster threatening life, property, water quality, the regional economy, major infrastructure and energy security. However, this event also provides a rare opportunity to learn how a large autogenic watershed disturbance and recovery evolve, with important lessons for interpreting the sedimentary record of volcanic landscapes.

Impact of alteration corridors on karst reservoir organisation and evolution of groundwater flow path: An example from the southern border of the Larzac Causse, southern France

All the features of karstic reservoirs result from the chemical and/or mechanical erosion of an initial rock volume, which modifies the initial petrophysical properties (i.e., porosity and permeability). The spatial distribution and organisation of the karst system in a carbonate massif are often overlooked in studies on karst hydrological functioning. However, these parameters are key to understand and accurately model dynamic flow. This contribution aims at characterising the nature and impact of alteration corridors on the organisation and evolution of the karstic reservoir and its present-day functioning. We focus on characterising the specific impact of the late onset of pocket valley regressive erosion on the organisation of the present-day drainage system. We used a 3D approach to correlate field observations on the surface and in caves, with remote sensing. The expression of alteration corridors is analysed in a 40 km2 area on the southern border of the Larzac Causse. This Jurassic carbonate massif is affected over its entire thickness by a network of vertically elongated alteration corridors containing dissolution-collapse breccia, mainly oriented in a N-S direction. Ghost-rock karstification played a significant part in the karstic reservoir structure and evolution. Alteration corridors result from the in-situ dissolution of the bedrock along an initial jointing pattern. The dissolution-collapse breccia corridors correspond to ghost-rock corridors selectively emptied of their alterite, under the effect of a hydraulic gradient. The vertically elongated structure of alteration corridors that cross-cut the Jurassic sequence enables fluid circulation from an upper to a lower aquifer, which were initially separated by a Toarcian marly seal unit. The subsequent initiation of pocket valleys led to the rapid evacuation of the residual alterite contained in ghost-rock corridors, under the influence of gravity. These alteration corridors determine the position of present-day pocket valley springs and enhance the regressive erosion dynamics, that progressively capture a north-east flowing watershed (Vis River). Finally, residual alterites are evacuated below the overflow spring altitude during high-flow events by flooding/dewatering of galleries. Such mechanisms of alterite evacuation provide insight into i) the part of the karstic reservoir that is connected to the spring, and ii) the dynamics of the associated flows. This study suggests that corridor networks constitute a substantial volume of porous and permeable materials that plays a major role in the present-day groundwater flow path. Such features should be considered valuable drilling targets for water exploration when located below the piezometric level.

The Processes of Aggradation and Incision in the Channels in the Terek River Basin, the North Caucasus: The Hydrological Fluvial Archives of the Recent Past

The rates of incision and aggradation in the channels in the Terek River basin (North Caucasus) for the last 50–85 years were estimated at 18 gauging stations. The stage–discharge method (annual low water stages at the same discharges) was applied. The stability of the Terek River channel was recorded on the tectonically subsiding Tersko–Kuma Lowland. On the subsiding Kabardian Plain, channel aggradation up to 14 mm a−1 was registered. The rapid (~32 mm a−1) incision of the Terek River occurs within the antecedent valley of the rising Sunzha Ridge, causing regressive erosion and incision (~25 mm a−1) of rivers on the Ossetian Plain, despite its tectonic subsiding. The rivers in the uplifting mountains of the North Caucasus transport the sediments delivered from slopes as climatically controlled debris flows. Aggradation and incision here alternate without a visible overall trend. The rates of modern channel bed deformations are 10 to 100 times higher than the mean rates of tectonic movements. The main effect of tectonics is the changes in river channel slopes, which cause changes in the bed load transport budget and channel bed deformation. Human-made constructions induce rapid deformations in the channels but have a local effect.

