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Storm waves transport and sort coarse gravel along coasts. This fundamental process is important under changing sea‐levels and increased storm frequency and intensity. However, limited information on intra‐storm clast motion restricts theory development for coastal gravel sorting and coastal management of longshore transport. Here, we use smart boulders equipped with loggers recording underwater, real‐time, intra‐storm clast motion, and measured longshore displacement of varied‐mass marked boulders during storms. We utilize the unique setting of the Dead Sea shores where rapidly falling water levels allow isolating boulder transport during individual storms. Guided by these observations, we develop a new model quantifying the critical wave height for a certain clast mass mobilization. Then, we obtain an expression for the longshore clast displacement under the fluid‐induced pressure impulse of a given wave. Finally, we formulate the sorting enforced by wave‐height distributions during a storm, demonstrating how sorting is a direct manifestation of regional hydroclimatology. Plain Language Summary: Beaches connect terrestrial and marine environments, frequently near large population centers. Sea‐level rise and increased storm intensities threaten this environment, causing enhanced coastal erosion and damage to cities and infrastructure, along with loss of coastal tourism. We combine real‐time measurements of clast movement during a storm with a newly‐developed theoretical model. This allows predicting longshore sediment transport and determine critical wave heights for mobilization and alongshore movement of various clast sizes under a distribution of wave heights. The outcome is a quantitative, process‐based tool for coarse‐gravel motion and beach evolution, a key for coastal management. We show how the wave‐induced pressure force and impulse exerted on clasts dictates the longshore clast motion and sorting, and how sorting is a direct manifestation of regional hydroclimatology. Key Points: Storm waves sort clasts according to mass along the shores of the Dead Sea; clast motion is traced by marked and smart bouldersA newly developed model predicts the critical wave height for motion initiation and the total longshore transport of cobbles‐bouldersCoastal sorting is a direct manifestation of regional hydroclimatology, derived by hydrodynamic pressure‐induced impulse exerted on clasts [ABSTRACT FROM AUTHOR]

Quantitative geomorphic field studies and modeling efforts have focused on the margins of southwestern Africa as an example for landscape evolution in prolonged aridity conditions and tectonic quiescence of passive margins. These efforts concluded that this region is a prime example of a steady state landscape, in which relief changes extremely slowly. Using cosmogenic isotopes, these studies suggested overall landscape exhumation rates of 5–10 m Ma −1 over the past 10 5 –10 6  yrs. Slightly slower rates on flat-lying exposed bedrock surfaces and faster exhumation rates along the Namibian Great Escarpment as well as on steep slopes of granitic inselbergs, such as the Gross Spitzkoppe are also documented. Here we explore the state of “steady state” in central Namibia. Concentrations of 10 Be were measured in bedrock and sediment samples collected throughout the watershed of the Ugab River (~29,000 km 2 ), which drains the highlands of central Namibia and flows to the Atlantic Ocean. Samples were collected from the main stem of the ephemeral Ugab River, from the slopes and streams draining the Brandberg, which is the largest inselberg in the Namib, and from smaller inselbergs around it. We also sampled several other formerly large, but currently subdued, inselbergs such as the Messum Crater. 10 Be concentrations in sediment transported along the axial Ugab River indicate that its drainage basin erodes uniformly at 5–6 m Ma −1 and sediment transport from its headwaters source to the ocean is rapid. 10 Be concentrations measured in sediment transported in ephemeral streams draining the Brandberg indicate its erosion at ~4 m Ma −1 . However, slower rates of 1–3 m Ma −1 were measured for bedrock samples collected from (a) flat lying bedrock surfaces within the Brandberg, (b) top of small tors that rise only a few meters above their surroundings, and (c) exhumed and denuded large magmatic complexes such as the Messum Crater. Furthermore, we found that bedrock buried under grus in the hyperarid zone of Namib (<100 mm yr −1 ) erodes at similar rates as the exposed bedrock. This difference between the rate of bedrock erosion and the overall average erosion rate of drainage basins has been previously attributed to the contribution of sediment weathered from underneath transported sediment and soil on the pediments. Our results do not fully support this explanation. Results from this and earlier studies point to two possible sources of relatively low dosed (i.e. more rapidly eroding) sediment: (a) the steep slopes and cliffs of the large inselbergs and the Great Escarpment, and (b) rock buried under soil in the upper, semi-arid, parts of the drainage systems, where soil and vegetation can promote weathering of plagioclase and biotite and the disintegration of granitic bedrock. We therefore suggest that the “steady state” landscape along the Namibian passive margin be viewed as follows: The entire landscape erodes slowly, generally at ~5 m Ma −1 and this maintains the view of steady state. Small differences in erosion rates between the landscape elements result in very slow and only small changes in relief over time scales ≥10 6  yrs. We find that the large inselbergs and the Great Escarpment erode primarily by retreat of steep slopes and cliffs within the drainage basins while preserving relief over considerable timescales. In the wetter upper reaches of the Namibian drainage systems, erosion of buried rock is most likely increased by the vegetation-covered soil. [ABSTRACT FROM AUTHOR]

