Base Level Of Erosion Research Articles

Paleo-lake evolution influenced by tectonic processes and climate changes in the Hetao Basin during the late Quaternary

Exploration of paleo-lake evolution is crucial for the understanding of climatic and tectonic roles in earth surface. Previous studies mainly focused on the climatic effect on river-lake transitions and lake evolutions through lacustrine deposits, but with limited consideration of tectonic drivers, especially for the tectonic rift lakes in the Hetao area.Based on the analyses of lacustrine and fluvial piedmont terraces and a 400-m core from the northern Hetao Basin, along with the optically stimulated luminescence and detrital zircon U-Pb dating, we adopted an integrated “tectonics-climate-surface processes” approach to explore the climatic and tectonic effects on the lake evolution of the Hetao rift basin. Results show that lacustrine deposition on the piedmont terrace T1 (60–47 ka), underlying the T3 fluvial (80–60 ka), has an erosion contact with pluvial deposits at 55 ka, implying the paleo-lake formation at ∼ 80–60 ka and shrinkage at ∼ 55–47 ka. Lake formation was forced by basin depression under the tensile stress of tectonic movement, and was recharged by the Yellow River due to obstruction of the outlet at Tuoketuo caused by uplift.Lake shrinkage was due to the combined effect of basin lifting and warm-wet climate conditions that promoted outflow. A substantial decrease in the erosion base level and rapid water drainage induced by river cutting caused erosion of lacustrine deposits in the basin. The limited sedimentary space of the lake basin in early MIS 2 should be considered a factor in lake disappearance in addition to the dry climate. This study highlights that tectonic effects may be more important than climatic effects in the evolution of rift lakes near the young fold mountain belts.

Assessment of check dams and afforestation in mitigating debris flows based on dendrogeomorphic reconstructions, field surveys and semi-empirical models

Check dams and afforestation are two common measures for debris-flow mitigation; however, there is a lack of methods allowing quantitative evaluation of check dam and afforestation effects on debris flow motion and deposition. Laogan Gully is an active debris-flow system with a large landslide on the right hillslope, currently representing the main source of debris flows in the catchment. Several debris flows have occurred since 1985 which led to the construction of check dams and the plantation of silver wattle (Acacia dealbata) trees between 1991 and 1993. These measures significantly reduced the volume of debris flows reaching downstream portions of the system. At the same time, large amounts of sediment were trapped on the gully bed and thereby increased the base level of the torrent, which again tended to stabilize the large landslide on the right hillslope. This paper analyzes sedimentation of debris-flow material on the gully bed and on the fan using 12 trial pits behind the check dams and 6 incised geological sections on the fan. The timing and extent of debris flow motion and deposition was reconstructed using scars and growth suppression events in the annual growth ring series of 306 Acacia trees trapped in the newly formed deposits. The gravitational potential energy of the sediment of the large landslide is calculated according to the change in the erosion base level behind the check dams. On the basis of these results, we constructed a semi-empirical vegetation coverage–landslide energy–debris flow volume model to quantitatively evaluate the effects of the check dams and afforestation on debris-flow mitigation. The model exhibited predictive capabilities for estimating the volume of debris flow generated by the reactivation of landslides. Check dams are found to play a major role in debris-flow mitigation in the early stages, whereas the Acacia trees play an increasingly important role once the check dams are filled. The partial resurgence of the landslide caused a sudden increase in the gravitational potential energy of the sediment source, which in turn affected the effectiveness of the debris-flow mitigation measures.

