Holocene Alluvial Fan Research Articles

Evolution of the Holocene alluvial fan of the River Stryi in the foreland of the Eastern Carpathians (Western Ukraine)

The research reconstructs the development of the alluvial fan of the River Stryi in the Holocene and dates the phases of increased river activity and their correlation with other valleys in the upper Dniester and Vistula river basins. The age of the palaeochannels and the stratigraphy of alluvial fills are based on radiocarbon dating supported by the results of palynological analyses. The oldest (fossil) palaeochannel of the Stryi was dated to the Younger Dryas. The large-radius meander was abandoned at the end of the Boreal Phase during the period of flood intensification at about 8700 BP. The uneven top of the gravels (cut by palaeotroughs of a depth ranging from 2 to 4 m) indicates that during periods of increased discharges (Younger Dryas, end of the Boreal Phase, late Atlantic and beginning of the Subboreal) the troughs were cut and filled with channel sands. From the beginning of the Subboreal Phase (5400-5300 BP), aggradation of the valley bottom has been predominant, which is manifested not only by the overbuilding of the floodplain but also by the gradual elevation of the channel. The accumulation of sandy-silty overbank sediments dated to about 8300, 5400 and 2800 BP correlates well with the beginning of humid phases and floods in the upper Vistula and upper Dniester basins as well as floods recorded in lakes in the northern foreland of the Alps.

Towards Better Visualisation of Alpine Quaternary Landform Features on High-Resolution Digital Elevation Models

Alpine topography is formed by a complex series of geomorphological processes that result in a vast number of different landforms. The youngest and most diverse landforms are various Quaternary sedimentary bodies, each characterised by its unique landform features. The formation of Quaternary sedimentary bodies and their features derive from the dominant building sedimentary processes. In recent years, studies of Quaternary sedimentary bodies and processes have been greatly aided by the use of digital elevation models (DEMs) derived by airborne laser scanning (ALS). High-resolution DEMs allow detailed mapping of sedimentary bodies, detection of surface changes, and recognition of the building sedimentary processes. DEMs are often displayed as hillshaded reliefs, the most common visualisation technique, which suffers from the limitation of a single illumination source. As a result, features can be barely visible or even invisible to the viewer if they are parallel to the light source or hidden in the shadow. These limitations become challenging when representing landforms and subtle landscape features in a diverse alpine topography. In this study, we focus on eleven visualisations of Quaternary sedimentary bodies and their sedimentary and morphological features on a 0.5 m resolution DEM. We qualitatively compare analytical hillshading with a set of visualisation techniques contained in the Raster Visualisation Toolbox software, primarily hillshading from multiple directions RGB, 8-bit sky view factor and 8-bit slope. The aim is to determine which visualisation technique is best suited for visual recognition of sedimentary bodies and sedimentation processes in complex alpine landscapes. Detailed visual examination of previously documented Pleistocene moraine and lacustrine deposits, Holocene alluvial fans, scree deposits, debris flow and fluvial deposits on the created visualisations revealed several small-scale morphological and sedimentary features that were previously difficult or impossible to detect on analytical hillshading and aerial photographs. Hillshading from multiple directions resulted in a visualisation that could be universally applied across the mountainous and hilly terrains. In contrast, 8-bit sky view factor and 8-bit slope visualisations created better visibility and facilitated interpretation of subtle and small-scale (less than ten metres) sedimentary and morphological features.

Holocene alluvial fan evolution, Schmidt‐hammer exposure‐age dating and paraglacial debris floods in the SE Jostedalsbreen region, southern Norway

The evolution of several sub‐alpine alluvial fans SE of the Jostedalsbreen ice cap was investigated based on their geomorphology and Schmidt‐hammer exposure‐age dating (SHD) applied to 47 boulder deposits on the fan surfaces. A debris‐flood rather than debrisflow or water‐flow origin for the deposits was inferred from their morphology, consisting of low ridges with terminal splays up to 100 m wide without lateral levees. This was supported by fan, catchment, and boulder characteristics. SHD ages ranged from 9480±765 to 1955±810 years. The greatest number of boulder deposits, peak debris‐flood activity and maximum fan aggradation occurred between ̃9.0 and 8.0 ka, following regional deglaciation at ̃9.7 ka. The high debris concentrations necessary for debris floods were attributed to paraglacial processes enhanced by unstable till deposits on steep slopes within the catchments. From ̃8.0 ka, fan aggradation became progressively less as the catchment sediment sources tended towards exhaustion, precipitation decreased during the Holocene Thermal Maximum, and tree cover increased. After ̃4.0 ka, some areas of fan surfaces stabilized, while Late‐Holocene climatic deterioration led to renewed fan aggradation in response to the neoglacial growth of glaciers, culminating in the Little Ice Age. These changes are generalized within a conceptual model of alluvial fan evolution in this recently‐deglaciated mountain region and in glacierized catchments. This study highlights the potential importance of debris floods, of which relatively little is known, especially in the context of alluvial fan evolution.