• Measured heat fluxes from a restored Mediterranean lake fit energy balance closure. • A Thermoregulation equation was formulated based on the heat balance equation. • Thermoregulation will occur until steady-state, scaled by the lakes response time. • Steady-state mainly depends on environmental forcing, response time on water depth. • The ratio of forcing/response dictates water temperature amplitude and time-lag. Air-water interactions regulate lake-water temperature by balancing the rate of change of water temperature (stored heat) with the incoming and outgoing heat fluxes, which are functions of water temperature and external forcing. Yet, there is a large knowledge gap in quantifying the thermoregulation of a lake, and especially managed lakes, which is hypothesized to be related to both external environmental forcing and management decisions on lake depth and water inflow. Here we explore the thermoregulation of a restored and managed Mediterranean lake (Agamon Hula, Israel), by direct measurements of all major heat fluxes. We interpret the results with a rigorous analysis of the thermoregulation equation, obtained by formulating the energy balance equation in terms of water temperature. The equation shows how water temperature of a lake shifts toward steady state, scaled by the lake's response time. Where the steady-state temperature was reached, it was controlled by external environmental forcing and not by lake depth. Whereas the thermal response time to re-attain steady state, following an abrupt change in various environmental conditions, is controlled by water depth. The lake-temperature response to pre-defined oscillations of the environmental forcing showed that the amplitude of water temperature fluctuations and the time delay from steady-state are controlled by the ratio between the environmental forcing's time period (diurnal, seasonal or other cycles) and the thermal response time of the lake. The summertime measured CO 2 fluxes of Agamon Hula revealed the lake acts as a CO 2 source to the atmosphere, overpassing similar water bodies from different climates. [ABSTRACT FROM AUTHOR]

This work presents a high-resolution lake-level record of the late Holocene Dead Sea, a hypersaline terminal lake whose drainage basin encompasses both Mediterranean and hyperarid climatic zones. The lake-level curve reflects the regional hydrologic variations in the drainage basin, which in turn represent the Levant paleoclimates. The curve is based on 46 radiocarbon ages of organic remains from well-exposed sedimentary sequences along the Dead Sea shores. These sequences record fluvial and lacustrine depositional environments. The paleolakeshores are marked by shore ridges, coarse-sand units, and aragonite crusts; in the modern Dead Sea, such features indicate the exact elevation of the shore. The late Holocene Dead Sea level fluctuated within the range of 390 to 415 m below sea level (mbsl). For most of the time the lake was below the topographic sill (402 mbsl) separating the northern and southern basins of the Dead Sea and was confined to the deep northern basin. Nevertheless, short-term rises in the late Holocene Dead Sea level caused the flooding of the shallow and flat southern basin. Highstands occurred in the second and first centuries B.C. and the fourth century A.D. during the Roman and early Byzantine periods, respectively, in the eleventh and twelfth centuries A.D. during the Crusader period, and at the end of the nineteenth century A.D. The rises mark a significant change in the annual rainfall in the region, which likely exceeded the instrumentally measured modern average. The curve also indicates drastic drops that exposed the sedimentary sequences to erosion. The oldest and probably deepest drop in the lake level culminated during the fifteenth and fourteenth centuries B.C. after a retreat from a higher lake stand. The longest lowstand occurred after the Byzantine period and continued at least until the ninth century A.D. This arid period coincided with the invasion of Moslem-Arab tribes into the area during the seventh century A.D. [ABSTRACT FROM AUTHOR]

Presents a report on research conducted on the sediments from Lunkaransar dry lake in northwestern India. Revelation that regional water table and lake fluctuations during the Holocene are attributed to changes in the southwestern Indian monsoon rains; Lake levels during the early Holocene; Approximate date when the lake completely dissipated; Belief that the 1500-year wet period coincided with a period of intense dune destabilization; Suggestion of when the major Harrapan-Indus civilization began.

