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To understand the timing of deglaciation of the northernmost marine-terminating glaciers of the Cordilleran Ice Sheet (CIS), we obtained 2610Be surface-exposure ages from glacially scoured bedrock surfaces in Prince William Sound (PWS), Alaska. We sampled six elevation transects between sea level and 620 m and spanning a distance of 14 to 70 km along ice flow paths. Most transect age–elevation patterns could not be explained by a simple model of thinning ice; the patterns provide evidence for lingering ice cover and possible inheritance. A reliable set of 20 ages ranges between 17.4 ± 2.0 and 11.6 ± 2.8 ka and indicates ice receded from northwestern PWS around 14.3 ± 1.6 ka, thinned at a rate of ~120–160 m/ka, and retreated from sea-level sites at 12.9 ± 1.1 ka at a rate of 20 m/yr. The retreat rate likely slowed as glaciers retreated into northern PWS. These results are consistent with the growing body of reported deglacial constraints on collapse of ice sheets along the Alaska margin indicating collapse of the CIS soon after 17 ka. These data are consistent with paleotemperature data indicating that a warming North Pacific Ocean caused catastrophic collapse of this part of the CIS.

The onset and intensification of eolian activity mark climatic transitions that promote wide-scale aridification, recorded by the generation and preservation of massive sand deposits. Evaluating the impact and implications of such repositories on Earth systems requires knowledge about the timing of their emplacement and the mechanisms responsible for their generation, which remain highly uncertain. Here we provide time constraints for the establishment of the Kalahari Erg, which is the largest continuous body of sand on Earth. We apply cosmogenic nuclide dating of sand from the Kalahari Desert combined with numerical modeling to determine when sand was introduced into the interior of southern Africa. Through the consideration of several scenarios, we show that major events of eolian sand transport and accumulation occurred between ~2.5 and 1 Myr ago. This substantial activity, which significantly altered environmental settings, corresponds to regional, continental, and global scale morphotectonic and climatic changes that contributed to the mass production and widespread dispersion of sand. These changes substantially altered existing habitats, thus constituting a crucial milestone for hominin evolution and migration throughout the African continent during the Pleistocene.

Glaciers in central Asia that developed under a range of climatic conditions from arid to humid provide an excellent opportunity to test glacial responses to changes in climate. To do this, we mapped and dated glacial deposits at 11 sites spread over five mountain ranges in central Asia: the Altai, Tian Shan, Altyn Tagh, Qilian Shan, and Kunlun. The glacial chronologies for these sites were determined from new 10Be and 26Al exposure ages for the mapped moraines, in addition to 10Be ages available in the literature. Paleo–equilibrium-line altitudes were estimated for past glacier extents from the dated moraines. The equilibrium-line altitudes (ELAs) were also estimated for existing glaciers to characterize the spatial pattern in modern climate across the study region. Differences between the modern and paleo-ELAs (ΔELAs) were used to explore the climatic reasons for variations in the glacier sensitivities and responses to past changes in climate. The results show that the glaciers in more humid regions advanced to their maximum during marine oxygen-isotope stage (MIS) 3–2 with ΔELAs of ~1100–600 m. However, glaciers in the arid interior of central Asia, in the rain shadows of the Karakorum and Pamir ranges and in the Gobi Desert ranges, reached their maximum between MIS 6 and 4, and glacier extents during the subsequent colder/drier MIS 3–2 were significantly smaller or did not extend beyond their cirques. Comparisons of our results and the sensitivity analysis of modern glaciers suggest that depression of air temperature was the primary driver of glacier advances in central Asia but that precipitation played a major role in shaping the spatial and temporal heterogeneity of glacier advances. Precipitation was especially important in hyperarid conditions. Therefore, inferences about paleoclimate parameters from past glacial extents must be made after careful consideration of the climatic setting in which the glaciers are found, as well as their sensitivity to climatic factors.

[Capture areas of the western Okavango Basin during the Pliocene (a) and the early Pleistocene (b). The change in provenance that occured around the Pliocene‐Pleistocene transition is attributed to adjustments of the drainage systems to axial crustal uplift, resulting in the formation of large waterbodies. , Abstract The structural depression that occupies the Okavango Basin in southern Africa comprises a depo‐centre within the intracratonic Kalahari Basin where sediments of the Cenozoic Kalahari Group have accumulated. The Okavango Basin has been formed due to stretching and subsidence at an area of diffused deformation, southwestwards to the main East African Rift System (EARS). Sediments from two full Kalahari Group sequences, located on opposite sides of the Gumare Fault that forms a major fault within the Okavango Basin, were studied to determine their provenance and chronology. Terrestrial Cosmogenic Nuclide (TCN) 26Al/10Be burial dating was used to constrain a chronostratigraphical framework, and Pb, Sr, and Nd isotopic ratios combined with geochemical and sedimentological analyses were applied to track the source areas of the sediments.Results indicate the following sequence of basin filling: (a) Accumulation between ca. 4–3 Ma during which the currently downthrown (southern) block received a mixture of sediments mostly from the Choma‐Kalomo, Ghanzi‐Chobe, and Damara terranes, and possibly from the Lufilian Belt and/or Karoo basalts during earlier stages of deposition. Simultaneously, the upthrown (northern) block received sediments from more distant Archean sources in the Zimbabwe and/or Kasai cratons, (b) Hiatus in sedimentation occurred at both sites between ca. 3–2 Ma, (c) Sediments on both sides of the Gumare Fault share a similar source (Angolan Shield) with minor distinct contributions to the downthrown block from the Kasai Craton and local sources input to the upthrown block, and (d) Regional distribution of aeolian sand since at least 1 Ma. The change in source areas is attributed to rearrangements of the drainage systems that were probably linked to vertical crustal movements on the margins of the Okavango Basin. The tectonically induced morphodynamics controlled the landscape evolution of the endorheic basin where vast lakes, wetlands and salt pans have developed through time.]

The long-term bedrock incision of streams in the northeastern Negev has been dictated, since the Early Pliocene, by the subsidence of the Dead Sea basin. However, this incision is accompanied by very long intervals of sediment aggradation. Here, we document the Quaternary-scale fluvial response to changing base-level, lithology, structure, and climate along the hyperarid Nahal Zafit, NE Negev. The oldest (~1–2 Ma) alluvial remnants point to a widespread beveled bedrock pediment at the base of the Hazera anticline. This pediment, like other stream-pediment-anticline relationships in the region, provides the baseline framework into which Nahal Zafit incises. During the Early to Middle Pleistocene, this pediment was the base-level for all streams emerging out of the anticlines. The tectonic subsidence of the regional base-level at the rift margin farther downstream, has caused incision and upstream migration of bedrock knickpoints, triggering the development of a wide incised valley in the Mazar syncline, adjacent to the Hazera anticline. Since ~330 ka, fluvial terraces, landslides and taluses record intervals of basin-wide fluvial deposition under prevailing hyperarid to arid climate. Despite the general arid climate, prolonged fluvial deposition intervals occurred at ca. 330–265, 230–125, and 110–20 ka. Rapid and quite short-duration bedrock incision occurred in-between these, much longer, intervals of aggradation. In addition to the proposed climatic imprint on fluvial aggradation-incision cycles and the first-order base-level control of the rift margin fault, the formation of strath terraces and distribution of stored sediments within the drainage basin point to the fundamental role that lithology and structure play in the Quaternary evolution of the NE Negev watersheds.