Regressive Erosion at River Coca in Northeast Ecuador: Landslide Monitoring with Sentinel-1 to Support Disaster Risk Management

After the collapse of the San Rafael waterfall in Northeast Ecuador on 2 February 2020, a regressive erosion started along the River Coca putting national infrastructure, the environment and indigenous communities at risk. A fast monitoring of areas exposed to landslides on local scales therefore is necessary to provide adequate risk management for the region. The study area, located in the Andean tropics close to the volcano Reventador, is characterized by steep slopes, seismic activity and high rainfall throughout the year. Sentinel-1 SAR data provide a solution for time-series monitoring in the region as imagery is available day and night and not affected by cloud cover. Landslide monitoring with Sentinel-1 SAR data was implemented using a bi-temporal change detection (BCD) with SNAP and a sequential change detection (SCD) with EESA Docker and the Google Earth Engine (GEE) aiming at the identification of a suited approach for fast disaster monitoring and management. The SCD showed an overall accuracy of 0.91 compared to 0.88 using the BCD approach validated with high-resolution imagery. Based on the landslide detection, hazard variables could be further identified to support future hazard and risk assessment. Fast processing of Sentinel-1 time-series data in a cloud-based environment allows for near real-time monitoring of ongoing erosion and provides a potential for pro-active measures to protect the national economy, the environment and the society.

Giant deep submarine depressions: A combined dissolution-mechanical process along carbonate margins

AbstractSubmarine depressions are common features on the eastern Bahamian seafloor but the genesis of the deepest ones (>4000 m in water depth) is not well understood. We conducted a morphometric analysis and compared them to a worldwide database of rounded depressions, whatever their genesis is. The deep Bahamian depressions are large elongated structures, among the largest on Earth, with a width greater than 1000 m and a depth sometimes greater than 200 m. They extend at the toe of the Blake Bahama Escarpment (BBE), one of the tallest escarpments on Earth. Some of them align parallel to the BBE. Other depressions align along large submarine canyon axes. When aligned along canyon axes, the depressions closest to the canyon head are flanked by a topographic high interpreted as a slope-break deposit, i.e., sediment deposited after flow expansion following a hydraulic jump. Turbidity currents in the carbonate canyon system are not permanent processes, but are rather triggered during sea-level highstands when the carbonate platform is flooded. In addition, some depressions are not located in canyon axes. Consequently, the size and location of the depressions are not likely explained by a simple plunge pool mechanical erosion. Rather, our data suggest that all depressions could be initiated by giant karstic dissolution structures (dolines or sinkholes). Under interpretation, those located in canyon axes are sporadically refreshed by carbonate-laden turbidity currents. The height of the outsized chutes marking the crossing of the BBE by the canyon mouth generates a hydraulic jump allowing sediment deposition toward the bottom of the depression. Large depressions observed at this location in the Bahamas were the result of an initial dissolution phase related to retreat of the BBE and the more recent sediment-laden flow activity. The depressions orientated along canyon axes facilitated the regressive erosion that formed the canyons. At present, the depressions located at canyon mouths act as regular plunge pools.

Pliocene-Pleistocene evolution of the lower Yellow River in eastern North China: Constraints on the age of the Sanmen Gorge connection

The Yellow River, the second longest river in China, originates in the northeastern Tibetan Plateau, flows in a contorted square-bend-shaped path through the Loess Plateau, then enters the Fenwei Graben before discharging through the Sanmen Gorge onto the North China Plain. Prior to its connection through the Sanmen Gorge, which cuts through the drainage divide of the Hua and Taihang mountain belt, the Yellow River had been partly impounded as a large lake filling the Fenwei Graben. To help decipher the Pliocene-Pleistocene history of the development of the lower reaches of the Yellow River, we analyzed the sedimentary histories of the Fenhe sub-basin in the northeast part of the Fenwei Graben and of fluvial-lacustrine sediments in the Huangdigou (HDG) section, which is now exposed at the upstream entrance to the current Sanmen Gorge. The Fenhe sub-basin changed from lacustrine/peat deposition to fluvial gravels at ~2.5 Ma. We suggest that this sedimentary facies change indicates the establishment of a significant outflow of the former Fenwei Graben Lake through the deepening Sanmen Gorge. The continuing lowering of base-level in the Fenwei Graben, which culminated in the direct flow of the Yellow River through the Sanmen Gorge and/or fluvial inland regressive erosion, also led to headward erosion of a new paleo-Fenhe River that cut through the Fenhe sub-basin. Tectonic activity and climate shifts may have contributed to the change to the modern path of the Yellow River. • The Fenhe sub-basin changed from lacustrine/peat deposits to fluvial gravels at ~2.5 Ma. • The detrital material deposited in the Sanmenxia isthmus was mainly from local sources at ~2.5 Ma. • Tectonic activity and climate shifts may have contributed to the change to the modern path of the Yellow River.

