Base Of Cliff Research Articles

Cliff Notching Due To Swash Abrasion: Insights From Physical Experiments

AbstractNotch development at the base of sea cliffs is an important control on cliff recession rates, but a detailed mechanistic understanding of notch formation by swash abrasion is lacking. We conducted physical experiments, using homogeneous erodible rock simulants, to study notch‐forming mechanisms under periodic sediment‐laden bore impacts. Our findings reveal shifts in the temporal dynamics of notch development. Initially, swash uprush and vortex formation contribute to a positive feedback loop that creates a shallow and wide notch. Subsequently, upward erosion ceases, and notch backwear and downwear are dominated by the vortex. Eventually, sediment deposition armors the notch floor; this negative feedback loop reduces erosion. The sediment size determines the amount of erosion, with a range of grain sizes generating maximum erosion. This indicates a dependence on the momentum of the sediment particles entrained within the bore. This research reveals fundamental notch formation mechanisms driven by swash abrasion.

Multitemporal analysis of cliffs evolution along an Atlantic African coast (Safi Region, Morocco)

Unstable coastal cliffs represent a major threat to coastal infrastructure, housing, and economic activities, which depend on coastal stability. Understanding recession rates and the factors influencing them is therefore essential for enhancing risk prediction and management. Here, we investigated the evolution of coastal cliffs in a crucial sector of the Atlantic African coast in Morocco, stretching from Cap Beddouza in the north to Jorf Lihoudi in the south, covering an area of around 48 km and including the large city of Safi. The instability of these cliffs constitutes the main coastal geological hazard of the area, which has its geomorphological expression in different types of landslides punctuating the coastal cliff. We employed multidecadal aerial imagery along with GIS technique to calculate the rate of change of the cliff over 66 years. Our results indicate that most of the Safi Region coastal zone has undergone recession with rates of change generally variable from 0.04 to 0.08 m/yr ± 0.01 m. The central part of the study area, conversely, experienced the highest retreat rate, exceeding 0.10 m/yr. The spatial variability of recession rates is explained through geological and morphological factors such as the nature of low-strength clay rock formations, favoring large-scale gravity movements. These data are crucial to better define the current level of coastal hazard in this densely populated portion of the Moroccan coast, given that cliff recession have considerable effects on the economic, social and environmental risk of the area. Moreover, this study represents one of the first applications of the Digital Shoreline Analysis System (DSAS) method to an African coastline segment, specifically from Cape Beddouza to the Lihoudi cliffs. More generally, it is among the few studies focused on cliff recession rates in Africa. While a similar application has been conducted for the cliff base in the northern part of the same study area (Raja et al., 2023), that study primarily addresses coastal cliff failure hazards along the Safi coastline in Morocco. In contrast, the present study is focused on determining long-term cliff recession rates and understanding the distribution of these rates and modes of retreat in relation to the physical processes affecting the study area.

An updated reconstruction of Campi Flegrei caldera (southern Italy) ground deformation history and its interaction with the human sphere since Roman time

Since the 19th century, many scientists have tried to reconstruct the ground motions that occurred in the Campi Flegrei caldera, one of the most dangerous volcanos in the Mediterranean area. This study aims to assess the joint effects of vertical ground movements and anthropic forcing along the coasts of this volcanic area. A huge dataset of hundreds of archeo-stratigraphic boreholes was coupled with direct and indirect surveys of the main underwater archaeological sites scattered along the whole coastal sector and with the reinterpretation of bibliographic sources. Clear evidence of a differential volcano-tectonic behaviour (highlighted for the first time in this study) led us to divide the study area into three coastal stretches with homogeneous vertical ground movements. In each sector, a new relative sea-level (RSL) curve was reconstructed, by interpreting our stratigraphic and archaeological data in terms of SL markers covering a wider timespan compared to the previous studies, from the first Roman urbanization to the present day. The comparison between RSL curves and GIA models allowed estimating vertical ground movements (See Supplementary material 2) that occurred along the coast with decimetres accuracy. For each of the 5 recognized phase of uplift or subsidence, we also studied the subsequent effects in terms of coastal geomorphological change, and advantages or negative impacts on ancient human activities. We measured an overall subsiding trend that brought the RSL from −12 ± 1 m (4th century BC) to 7 ± 0.2 m during three different episodes between 5th and 15th centuries (1450–450 y BP), which was interrupted by short-lived falls (less of 100 years) of RSL. During the phases of RSL fall and/or volcano-tectonic stability, detected for the first time in the eastern and western part of the caldera (1st-2nd century AD and 3rd-4th century AD), a basinward shift of the coastline created newly emerged land even at the base of the local sea cliffs, where shore platforms emerged, favouring intense phases of urbanization on them along the Baia – Miseno sector and at the footslope of Rione Terra. This trend also favoured the closure of the Lucrino lagoon with an extended spit bar during the 2nd century BC, allowing the establishment of a large oyster farming system belonging to Sergio Orata. On the contrary, the subsiding phases resulted in the flooding of coastal areas and anthropic structures such as villas, nymphaea and ports inducing the construction of coastal protection structures. In the extreme case of Portus Julius, subsidence led to the abandonment of the military port and its move to nearby Miseno.