Presents research looking at a drill core in the Silver Lake playa at the terminus of the Mojave River and finding Holocene lake deposits which indicate that shallow lakes existed for at least a few decades. Suggestion that late Holocene lakes may have resulted from persistent similar atmospheric circulation patterns and winter floods. Research methods.

Namibia, with its passive margin setting, long-term tectonic stability, and long-lasting arid climate is a typical granitic landscape characterized by numerous dominating inselbergs. The Namib has been the focus of quantitative studies on the overall rates of bedrock exhumation, escarpment retreat, and sediment generation, transport, and deposition. Results from these studies indicate steady bedrock erosion rates ranging between 1 and 5mmkyr−1 over the last 105–106 yr. This rate was determined from samples collected mostly from small inselbergs with low relief. How fast the large and “classic” inselbergs, which dominate the Namib Desert landscape, erode, generate sediment, and contribute to the overall sediment supply has yet to be systematically examined. We document erosion rates of the Gross Spitzkoppe (GS), one of the largest inselbergs in the Namib Desert, Namibia, based on measured concentrations of 10Be in samples collected from bedrock, boulders, and surface grus. The results suggest a slow lowering rate (1–2mmkyr−1), while the overall slope processes deliver sediment to the base of the cliff with 5–6×105 atomsg−1 quartz. This concentration is equivalent to an average erosion rate of ~8mmkyr−1, 2–3 times faster than the bedrock lowering rate. Thus, the inselberg has been eroding by cliff retreat. The concentration of cosmogenic isotopes in slope sediment is controlled by exposure time on the slope, weathering of exposed bedrock, and weathering of subsurface bedrock. Sediment continues to accumulate cosmogenic isotopes while being transported on the flat pediments surrounding the inselberg. Within 1–2km from the base of the GS, the concentration doubles to ~10×105 atomsg−1 quartz. The increase is achieved by dosing due to exposure and mixing with highly dosed sediment eroded from near subsurface bedrock. From this area, grus is transported through a network of low gradient channels to the Atlantic Ocean, ~100km away. Cosmogenic isotope concentration in sediment increases to ~30×105 atoms of 10Beg−1 quartz, which is 3–4 times higher than that measured in the grus close to the GS and is controlled by the erosion rate of stable bedrock throughout the entire drainage basin. Dosing due to exposure during transport obviously contributes to the overall measured concentration in the sediment as it approaches the ocean. [ABSTRACT FROM AUTHOR]

Abstract: Dating the time of abandonment of geomorphic surfaces in the arid mid latitudes is necessary for studies ranging from tectonics, landscape evolution and paleoclimate. It has often been hampered by the limited material suitable for conventional isotopic methods and the uncertainties inherent in cosmogenic radionuclide methods. We propose luminescence dating as a suitable method for dating the time of abandonment of aggradational geomorphic surfaces in the hyperarid regions. We dated the top of such surfaces with different age ranges and geomorphic settings in a sequence of alluvial fans in Nahal Shehoret in the southern Negev and in a sequence of terraces in Nahal Ze''elim and in Nahal Zin, two adjacent drainage basins in the Judean Desert, Israel. Samples were collected from beneath the gypsic horizon at a depth of 0.3–0.7m, below which sand grains do not penetrate. Depositional ages for the uppermost beds of the landforms, which are proxies for abandonment, range from ∼90ka to ∼5ka. In all three basins, the ages are in morphostratigraphic order and agree well with relative age estimates based on soil chronosequences and on Lake Lisan levels. Abandonment ages for an individual alluvial fan cluster within ±10–20%, therefore it is possible to distinguish between surfaces with ages differing by more than 20%. Thus, in hyperarid areas, the luminescence methods can be used for surface dating. [Copyright &y& Elsevier]