Late Quaternary landscape evolution and bioclimatic change in the central Great Plains, USA

AbstractA systematic study of floodplains, terraces, and alluvial fans in the Republican River valley of south-central Nebraska provided a well-dated, detailed reconstruction of late Quaternary landscape evolution and resolved outstanding issues related to previously proposed Holocene terrace sequences. Stable carbon isotope (δ13C) values determined on soil organic matter from buried soils in alluvial landforms were used to reconstruct the structure of vegetation communities and provided a means to investigate the relationships between bioclimatic change and fluvial activity for the period of record. Our study serves as a model for geomorphological and geoarcheological investigations in stream valleys throughout the central Great Plains and wherever loess-derived late Quaternary alluvial fans occur, in particular.Holocene alluvial landforms in the river valley include a broad floodplain complex (T-0a, T-0b, and T-0c), a single alluvial terrace (T-1), and alluvial fans that mostly grade to the T-1 (AF-1) and T-0c (AF-0c) surfaces. Remnants of a late Pleistocene terrace (T-2), mantled by Holocene (Bignell) loess, are also preserved, and some Holocene alluvial fans (AF-2) grade to T-2 surfaces.Radiocarbon ages suggest that the T-1 fill and AF-1 fans aggraded between ca. 9000–1000 yr B.P. Hence, nearly all of the Holocene alluvium in the river valley is stored in these landforms. Sedimentation, however, was interrupted by several periods of landscape stability and soil formation. Radiocarbon ages from the upper A horizons of buried soils in the T-1 and AF-1 fills, indicating approximate burial ages, cluster at ca. 6500, 4500, 3500, and 1000 yr B.P. Also, based on the radiocarbon ages, the T-0c fill and AF-0c fans were aggrading between ca. 2000–900 yr B.P. Given that the T-0c fill and upper parts of the T-1 fill were both aggrading after ca. 2000 yr B.P., we suggest that the T-1 surface was abandoned between ca. 4500–3500 yr B.P., but subsequent aggradation of both the T-1 and T-0c fills occurred due to large-magnitude flood events during the late Holocene.The δ13C data indicate a shift from ∼40% C4 biomass at ca. 6000 to ∼85% at ca. 4500 yr B.P. We propose a scenario where (1) a reduction in C3 vegetation after 6000 yr B.P. destabilized the uplands, resulting in an increase in sediment supply and aggradation of the T-1 fill and AF-1 fans, and (2) the establishment of C4 vegetation by ca. 4500 yr B.P. stabilized the uplands, resulting in a reduction in sediment supply and subsequent incision and abandonment of the T-1 and most AF-1 surfaces. The proposed timing and nature of landscape and bioclimatic change are consistent with regional records from the central Great Plains.

Coupled stalagmite – Alluvial fan response to the 8.2 ka event and early Holocene palaeoclimate change in Greece

We explore the expression of early Holocene climatic change in the terrestrial Mediterranean of southern Greece. A regional palaeoclimate record from stable isotope and trace element geochemical proxies in an early Holocene (~12.4 ka to 6.7 ka) stalagmite is compared to the timing of palaeosol (entisol) development on an early Holocene alluvial fan located <100 km from the stalagmite site. Radiocarbon dated entisol development records fan abandonment surfaces, which can be coupled to the stalagmite climate signal. Variations in δ13C best record the main elements of palaeoclimatic change, more negative values indicating soil carbon input to karst groundwater under wetter conditions. The wettest conditions begin around 10.3 ka, coincident with the start of sapropel 1 deposition in the eastern Mediterranean. The widely documented northern hemisphere ‘8.2 ka event’ of cooler and drier conditions has a muted δ18O climatic signal in common with other stalagmite climate records from the wider Mediterranean. However, less negative δ13C values do record a period of episodic dryness between ~8.8 and ending at 8.2 ka. Wetter conditions re-established after 8.1 ka to the end of the record. The oldest alluvial fan entisols were developing by ~9.5 ka, and a prominent rubified entisol developed ~8.3 to 8.4 ka, indicating pedogenesis within dating error of the 8.2 ka event. The speleothem record of episodic dryness between ~8.8 and 8.2 ka, combined with other regional proxies, is consistent with the notion that precipitation patterns in Greece may have changed from predominantly winter frontal to summer convective during this period. Palaeosol formation on the alluvial fan may have been an allocyclic response to this change. It is plausible that fan-channel incision, driven by temporary development of a ‘flashier’ summer rainfall regime, isolated large areas of the fan surface allowing onset of prolonged pedogenesis there.