DIGITAL INVESTIGATION OF LAMNIFORM SHARK VERTEBRAE FROM THE SIBILLINI MTS. (NORTHERN APENNINES, ITALY)

During the sampling of a stratigraphic section along the shore of the Fiastra Lake (Carg Project - Sheet 313 “Camerino” of the Geological Map of Italy at 1:50 000 scale), a small rock boulder with partially exposed bony material was discovered at the base of a small cliff at the northern termination of the Sibillini Mts. In this area, the classical facies of Umbria-Marche stratigraphic succession are well exposed. The Oligocene-Miocene portion of the succession is represented by the ~200 m-thick Scaglia Cinerea Formation, passing upwards to the ~100 m-thick Bisciaro Formation. The microfossil assemblage has allowed the specimen to be constrained to the lower Burdigalian. The skeletal remains were examined using a CT-SCAN, a non-invasive method that has proven to be highly performing. The analysis revealed some articulated vertebrae, deformed by lithostatic compaction, which are attributed to a shark of the Order Lamniformes. Subsequently, the vertebrae were digitally isolated, extracted from the surrounding matrix, and rendered into three-dimensional prints. Through digital retro-deformation, the body length of the lamniform shark was estimated to be approximately 4 metres. Further considerations on the vertebrae allowed us to infer that the studied shark had similarities to either Isurus oxyrinchus Rafinesque, 1810 or Carcharodon carcharias Linnaeus, 1758. The development of a dead-fall microbial community likely facilitated the preservation of the vertebrae. The studied specimen represents the first occurrence of a lamniform shark in the Lower Miocene of the Umbria-Marche Domain and represents one of the very rare recorded occurrences of lamniforms from the Lower Miocene of Italy.

Stream hydrology controls on ice cliff evolution and survival on debris-covered glaciers

Abstract. Ice cliffs are melt hot spots that contribute disproportionately to melt on debris-covered glaciers. In this study, we investigate the impact of supraglacial stream hydrology on ice cliffs using in situ and remote sensing observations, streamflow measurements, and a conceptual geomorphic model of ice cliff backwasting applied to ice cliffs on Kennicott Glacier, Alaska. We found that 33 % of ice cliffs (accounting for 69 % of the ice cliff area) are actively influenced by streams, while half are nearer than 10 m from the nearest stream. Supraglacial streams contribute to ice cliff formation and maintenance by horizontal meandering, vertical incision, and debris transport. These processes produce an undercut lip at the ice cliff base and transport clasts up to tens of centimeters in diameter, preventing reburial of ice cliffs by debris. Stream meander morphology reminiscent of sedimentary river channel meanders and oxbow lakes produces sinuous and crescent ice cliff shapes. Stream avulsions result in rapid ice cliff collapse and local channel abandonment. Ice cliffs abandoned by streams are observed to be reburied by supraglacial debris, indicating a strong role played by streams in ice cliff persistence. We also report on a localized surge-like event at the glacier's western margin which drove the formation of ice cliffs from crevassing; these cliffs occur in sets with parallel linear morphologies contrasting with the crescent planform shape of stream-driven cliffs. The development of landscape evolution models may assist in quantifying the total net effect of these processes on steady-state ice cliff coverage and mass balance, contextualizing them with other drivers including supraglacial ponds, differential melt, ice dynamics, and collapse of englacial voids.