Abstract: The dramatic lake level drop of the Dead Sea during the twentieth century (∼30 m) provides a field-scale experiment in transport-limited incision of gravel-bed channels in response to quasi-continuous base level fall at approximately constant rate. We apply a one-dimensional numerical incision model based on a linear diffusion equation to seven ephemeral channels draining into the Dead Sea. The model inputs include the measured twentieth century lake level curve, annual shoreline location (i.e., annual channel lengthening following the lake level drop), reconstructed longitudinal profiles of each of the channels based on mapped and surveyed terraces, and the current profiles of the active channels. The model parameters included the diffusion coefficient and the upstream-derived sediment flux. Both were first calibrated using a set of longitudinal profiles of known ages and then validated using additional sets of longitudinal profiles. The maximum at-station total incision observed at each of the studied channels was significantly less then the total lake level drop and varied in response to both drainage area and lake bathymetry. The model applied predicted degradation rates and the pattern of degradation with high accuracy. This suggests that sediment flux in the modeled channels is indeed linearly dependent on slope. Further support for this linear dependency is provided by a linear correlation between the diffusion coefficient and the mean annual rain volume over each basin (a proxy for discharge). The model presented could be a valuable tool for planning in rapid base level fall environments where incision may risk infrastructure. [Copyright &y& Elsevier]

The Messinian Salinity Crisis (5.97–5.33 Ma) is one of the most dramatic sea level change events in the global geological record. During this event, marine connection between the Atlantic Ocean and the Mediterranean Sea was restricted, and episodically blocked. While division of the Messinian Salinity Crisis to three major stages is well established and accepted, the scale of sea level change at each stage is still debated. The magnitudes of the Mediterranean fluctuations throughout the Messinian Salinity Crisis have implications for contemporary connectivity between the eastern and western Mediterranean basins. During the third stage of the Messinian Salinity Crisis, commonly known as the Lago Mare, Mediterranean Sea level fluctuated repeatedly. Lago Mare drawdowns in the eastern Mediterranean were estimated earlier to vary between <200 m and all the way down to the abyssal basin. Here we assemble morphological, lithological and stratigraphic evidence for Lago Mare levels across the Israeli margin. We differentiate between low-stands of various scales and durations to constrain the magnitude of discrete Lago Mare drawdowns. Since the rates of syn -Messinian isostatic rebounds in response to water column removal are ambiguous, drawdown magnitudes are estimated here as a range and not as an absolute value. We propose that during the Lago Mare, ravinement along a continuously regressing-transgressing coastline abraded the upper continental margin offshore Israel. The Mediterranean regressed to a depth of 380–550 m below present-day mean sea level, and the eroded strata were evacuated downslope and deposited basinward of this depth as wedge-shape clastic complexes. During relatively short intervals, sea level receded to altitudes ~100 m below the erosional surface. These sea level recessions exposed a pronounced inflection in the slope gradient to sub-aerial processes, generating knickpoints and headward migration of incising gullies. These gullies developed later into channels, conduits for sediment bypass. Fan-deltas were deposited off these channels outlets. A major sea level fall towards the end of the Messinian Salinity Crisis reached 630–900 m below present-day mean sea level. Streams incised into the exposed tops of the clastic wedges and fan-deltas. Additionally, meteoric water dissolved evaporites within the clastic complexes and formed sinkholes and dolines. During this interval the Mediterranean Sea level fell to below the depth of the Sicily Sill, which separated the eastern and western Mediterranean basins. This finding reinforces previously proposed paradigms, which suggested that the Messinian Salinity Crisis was terminated by spillover events from the Atlantic Ocean to the western Mediterranean basin, and consequently from the western to the eastern basin. • Successive falling and rising sea levels shaped the morphology and stratigraphy of the Levant margin during the Lago Mare stage. • Ravinement along the shifting coastline abraded the upper margin down to a depth of 365–535 m bmsl. • During the late Lago Mare stage sea level receded to 615–885 m bmsl. • Towards the end of the Messinian salinity Crisis, the eastern and western Mediterranean basins were not connected. [ABSTRACT FROM AUTHOR]