The endorheic – Exorheic transition and later stage of fluvial incision in a wet tropical margin setting: The Atlantic draining Paraíba do Sul River basin (Brazil)

Present-day endorheic drainage systems are rare in tropical humid regions and/or close to the coast. During the late Cenozoic, under a humid tropical climate, the Paraíba do Sul River basin (SE Brazil) has developed along the South America passive margin. This basin currently drains into the South Atlantic Ocean, but it preserves landforms that are indicative of previous endorheic paleodrainage. This study examines the possibility that this region was endorheic for most of the Neogene, prior to the establishment of the present-day drainage to the Atlantic and discusses the transition from an endorheic to an exorheic system. Data was obtained through analysis of geomorphological features identified by remote-sensing techniques and verified by fieldwork, as well as the interpretation of landscape evolution models elaborated by the Seppômen method. Five drainage convergence areas and possible endorheic paleobasins, previous to the Quaternary (or to the Pliocene) have been identified within the present-day Paraíba do Sul River basin. Each area is associated with a Cenozoic graben and is separated by structural highs which would have formed paleodrainage divides. The mechanism for the transition endorheic-exorheic is the overspill, the inland regressive erosion or, more probable, a combination between these two processes. In fact, these two processes often occur concomitantly and both contribute to the same result: the expansion of an exorheic basin by the incision of a permanent channel into the endorheic basin infill. The geological evolution of the ancestral Paraíba do Sul River, draining to the Atlantic Ocean, was later strongly controlled by the very low sea levels during the Quaternary which determined the stage of fluvial incision. No numerical dating has been yet obtained for the proposed endorheic-exorheic transition; nonetheless, published regional denudation rates suggest that this transition occurred sometime in the interval between 21 and 5 Ma (Miocene to Pliocene). This transition was controlled by a previous decrease in subsidence within the aforementioned grabens and by a much wetter climate that promoted overspill and connection to the Atlantic.

Impacts of Market Gardening Practices on Environmental Resources: The Case of Irrigable Lands in Bonkoukou (Imanan Rural Municipality, SW Niger Republic)

Due to increasingly extreme climatic conditions in the Sahel, irrigated crops are emerging as imperative innovations for agricultural transformation and resilience. This study is designed to assess the impact of market gardening on soil, water and plant cover in the western Niger Republic. Semi-structured survey data were collected from 78 site operators in the Imanan rural municipality (Filingué, Tillabéry). In addition to the survey, a photographic collection illustrated certain observable facts in the field. The survey shows that the wooden enclosures (70.65% of respondents) around the fields are renewed every year. The impacts are then substantial: deforestation of plateaus, clearing of valleys for new extensions, loss of wildlife habitat, changes in the water flow regime resulting from a geomorphological change in the commune. Itou, the preparation of the planks consumes a lot of water. Thus, the new sinking of water points and the load pressure increase the drawdowns of wells and boreholes in the sites (75.46% of respondents). The frequent spills of waste oil on the sites, as well as the numerous potato storage pits, are among the factors and vectors most likely to contaminate the soils and aquifers of the study area. Market gardening destabilizes the soils and induces regressive erosion as well as area runoff of rainwater on all sites and on the slopes. On the other hand, slash-and-burn practices, drying of branches intended for fences, as well as rain-fed cowpea crops, promote improved physical properties and soil fertilization. To reduce the risks of disintegration and especially of silting up of sites, the study suggests a policy of live hedges and wire fences so that common spaces can be imposed on operators.