Geomorphological and cryostratigraphical analyses of the Zackenberg Valley, NE Greenland and significance of Holocene alluvial fans

In High Arctic northern Greenland, future responses to climatic changes are poorly understood on a landscape scale. Here, we present a study of the geomorphology and cryostratigraphy in the Zackenberg Valley in NE Greenland (74°N) containing a geomorphological map and a simplified geocryological map, combined with analyses of 13 permafrost cores and two exposures. Cores from a solifluction sheet, alluvial fans, and an emerged delta were studied with regards to cryostructures, ice and total carbon contents, grain size distribution, and pore water electrical conductivity; and the samples were AMS 14C dated. The near-surface permafrost on slopes and alluvial fans is ice rich, as opposed to the ice-poor epigenetic permafrost in the emerged delta. Ground ice and carbon distribution are closely linked to sediment transport processes, which largely depend on lithology and topography. Holocene alluvial fans on the lowermost hillslopes, covering 12% of the study area, represent paleoenvironmental archives. During the contrasting climates of the Holocene, the alluvial fans continued to aggrade – through the warmer early Holocene Optimum, the colder late Holocene, and the following climate warming – and by 0.45mma−1, on average. This is caused by three factors: sedimentation, ground ice aggradation, and vegetation growth and is reflected by AMS 14C dating and continuously alternating cryostructures. Highly variable sedimentation rates in space and time at the alluvial fans have been detected. This is also reflected by alternating lenticular and microlenticular cryostructures indicating syngenetic permafrost aggradation during sedimentation with suspended and organic-matrix cryostructures indicating quasi-syngenetic permafrost aggradation in response to vegetation growth in periods with reduced or no sedimentation. Over time, this causes organic matter to become buried, indicating that alluvial fans represent effective carbon sinks that have previously been overlooked.

Late Quaternary Activity of the Huashan Piedmont Fault and Associated Hazards in the Southeastern Weihe Graben, Central China

The Weihe Graben is not only an important Cenozoic fault basin in China but also a significant active seismic zone. The Huashan piedmont fault is an important active fault on the southeast side of the Weihe Graben and has been highly active since the Cenozoic. The well–known Great Huaxian County Earthquake of 1556 occurred on the Huashan piedmont fault. This earthquake, which claimed the lives of approximately 830000 people, is one of the few large earthquakes known to have occurred on a high–angle normal fault. The Huashan piedmont fault is a typical active normal fault that can be used to study tectonic activity and the associated hazards. In this study, the types and characteristics of late Quaternary deformation along this fault are discussed from geological investigations, historical research and comprehensive analysis. On the basis of its characteristics and activity, the fault can be divided into three sections, namely eastern, central and western. The eastern and western sections display normal slip. Intense deformation has occurred along the two sections during the Quaternary; however, no deformation has occurred during the Holocene. The central section has experienced significant high–angle normal fault activity during the Quaternary, including the Holocene. Holocene alluvial fans and loess cut by the fault have been identified at the mouths of many stream valleys of the Huashan Mountains along the central section of the Huashan piedmont fault zone. Of the three sections of the Huashan piedmont fault, the central section is the most active and was very active during the late Quaternary. The rate of normal dip–slip was 1.67–2.71±0.11 mm/a in the Holocene and 0.61±0.15 mm/a during the Mid–Late Pleistocene. As is typical of normal faults, the late Quaternary activity of the Huashan piedmont fault has produced a set of disasters, which include frequent earthquakes, collapses, landslides, mudslides and ground fissures. Ground fissures mainly occur on the hanging–wall of the Huashan piedmont fault, with landslides, collapses and mudslides occurring on the footwall.