Water volume estimates of shallow desert lakes are the basis for water balance calculations, important both for water resource management and paleohydrology/climatology. Water volumes are typically inferred from bathymetry mapping; however, being shallow, ephemeral, and remote, bathymetric surveys are scarce in such lakes. We propose a new, remote‐sensing‐based, method to derive the bathymetry of such lakes using the relation between water occurrence, during >30 year of optical satellite data, and accurate elevation measurements from the new Ice, Cloud, and Land Elevation Satellite‐2 (ICESat‐2). We demonstrate our method at three locations where we map bathymetries with ~0.3 m error. This method complements other remotely sensed, bathymetry‐mapping methods as it can be applied to: (a) complex lake systems with subbasins, (b) remote lakes with no in‐situ records, and (c) flooded lakes. The proposed method can be easily implemented in other shallow lakes as it builds on publically accessible global data sets. Plain Language Summary: Lakes in desert environments are often remote and shallow and only get filled once in a long while. They are an important water resource and could be used to decipher past environmental conditions. However, detailed maps of lake‐floor terrain, which are required to effectively study these lakes are typically not available. The deepest parts of the lakes are filled with water more frequently than their shallow margins. Thus, we suggest here to relate water occurrence in those lakes with accurate satellite‐based elevation measurements, to obtain a valuable lake‐floor terrain map. We demonstrate the usefulness of our method by comparing results with other globally available data. Previous methods struggle with complex‐terrain lakes or lakes that are partially flooded during their survey, while our method yields high‐resolution accurate maps even in such lakes. Key Points: A new methodology to produce bathymetry maps of shallow desert lakes was developed, based on globally available data setsThe methodology enables mapping the bathymetry of lakes with subbasins or partially flooded lakes, both major limitations of other methodsThe derived bathymetry error is ~30 cm, rather than ~2.5 m for other globally available data [ABSTRACT FROM AUTHOR]

Abstract Ephemeral rivers in dryland regions exhibit a high interannual variability of streamflow regime, mainly dominated by floods. In these environments, floods are a water resource and a potential hazard with important socioeconomic implications. The Fish River (86,600 km2) is the largest ephemeral stream in Namibia and, recently, also the focus of new development plans, including construction of the largest dam in Namibia. The hydrological analysis to support decisions implies large uncertainties owing to spatial-limited and short hydrological records (since 1962). Here we investigate the current and past patterns of extreme floods combining instrumental, historical, and palaeoflood records. Palaeoflood studies were performed at two reaches with preserved sedimentary evidence: at the upper sector (Vogelkranz) upstream of Hardap Dam (~13% catchment area) and in the lower part of the river, in the Fish River Canyon National Park (70% catchment area). In the Hardap reach, the palaeoflood record identified at least eight large floods during the last 350 years, with the largest flood reaching a minimum discharge of 4800 m3 s−1 (150-year return period). In the Fish River Canyon reach, the sedimentary record shows at least 12 large floods over the last 400 years, the largest with an estimated minimum discharge of 8700 m3 s−1. The elevation of alluvial surfaces without flood evidence provided an upper bound for flood stages, associated with discharges of 6400 m3 s−1 and 16,140 m3 s−1 for the upper and mid-lower Fish River respectively. In the upper reach, the flood frequency analysis (FFA) combining systematic and palaeoflood data provided lower discharges (~25%) of the flood quantiles than the ones using only systematic data sets. In the Fish River Canyon reach, incorporation of the palaeoflood data into the FFA results in slightly higher values in the magnitude of the higher flood quantiles (~4–7%). The FFA analysis using an upper limited lognormal distribution function (LN4) fitted with palaeoflood data shows a good performance with a slow behaviour approaching the upper limit. Our flood frequency results suggest that the Hardap Dam should increase the spillway capacity and safety check flood of the original design in order to satisfy the dam safety criteria. However, the projected reevaluation figures calculated from conventional hydrological methods results in an overestimation of the safety floods according to our estimations. Graphical abstract Unlabelled Image Highlights • Flood deposits in the largest ephemeral river in Namibia are described and dated. • Frequency of extreme floods over the last three centuries shown low variability. • Palaeoflood based upper bound discharge was used for flood frequency analysis. • Palaeoflood quantiles give lower discharge than re-evaluated for Hardap dam safety. • Flood hydrology in the Fish River required a review for dam-safety. [ABSTRACT FROM AUTHOR]