Dynamics and Vulnerability of Hydrogeomorphological Units to the Degradation of Climatic Conditions in the Watershed of the Birnin Lokoyo Pond (Iullemmeden Basin, Southwestern Niger)

The present study concerns the lowlands of the Birnin Lokoyo watershed located in the Matankari Rural Commune (Southwestern borders of the large Iullemmeden basin in the Niger). Dominated by the Birnin Lokoyo pond, this watershed faced with the continuous silting up of the minor bed, dissipates further upstream in the east, so that it moves downstream to the west for the benefit of the populations of Matankari city. The main objective of this work is to analyze the representative elements of the new climatic and environmental situation as well as the various factors determining the surface conditions in the watershed. The methodological approach is based on documentary research, field observations, individual surveys and interviews with targeted groups. The results show that the silting up of the lowlands is the result of the concomitant degradation of the plant cover and the soils, which, as a result, triggered the development of crusting surfaces and area erosion on the slopes. The study underlined the importance of endogenous knowledge in the choice of remedies against the silting up of lowlands. In addition, rational land management practices on plateaus and structures (within the watershed) do not seem to be in phase with topographical factors and the tectonic framework. This work is part of the vision of better management of glacis on the banks, but also of sills subject to regressive erosion upstream and in order to guide the policies of resilience of the populations.

Eustatic knickpoint dynamics in an uplifting sequence of coral reef terraces, Sumba Island, Indonesia

An emerged coral reef terrace sequence flanks the northern coast of Sumba Island in Indonesia. The sequence was created by the joint effects of uplift and Quaternary sea level oscillations. Since its emergence, it undergoes chemical erosion, which is facilitated by its carbonate lithology. The morphology is dissected by multiple catchments drained by deep canyons, whose stream profiles display several knickpoints. We applied a multi-methods approach using high-resolution topographic data (Pleiades imagery), geomorphological analysis and denudation rates derived from 36Cl cosmogenic nuclide concentrations to characterize the dynamics of these coastal drainages. We specifically investigate (1) the channel response to eustatic forcing, by analyzing knickpoint dynamics along a longitudinal river profile, and (2) the control of internal and external forcing over the catchment-scale erosion. Firstly, knickpoints form at the distal edge of the emergent reef at each regressive stage following a sea level highstand. The knickpoint propagates and rotates upward by regressive erosion. Knickpoint propagation rate decreases sharply over time until it becomes negligible before the next sea-level rise, which implies a marked decline in knickpoint retreat rate before its resorption. We attribute the inability of the river at Cape Laundi to fully propagate eustatic oscillations to its low stream discharge and low sediment supply, related to its small drainage area, to the karstic nature of the coral reef terraces composing the sequence, and to the high frequency of eustatic forcing. Secondly, average denudation rates calculated from 36Cl cosmogenic nuclide concentrations of sands collected at the outlet of five catchments draining the sequence amount to 69 ± 8 mm·ka−1. We emphasize the role of canyon areas in driving the denudation of the major catchments. However, no first-order correlation has been observed between catchment metrics, uplift rates and denudation rates. Finally, our correlations between catchment finite eroded volumes and uplift rates highlight the tendency of catchments to widen with low uplift rate and to lengthen while incising the sequence deeply with higher uplift rates.

Exceptionally uncommon overburden collapse behind a natural lava dam: Abandonment of the San-Rafael Waterfall in northeastern Ecuador

On February 2, 2020, a sudden collapse of the volcaniclastic debris avalanche deposit behind the natural lava-dam barrier of the San-Rafael waterfall, the highest of Ecuador before the collapse, changed the Coca River course through a stream bypass beneath the lava dam leading to both waterfall abandonment and rapid regressive erosion. An initially slow retreat process which occurred during the waterfall stage involved two concomitant mechanisms, a basal plunge-pool undermining and a vertical plunge-pool drilling, each of which acting on both the basal debris avalanche deposits and the overlaying solid lava body, respectively. The lava-dam failure process did not occur as expected, but instead an early overburden collapse of the debris avalanche sequence behind the lava dam took place through two consecutive process: undermining of a basal cavity beneath the lava dam followed by a gradual down-washing of matrix particles from the debris avalanche deposit. Thus, the newly formed sinkhole captured the Coca River discharge. A rapid knickpoint retreat occurred upstream from the collapsed sinkhole which in turn evolved into a deep, steep-sided canyon gorge carved into loose sediments of the debris avalanche deposit thereby creating new transient small waterfalls and rapids. Valley-side slopes and floodplain bottom elevations, upstream from waterfall point, were modified by regressive erosion and canyon gorge formation.