Erosion related to glacial activity produces enormous amounts of sediment. However, sediment mobilization in glacial systems is extremely complex. Sediment is derived from headwalls, slopes along the margins of glaciers, and basal erosion; however, the rates and relative contributions of each are unknown. To test and quantify conceptual models for sediment generation and transport in a simple valley glacier system, we collected samples for 10Be analysis from the Kahiltna Glacier, which flows off Denali, the tallest mountain in North America. We collected angular quartz clasts on bedrock ledges from a high mountainside above the equilibrium line altitude (ELA), amalgamated clast samples from medial moraines, and sand samples from the river below the glacier. We also collected sand from nine other rivers along the south flank of the Alaska Range. In the upper catchment of the Kahiltna drainage system, toppling, rockfall, and slab collapse are significant erosional processes. Erosion rates of hundreds of millimeters per thousand years were calculated from 10Be concentrations. The 10Be concentrations in amalgamated samples from medial moraines showed concentrations much lower than those measured from the high mountainside, a result of the incorporation of thick, and effectively unexposed, blocks into the moraine, as well as the incorporation of material from lower-elevation nearby slopes above the moraines. The 10Be sediment samples from downstream of the Kahiltna Glacier terminus showed decreasing concentrations with increasing distance from the moraine, indicating the incorporation of material that was less exposed to cosmic rays, most likely from the glacier base as well as from slopes downstream of the glacier. Taken together, 10Be concentrations in various samples from the Kahiltna drainage system indicated erosion rates of hundreds of millimeters per thousand years, which is typical of tectonically active terrains. We also measured 10Be concentrations from river sediment samples collected from across the south flank of the Alaska Range. Calculation of basinwide weighted erosion rates that incorporated hypsometric curves produced unrealistically high erosion rates, which indicates that the major source of sediment was not exposed to cosmic rays and was primarily derived from the base of glaciers. Moreover, the apparently high erosion rates suggest that parts of each drainage system are not in erosional steady state with respect to cosmogenic isotope accumulation.

Sand deposits cover extensive areas both in the northern and southern hemispheres and the timing and chronology and processes that govern their dynamics are of major interest. Luminescence-based dating methods, are used to date episodic aeolian events but are restricted to late Quaternary deposits, and only reveal the last cycle of sediment burial and not the time of sand existence in the landscape. Burial ages modelled from cosmogenic nuclides reach further back in time, but are usually inferred as minimal deposition ages. It is apparent that standard dating methods, when applied individually, have limited applicability for determining both the age and the processes that form aeolian deposits. This study presents an approach that integrates luminescence dating and cosmogenic burial dating into a stochastic model developed to reproduce sand formation and migration. The model is based on a process in which quartz grains are vertically displaced through a sand column simulating dune migration across the landscape. A range of vertical displacement rates is compiled from published luminescence ages of dated dune fields of varied settings throughout the world. Using these vertical movement rates, sand is recycled up and down a depth profile coupled with a step-wise calculations of cosmogenic nuclides accumulation and decay, alongside OSL signal accumulation. When the modelled sand grains are buried, their luminescence signal grows while 26Al and 10Be decay or accumulate as a function of their respective radioactive decay and production rate, which is governed by cosmic rays attenuation. When sand is exposed at the surface, the luminescence signal is reset and cosmogenic nuclide production is maximized. Each simulation is terminated when the modelled concentrations of 26Al and 10Be reach measured concentrations in actual sand samples. Luminescence data therefore provide the time since last exposure at the surface (i.e. the last depositional cycle), whereas the cosmogenic nuclides provide a long-term estimate of sand residence in the landscape reflecting also weathering and erosion of the source bedrock. The southern Kalahari dune field at Mamatwan, South Africa, is used as a case study to test the presented approach. Model results show that optically stimulated luminescence ages which range between 1 and 10 Ka, only reflect the last cycle of sand migration, while cosmogenic nuclides minimal burial ages are greater than 1 Ma. Furthermore, the simulation results indicate two peaks at 1.5–2.2 Ma and at 4.2–5.2 Ma, suggesting two main phases of sand introduction to the Kalahari during the Pliocene and Pleistocene. Finally, the modelled ages are concurrent with regional environmental and climatic events. The model presented in this study provides a powerful tool for estimating the emergence of sand in a given landscape, and also for understanding the dynamic evolution of any dune field and the mechanisms behind dune migration.

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 105–106 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 10Be were measured in bedrock and sediment samples collected throughout the watershed of the Ugab River (~29,000 km2), 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. 10Be 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. 10Be 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 ( 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 ≥106 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.

Mountain glaciers at ∼26–19 ka, during the global Last Glacial Maximum near the end of the last 10 5 yr glacial cycle, are commonly considered on the basis of dating and field mapping in several well-studied areas to have been the largest of the late Quaternary and to have advanced synchronously from region to region. However, a numerical sensitivity model (Rupper and Roe, 2008) predicts that the fraction of ablation due to melting varies across Central Asia in proportion to the annual precipitation. The equilibrium-line altitude of glaciers across this region likely varies accordingly: in high altitude, cold and arid regions sublimation can ablate most of the ice, whereas glaciers fed by high precipitation cannot ablate completely due to sublimation alone, but extend downhill until higher temperatures there cause them to melt. We have conducted field studies and 10 Be dating at five glaciated sites along a precipitation gradient in Mongolia to test the Rupper/Roe model. The sites are located in nearby 1.875 × 1.875° cells of the Rupper/Roe model, each with a different melt fraction, in this little-studied region. The modern environment of the sites ranges from dry subhumid in the north (47.7° N) to arid in the south (45° N). Our findings show that the maximum local advances in the dry subhumid conditions predated the global Last Glacial Maximum and were likely from MIS 3. However, we also found that at ∼8–7 ka a cirque glacier in one mountain range of the arid Gobi desert grew to a magnitude comparable to that of the local maximum extent. This Holocene maximum occurred during a regional pluvial period thousands of years after the retreat of the Pleistocene glaciers globally. This asynchronous behavior is not predicted by the prevailing and generally correct presumption that glacier advances are dominantly driven by temperature, although precipitation also plays a role. Our findings are consistent with and support the Rupper/Roe model, which calls for glaciation in arid conditions only at high altitudes of sub-freezing temperatures, where the melt fraction in ablation is low. We expect a heterogeneous pattern of glacial responses to a changing modern climate in cold arid regions; an individual glacier advance should not be necessarily interpreted as evidence of cooling climate.

The presence of boulders, a result of rockfall events, at the foot of cliffs testifies for a mass wasting process which is widely observed and is often considered to be triggered by earthquakes. Here we investigate boulders under an overhanging cliff with an emphasis on the principal factors that control boulder size. We used a conceptual cantilever beam model to predict the expected maximum length of the overhanging cliff. We then compared these calculated lengths to those of the field observed boulders and the length of the overhanging cliff ledge. Our observations show that the actual lengths of the boulders and overhanging cliff are much shorter than expected from the model. As the study area is located in a tectonically active region, we first suggested solving this discrepancy by adding the possible effect of ground motion on the size of a boulder. Detailed pseudo-static and dynamic analysis of the effect of earthquakes on the failure of rock beams shows that boulder length may not significantly be shortened by induced ground motions. We therefore conclude that strong earthquakes, although triggering rockfalls, are not expected to control the resultant size of the boulders found at the base of overhanging cliffs. We alternatively suggest that the maximum length of a boulder is strongly controlled by the rock strength. We conclude that the maximum boulder size that may fall during an earthquake event can be predicted by calculating the cantilever critical length including the effect of the rock size on its tensile strength. This, together with the measured rock discontinuities in an overhanging cliff suggests an upper-bound for the volume of the falling boulders, a crucial factor in assessing rockfall hazards.

The Miocene Hazeva River was a large fluvial system (estimated catchment size > 100 000 km2) that drained the Arabian Plateau and Sinai Peninsula into the Mediterranean Sea during the Early–Mid Miocene. It was established after rifting of the Red Sea uplifted the Arabian Plateau during the Oligocene. Following late Miocene to early Pliocene subsidence along the Dead Sea Rift, the Hazeva drainage system was abandoned and dissected, resulting in new drainage divides on either side of the rift. We utilized a novel application of cosmogenic 21Ne measurements in chert to compare modern erosion rates with Miocene erosion rates that operated when the Hazeva River was active. We find that modern erosion rates derived from cosmogenic 21Ne, 26Al, and 10Be in exposed in situ chert nodules to be extremely slow, between 2–4 mm/kyr. Comparison between modern and paleo erosion rates, measured in chert pebbles, is not straightforward, as cosmogenic 21Ne was acquired partly during bedrock exhumation and partly during transport of these pebbles in the Hazeva River. However, even with bedrock erosion and maintained transport along this big river, 21Ne concentrations measured in Miocene cherts are lower (range between 3.66 ± 1.9 × 106 and 8.97 ± 1.39 × 106 atoms/g SiO2) compared to 21Ne concentrations measured in the currently eroding chert nodules (8.08 ± 1.48 × 106 and 12.10 ± 2.43 × 106 atoms/g SiO2). 21Ne concentrations in Miocene cherts correspond to minimum erosion rates that are at least twice as fast as rates calculated today. We attribute these faster erosion rates to a combination of continuous uplift and significantly wetter climatic conditions during the Miocene.