The Sahara was wetter and greener during multiple interglacial periods of the Quaternary, when some have suggested it featured very large (mega) lakes, ranging in surface area from 30,000 to 350,000 km2. In this paper, we review the physical and biological evidence for these large lakes, especially during the African Humid Period (AHP) 11–5 ka. Megalake systems from around the world provide a checklist of diagnostic features, such as multiple well-defined shoreline benches, wave-rounded beach gravels where coarse material is present, landscape smoothing by lacustrine sediment, large-scale deltaic deposits, and in places, tufas encrusting shorelines. Our survey reveals no clear evidence of these features in the Sahara, except in the Chad basin. Hydrologic modeling of the proposed megalakes requires mean annual rainfall ≥1.2 m/yr and a northward displacement of tropical rainfall belts by ≥1000 km. Such a profound displacement is not supported by other paleo-climate proxies and comprehensive climate models, challenging the existence of megalakes in the Sahara. Rather than megalakes, isolated wetlands and small lakes are more consistent with the Sahelo-Sudanian paleoenvironment that prevailed in the Sahara during the AHP. A pale-green and discontinuously wet Sahara is the likelier context for human migrations out of Africa during the late Quaternary. [ABSTRACT FROM AUTHOR]

In the Levant Basin, submarine channels are abundant around the Nile deep-sea fan (NDSF), an area which is also affected by salt tectonics related to the Messinian salt giant. Here we focus on the relationship between submarine channels and obstacles formed by salt tectonics. Initially, we use methods developed for terrestrial morphological analysis and quantify channel sinuosity, width and slope in search for consistent relationships between morphometric parameters and channel response to obstacles. However, this traditional analysis did not yield robust conclusions. Then, we apply two new morphometric parameters suggested here to express the distortion of channels by obstacles: incident angle (α), defined as the acute angle between the regionally influenced channel direction and the strike of the tectonic obstacle and diversion angle (Ω), defined as the angle between the direction of the regional bathymetric slope and the average direction of the channel. These parameters illustrate the influence of the regional-scale basin geometry and the superimposed tectonic-influenced seabed patterns, on channel development. We found hyperbolic relationships between incident angle (α) and diversion angle (Ω) in which channels flowing approximately parallel (α ≈ 0°) to tectonic folds are (obviously) not diverted; channels nearly orthogonal (α ≈ 90°) to obstacles, crosscut them right through and, again, not diverted much. In contrast, channels with a general direction diagonal to the obstacles (α ≈ 40°), are diverted by ten degrees (Ω ≈ 10°). This diversion accumulates along large distances and significantly influences the regional development of channels around the NDSF. Noteworthy, this phenomenon of channel diversion, indirectly deteriorate normal slope-sinuosity relationships known from terrestrial studies. In light of these findings, we suggest that these new parameters can be applied to other basins, where submarine channels interact with seabed obstacles. [ABSTRACT FROM AUTHOR]

Abstract: Talus flatiron sequences are ubiquitous landforms in arid and semiarid regions characterized by horizontal erodible rocks capped by more resistant rocks. Alternating phases of deposition and erosion lead to the formation of generations of talus flatirons in which ancient ones are located farther from the source cliff. The existing conceptual model of this systematic spatial distribution of talus flatirons is related to glacial–interglacial climatic cycles and to relatively high rates of cliff retreat. Three groups of talus flatirons were analyzed in the northeastern hyperarid Negev desert. The analyses include mapping, age determination using optically stimulated luminescence and cosmogenic nuclide exposure dating, electrical resistivity tomography and sedimentological and soil analyses. All talus flatirons contain gypsic-salic soil catena typical to hyperarid climate (<80mmyr−1). No pedogenic indicators of past wetter environments such as buried calcic soil horizons, evidence of intense biogenic activity, or buried organic material were observed. 10Be exposure ages of the talus flatirons suggest that they were deposited during the middle Pleistocene; ~610ka and ~170ka for the oldest and intermediate-aged talus flatiron groups, respectively. These ages, combined with the present location of the talus flatirons relative to the source cliff yield retreat rates of 6–12 and ~200mMa−1 for the bedrock cliff and talus flatiron apex, respectively, and in opposite directions. Our results show that (a) climatic changes at glacial–interglacial time scales are not the main controls over the formation of talus flatiron generation, and (b) that significant cliff retreat is not the main cause for the systematic spatial distribution of talus flatiron generations relative to the cliff. Our results indicate that the process of talus flatiron formation in the Negev desert must be associated with the balance between production, deposition, and removal of clasts under hyperarid conditions with only a minor cliff retreat. [Copyright &y& Elsevier]