Based on physical model test and analysis of hydraulic erosion of warping dam

As a common engineering measure in “Gully consolidation and highland protection” project, warping dam plays a great role in soil and water conservation in the loess Plateau region. This paper selects the Yangjiagou small watershed in Qingyang City, Gansu Province as the research object, sets up a warping dam to simulate erosion reduction, and establishes a physical channel model with equal scale reduction, to reveal the reciprocal feeding mechanism of hydraulic erosion to the “Gully consolidation and highland protection” project. According to experimental calculations, the total erosion amount of the three erosion tests before the construction of the warping dam is 7.25kg, 8.02kg and 9.20kg, and the total erosion amount of the three erosion tests after the construction of the silt dam is 4.51kg, 5.25kg and 6.18kg. The sand interception efficiency in the three water flushing tests is 37.8%, 34.5% and 32.8%. The results show that the construction of warping dam can raise erosion base level and alleviate soil erosion effectively. And the warping dam can still play a part of its sediment reduction capacity after it has been scoured several times and partially destroyed. With the increase of use time, the effectiveness of the warping dam for blocking sand gradually decreases.

A remarkable last glacial loess sedimentation at Roxolany in the Dniester Liman (Southern Ukraine)

The study focuses on the loess–palaeosol sequence at Roxolany, exposed in the cliffs on the left bank of the Dniester Liman in the Black Sea Lowland. The sequence is one of the longest and most complete terrestrial records of Quaternary climate change in Ukraine. The Pleistocene sequence, i.e. loess, soil and fluvial units, is quite thick, i.e. about 60 m, including 30 m of L1 (Weichselian) loess: the greatest thickness in the entire Black Sea Lowland region. The paper presents the characteristics of the unique aeolian sedimentation environment in the Lower Dniester region during the last glacial cycle; our observations indicate exceptionally intense local deposition in the Last Pleniglacial. A number of luminescence dating results were obtained in several laboratories, based on various fractions and methods. The dating results for L1 loess turned out to contradict the stratigraphy of the section determined with geological methods. They were similar to each other and were clearly older than expected. Hence, to confirm the age of the deposits, various underlying factors were analysed. Our findings indicate that a combination of several circumstances could be directly or indirectly responsible for the local intensification of aeolian and depositional processes at Roxolany: (1) regional atmospheric circulation vs. orientation of relief; (2) the location and environment where the aeolian source material formed, as well as the great abundance of the deflation zone; (3) the emergence of considerable tracts of sea shelf as a result of the recession of the Black Sea, which had the effect of lowering the base level of erosion, but also of (4) revealing significant positive forms in the relief of the shelf, which undoubtedly modified anemometric conditions. The uniquely thick fossil soils within the L1 loess in the Roxolany sections may have had their origin in a continuous supply of dust during pedogenic periods.

Age of the epigenetic karst from the central region of Sierra de los Órganos, Pinar del Río, Cuba

The epigenetic karst age in the central region of Sierra de los Órganos, is defined from the moment the carbonated sequences are uncovered and denudation processes begin at the end of the Oligocene and early Miocene (approximately 25 Ma). Although the karstic forms in this region originated at different times, they all coexist in today’s landscape. While the area was rising up slowly and sea level changes were taking place, the regional erosion base level descended giving rise to leveling surfaces desiccated by numerous sinkholes. At this time, surface currents disappear to become underground streams, which have carved out an extensive network of galleries. Satellite images and aerial photos interpretation, geological survey, measurements of morphostructures and multivariate statistical analysis, were the methods used to establish the epigenetic karst evolution model for the region. The model includes nine surfaces of erosion base levels, in a range that goes from the 410 m a.s.l., coinciding with the older erosion base levels conserved in the area (23 Ma before the present), until the 50 m a.s.l., corresponding to the surface of current erosion.