A multidisciplinary study was conducted in a newly discovered Paleolithic locality, named ‘Evron Landfill. This locality is a part of the Lower Paleolithic complex of ‘Evron located at the western Galilee, Israel. Examination of artifacts has enabled the cultural attribution of ‘Evron Landfill to the Early Acheulian, while detailed paleomagnetic stratigraphy places the hominin occupations near the Brunhes–Matuyama transition ~0.77 Ma. This age is constrained by cosmogenic isotope burial dating of the sediments overlying the Paleolithic finds, providing a minimum age of ~0.66±0.11 Ma for hominin activity at the site. These results are further supported by the biochronological information derived from the faunal assemblage. Comparative analyses of faunal remains and lithic artifacts from ‘Evron Landfill demonstrate similarities to the assemblages from the Early Acheulian site of Evron Quarry, located ~300 m to the south. Pedo-sedimentological analyses indicate that hominin activity took place in a marsh environment in proximity to the Mediterranean coast, which probably fluctuated in both space and time with a fluvial environment. In addition, this study provides important data about ancient coastal activity during the early to middle Pleistocene.

Cave sediments pose dating challenges due to complex depositional and post-depositional processes that operate during their transport and accumulation. Here, we confront these challenges and investigate the stratified sedimentary sequence from Wonderwerk Cave, which is a key site for the Earlier Stone Age (ESA) in Southern Africa. The precise ages of the Wonderwerk sediments are crucial for our understanding of the timing of critical events in hominin biological and cultural evolution in the region, and its correlation with the global paleontological and archaeological records. We report new constraints for the Wonderwerk ESA chronology based on magnetostratigraphy, with 178 samples passing our rigorous selection criteria, and fourteen cosmogenic burial ages. We identify a previously unrecognized reversal within the Acheulean sequence attributed to the base of the Jaramillo (1.07 Ma) or Cobb Mtn. subchrons (1.22 Ma). This reversal sets an early age constraint for the onset of the Acheulean, and supports the assignment of the basal stratum to the Olduvai subchron (1.77–1.93 Ma). This temporal framework offers strong evidence for the early establishment of the Oldowan and associated hominins in Southern Africa. Notably, we found that cosmogenic burial ages of sediments older than 1 Ma are underestimated due to changes in the inherited 26Al/10Be ratio of the quartz particles entering the cave. Back calculation of the inherited 26Al/10Be ratios using magnetostratigraphic constraints reveals a decrease in the 26Al/10Be ratio of the Kalahari sands with time. These results imply rapid aeolian transport in the Kalahari during the early Pleistocene which slowed during the Middle Pleistocene and enabled prolonged and deeper burial of sand while transported across the Kalahari Basin.

We investigated the mid-Pleistocene to recent aggradation-incision pattern of two drainage systems (Nahal Peres and Nahal Tahmas) in the hyperarid north eastern Negev desert, southern Israel. Although these drainage systems drain into the tectonically active Dead Sea basin, lake level fluctuations cannot account for the aggradation-incision pattern as bedrock knickpoints disconnect the investigated parts of these drainage systems from base level influence. We applied geomorphic mapping, soil stratigraphy, optically stimulated luminescence (OSL) and cosmogenic (in situ 10Be) exposure dating to reconstruct cycles of aggradation and incision of alluvial terraces and to study their temporal association with regional periods of humidity and aridity and global glacial-interglacial cycles. The spatial and temporal relationships between the alluvial units suggest changes in the drainage system behavior since the middle Pleistocene, and show a pattern in which prolonged periods of sediment aggradation alternated with short periods of rapid and intense degradation through erosion and incision into sediment and bedrock. We obtain ages for several Pleistocene-Holocene periods of incision: ~ 1.1 Ma, ~ 300 ka, ~ 120 ka, ~ 20 ka, ~ 12 ka and ~ 2 ka. Although broadly synchronous, the Nahal Peres and Nahal Tahmas systems exhibit temporal differences in aggradation and incision. Hyperarid conditions have persisted in the region at least since the middle Pleistocene, as evidenced by gypsic-salic soils that ubiquitously cap the investigated alluvial terraces. This observation is consistent with other observations throughout the Negev indicating prolonged aridity. Thus, alternation between sediment aggradation and degradation cannot be correlated in a simple and straightforward way to climatic changes. We explain the temporal differences in aggradation and incision between Nahal Peres and Nahal Tahmas as resulting from the differences in stream gradient, basin hypsometry, and drainage basin area (which influences the amount of water passing through the system). Regardless of humidity source (tropical plumes, Red Sea trough or Mediterranean fronts) and the frequency and intensity of rainfall in the region, our study shows that: 1) unlike other climatic proxies, such as speleothems, the evolution of alluvial terraces, which involves many stages (sediment generation, transport, deposition, and subsequent incision), results in a significant time gap between the actual ages of terraces and the timing of external triggers such as climatic fluctuations, and 2) such time-gaps may vary, even within nearby drainage systems, due to differences in drainage systems specific characteristics, and thus result in asynchronicity (or at least poor synchronicity) of alluvial terrace deposition and incision.

Water plays a critical role in erosion and sediment transport and this relationship is most evident in the hyperarid Atacama Desert of Northern Chile, a region characterized by erosion rates that fall to near zero and cobbles and boulders with cosmogenic nuclide concentrations indicative of exposure for many millions of years. Cosmogenic nuclide concentrations from the Atacama are used to both determine the age of hyperaridity onset and to place important constraints on rates of geomorphic processes in this uniquely arid environment. Prior determinations of cosmogenic nuclide concentrations from the Atacama Desert focus primarily on exposure ages from boulders/cobbles or erosion rates from bedrock. However, recent determinations of cosmogenic nuclide concentrations from boulders, bedrock, and sediment at the same location suggests that material from diverse sample types have different cosmogenic nuclide concentrations. Therefore, it is critical to determine which concentrations of cosmogenic nuclides are most representative of overall erosion rates from the Atacama. Here, concentrations of cosmogenic nuclides in more than 100 samples across two east-west transects within the central Atacama Desert (22-26°S) of Northern Chile are considered. Concentrations of 10Be and 26Al were measured in samples of bedrock, alluvial sediment, active stream sediment, and boulders within several sub-regions of the Atacama Desert, including: the western and eastern Coastal Cordillera, the inner absolute desert (including the Cerro de los Tetas), the Cordillera Domeyko, and the western flank of the Andes. This data allows detailed comparisons of cosmogenic nuclides concentrations both within diverse sample types at a given site and between major geomorphic sub-regions of the Atacama. The general pattern of cosmogenic nuclide concentrations in hyperarid environments is characterized by concentrations that are higher in boulders, moderately high in bedrock, lower in hillslope sediment, and lowest in channels that flow across the desert. At many locations in the central Atacama, boulders and bedrock have erosion rates as much as an order of magnitude slower than that of finer grained sediment at the same location, a relationship that is attributed to the fact that boulders sit above thick gypcrete soils. The hillslope to basin concentrations of cosmogenic nuclides within each sub-region, along with 26Al/10Be ratios, suggests that concentrations of 10Be in most bedrock and sediments reflects erosion rates. However, in the western Coastal Cordillera 10Be concentrations in sediment also reflects transport time. The overarching trend in this data set is that inferred erosion rates are lower to both the east and the west, corresponding with increases in both precipitation and erosion rates towards both the Andean Flank and in the Coastal Cordillera. This trend is previously noted for the Atacama; however, this large data set allows the first observation of the influence of other variables upon erosion rates. Most notably, another clear influence on erosion rates in the Atacama is slope. In some cases, differences in slope are enough to overcome the influence of aridity. For example, erosion rates on the flanks of the Cordillera Domeyko are faster (>1 m/Ma) than that at the crest (