Kinematics of late Quaternary slip along the Yabrai fault: Implications for Cenozoic tectonics across the Gobi Alashan block, China

The Yabrai range-front fault accommodates deformation within the middle Gobi Alashan block between the Tibetan Plateau and the Ordos block. As such, it provides the opportunity to examine the transition between contractional deformation associated with the growth of the Tibetan Plateau and extensional deformation across North China. Geomorphic mapping of the active fault trace and trench investigations reveal that the Yabrai range-front fault is composed of three segments of varying fault strike, but for which the sense of motion, scarp height, and slip history appear to be kinematically compatible along the fault. Displaced Holocene and late Pleistocene alluvial deposits indicate that the southwestern segment is characterized by oblique-normal displacement with a minor sinistral component, whereas the middle segment appears to exhibit nearly dip-slip normal displacement. In contrast, slip along the northeastern segment appears to be primarily sinistral strike-slip with a minor reverse component. Geomorphically fresh fault scarps are developed within late Pleistocene–Holocene alluvial fans and terraces along the southwestern and northeastern segments, whereas the middle segment of the fault defines the bedrock-alluvial contact along the range front. The 10Be exposure ages of displaced alluvial fans along the southwestern segment yield a throw rate of ∼0.1 mm/yr over late Pleistocene time. Lateral slip rates along the northeastern fault segment range between 0.23 ± 0.02 and 0.78 ± 0.12 mm/yr. Regionally, the orientation and sense of motion along the Yabrai range-front fault are consistent with NE-SW shortening, and we suggest that recent activity along this fault system reflects incipient deformation of the foreland at the northeastern margin of the Tibetan Plateau.

Late Quaternary Geomorphology of the Tonami Plain and Activity of the Tonami-Heiya Fault Zone, Toyama Prefecture, Central Japan

The Holocene alluvial fans and flood plains formed by the Sho and Oyabe Rivers spread out in the Tonami plain from the central through the northern parts in the Toyama Prefecture, central Japan. Along the foot of the surrounding mountains and hills, higher, middle and lower terraces of late Pleistocene-Holocene in age are distributed. These terraces have been displaced, by the reverse dip-slip activities of Tonami-heiya fault zone in a sense of upheaval in the mountains side, even during the Holocene time. We examined stratigraphic cross section utilizing borehole data and geomorphologically analyzed 5 m-DEM data in order to elucidate the fault trace of the Isurugi fault which Tonami-heiya fault zone. As the results, the northern segment of Isurugi fault seems to run along the northeastern foot of Hodatsu Hills and extends underground through the lower-most Oyabe River into the Toyama Bay. Consequently, its total length reaches about 30 km. In the southern segment, a continuous fault scarplet was recognized to cut across the lower dissected fans. The slip-rate of Isurugi fault is estimated to be 0.31 - 0.64 m/kyr. In the Hokuriku region, reverse faulting and related folding with strike in a NE-SW direction have occurred during the late Quaternary. The hinge line of block movement due to the activities of the Tonami-heiya fault zone is revealed to have shifted from the mountain side into the plain side within the Holocene time. In conclusion, the Quaternary folding and faulting associated with the crustal warping at a wavelength of about 20 km is currently in progress, causing both the subsidence of Tonami plain and the upheaval of surrounding mountains and hills.

Phases of alluvial fan development in a loess area, Lublin Upland, E Poland

Holocene alluvial fans are a record of the evolution of the environment and human impact over the last 10 000 years. The study presents the structure of fans at the mouth of gullies as well as their development in the loess areas of the Lublin Upland. Sediment-soil sequences of seven alluvial fans and the adjoining flood sediments and dry valley bottom sediments were studied in detail. The development of fans occurred in three phases: i) the Eneolithic; ii) the middle and late Bronze Age and the Hallstatt period and iii) the Middle Ages and the modern times. The middle phase consists of two sub-phases while last phase consists of three sub-phases: the early Middle Ages; the Little Ice Age; the 19th and first half of the 20th century. These phases were interspersed with longer or shorter periods of stabilization of the alluvial fan surface. The different course of land use changes in the catchments was the reason for this metachronous development of the alluvial fans. Our studies indicate that heavy and catastrophic rainfall and rapid thaw had a considerable role in the development of the alluvial fans. The establishment of roads along the axes of valleys and across the slopes had a key impact on alluvial fan development. The deforestation of the catchment was not an essential condition for the formation of gullies and alluvial fans.