Hiding in the mists: molecular phylogenetic position and description of a new genus and species of snake (Dipsadidae: Xenodontinae) from the remote cloud forest of the Lost World

AbstractPantepui s.l. is a remote, biodiverse region of ~400 000 km2 containing at least five endemic reptile genera and a number of ancient vertebrate lineages. Here, we describe an additional endemic snake genus and species, Paikwaophis krukigen. nov., sp. nov. (Dipsadidae: Xenodontinae), recently collected in the Pantepui cloud forest that sits at the base of the steep cliffs of Roraima-tepui and Wei-Assipu-tepui (table mountains of the Eastern Tepui Chain) in Guyana, South America. Multilocus molecular data strongly support Paikwaophisgen. nov. to be most closely related to Xenopholis Peters, 1869, although both genera are strikingly different morphologically. Osteological and other phenotypic data suggest that Paikwaophis is semi-fossorial; its diet includes minute lizards. Paikwaophis is currently the only known Pantepui endemic snake genus. The immature female holotype is the only known specimen.

Late Holocene Cliff Retreat in Del Mar, CA, Revealed From Shore Platform 10Be Concentrations and Numerical Modeling

AbstractRocky coast cliff retreat presents a hazard to coastal communities and infrastructure that is potentially amplified under rising sea level conditions, among other factors. Unfortunately, constraints on retreat rates are typically limited to those derived from imagery and maps spanning the last ∼100 years. Here, we use a newly developed coupled model of shore platform profile evolution and cosmogenic radionuclide production that considers the influence of relative sea level (RSL) rise, weathering, material resistance, and wave height decay to model cliff retreat over millennial timescales and its potential drivers in Del Mar, California. We demonstrate the ability to use topographic and bathymetric measurements from a narrow shore platform along with a limited data set of nine cosmogenic 10Be concentrations extending ∼125 m from the cliff base to obtain modeled cliff retreat rates that steadily range from 5.0 to 12.5 cm yr−1 over the last two millennia until 100 years before present. These rates are consistent with modern retreat rates of about 2–19 cm yr−1 here. RSL rise in Southern California remained relatively constant during the late Holocene, potentially explaining the relatively stable modeled cliff retreat rate over this time. We also explore the relative influence of weathering, material resistance, and wave erosion efficacy and find that both weathering and wave‐driven erosion are necessary to replicate the measured data at this location, with the latter exerting a stronger control on model acceptance, suggesting that waves may provide a possible mechanism by which RSL rise may influence coastal cliff erosion in southern California.

Fault mapping and characterization of a coastal aquifer related to a mangrove ecosystem, using electrical resistivity tomography (ERT), ground penetrating radar (GPR) and hydrochemical data: The case of the Mangue de Pedra Aquifer, Armação dos Búzios, Brazil

The Mangue de Pedra is a rare and fragile ecosystem. It stands above a sandstone-conglomerate substratum of the Neogene Barreiras Formation, which also hosts the local coastal aquifer, known as the Mangue de Pedra Aquifer. The Pai Vitório Fault, a regional structure, which represents the south border of the São João da Barra Graben, separates the Paleoproterozoic crystalline basement from these sediments and limits the occurrence of both the mangrove and aquifer. Aside from hydrochemical data, geophysical surveys, including electrical resistivity tomography (ERT) and ground penetrating radar (GPR), allowed to investigate the local substrate and the role of fault structures affecting the aquifer-mangrove ecosystem, as well as to provide a better understanding on groundwater circulation and effects of seawater interface dynamics. The hydrochemical data for 11 water samples were used for interpolation to generate pH, Eh and electrical conductivity (EC) maps, and the results revealed a zone of less saline water flow and a discharge zone at the cliff's base. The survey of five ERT lines, using the dipole-dipole configuration, provided a picture of the saturated zone of the aquifer. The interpreted sedimentary units have been divided in three different layers, based on water content and variation of the water quality: 1) unsaturated zone; 2) good/intermediate-quality freshwater (34.4–137 Ω-m); 3) brackish/poor-quality freshwater (4.46–34.4 Ω-m). This method indicated the presence of at least five normal faults, including major and shallow structures along the mangrove, and the basement 5 m below sea level. The radargrams also confirmed the presence of most of these faults, recognized as complex fault zones at shallow levels. The interpretation on orientation of these structures was then enhanced by geoprocessing techniques, indicating a major NE-SW trend. This set of faults provides some of the requirements for the mangrove existence, including: a) the shape and materials of the beach and surrounding landscape, composed by chalcedony breccias blocks which are resistant to erosion, protecting the local environment from impact of sea waves; b) pathways for groundwater flow; and c) traps or barriers within the aquifer, which channel less saline waters to that specific site. This set of factors creates a unique ecosystem, which normally does not occur in beaches from open sea shorelines.