Carbonate minerals, unlike silicates, have the potential to dissolve almost completely and with high efficiency. Thus, in carbonate terrains denudation rate and style (the governing process of denudation, mechanical or chemical) should be more sensitive to climatic forcing. Using 36 Cl measurements in 39 carbonate bedrock and sediment samples, we calculate long-term denudation rates across a sharp climatic gradient from Mediterranean to hyper-arid conditions. Our samples were collected along the Arugot watershed, which drains the eastern flank of the Judea Range (central Israel) to the Dead Sea and is characterized by a pronounced rain shadow. Denudation rates of flat-lying bedrock outcrops sampled along interfluves differ by an order of magnitude from ∼20 mm ka −1 in the Mediterranean zone to 1–3 mm ka −1 in the hyper-arid zone. These rates are strongly correlated with precipitation, and thus reflect the importance of carbonate mineral dissolution in the overall denudation process. In contrast, denudation rates of steep bedrock surfaces depend on the hillslope gradient, but only in the hyper-arid climate zone, indicating that mechanical processes dominate the overall hillslope denudation within this zone. The dominance of slope-dependent mechanical erosion in the hyper-arid zone is also reflected by an increase in spatially-average denudation rates from 17–19 mm ka −1 in the Mediterranean–semi-arid zones to 21–25 mm ka −1 in the hyper-arid zone. These higher rates are attributed to clast contribution from steep slopes under arid climate. This suggests an increased importance of mechanical processes to the overall denudation in the hyper-arid zone. We demonstrate that the transition between chemically-dominated denudation to mechanically-dominated denudation occurs between 100 and 200 mm of mean annual precipitation. Long-term denudation rates across the Judea Range indicate that between Mediterranean and hyper-arid climates, chemical weathering rates are limited by precipitation. Nevertheless, in more humid climates, chemical weathering rates are apparently limited by the rates of carbonate mineral dissolution. This study demonstrates that carbonate terrains have the capacity to shift between mechanically and chemically dominated denudation in response to changes in precipitation. Similar transitions in response to changes in temperature or the level of tectonic activity have been previously reported. We suggest that the abrupt nature of such transitions can be primarily attributed to the efficiency of carbonate dissolution processes and the competition between surface and subsurface drainage systems in carbonate terrains.

The evolution of Terrestrial Cosmogenic Nuclides (TCN) from an alluvial section in the Atacama Desert is examined. We reconstruct a burial history for the last ∼10 Ma using 40Ar/39Ar dating of volcanic ash layers interbedded with alluvial sediments; this independent dating allows us to distinguish between the effects of erosion, post-burial subsurface production, and radioactive decay during burial on TCN concentrations. Our TCN results show significant post-burial production, which is the result of the extremely slow sedimentation rate (∼3 m/Ma) and the old age of the sediments. Although distinct differences in TCN concentrations are apparent between the lower and upper parts of the sedimentary section, we show that these differences are most likely related to post-burial production and age, and not to changes in bedrock erosion rates or changes in elevation due to tectonic activity. Our approach provides a test to the applicability of the two-isotope cosmogenic burial dating system (26Al–10Be) in regions of extremely slow sedimentation rates. Our results reveal geomorphic stability in terms of erosion and sedimentation rates for the late Miocene–Pliocene in the Atacama Desert.

Using cosmogenic isotopes and solute load analysis, we quantify chemical weathering (solutional erosion) and denudation rates over variable time scales in a tectonically stable, moderate-relief, carbonate terrain (Soreq drainage, Judea Hills, Israel), located in a semihumid Mediterranean climate. Long-term (>10 4 yr) denudation rates were calculated from 36 Cl concentrations in 51 bedrock and sediment samples. Bedrock samples range in elevation (340–850 m), hillslope gradient (0°–30°), and mean annual precipitation (MAP; 500–630 mm) and vary in soil cover thickness (0–75 cm), Mg/Ca ratio (0.0–1.0 mol), clay mineral contents (0–6 wt%), and mechanical strength (41–58 Schmidt hammer rebound units). Soil pCO2 values at a single location during the course of 1 yr, range between 0.4 and 9.0 mmol mol –1 . Average long-term denudation rate of exposed bedrock samples is 21 ± 7 mm k.y. –1 . Field observations and 36 Cl measurements indicate that soil pockets undergo cycles in the rate of deepening, and that over 10 5 yr time scale, average denudation rates beneath soil pockets are similar to those of exposed bedrock. Sediment samples yield even higher denudation rates, which are probably anthropogenically induced, but could also indicate that the sediment source is soil pockets. Long-term denudation rates are decoupled from hillslope gradient, elevation, and rock strength. Denudation rates show a positive correlation with present-day MAP values, exhibit a complex relation with rock Mg content, and show a weak correlation with clay content. Annual chemical weathering rates were calculated from modern-day solute load measured in waters of perched springs and the regional carbonate aquifer. Our results indicate that on annual, decadal, and 10 4 yr time scales, chemical weathering and denudation are controlled by carbonate dissolution, while mechanical processes are far less signifi cant. Overlap between the distributions of HCO3 – concentrations measured in runoff, springs, and the regional aquifer water suggests that chemical weathering focuses at the bedrock surface and therefore is comparable with solutional denudation. This result is in contrast to the features of ancient fl uvial and colluvial activity (steep nonconcave hillslopes and stream profi les and knickzones in the streams) preserved in the present landscape. Such features were formed in response to mid-Pleistocene uplift and could have been preserved due to a decrease in stream power following the formation of subsurface drainage and the lowering in abrasive clast supply that followed the stabilization of hillslopes in the drainage. Long-term denudation rates calculated from exposed bedrock samples are higher by factor of 1.4 relative to annual, contemporary chemical weathering rates. Increased precipitation by a similar factor, averaged over the last glacial and present interglacial, can explain this difference.

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 5 mm kyr− 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 (1–2 mm kyr− 1), while the overall slope processes deliver sediment to the base of the cliff with 5–6 × 105 atoms g− 1 quartz. This concentration is equivalent to an average erosion rate of ~ 8 mm kyr− 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 1–2 km from the base of the GS, the concentration doubles to ~ 10 × 105 atoms g− 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, ~ 100 km away. Cosmogenic isotope concentration in sediment increases to ~ 30 × 105 atoms of 10Be g− 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.

Colluvial sediments of talus relicts (“talus flatirons”) around mesas preserve a record that sheds light on slope-forming processes at temporal scales > 103 yr. The sedimentology and soil stratigraphy of two groups of talus flatirons in the northeastern hyperarid Negev desert reveal four deposition events in the younger talus and at least two in the older one. Numerical modeling of high-resolution 10Be depth profiles suggests that these taluses were deposited during the middle Pleistocene; the younger talus group first depositional event occurred at 551 − 142+ 80 ka and its abandonment occurred at 270 − 38+ 17 ka. The abandonment of the older talus group and stabilization of its surface occurred at 497 − 114+ 176 ka. These ages indicate that the development of the studied talus sequence is not specifically associated with Pleistocene glacial–interglacial cycles. The 10Be modeled concentrations indicate significant differences in the average inheritance of talus flatirons of different groups. These differences can be attributed to variability in the transport distance and duration of gravel exposure during transport but could also reflect some temporal variability in cliff retreat. Our results also demonstrate that talus slopes in hyperarid areas, despite their steepness, can store sediment for long periods (~ 500 ka) and thus constitute a valuable archive.

Calcrete-coated remnants of landslide debris and alluvial deposits are exposed along the presently stable hillslopes of the Soreq drainage, Judea Hills, Israel. These remnants indicate that a transition from landslide-dominated terrain to dissolution-controlled hillslope erosion had occurred. This transition possibly occurred due to the significant decrease in tectonic uplift during the late Cenozoic. The study area is characterized by sub-humid Mediterranean climate. The drainage hillslopes are typically mantled by thick calcrete crusts overlying Upper Cretaceous marine carbonate rocks. Using TT-OSL dating of aeolian quartz grains incorporated in the calcrete which cements an ancient landslide deposit, we conclude that incision of ~100 m occurred from 1056 ± 262 to 688 ± 86 ka due to ~0·3° westward tilt of the region; such incision invoked high frequency of landslide activity in the drainage. The ages of a younger landslide remnant, alluvial terrace, and alluvial fan, all situated only a few meters above the present level of the active streambed, range between 688 ± 86 ka and 244 ± 25 ka and indicate that since 688 ± 86 the Soreq base level had stabilized and that landslide activity decreased significantly by the middle Pleistocene. Copyright © 2012 John Wiley & Sons, Ltd.