Geo-hazards of the San Vito peninsula offshore (southwestern Tyrrhenian Sea)

ABSTRACT In this paper we present geomorphological hazard mapping of the San Vito Peninsula offshore (Sicilian margin of Tyrrhenian Sea), characterised by a very narrow continental shelf and a very dipping, tectonically active continental slope, no far from a seismogenic belt. The data set consists of morpho-bathymetric models achieved by means of multibeam survey and scattered high resolution seismic profiles. The morpho-bathymetric study highlighted some potential sites of geomorphological hazards, the most representative of which are: (i) two canyons developing from the upper slope off San Vito Cape down to the Erice basin; (ii) a dense network of small incisions across the upper slope; (iii) a very active landslide, developed onland and extending in the continental shelf close to the Scopello village. The geomorphological features that can generate submarine hazard are represented by: unstable sediment packages into canyon heads or along the upper slope; submarine canyons with regressive erosion; coastal landslides.

Compartimentação geoambiental no município de São Vicente do Sul, RS, Brasil

Landscape studies and compartmentalization through shapes, defined by relief, and composition understood as elements of rocky substrate and soils integrate information of use and occupation are fundamental to understand geomorphological dynamics and assist in the management and planning of agricultural and urban areas. The present work aims at the geoenvironmental compartmentalization of the São Vicente do Sul municipality, through combinations of elements in a GIS environment. The study identifies four units and five subunits geoenvironmental defined: Floodplain Units subdivided into Ibicuí floodplain, Jaguari floodplain, Toropi floodplain; Hills Unit with fields and crops and with Forestry; Buttes of the São Vicente do Sul resulting from the regressive erosion and; Urban Unit.

Sedimentology and basin-fill history of the Cenozoic succession of the Sylhet Trough, Bengal Basin, Bangladesh

The Sylhet Trough, a petroleum province of the Bengal Basin, accommodates a huge thickness of Eocene to Recent sedimentary successions. However, the basin-fill history of the trough is poorly understood; specifically, constrains on timing of deposition of the individual units are yet to be established. Therefore, we aimed at establishing sedimentation and basin-fill history of the Sylhet Trough based on detailed lithofacies analysis of the outcropping Cenozoic succession. We have divided the entire Cenozoic succession into three megasequences which can be further sub-divided into nine lithostratigraphic units based on bounding discontinuities, such as transgressive erosion surface, regressive erosion surface, transgressive surface, marine flooding surface, and incised valley floor. The oldest is the Megasequence 1, comprised of shallow marine shelfal deposits overlain by shallow marine to nearshore deposits. In the middle, the Megasequence 2 is representing tide-dominated marine to coastal (deltaic) depositional systems with evidence of cyclic marine regression and transgression. Repetitive occurrence of incised channel, tidal inlet, tidal ridge/shoal, tidal flat and other tidal deposits are separated by shelfal deposits. The top of the Megasequence 2 is marked by a pronounced erosion surface interpreted as an incised valley floor indicating the final phase of marine regression followed by the gradual establishment of the overlying continental-fluvial depositional systems (i.e., the Megasequence 3). This youngest megasequence is characterized by stacked braided river sand bars that pass up-sequence into meandering river deposits. Based on the Cenozoic eustatic sea level curve, we suggest that the upper boundaries of the Megasequence 1 and Megasequence 2 are approximately at 39.5 Ma and 5.0 Ma, respectively.

The future of endangered crayfish in light of protected areas and habitat fragmentation

The long-term survival of a species requires, among other things, gene flow between populations. Approaches for the evaluation of fragmentation in the frame of freshwater habitats consider only a small amount of the information that combined demography and geography are currently able to provide. This study addresses two species of Austropotamobius crayfish in the light of population genetics, spatial ecology and protected areas of the Carpathians. Advancing the classical approaches, we defined ecological distances upon the rasterised river network as a surrogate of habitat resistance to migration, quantifying the deviations from the species´ suitability range for a set of relevant geospatial variables in each cell of the network. Molecular analyses revealed the populations of the two Austropotamobius crayfish species are clearly distinct, lacking hybridisation. Comparing pairs of populations, we found, in some cases, a strong disagreement regarding genetic and ecological distances, potentially due to human-mediated translocations or the geophysical phenomena of regressive erosion, which may have led to unexpected colonisation routes. Protected areas were found to offer appropriate local habitat conditions but failed to ensure connectivity. The methodology applied in this study allowed us to quantify the contribution of each geospatial (environmental) variable to the overall effect of fragmentation, and we found that water quality was the most important variable. A multilevel approach proved to reveal a better understanding of drivers behind the distribution patterns, which can lead to more adequate conservation measures.