Optically stimulated luminescence dating of Holocene alluvial fans, East Anatolian Fault System, Turkey

In this study, the optically stimulated luminescence dating technique was used to determine the time of deposition of alluvial sediment samples from the Türkoğlu-Antakya segment of the East Anatolian Fault System (EAFS) in Turkey. The double-single aliquot regenerative dose protocol on fine grain samples was used to estimate equivalent doses (De). Annual dose rate was computed using elemental concentration of uranium (U) and thorium (Th) determined by using thick-source alpha counting and potassium (K) concentrations using X-ray fluorescence and/or atomic absorption spectroscopy. The environmental dose was measured in situ using α-Al2O3:C chips inside plastic tubes for a year. The two different bulk sediment samples collected from the Islahiye trench yielded ages of 4.54 ± 0.28 and 2.91 ± 0.23 ka. We also obtained a 2.60 ± 0.18 ka age for the alluvial deposit in the Kıranyurdu trench and 2.31 ± 0.14 ka age for an excavation area called Malzeme Ocağı. These ages were consistent with the corresponding calibrated Carbon-14 (14C) ages of the region. The differences between the determined ages were insufficient to clearly distinguish the disturbance event from the effects of bioturbation, biological mixing, or other sources of De variation in the region. They provide a record of alluvial aggradation in the region and may determine undocumented historical earthquake events.

Temporal variations in Holocene slip rate along the central Garlock fault, Pilot Knob Valley, California

Average geologic slip rates along the central Garlock fault, in eastern California, are thought to have been relatively steady at 5–7 mm/yr since at least the Late Pleistocene, yet present-day rates inferred from geodetic velocity fields are indistinguishable from zero. We evaluate the possibility of non-steady slip over millennial timescales using displaced Late Holocene alluvium along the central Garlock fault in Pilot Knob Valley. Truncation of a Late Holocene alluvial fan deposit against a shutter ridge requires a minimum of 30–37 m of displacement since deposition of the fan; maximum allowable displacement is 43–50 m. The extent of soil development atop the fan surface and optically stimulated luminescence ages bracket fan deposition between 3.5 and 4.5 ka. Together, these data require that slip rates during the Late Holocene were ∼7–14 mm/yr, with a preferred rate of ∼11–13 mm/yr. Our results, in conjunction with previous estimates of displacement over the past ∼15 ka, require significant temporal variations in strain release along the Garlock fault and confirm previous suggestions that interactions among fault systems in eastern California give rise to alternating periods of fault activity and quiescence.

Alluvial sediment or playas: What is the dominant source of sand and silt in desert soil vesicular A horizons, southwest USA

Vesicular A (Av) soil horizons form beneath desert pavements from the accretion of aeolian sediment (dust) commonly thought to be derived primarily from desiccating pluvial lakes and playas, with contributions from ephemeral washes and alluvial fans. Particle size distributions of Av horizons are typically bimodal with primary modes of very fine silt and fine sand, suggesting that the horizon matrix is derived from multiple sources. Here we conduct detailed chemical and physical analysis of both Av horizon soil samples and potential sources of aeolian sediment to better constrain the relative contributions of dust associated with the development of Av horizons. Geochemical data from both sand (125–250 µm) and silt (2–32 µm) fractions in Av horizons and potential dust sources in the eastern Mojave Desert and western Sonora Desert, USA, point to large contributions from nearby sources including distal alluvial fans and washes, and comparably lower contributions from regional sources such as playas. The silt mode is derived from suspension transport of dust, and the fine sand mode is derived from saltating sand. The desiccation of pluvial lakes in the Mojave Desert is commonly believed to have driven episodes of aeolian activity, contributing to sand dunes and Av horizon formation. We propose that alluvial fans and washes are underappreciated as desert dust sources and that pulses of dust from late Pleistocene and Holocene alluvial fans dwarfed pulses of dust from desiccating pluvial lakes in the eastern Mojave Desert.