Quartz sand in the eastern Mediterranean coastal plain is supplied through an extended transport system, which includes the Nile River, east Mediterranean longshore currents, and inland eolian transport. While the concentrations of cosmogenic nuclides ( 26 Al and 10 Be), and their ratio, in modern sand deposited along the coast of the eastern Mediterranean reflect the combined effect of exposure and burial during transport, the concentrations of these nuclides in buried sands are the result of decay of this initial dosing. Samples of modern exposed sand (n = 3) collected from the coastal plain of Israel yield an average 26 Al/ 10 Be ratio of 4.8 ± 0.2, significantly lower than the expected ratio of 6.8 for exposed quartz grains at the surface. A similar ratio of 4.5 ± 0.3 was measured in a late Pleistocene sand sample, indicating similar exposure-burial histories during transport in spite of the difference in climatic conditions. The results imply a steady, preburial cosmogenic nuclide ratio related to the Nile River9s ability, through storage and recycling, to buffer the effects of climatic and tectonic perturbations on cosmogenic nuclide concentrations in the transported quartz. All ancient and buried sand samples (n = 11) fall on a decay path that originates from the concentrations and ratio of 26 Al and 10 Be in modern sand, suggesting steady preburial concentrations of cosmogenic nuclides in quartz sand over the past 2.5 m.y.

To better understand the sedimentary history of the erosional crater of Makhtesh Hazera in the hyper-arid Negev Desert of southern Israel we have measured concentrations of in situ 10 Be in alluvial sediments from the active drainage system and from abandoned alluvial terraces and dated them using optically stimulated luminescence (OSL). These sedimentary sequences suggest changes in the drainage system behavior over time and show a periodic pattern in which periods of sediment aggradation alternate with periods of degradation through incision and erosion. In alluvial terrace sediments, 10 Be concentrations were combined with OSL ages to gain insight of the temporal framework of sediment deposition and shed light on the process of sediment storage. OSL and simple 10 Be exposure ages of terrace sediments give deposition ages between ~ 340 ka to ~ 50 ka, at which time the youngest alluvial terrace was incised. Deposition was interrupted twice, at ~ 300 ka and ~ 160 ka, when periods of rapid incision caused the abandonment of the active fluvial surface and the stabilization of a younger and lower fluvial surface. In the active drainage system, 10 Be concentrations suggest several possible quartz sources, of which the Lower Cretaceous sandstone bedrock exposed at the base of the cliff enclosing the Makhtesh is the most dominant. The results suggest that sediment eroding form these cliffs are conveyed through the active alluvial channels without significant sediment contribution from alluvial terraces or from eroded bedrock exposed within the Makhtesh. In contrast to our measurements in the active drainage system, 10 Be concentrations in alluvial terrace sediments record significant storage within the Makhtesh. We suggest that the geometry of the Makhtesh, mainly the disproportion between the size of the Makhtesh and its narrow outlet, leads to significant accumulation of sediment within the Makhtesh. Episodic breaching of the barrier is followed by rapid and short-lived incision into the stored sediment. The long residence time of sediment within the Makhtesh results in high measured 10 Be concentrations. At the end of each of these short incision episodes, when channels are already carved into the alluvial sediment and terraces are formed, the channels only convey sediment directly eroded from the bounding cliff of the Makhtesh; a situation presently observed.

We applied cosmogenic isotope burial dating, magnetostratigraphy, and grain-size distribution analysis to elucidate the history of the sedimentary sequence, composed of fine quartz sands and silts, of Wonderwerk Cave, located on the southern edge of the Kalahari Desert, South Africa. The source for the quartz sand is the Kalahari sand dunes, presently located ∼100 km to the north of the cave. Field observations and grain-size analysis suggest a sediment transport scenario that includes eolian transport of Kalahari sand, abraded to a size of 70–100 µm, to the Kuruman Hills, temporary storage on the hill slopes and valleys surrounding Wonderwerk Cave, and later transport and deposition inside the cave. Our results suggest simple burial ages for sediments from both the front and back of the cave that range between 2.63 ± 0.17 Ma and 1.56 ± 0.10 Ma following initial exposure of 310–620 k.y. However, 26 Al/ 10 Be ratios of 3.98 ± 0.24 and 4.08 ± 0.22 measured in a sand sample collected from the surface outside the cave may imply an initial burial signal equivalent to 0.78 ± 0.15 Ma, thus reducing the possible age range of the buried samples to between 1.85 ± 0.23 and 0.78 ± 0.18 Ma. The paleomagnetic results for the front of the cave gave a polarity sequence of N > R > N||N, where N indicates normal polarity, and R indicates reverse polarity. This sequence can be correlated with both the older and younger cosmogenic burial age ranges. The correlation suggests that in the cave front, cosmogenic burial ages and the acquisition of stable remanent magnetization were not significantly affected by chemical and physical processes and that postburial production of cosmogenic isotopes was insignificant. In contrast, at the back of the cave, the paleomagnetic polarity sequence of R > N cannot be correlated with the cosmogenic burial ages, since the temporal gap between the initial penetration of the sediment into the cave and the final acquisition of a stable remanent magnetization may have been long (∼10 5 yr), and the single polarity transition can be correlated to any reverse-normal transition that occurred during the Quaternary. This highlights the need for caution when cosmogenic burial ages and paleomagnetic sequences are compared. The buried sediments in Wonderwerk Cave show similar grain-size distributions to the fine sand sediment presently exposed at the surface in the vicinity of the cave. Furthermore, calculated preburial 10 Be concentrations for the buried sediment are similar to those measured in sediment outside the cave. These similarities suggest that the environmental conditions and rates of geomorphic processes that persisted during sand deposition in Wonderwerk Cave during the late Pliocene and early Pleistocene may have been similar to those currently experienced in the southern Kalahari, the Kuruman Hills, and the western Ghaap Plain. These conditions favor the transport of fine-grained quartz sand to the vicinity of the cave.

We applied cosmogenic 26 Al/ 10 Be burial dating to sedimentary deposits of the ancestral Colorado River. We compared cosmogenic burial ages of sediments to the age of an independently well-dated overlying basalt flow at one site, and also applied cosmogenic burial dating to sediments with less precise independent age constraints. All dated gravels yielded old ages that suggest several episodes of sediment burial over the past ∼5.3 m.y. Comparison of burial ages to the overlying 4.4 Ma basalt yielded good agreement and suggests that under the most favorable conditions, cosmogenic burial dating can extend back 4–5 m.y. In contrast, results from other sites with more broadly independent age constraints highlight the complexities inherent in burial dating; these complexities arise from unknown and complicated burial histories, insufficient shielding, postburial production of cosmogenic isotopes by muons, and unknown initial 26 Al/ 10 Be ratios. Nevertheless, and in spite of the large range of burial ages and large uncertainties, we identify samples that provide reasonable burial age constraints on the depositional history of sediment along the lower ancestral Colorado River. These samples suggest possible sediment deposition and burial at ca. 5.3, 4.7, and 3.6 Ma. Our calculated basinwide erosion rate for sediment transported by the modern Colorado River (∼187 mm k.y. −1 ) is higher than the modern erosion rates inferred from the historic sediment load (80–100 mm k.y. −1 ). In contrast, basinwide paleo-erosion rates calculated from Pliocene sediments are all under 40 mm k.y. −1 The comparatively lower denudation rates calculated for the Pliocene sediment samples are surprising given that the sampled time intervals include significant Pliocene aggradation and may include much incision of the Grand Canyon and its tributaries. This conflict may arise from extensive storage of sediment along the route of the Colorado River, slower paleobedrock erosion, or the inclusion of sediments that were derived preferentially from higher elevations in the watershed.

article i nfo 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 (b80 mm yr −1 ). No pedogenic indicators of past wetter environments such as buried calcic soil 10 Be exposure ages of the talus flatirons suggest that they were deposited during the middle Pleistocene; ~610 ka and ~170 ka 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 ~200 m Ma −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.