An integrated approach for coastal cliff susceptibility: The case study of Procida Island (southern Italy)

Procida Island, located in the Gulf of Naples (southern Italy), is characterized by steep cliffed coasts, articulated in a succession of headlands and small embayments with narrow pocket beaches, such as Ciraccio and Chiaia, often characterized by instability.In this study, a methodology for coastal cliff susceptibility assessment has been conceived based on hydraulic and geomorphological characteristics, which supported the construction of a Cliff Stability Index (CSI). The geomorphological characteristics are related to the whole cliff face, the cliff material resistance, and the cliff failure mechanisms. The hydraulic actions on the cliff are related to the wave impact which is exerted by the breaking waves once the wave run-up distance exceeds the beach width. The index takes into account the slope of the cliff, the rock strength, the wave energy at the cliff base produced by the broken wave and the presence of defence structures at the cliff base. The resulting index classification, obtained by addition of the partial sub-indices, has been compared with the observed coastal cliff evolution from 1954 to 2021.

A new association of relict maquis with Ptilostemon greuteri (Oleo-Ceratonion, Quercetea ilicis), located in a circumscribed area of north-western Sicily

This paper illustrates the results of a survey aimed at deepening available knowledge on the ecology of Ptilostemon greuteri (Asteraceae), a very rare palaeoendemic and relict nano-phanerophyte discovered about 15 years ago on Monte Inici, near Castellammare del Golfo (province of Trapani, north-western Sicily). Two plant communities characterised by P. greuteri are described in detail; they occur in the locus classicus and in a second, recently discovered stand, which is also very localised and threatened by fire. The field investigations revealed that the sites where the species grows are very similar from the ecological point of view; in fact, both of them are located on the steep slopes of deep gullies, benefitting from constantly cool and shady microclimatic conditions, and allowed to a) better identify the currently preferred habitat (ledges, screes at the base of cliffs), b) analyse from a floristic and phytosociological point of view the maquis communities where P. greuteri grows as co-dominant or dominant species, referable to the class Quercetea ilicis, c) to identify the syndynamic role that these coenoses play within the series and microgeoseries of local vegetation. As far as syntaxonomy is concerned, the Malvo olbiae-Ptilostemonetum greuteri ass. nova is described, a basiphilous, thermophilous and shade-tolerant maquis framed in the Oleo-Ceratonion alliance. Moreover, two subassociations are described: 1) typicum subass. nova, corresponding to a pioneer maquis community prevailing on the coarse, loose and mobile debris located along the slopes at the base of rock cliffs, where P. greuteri is clearly dominant and shows a nano-phanerophytic habitus, and 2) euphorbietosum bivonae subass. nova, a primary aspect found of the ledges of carbonate cliffs, where the species can play either a dominant or co-dominant role with other elements of the maquis (Euphorbia bivonae, Chamaerops humilis, etc.), sometimes showing a slightly smaller size.

CliffDelineaTool v1.2.0: an algorithm for identifying coastal cliff base and top positions

Abstract. Correct quantification of coastal cliff erosion requires accurate delineation of the cliff face bounded by the cliff top and base lines. Manual mapping is time consuming and relies on the mapper's decisions and skills. Existing algorithms are generally site specific and may be less suitable for areas with diverse cross-shore cliff geometries. Here we describe CliffDelineaTool (v1.2.0), a MATLAB/Python-based algorithm that identifies cliff base and top positions on complex cliffs using cross-shore transects extracted from digital elevation models. Testing on four 750–1200 m cliffed coastlines shows that the model performance is comparable to manual mapping and provides some advantages over existing methods but provides poor results for cliff sections with ambiguous cliff top edges. The results can form the basis for a range of analyses, including coastal inventories, erosion measurements, spatiotemporal erosion trends, and coastline evolution modeling.