Controls on Holocene Alluvial Fans in the Kaikos Valley, Turkish Aegean Coast - Alluvial Fans as Geoarchaeological Archives

Controls on Holocene Alluvial Fans in the Kaikos Valley, Turkish Aegean Coast - Alluvial Fans as Geoarchaeological Archives

High-resolution controlled-source seismic tomography across the Middle Aterno basin in the epicentral area of the 2009, Mw 6.3, L’Aquila earthquake (central Apennines, Italy)

We present high-resolution Vp models of the Middle Aterno basin obtained by multi-scale non-linear controlled-source tomography.Seismic data have been collected along four dense wide-aperture profiles, that run SW-NE for a total length of ~6 km in the hangingwall of the Paganica-S. Demetrio Fault, source of the 6th April 2009 (Mw 6.3) L'Aquila normal-faulting earthquake. Seismic tomography expands the knowledge of the basin with high spatial resolution and depth penetration (>300 m), illuminating the Meso-Cenozoic substratum that corresponds to high-Vp regions (Vp>3500-4000 m/s).Low Vp (1500-2000 m/s) lacustrine sediments (Early Pleistocene in age) are imaged only in the SW sector of the basin, where they are up to 200 m thick and lie below coarse fluvial and alluvial fan deposits. The overall infill consists of Early Pleistocene to Holocene alluvial fan and fluvial sediments between the Paganica Fault and the Bazzano ridge, with Vp reaching 3000 m/s for the oldest conglomeratic bodies. The substratum has an articulated topography. The main depocenter, ~350 m deep, is in the SW sector of the basin south of the Bazzano ridge. Remarkably, this depocenter and the overlying thick lacustrine body match the area of maximum coseismic subsidence observed after the 2009 earthquake. In the Paganica area, Vp images unravel large steps in the substratum related to two unreported SW-dipping buried strands, synthetic to the Paganica Fault, with ~250 m associated total vertical throw. This finding has important implications on the long-term history of the Paganica-S. Demetrio Fault system, whose total vertical displacement has been previously underestimated. An additional ~250 m vertical offset along this complex Quaternary extensional structure should therefore be considered.

Quaternary alluvial fan systems of the Agri intermontane basin (southern Italy): tectonic and climatic controls

Quaternary alluvial fan systems of the Agri intermontane basin (southern Italy): tectonic and climatic controlsThe Agri River high valley is a Quaternary intermontane basin located in southern Italy. The tectonic evolution of this basin was controlled by Lower Pleistocene strike-slip master faults, subsequently reactivated as normal faults until the Middle Pleistocene. The Quaternary sediments of the basin infill are mainly constituted of continental clastics, represented by coarse-grained alluvial deposits divided by unconformities. The arrangement of clastic deposits suggests that the Pleistocene to Holocene alluvial fan system developed along the eastern margin of the valley. Five generations of slope and alluvial fan systems have been recognized in the Agri basin. The oldest fans have formed on both slope and alluvial deposits. The younger alluvial fans are located along the entire valley floor and arose upon the earlier fan apexes originating in these valleys. The youngest fans are arranged in two different generations and show proximal facies distributed along the foot slopes. Plan view morphology, fan slope profiles, and sedimentary features of the fan system have been used here to determine the magnitude of the tectonic deformation episode affecting the faulted mountainous front of the Agri basin eastern margin. Both fast and slow tectonic episodes occurred during the different regional Quaternary tectonic stages that affected the southern Apennine chain. These tectonic episodes have therefore been analysed in relation to climatic conditions in order to determine their contributions to the evolution of the Pleistocene to Holocene fan systems.

Late Quaternary tectonics of the Vallo di Diano basin (southern Apennines, Italy)

We discuss new data concerning the late Quaternary tectonics of the Vallo di Diano basin, the largest intramontane depression in the southern Apennines chain (Italy). The southern Apennines axis is currently subject to NE–SW extension. Here, active NW-trending normal faults are associated with strong earthquakes ( M > 6), with average recurrence times >1 ka. The Vallo di Diano basin is a half-graben bounded by an extensional fault system VDFS (Vallo di Diano Fault System), featuring three major NW-trending, SW-dipping, ∼15–17 km long fault segments. Holocene faulting and possible historical seismicity have been documented only for the northern fault segment. No major historical earthquakes can be associated with the other fault segments, and the recent sedimentary and structural evolution of the basin is still poorly constrained. As a consequence, its seismogenetic potential has probably been underestimated. We found evidence of late Pleistocene–Holocene faulting in the relay zone of the central and southern fault segments bordering the basin. Here, late Pleistocene volcaniclastic layers at the apex of an alluvial fan are affected by normal displacements on the order of ∼1 m. Additionally, in the same area we recognized a previously unreported, 9 km long and 0.5–1.4 km wide set of scarplets (ranging in height between ∼1 m and 2.5 m) affecting late Pleistocene–late Holocene alluvial fans. The last deformation is younger than 3 ka BP. Due to the geometric arrangement of these scarplets and the long-term displacement along the Vallo di Diano Fault System, we hypothesize that the central and southern fault segments belong to a ∼32 km long hard-linked system, capable of generating Mw > 6.5 earthquakes. The Vallo di Diano basin is thus bounded to the east for its entire length (∼45 km) by an active segmented extensional fault system. Therefore it has to be considered one of the major seismogenic sources in southern Italy.