We present a framework for consistent incorporation of optically-stimulated luminescence dates with cosmogenic radionuclide concentrations measured in a single alluvial section, and apply it on two late Quaternary terraces in the Negev Desert, Israel, to derive constraints on their evolution. We solve an integrated, self-consistent and co-dependant set of equations to reproduce either dataset based on three model parameters of (i) uniform cosmogenic inheritance, (ii) constant terrace aggradation rate and (iii) subsequent exposure time. A subset of all possible parameter combinations, which approximates the measurements within the uncertainties of their best-fits, yields a better constraint of the alluvial history than that obtained by any of these dating proxies alone. The derived set of common solutions indicates similar paleo-inheritances of ∼1 × 10 5 10 Be atoms g −1 in both terraces; progressive deposition of the higher terrace (T2) began at ∼250 ka, lasted for a period of ∼80 ka, was abandoned at ∼170 ka and since that time has remained intact; the lower terrace (T1) was most likely deposited at ∼3 ka and rapidly abandoned by ∼2 ka. In an alternative interpretation for T2, which treats the two geochronometers separately, this terrace might have experienced discrete events of aggradation at (216 ± 13) ka and deep truncation at 118 − 29 + 42 ka, significantly separated in time. In the currently active channel of the Neqarot canyon, contemporary stripping of the lowest terrace located along the stream is suggested by decreasing values of 10 Be downstream along the river channel.

We present 10Be exposure ages from moraines in the Delta River Valley, a reference locality for Pleistocene glaciation in the northern Alaska Range. The ages are from material deposited during the Delta and Donnelly glaciations, which have been correlated with MIS 6 and 2, respectively. 10Be chronology indicates that at least part of the Delta moraine stabilized during MIS 4/3, and that the Donnelly moraine stabilized ∼ 17 ka. These ages correlate with other dates from the Alaska Range and other regions in Alaska, suggesting synchronicity across Beringia during pulses of late Pleistocene glaciation. Several sample types were collected: boulders, single clasts, and gravel samples (amalgamated small clasts) from around boulders as well as from surfaces devoid of boulders. Comparing 10Be ages of these sample types reveals the influence of pre/post-depositional processes, including boulder erosion, boulder exhumation, and moraine surface lowering. These processes occur continuously but seem to accelerate during and immediately after successive glacial episodes. The result is a multi-peak age distribution indicating that once a moraine persists through subsequent glaciations the chronological significance of cosmogenic ages derived from samples collected on that moraine diminishes significantly. The absence of Holocene ages implies relatively minor exhumation and/or weathering since 12 ka.

The Atacama Desert is one of the driest places on Earth. Multiple lines of evidence show that the Atacama has been hyperarid since at least the late Miocene, among these are cosmic-ray exposure ages indicating that individual clasts on some surfaces have been preserved for > 9 Ma and possibly since the Oligocene. Although these remarkably old ages indicate slow landscape evolution, it is not clear whether this pace is characteristic of the entire Atacama, or only of specific regions, landforms, or landscape elements. To address this question, we measured cosmogenic 10Be, 26Al, and 21Ne from a wide variety of landscape elements in a transect across the Central Atacama, where modern precipitation is at an extreme minimum, but where the concentration of cosmogenic nuclides in stable landscape elements has not previously been recorded. We find that the hyperarid core of the Central Atacama has substantially slower erosion rates than its eastern and western margins; however, even the driest part of this transect has erosion rates comparable to those of other deserts, ranging from 0.2–0.4 m/Ma. The most stable landscape elements are boulder fields, with exposure ages of 1.5–2.6 Ma. The vast majority of samples in the Central Atacama Desert, however, have cosmogenic nuclide concentrations corresponding to ages 5 Ma documented elsewhere in the Atacama were not found in our area and appear to be limited to exceptionally stable boulders or cobbles in either the northern or southern extremes of the Atacama Desert. We suggest that the Central Atacama has been subject to episodic Pliocene and Pleistocene rainfall and geomorphic activity, perhaps due to intrusion of Pacific moisture.

Early to late Pleistocene 10 Be exposure ages of abandoned surfaces in the Negev desert reveal the regional drainage evolution history and its relationship with the subsidence of the western margin of the Dead Sea Rift. The dated desert paved surfaces have developed over originally westward-flowing rivers, which were abandoned by early Pleistocene and whose relicts are now progressively tilted towards the rift axis. The slow and non-destructive subsidence coupled with extreme hyperaridity enabled the preservation of these ancient surfaces along some of the main water divides in the Negev, nearly irrespective of their distance from the rift axis. Constraints on the tilting history are obtained from analyzing the spatial pattern of the exposure ages, suggesting subsidence rates as low as 120–300 m Ma –1 in the southern Arava Valley since the late Pliocene. It is shown that the transition from the Pliocene to current drainage pattern occurred over a short period during the early Pleistocene, and that the governing fluvial response that followed the delineation of current basins is represented by a continuous spectrum of ages of inset terraces.

Over the last eight years, we have developed several paleoenvironmental records from a broad geographic region spanning the Altiplano in Bolivia (18°S–22°S) and continuing south along the western Andean flank to ca. 26°S. These records include: cosmogenic nuclide concentrations in surface deposits, dated nitrate paleosoils, lake levels, groundwater levels from wetland deposits, and plant macrofossils from urine-encrusted rodent middens. Arid environments are often uniquely sensitive to climate perturbations, and there is evidence of significant changes in precipitation on the western flank of the central Andes and the adjacent Altiplano. In contrast, the Atacama Desert of northern Chile is hyperarid over many millions of years. This uniquely prolonged arid climate requires the isolation of the Atacama from the Amazon Basin, a situation that has existed for more than 10 million years and that resulted from the uplift of the Andes and/or formation of the Altiplano plateau. New evidence from multiple terrestrial cosmogenic nuclides, however, suggests that overall aridity is occasionally punctuated by rare rainfall events that likely originate from the Pacific. East of the hyperarid zone, climate history from multiple proxies reveals alternating wet and dry intervals where changes in precipitation originating from the Atlantic may exceed 50%. An analysis of Pleistocene climate records across the region allows reconstruction of the spatial and temporal components of climate change. These Pleistocene wet events span the modern transition between two modes of interannual precipitation variability, and regional climate history for the Central Andean Pluvial Event (CAPE; ca. 18–8 ka) points toward similar drivers of modern interannual and past millennial-scale climate variability. The north-northeast mode of climate variability is linked to El Nino–Southern Oscillation (ENSO) variability, and the southeast mode is linked to aridity in the Chaco region of Argentina.

The ‘African Cultural Heritage and Landscape Database’ project, initiated and directed by the senior author and administered by Aluka (www.aluka.org), is aimed at the creation of a digital library of spatial and non-spatial materials relating to cultural heritage sites in Africa. The archaeological site of Wonderwerk Cave (South Africa) is one of the 19 sites documented to date using laser scanning, conventional survey, digital photogrammetry and 3D modelling. To date, it is one of the few archaeological caves worldwide to be fully scanned. This paper explores the different uses to which the spatial data derived from this cave have been, or will be, put – for historical and educational purposes, scientific research and site conservation and development.

This paper examines the millennial-scale evolution of the longitude profile of Nahal (Wadi) Zin in the Dead Sea basin in the northern Arava valley, Israel. Nahal Zin has incised ~ 50 m into relatively soft late Pleistocene Lake Lisan sediments. Incision was forced by the regressive (> 10 km) lake level fall of a total of > 200 m of Lake Lisan from its highest stand at ~ 25 ka and exposure of the lake-floor sediments to fluvial and coastal processes. Alluvial cut terraces of the incising channel are well preserved along the 17.5 km of the lowermost reach of Nahal Zin. At its outlet into the Dead Sea basin, Nahal Zin deposited a Holocene alluvial fan at the base of a 10–80 m high escarpment in unconsolidated sediments. The escarpment is associated with the Amazyahu fault, which forms the southern structural boundary of the present Dead Sea basin. Geomorphic mapping, optically stimulated luminescence (OSL) ages, and soil stratigraphy allowed correlation of terrace remnants and reconstruction of several past longitudinal profiles of Nahal Zin and its incision history. Together with the published lake level chronology, these data provide an opportunity to examine stream incision related to base level lowering at a millennial scale. OSL ages of the terraces fit relatively well with the established lake level chronology and follow its regression and fall. For a few thousands of years the longitudinal profile response to the lake level fall was downstream lengthening onto the exposed former lake bed. Most of the incision (~ 40 m) occurred later, when the lake level reached the top of the Amazyahu fault escarpment and continued to drop. The incision was a relatively short episode at about 17 ka and cut through this escarpment almost to its base. The fast incision, its timing, and the profiles of the incising channels indicate that the escarpment was an underwater feature and was not formed after the lake retreated. This fairly simple scenario of regressive lake level fall and knickpoint exposure and incision is modeled here using a one-dimensional numerical incision model based on a linear diffusion equation. The calculated diffusion coefficient fits earlier results and data obtained from other streams in the area and confirms the upscaling of this simple model to the millennial scale.