Investigating the slope failures at the Lou rock glacier front, French Alps

AbstractOn August 14 2015 a large debris flow initiated by the occurrence of two slope failures at the front of the Lou rock glacier flooded part of the town of Lanslevillard, France. The present study aims to understand the meteorological and geomorphological context that led to these failures. Investigations were conducted by combining meteorological data, surface movements, and geophysical transects. The analysis indicates that the Lou rock glacier is directly connected to an active torrential channel and has a natural predisposition to frontal failure due to the steepness of its front. The slope failures were triggered after a heat wave followed by a three‐week period of almost continuous rainfall. Water flowing on top of the permafrost table was observed in the two head scarps, suggesting that regressive erosion consecutive to this concentrated subsurface water flow triggered the failures. For one of the slides, traces of previous failures were observable on historical aerial imagery dating back to the 1950's, while the second slide corresponded to a novel event and developed on the frontal slope of a fast‐moving and destabilized rock glacier lobe. We also discuss the increase in local predisposition to failure related to the remarkable morphological modifications such as frontal advance and development of surface cracks associated with the lobe destabilization.

Fluvial Dynamic in Oued El Abid Basin: Monitoring and Quantification at an Upstream River Section in Bin El Ouidane Dam - 2016 / 2017-(Central High Atlas / Morocco)

Soil erosion is a complex phenomenon, which particularly influences water and soil potentials. In the mountainous areas, water erosion phenomenon is accentuated by steep slopes and the degradation of vegetation cover. soil erosion is a worldwide phenomenon threatening the social, environmental and the economic life. In Morocco, fluvial erosion is one of the issues that affects the national territory. The location of Morocco, in the south of Mediterranean region provides remarkable climatic and ecological diversity. Located in the Moroccan High Atlas, El Abid basin belongs to a semi-arid climate. It is characterized by steep slopes and abundant precipitation which gives mountain flows a torrential characteristic. The discharge can reach very important values. Long term hydrological records for El Abid river (1970–2017) demonstrate the annual and seasonal variability in discharge with winter and spring periods typically representing 87% of the flow. Soils are increasingly degraded and sediments from erosion contribute to the siltation of Bin Ouidane dam. This siltation is the result of deposits of soil erosion. During flood periods this dam is silted by the sediment transport. This article aims to quantify the rate of fluvial erosion in the upstream section of the Bin El Ouidane dam. Then, to understand the process of river dynamics and its impact on silting issue, through the application of an approach technique based on the realization of several cross profiles, and with a main objective being to compare the results of the river dynamics of the two campaigns during 2016 and 2017. In addition, the measurements taken were supplemented by qualitative observations, particularly during the baseflow of the river, the incision of the bed (or stream), the regressive erosion of the banks, the apparent nature of the substrate, and certain anthropogenic actions.

Geomorphic processes and risk related to a large landslide dam in a highly urbanized Mediterranean catchment (Genova, Italy)

We present our research on the Prato Casarile landslide dam in Genoa city to illustrate the interactions between slope instability processes and structural stabilization interventions aimed to reduce the hazard in a densely-populated area. Analysis of the degradation of structural interventions constructed after flood events in 1953, 1970 and 2014 contributed to an improved mitigation strategy. At the same time, the slope instability processes intensively advanced, and regressive erosion quickly proceeded to the landslide dam threshold. The discontinuity in human interactions in a geomorphic system, after the initial hazard reduction, resulted in an increased threat that combined with a rise in vulnerability due to urbanization expansion. The research findings underline the necessity of constantly assessing the geomorphic evolution and active processes involved in order to determine the specific actions and interventions required to ensure the stability of the landslide dam. Finally, and more generally, we illustrated that anthropogenic interaction in the geomorphic system, specifically when finalized for hazard mitigation, needs to be continuously performed through both the monitoring and maintenance operation phases of the artificial structures.