Abstract: In this study, we explored the spatial and temporal relations between boulders and their original in-situ locations on sandstone bedrock cliffs. This was accomplished by combining field observations with dating methods using cosmogenic isotopes (10Be and 14C) and optically stimulated luminescence (OSL). Our conclusions bear both on the landscape evolution and cliff retreat process in the hyperarid region of Timna and on the methodology of estimating exposure ages using cosmogenic isotopes. We recognize three discrete rock fall events, at 31 ka, 15 ka, and 4 ka. In this hyperarid region, the most plausible triggering mechanism for rock fall events is strong ground acceleration caused by earthquakes generated by the nearby Dead Sea fault (DSF). Our record, however, under represents the regional earthquake record implying that ongoing development of detachment cracks prior to the triggering event might be slower than the earthquake cycle. Cliff retreat rates calculated using the timing of rock fall events and estimated thickness of rock removed in each event range between 0.14 m ky−1 and 2 m ky−1. When only full cycles are considered, we derive a more realistic range of 0.4 m ky−1 to 0.7 m ky−1. These rates are an order of magnitude faster than the calculated rate of surface lowering in the area. We conclude that sandstone cliffs at Timna retreat through episodic rock fall events that preserve the sharp, imposing, landscape characteristic to this region and that ongoing weathering of the cliff faces is minor. A 10%–20% difference in the 10Be concentrations in samples from matching boulder and cliff faces that have identical exposure histories and are located only a few meters apart indicates that cosmogenic nuclide production rates are sensitive to shielding and vary spatially over short distances. However, uncertainties associated with age calculations yielded boulder and matching cliff face ages that are similar within 1 σ. The use of external constraints in the form of field relations and OSL dating helped to establish each pair''s age. The agreement between calculated 14C and 10Be ages indicates that the accumulation of 10Be at depth by the capture of slow deep-penetrating muons was properly accounted for in the study. [Copyright &y& Elsevier]

Abstract: The Elat fault (a segment of the Dead Sea Transform) runs along the southern Arava valley (part of the Dead Sea Rift, Israel) forming a complex fault zone that displays a time-dependent seismic behaviour. Paleoseismic evidence shows that this fault zone has generated at least 15 earthquakes of magnitude larger than M 6 during the late Pleistocene and the Holocene. However, at present the Elat fault is one of the quietest segments of the Dead Sea Transform, lacking even microsesimicity. The last event detected in the southern Arava valley occurred in the Avrona playa and was strong enough to have deformed the playa and to change it from a closed basin with internal drainage into an open basin draining to the south. Paleoseismological, geophysical and archaeological evidences indicate that this event was the historical devastating earthquake, which occurred in 1068 AD in the eastern Mediterranean region. According to the present study this event was strong enough to rupture the surface, reactivate at least two fault branches of the Elat fault and vertically displace the surface and an early Islamic irrigation system by at least 1 m. In addition, the playa area was uplifted between 2.5 and 3 m along the eastern part of the Elat fault shear zone. Such values are compatible with an earthquake magnitude ranging between M 6.6 and 7. Since the average recurrence interval of strong earthquakes during the Holocene along the Elat fault is about 1.2±0.3 ky and the last earthquake occurred more about 1000 years ago, the possibility of a very strong earthquake in this area in the future should be seriously considered in assessing seismic hazards. [Copyright &y& Elsevier]