All exposed rocks on Earth’s surface experience erosion; the fastest rates are documented in rapidly uplifted monsoonal mountain ranges, and the slowest occur in extreme cold or warm deserts—millennial submeterscale erosion may be approached only in the latter. The oldest previously reported exposure ages are from boulders and clasts of resistant lithologies lying at the surface, and the slowest reported erosion rates are derived from bedrock outcrops or boulders that erode more slowly than their surroundings; thus, these oldest reported ages and slowest erosion rates relate to outstanding features in the landscape, while the surrounding landscape may erode faster and be younger. We present erosion rate and exposure age data from the Paran Plains, a typical environment in the Near East where vast abandoned alluvial surfaces (10 2 –10 4 km 2 ) are covered by well-developed desert pavements. These surfaces may experience erosion rates that are slower than those documented elsewhere on our planet and can retain their original geometry for more than 2 m.y. Major factors that reduce erosion converge in these regions: extreme hyperaridity, tectonic stability, fl at and horizontal surfaces (i.e., no relief), and effective surface armoring by a clast mosaic of highly resistant lithology. The 10 Be concentrations in amalgamated desert pavement chert clasts collected from abandoned alluvial surfaces in the southern Negev, Israel (representing the Sahara-Arabia Deserts), indicate simple exposure ages of 1.5–1.8 Ma or correspond to maximum erosion rates of 0.25–0.3 m m.y. –1 . The 36

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.

In this study, we explored the spatial and temporal relations between boulders and their original in-situ locations on sandstone bedrock cliffs. Thiswas accomplished bycombining field observations withdating methods using cosmogenicisotopes ( 10 Be and 14 C) 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 mk y � 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 10 Be 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

Analysis of 10Be and 26Al in bedrock (n=10), colluvium (n=5 including grain size splits), and alluvial sediments (n=59 including grain size splits), coupled with field observations and GIS analysis, suggest that erosion rates in the Great Smoky Mountains are controlled by subsurface bedrock erosion and diffusive slope processes. The results indicate rapid alluvial transport, minimal alluvial storage, and suggest that most of the cosmogenic nuclide inventory in sediments is accumulated while they are eroding from bedrock and traveling down hill slopes. Spatially homogeneous erosion rates of 25 - 30 mm Ky−1 are calculated throughout the Great Smoky Mountains using measured concentrations of cosmogenic 10Be and 26Al in quartz separated from alluvial sediment. 10Be and 26Al concentrations in sediments collected from headwater tributaries that have no upstream samples (n=18) are consistent with an average erosion rate of 28 ± 8 mm Ky−1, similar to that of the outlet rivers (n=16, 24 ± 6 mm Ky−1), which carry most of the sediment out of the mountain range. Grain-size-specific analysis of 6 alluvial sediment samples shows higher nuclide concentrations in smaller grain sizes than in larger ones. The difference in concentrations arises from the large elevation distribution of the source of the smaller grains compared with the narrow and relatively low source elevation of the large grains. Large sandstone clasts disaggregate into sand-size grains rapidly during weathering and downslope transport; thus, only clasts from the lower parts of slopes reach the streams. 26Al/10Be ratios do not suggest significant burial periods for our samples. However, alluvial samples have lower 26Al/10Be ratios than bedrock and colluvial samples, a trend consistent with a longer integrated cosmic ray exposure history that includes periods of burial during down-slope transport. The results confirm some of the basic ideas embedded in Davis’ geographic cycle model, such as the reduction of relief through slope processes, and of Hack’s dynamic equilibrium model such as the similarity of erosion rates across different lithologies. Comparing cosmogenic nuclide data with other measured and calculated erosion rates for the Appalachians, we conclude that rates of erosion, integrated over varying time periods from decades to a hundred million years are similar, the result of equilibrium between erosion and isostatic uplift in the southern Appalachian Mountains.

The Lower Galilee and the Yizre’el Valley, northern Israel, are an extensional domain that has been developing since the Miocene, prior and contemporaneously to the development of the Dead Sea Fault (DSF). It is a fan-shaped region bounded in the east by the N–S trending main trace of the DSF, in the north by the Bet-Kerem Fault system, and in the south by the NW– SE trending Carmel Fault. The study area is characterized by high relief topography that follows fault-bounded blocks and flexures at a wavelength of tens of km. A synthesis of the morphologic–structural relations across the entire Galilee region suggests the following characteristics: (1) Blocks within the Lower Galilee tilt toward both the southern and northern boundaries, forming two asymmetrical half-graben structures, opposite facing, and oblique to one another. (2) The Lower Galilee’s neighboring blocks, which are the Upper Galilee in the north and the Carmel block in the southwest, are topographically and structurally uplifted and tilted away from the Lower Galilee. (3) The southern half-graben, along the Carmel Fault, is topographically and structurally lower than the northern one. Combining structural and geological data with topographic analysis enables us to distinguish several stages of structural and morphological development in the region. Using a semi-quantitative evolutionary model, we explain the morpho-structural evolution of the region. Our results indicate that the Galilee developed as a set of two isostatically supported opposite facing half-grabens under varying stress fields. The southern one had started developing as early as the early Miocene prior to the formation of the DSF. The northern and younger one has been developing since the middle Pliocene as part of the extension process in the Galilee. Elevation differences between the two half-grabens and their bounding blocks are explained by differences in isostatic subsidence due to sedimentary loading and uplift of the northern half-graben due to differential influences of the regional folding. D 2003 Elsevier B.V. All rights reserved.

Activities of 26 Al and 10 Be in five chert clasts sampled from two beach ridges of late Pleistocene Lake Lisan, precursor of the Dead Sea in southern Israel, indicate low rates of chert bedrock erosion and complex exposure, burial, and by inference, transport histories. The chert clasts were derived from the Senonian Mishash Formation, a chert-bearing chalk, which is widely exposed in the Nahal Zin drainage basin, the drainage system that supplied most of the material to the beach ridges. Simple exposure ages, assuming only exposure at the beach ridge sampling sites, range from 35 to 354 ky; using the ratio 26 Al/ 10 Be, total clast histories range from 0Ð46 to 4Ð3 My, unrelated to the clasts’ current position and exposure period on the late Pleistocene beach ridges, 160–177 m below sea level. Optically stimulated luminescence dating of fine sediments from the same and nearby beach ridges yielded ages of 20Ð0 s 1Ð4 ka and 36Ð1 s 3Ð3 ka. These ages are supported by the degree of soil development on the beach ridges and correspond well with previously determined ages of Lake Lisan, which suggest that the lake reached its highest stand around 27 000 cal. years BP. If the clasts were exposed only once and than buried beyond the range of significant cosmogenic nuclide production, then the minimum initial exposure and the total burial times before delivery to the beach ridge are in the ranges 50–1300 ky and 390–3130 ky respectively. Alternatively, the initial cosmogenic dosing could have occurred during steady erosion of the source bedrock. Back calculating such rates of rock erosion suggests values between 0Ð4 and 12 m My � 1 .T he relatively long burial periods indicate extended sediment storage as colluvium on slopes and/or as alluvial deposits in river terraces. Some clasts may have been stored for long periods in abandoned Pliocene and early Pleistocene routes of Nahal Zin to the Mediterranean before being transported again back into the Nahal Zin drainage system and washed on to the shores of Lake Lisan during the late Pleistocene. Copyright  2003 John Wiley & Sons, Ltd.