Triggering and propagation of exogenous sediment pulses in mountain channels: insights from flume experiments with seismic monitoring

Abstract. In the upper part of mountain river catchments, large amounts of loose debris produced by mass-wasting processes can accumulate at the base of slopes and cliffs. Sudden destabilizations of these deposits are thought to trigger energetic sediment pulses that may travel in downstream rivers with little exchange with the local bed. The dynamics of these exogenous sediment pulses remain poorly known because direct field observations are lacking, and the processes that control their formation and propagation have rarely been explored. Here we carry out flume experiments with the aims of investigating (i) the role of sediment accumulation zones in the generation of sediment pulses, (ii) their propagation dynamics in low-order mountain channels, and (iii) the capability of seismic methods to unravel their physical properties. We use an original setup wherein we supply liquid and solid discharge to a low-slope storage zone acting like a natural sediment accumulation zone that is connected to a downstream 18 % steep channel equipped with geophones. We show that the ability of the self-formed deposit to generate sediment pulses is controlled by the fine fraction of the mixture. In particular, when coarse grains coexist with a high content of finer particles, the storage area experiences alternating phases of aggradation and erosion strongly impacted by grain sorting. The upstream processes also influence the composition of the sediment pulses, which are formed by a front made of the coarsest fraction of the sediment mixture, a body composed of a high concentration of sand corresponding to the peak of solid discharge, and a diluted tail that exhibits a wide grain size distribution. Seismic measurements reveal that the front dominates the overall seismic noise, but we observe a complex dependency between seismic power and sediment pulse transport characteristics, which questions the applicability of existing seismic theories in such a context. These findings challenge the classical approach for which the sediment budget of mountain catchments is merely reduced to an available volume, since not only hydrological but also granular conditions should be considered to predict the occurrence and propagation of such sediment pulses.

Modelling and simulation of a lava flow affecting a shore platform: a case study of Montaña de Aguarijo eruption, El Hierro (Canary Islands, Spain)

ABSTRACT Recent subaerial volcanism at El Hierro Island (Canary Islands, Spain) consists of monogenetic volcanic fields. This volcanism generated cinder cones, tephra air-fall deposits, and lava flows. The lava flows reach several kilometres in length extending through shore platforms and, sometimes, penetrating under the sea level. The volcanic landforms of El Hierro convert it into a natural laboratory for topographic and morphometric modelling and lava flow simulations. We perform the modelling and simulation of the Montaña de Aguarijo eruption, a cinder cone at the NE rift. The associated lava flow channelled through a V-shaped ravine until reaching a cliff, where formed cascades. The flow spread at the cliff base over a platform before reaching the sea modifying the coastline. Different maps were designed to show the results, including the geomorphologic reconstruction of the area affected by this eruption and the lava flow simulations obtained with the Q-LavHA plugin.

The Use of Rain Gauge Measurements and Radar Data for the Model‐Based Prediction of Runoff‐Generated Debris‐Flow Occurrence in Early Warning Systems

AbstractHigh‐intensity and short‐duration rainfalls can generate sudden and abundant runoff at the base of rocky cliffs that, entraining sediments, may originate debris flows. Two gauge networks have been set up in headwater sites of Dolomites (Northeastern Italian Alps) to monitor rainfall corresponding to the debris‐flow activity occurring there. The rain gauges are positioned both upstream and downstream the initiation areas of debris flows. Other five rain gauges sparse in the area integrate the two networks. In the years 2009–2020, rain gauges recorded rainfalls that triggered 41 debris flows. In most cases, rainfalls show a higher spatial variability along with both distance and altitude. Precipitation data are then compared with rainfalls estimated through a weather radar far about 70 km from there, to verify the possible interchangeability of the two measurement systems for the prediction of debris‐flow occurrence through suitable modeling of triggering discharges. The following results are obtained: (1) raw‐radar images mostly tend to underestimate precipitations recorded by rain gauges; (2) such underestimation entails, on average, a larger one on the simulated discharges and the prediction of debris‐flow occurrences (missed in 65% of the cases). Some methods for the correction on ground truth of raw‐radar images are applied to assess their use for evaluating the triggering discharges. Results show that once corrected using rain gauge data, radar‐derived rainfall estimates produce debris‐flow initiation predictions that more frequently match observations. Therefore, the presence of rain gauges close to the watershed centroids results essential for early warning systems based on triggering discharge modeling.