Bathymetry of Lake Lisan controls late Pleistocene and Holocene stream incision in response to base level fall

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.

Late Quaternary activity and dextral strike-slip movement on the Karakax Fault Zone, northwest Tibet

Field observations and interpretations of satellite images reveal that the westernmost segment of the Altyn Tagh Fault (called Karakax Fault Zone) striking WNW located in the northwestern margin of the Tibetan Plateau has distinctive geomorphic and tectonic features indicative of right-lateral strike-slip fault in the Late Quaternary. South-flowing gullies and N–S-trending ridges are systematically deflected and offset by up to ~ 1250 m, and Late Pleistocene–Holocene alluvial fans and small gullies that incise south-sloping fans record dextral offset up to ~ 150 m along the fault zone. Fault scarps developed on alluvial fans vary in height from 1 to 24 m. Riedel composite fabrics of foliated cataclastic rocks including cataclasite and fault gouge developed in the shear zone indicate a principal right-lateral shear sense with a thrust component. Based on offset Late Quaternary alluvial fans, 14C ages and composite fabrics of cataclastic fault rocks, it is inferred that the average right-lateral strike-slip rate along the Karakax Fault Zone is ~ 9 mm/a in the Late Quaternary, with a vertical component of ~ 2 mm/a, and that a M 7.5 morphogenic earthquake occurred along this fault in 1902. We suggest that right-lateral slip in the Late Quaternary along the WNW-trending Karakax Fault Zone is caused by escape tectonics that accommodate north–south shortening of the western Tibetan Plateau due to ongoing northward penetration of the Indian plate into the Eurasian plate.

Recent faulting in the southern Arava, Dead Sea Transform: Evidence from single grain luminescence dating

Colluvial sediments in tectonically active areas are associated with faults, and dating them is important for timing earthquakes and assessing seismic hazards. In hyperarid regions organic matter for radiocarbon is scarce, and the dating method of choice is luminescence. However, colluvial sediments are difficult to date due to the short transport distance that is commonly involved and the resulting incomplete bleaching of the sediment. Single grain and small aliquot measurements of fault-related colluvial sediments may isolate well-bleached grains and provide reliable ages of faulting events. Elat, southern Israel, lies on the active Dead Sea Transform and paleoseismic data are crucial for city planners. A small fresh-looking NNE trending graben within the late Pleistocene to Holocene alluvial fan of Nahal Shehoret near Elat was trenched to expose recently active normal faults with a stack of colluvial wedges on the footwalls. Samples for luminescence dating were collected near the eastern fault, from the alluvial fan and from the heels (less than 1 m from the fault plane) and toes (∼2 m away from the fault plane) of a stack of five colluvial wedges. Single grain measurements of quartz were compared with large (thousands of grains) and small (hundreds of grains) single aliquots of quartz and alkali feldspar (KF). KF was measured using the infrared stimulated luminescence (IRSL) signal and the single aliquot added dose (SAAD) or single aliquot regenerative dose (SAR) protocols. Large aliquots and single grains of quartz were measured using the optically stimulated luminescence (OSL) signal and the SAR protocol. Large and small aliquots show large scatter in equivalent dose values, with a distinct population of young ages. Quartz large aliquot ages of samples taken from the toes of the wedges range from 5200 to 2600 years, however the ages of samples taken from the heels, close to the fault, are in reversed order, from 4300 years at the base to 13,000 years at the upper wedge. This results from progressive exposure and erosion of deeper and older beds on the fault scarp with continued faulting, and incorporation of older poorly bleached grains into the upper wedges. Only single grain measurements could isolate a distinct, small population of grains that were fully bleached at the time of deposition, dating the colluvial wedges to between 500 and 1300 years. Large aliquots ages substantially overestimated the time of faulting. The single grain ages record very young faulting events which may be correlated with the known historical earthquakes of the past 1500 years.