Mesas are ubiquitous landforms in arid and semiarid regions and are often characterized by horizontal stratified erodible rocks capped by more resistant strata. The accepted conceptual model for mesa evolution and degradation considers reduction in the width of the mesa flat-top plateau due to cliff retreat but ignores possible denudation of the mesa flat-top and the rates and mechanism of erosion. In this study we examine mesas in the northeastern hyperarid Negev Desert where they appear in various sizes and morphologies and represent different stages of mesa evolution. The variety of mesas within a single climatic zone allows examination of the process of mesa evolution through time. Two of the four sites examined are characterized by a relatively wide (200–230 m) flat-top and a thick caprock whereas the other two are characterized by a much narrower remnant flat-top (several meters) and thinner caprock. We use the concentration of the cosmogenic nuclide 10Be for: (a) determining the chronology of the various geomorphic features associated with the mesa; and (b) understanding geomorphic processes forming the mesa. The 10Be data, combined with field observations, suggest a correlation between the width of flat-top mesa and the denudation and cliff retreat rates. Our results demonstrate that: (a) cliff retreat rates decrease with decreasing width of the flat-top mesa; (b) vertical denudation rates increase with decreasing width of the flat-top mesa below a critical value (~60 m, for the Negev Desert); (c) the reduction in the width of the flat-top mesa is driven mainly by cliff retreat accompanied by extremely slow vertical denudation rate which can persist for a very long time (>106 Ma); and (d) when the width of the mesa decreases below a certain threshold, its rate of denudation increases dramatically and mesa degradation is completed in a short time. Copyright © 2014 John Wiley & Sons, Ltd.

Rockfall ages in tectonically active regions provide information regarding frequency and magnitude of earthquakes. In the hyper-arid environment of the Dead Sea fault (DSF), southern Israel, rockfalls are most probably triggered by earthquakes. We dated rockfalls along the western margin of the DSF using terrestrial cosmogenic nuclides (TCN). At each rockfall site, samples were collected from simultaneously exposed conjugate boulders and cliff surfaces. Such conjugate samples initially had identical pre-fall (“inherited”) TCN concentrations. After boulder detachment, these surfaces were dosed by different production rates due to differences in post-fall shielding and geometry. However, in our study area, pre-rockfall inheritance and post-rockfall production rates of TCN cannot be evaluated. Therefore, we developed a numerical approach and demonstrated a way to overcome the above-mentioned problems. This approach can be applied in other settings where rockfalls cannot be dated by simple exposure dating. Results suggest rockfall ages between 3.6 ± 0.8 and 4.7 ± 0.7 ka. OSL ages of sediment accumulated behind the boulders range between 0.6 ± 0.1 and 3.4 ± 1.4 ka and support the TCN results. Our ages agree with dated earthquakes determined in paleoseismic studies along the entire length of the DSF and support the observation of intensive earthquake activity around 4–5 ka.

The Dead Sea fault (DSF) is one of the most active plate boundaries in the world. Understanding the Quaternary history and sediments of the DSF requires investigation into the Neogene development of this plate boundary. DSF lateral motion preceded significant extension and rift morphology by ~10 Ma. Sediments of the Sedom Formation, dated here between 5.0 ± 0.5 Ma and 6.2−2.1+inf Ma, yielded extremely low 10Be concentrations and 26Al is absent. These reflect the antiquity of the sediments, deposited in the Sedom Lagoon, which evolved in a subdued landscape and was connected to the Mediterranean Sea. The base of the overlying Amora Formation, deposited in the terminal Amora Lake which developed under increasing relief that promoted escarpment incision, was dated at 3.3−0.8+0.9 Ma. Burial ages of fluvial sediments within caves (3.4 ± 0.2 Ma and 3.6 ± 0.4 Ma) represent the timing of initial incision. Initial DSF topography coincides with the earliest Red Sea MORB's and the East Anatolian fault initiation. These suggest a change in the relative Arabian–African plate motion. This change introduced the rifting component to the DSF followed by a significant subsidence, margin uplift, and a reorganization of relief and drainage pattern in the region resulting in the topographic framework observed today.

The abundance of cosmogenic 36 Cl, measured in 41 limestone samples from a 9 m high bedrock fault scarp, allows us to construct the 14 kyr fault displacement history of the Nahef East normal fault, northern Israel (300 m above sea level, N33° latitude). The Nahef East fault is one of a series of fault scarps located along the 700 m high Zurim Escarpment, a major geomorphic feature. Samples at the top of the scarp have the highest nuclide concentrations (79 x 10 4 atoms (g rock) -1 ); samples at the base have the lowest (11 x 10 4 atoms (g rock) -1 ), Using chemical data from the samples, Nahef East fault scarp geometry, and surface and subsurface production rates for the 36 Cl-producing reactions, we have constructed a numerical model that calculates 36 Cl accumulation on a scarp through time, given a series of unique displacement scenarios. The resulting model 36 Cl concentrations are compared to those measured in the scarp samples. Faulting histories that result in a good match between measured and modeled 36 Cl abundances show three distinct periods of fault activity during the past 14 kyr with over 6 vertical meters of motion occurring during a 3 kyr time period in the middle Holocene. Smaller amounts of displacement occurred before and after the period of most rapid motion. The episodic behavior of the Nahef East fault indicates that the average displacement rate of this fault system has varied through time.

We used topographic and structural data and very limited age control to perform quantitative morphometric analyses and to determine relative ages of escarpments bounded by late Cenozoic normal faults in the Galilee, Israel. The Galilee is an extensional zone composed of a series of uplifted and tilted blocks forming large escarpments built mainly of carbonate rocks. Two parameters used to discriminate tectonic stages are the ratio between the height of the escarpment and the total stratigraphic displacement ( L ) and the degree of concavity of escarpment slopes relative to a reference slope. The only dated reference slope is Mount Tur9an, ∼300 m high and formed by the Tur9an fault system, which has a total stratigraphic displacement of 625 m. A basalt flow that delimits the age of the Tur9an escarpment is dated to 4.23 ± 0.23 Ma and displaced 300 m, which is identical to the present-day topographic expression of this escarpment. The L value for this escarpment is ∼0.5. The Tur9an fault system was active prior to 4.23 Ma at slow uplift rates that enabled erosion to maintain the gentle slope over which the basalt flowed. Increased offset rates following the basalt extrusion led to the formation of the escarpment. The preservation of the basalt at the top of the escarpment indicates that erosional lowering of the upper surface of the Tur9an block has been minor since its formation. The L values indicate two stages of uplift; an early stage during which offset rates were probably low enough that they did not form topography, and a later stage that formed topography, which is preserved. The timing of the change in displacement rates from a slow continuous stage to a fast, topography-forming stage was determined by comparing the shape of the dated slope of Tur9an to that of other slopes. We conclude the following: (1) generally, the topographic profiles of different parts of each individual escarpment have similar shapes indicating similar ages; (2) escarpments having slopes that are more concave or convex than the reference Tur9an escarpment are older or younger than 4 Ma, respectively; and (3) the Galilee escarpments did not form simultaneously. A few escarpments were already major morphologic features by the early to middle Pliocene, whereas the rest formed during the late Pliocene. Morphometric analysis is a useful method for studying the geologic history of a landscape controlled by normal fault uplift and characterized by the absence of sediment deposition and where carbonate dissolution is the main erosional process. This and similar approaches can be used to discriminate tectonic stages and understand the relationship between tectonic activity and surface processes in other extensional regions.

The arching of the Galilee, northern Israel, is associated with sediment loading in the Dead Sea Transform and Rift. During the Pleistocene, the arching caused the formation of the main North–South water divide in the region and the reversal of stream flow direction. A reconstruction of a main paleochannel which drained large areas in the eastern Galilee to the Mediterranean enabled the determination of age and amplitude of the arching. This reconstruction is based on topographic analysis of thirteen sites containing fluvial remnants in the Beit-Hakerem Valley. We demonstrate that the widespread normal faulting cannot explain the present-day drainage pattern. Dating of basalt clasts from ancient alluvial remnants along the Beit-Hakerem Valley provides a maximum age limit of 1.8 Ma to the paleochannel. The Pleistocene tectonism arched the Galilee by 200 m over a wavelength of 40–60 km. A comparison between arched and unarched segments of the rift's margins indicates that fluvial and slope processes on the rift escarpment cannot explain the location and shape of the main water divide. In the Galilee, tectonism is the only factor that controls the formation, location and shape of the main water divide.