Three years of weekly observations of coastal cliff erosion by waves and rainfall

Erosion of a 2.5 km-long sedimentary coastal cliff by waves and rainfall is explored with three years of weekly observations. A truck-mounted lidar resolved the fronting beach and convoluted surface of the ~10–25 m high cliffs. Volumes of 4362 cliff erosion events ranged up to 885 m3 (mean 3.3 m3). The three-year cumulative erosion was clustered and alongshore variable. Cliff base wave impact heights were estimated with a wave model and empirical runup formula, and validated with cliff base observations. Cliff erosion rates, incident wave heights, wave-cliff impacts, and rainfall were all elevated during winters. The high temporal resolution of the multiyear dataset is unique, and allows separation of erosion from waves and rainfall by, for example, isolating time periods with no rainfall and high wave runup. Upper cliff erosion was best correlated with rainfall (r2 = 0.57), and lower cliff erosion with wave impacts (r2 = 0.56).

Influence of mechanical layering and natural fractures on undercutting and rapid headward erosion (recession) at Canyon Lake spillway, Texas, U.S.A

This study investigates the role of mechanical layering and fractures on flood-related erosional undercutting and resulting rapid spillway recession. In the summer of 2002, 86 cm of rain fell in an 8-day period across the Guadalupe River drainage basin in central Texas, causing Canyon Lake reservoir to completely fill and overtop the emergency spillway for the first time. The resulting flood incised a gorge into the mechanically layered Glen Rose Formation and caused headward erosion (recession) at the downstream edge of the emergency spillway. Comparison of pre- and post-flood imagery and assessment of flood records indicates that maximum recession localized at the northern end of the emergency spillway where 28 m recession occurred. This recession occurred at an estimated rate of up to 10 m/day during the first ~3 days of the flood, which is among the highest rates of recorded bedrock recession. Analysis of historical photographs, field observations and measurement of erosional undercutting, along with measurements of fracture orientation, fracture spacing, and mechanical rebound are used to understand rock mass characteristics that influenced erosional undercutting and rapid recession of the spillway. Evidence of significant undercutting was observed where incompetent argillaceous wackestone (marl) underlies competent limestone. These results reveal that the greatest amount and rate of recession of the spillway was associated with undercutting and toppling collapse of fracture-bounded limestone blocks. Block size may be a factor in continuation of the process, in that large blocks may accumulate at the base of the scarp and inhibit continued erosional undercutting, whereas in other areas smaller eroded blocks can be carried away by the floodwaters and undercutting may continue, facilitating recession. The combination of mechanical contrast between layers and natural fractures in competent layers together contributed to exceptionally high rates of headward erosion. Observed rock mass erodibility behavior was in the range of medium to high erodibility in limestone with widely spaced fractures that would normally be expected to have very low erodibility. Bulk rock mass erodibility in this situation was similar to the most erodibile layer, specifically, the marl at base of spillway pour-off cliff.

The Age and Vertebrate Paleontology of Labor-of-Love Cave, White Pine County, Nevada

We report the first radiocarbon ages on vertebrate fossils from Labor-of-Love Cave, White Pine County, Nevada, based on purified collagen in teeth and bone, as well as a description of the cave's vertebrate paleontology. This cave was discovered in 1982 with the recovery of an associated partial skeleton of the extinct giant short-faced bear (Arctodus simus). Subsequent excavations in 1985 recovered additional fossil material of birds and mammals from stream deposits in the cave. These fossils, along with fossils collected from the surface during surveys in 2018, are reported here. Radiocarbon ages indicate that most fossil material was deposited in the cave before and during the Last Glacial Maximum (LGM; 21,441–27,774 cal yr BP) and eroded from stream deposits inside the cave following the LGM, presumably from increased precipitation and stream flow. The vertebrate assemblage includes 4 other extinct taxa including 1 carnivore (Panthera atrox) and 3 ungulates (Equus sp., Oreamnos harringtoni, Euceratherium collinum) and the first record of Canada lynx (Lynx canadensis) from the Great Basin. If contemporaneous, the assemblage as a whole indicates an open grassland/sagebrush/tundra environment in Spring Valley during the late Pleistocene, with coniferous forest on mountain slopes facing this valley and where the cave is situated. Although the entrance to the cave is now blocked by slumped talus and breakdown, in the Pleistocene it was likely a large accessible opening at the base of a limestone cliff, with stream flow emerging and flowing into the valley below during the late Pleistocene, when bears and other species possibly used the cave as a shelter or den.

Multiple related flank collapses on volcanic oceanic islands: Evidence from the debris avalanche deposits in the Orotava Valley water galleries (Tenerife, Canary Islands)

Catastrophic flank collapses are common on oceanic islands of volcanic origin and often recognizable from the resulting morphology as large U-shaped embayments. However, post-collapse volcanic activity can infill such features, thereby obscuring them. This study takes advantage of a dense network of long sub-horizontal galleries for groundwater extraction in the flank collapse structure of the Orotava Valley (Tenerife, Canary Islands). This impressive landform is located in the overlapping zone of the NE Rift and the Cañadas Edifice of this volcanic island. Three debris avalanche deposits (DADs) have been identified inside the waterworks bored into the valley's western sector. The deeper layer, the Lower-DAD (L-DAD) was previously described under the local name of mortalón. This deposit lies unconformably over older volcanic rocks, where a prominent shear-zone is developed, here interpreted as the detachment plane of a massive rockslide. The L-DAD was therefore produced during the large failure event, the Orotava Landslide (OL), which carved the depression. Two younger DADs, much smaller in volume and not previously described, were also identified in the underground strata: the Intermediate- (I-DAD) and Upper-DAD (U-DAD). Both correlate well with the thick breccia deposits cropping out at the base of the marine cliff along the western coast of the valley. The I-DAD and U-DAD are conformably intercalated between the lava flows and other volcanics infilling the depression, and their bases are erosive/depositional features without structural deformation zones below them. Their stratigraphic setting and geometrical reconstruction indicate that both deposits were emplaced after the valley was formed by the OL event, in two successive failures here called Western Orotava Landslides (WOLs). The younger, called WOL-2, was dated at 494 ± 22 ka using the 40Ar/39Ar method. These two subaerial failures affected the upper eastern flank of the Cañadas III Edifice, previously destabilized when the OL failure event carved a steep wall at its foot, the western lateral escarpment of the Orotava Valley.

Aeolian-alluvial interactions at Formentera (Balearic Islands, Western Mediterranean): The late Pleistocence evolution of a costal system

This study deals with the sedimentological and stratigraphic description of Pleistocene coastal deposits of Formentera Island that show evidence of interference between processes characteristic of alluvial and aeolian environments. Here we analyze the sedimentology and stratigraphy of a Pleistocene succession located at Northeast of Formentera and we constrain its chronology by optically stimulated luminescence (OSL) dating. Main sedimentary facies representing the succession of aeolian, alluvial, marine and coastal environments are described in this study. We conclude that although there were two prevailing environments such as coastal aeolian and alluvial, with different processes and resulting forms, the interaction resulted in deposits that share characteristics of both environments, as well as maintain elements inherited from each environment in terms of sedimentary supply, precipitation, runoff or aeolian transport. These coastal deposits represent a small alluvial apron covering the base of a vertical cliff. Most of the sediment that composes these deposits is marine bioclastic sand which was transported in the form of coastal dunes during periods of low sea level. Our results are a useful indicator of the geomorphological processes and changes that occurred during the Pleistocene, unraveling the environmental evolution and contributing to the growing knowledge on the Western Mediterranean aeolian-alluvial interacting environments.

Increasing the public activity cliff knowledge base with new categories of activity cliffs.

Aim:Extending the public knowledge base of activity cliffs (ACs) with new categories of ACs having special structural characteristics.Methodology:Dual-site ACs, isomer ACs and ACs with privileged substructures are described and their systematic identification is detailed.Exemplary results & data:More than 7400 new ACs belonging to different categories with activity against more than 200 targets were identified and are made publicly available.Limitations & next steps:For dual-site ACs, limited numbers of isomers are available as structural analogs for rationalizing contributions to AC formation. The search for such analogs will continue. In addition, the target distribution of ACs containing privileged substructures will be further analyzed.