Impact of lake water level decline on river evolution in Ebinur Lake Basin (an ungauged terminal lake basin)

Most of the terminal lakes in inland basins, which account for half of the world's lake reserves, have been shrinking at an alarming rate in recent years. In a Terminal Lake Basin, changes in the water level of the lake can lead to variations in the local erosion base level. From the perspective of local erosion base level, we revealed the response of river evolution to change in the water level of lake in Ebinur Lake Basin for the past 5000 years. Our results verified the three geomorphic development stages of natural decline, balance maintenance, and imbalanced decline. In modern times, the decline in the number of rivers entering the lake due to human activities has made the water level of the lake drop 15–30 times that observed from 5 kaBP–0.1 kaBP. The results showed that the average undercut erosion rate of the river entering the lake tends to increase with a rapid decrease in the water level of the lake in the past 5000 years. The instantaneous undercutting rate of the Bortala river section in the basin was 1.6–4.2 times that observed from 5 kaBP–0.1 kaBP. This result showed that a rapid decline in the water level of the lake due to human activities will accelerate the erosion of rivers. Therefore, from the perspective of geomorphology, the river erosion triggered by the rapid decline in the local erosion base level is an important reason for the continuous shrinkage of Ebinur Lake.

Morphometry and morphology of fan-shaped landforms in the high-Arctic settings of central Spitsbergen, Svalbard

In this study, the distribution, morphometry and morphology of alluvial fans and colluvial cones were investigated in a high-Arctic, periglacial environment. The main aims were to present their surface morphology types, analyse the relationship between the morphometric properties of fans and their catchments, and to investigate potential factors controlling the morphometry of fans. Data from a set of 297 fan-shaped landforms in central Spitsbergen, Svalbard, were presented and analysed to ascertain factors likely to influence their distribution and character. First, based on the dominant morphological processes, the studied landforms were divided into three groups: fluvial-flow-dominated fans, debris-flow-dominated fans, and colluvial fans. Then, to analyse the relationship between fans and their catchments, 20 variables were investigated. Those analyses indicate that small catchments, characterised by a low relief and high Melton's R number, tend to produce small and steep fans. This tendency was most visible for colluvial fans and debris-flow-dominated fans but less so for fluvial-flow-dominated fans. The latter tend to adjust stronger to the local topography. However, in all cases, these associations were weaker than in morphometry studies based on data from other climatic settings. The most important controls on the distribution of the studied fan-shaped landforms seem to be the availability of accommodation space (related to deglaciation time) and local erosion base level.

Soil Erosion and Controls in the Slope-Gully System of the Loess Plateau of China: A Review

The Loess Plateau has long been suffering from serious soil erosion of which erosion from the slope-gully system is now dominant. The slope-gully system is characterized with distinctive erosion distribution zones consisting of inner and inter gully areas wherein erosion patterns spatially vary, acting as both sediment source and the dominant sediment and water transport mechanism. In this paper, a substantial body of research is reviewed concentrating on the soil erosion processes and control practices in the slope-gully system. The inner gully area is identified as the main sediment source while runoff and sediment from the inter-gully upland is found to significantly affect down slope erosion processes. Correspondingly, the protective vegetation pattern and coverage should be strategically designed for different erosion zones with an emphasis on the critical vegetation cover and pattern to reduce sediment yield of the whole slope-gully system. Check-dam could change the base level of erosion and reduce the slope length of the gully side, which will further decrease the possibility and magnitude of gravity erosion. We concluded that understanding the erosion processes and implementing erosion practices for the slope-gully system are of importance and require more research efforts that emphasize: 1) the influence of upland runoff on erosion processes at downslope; 2) the relationship between hydraulic characteristics of overland flow and erosion process at a slope-gully system scale; 3) physical mechanisms of different vegetation patterns on the slope-gully erosion process.

Correction to: Chronological evolution of the channel functional units in association with palaeo-hydrogeomorphological environment in the ancient delta fan of Subarnarekha basin, India

The assessment of chronological evolution of the channel functional units is an imperative aspect to understand the channel avulsion nature and planform change. In this study, the channel functional units (channel, aggradational and abandoned) and their distinct micro-morphologies have been assessed through the landuse and landcover classification, terrain analysis, lithostratigraphic records and fluctuating flow regimes in the ancient delta fan of the Subarnarekha basin. The distinct micro-morphological features of the functional units have been formed and evolved under the dominance of fluvial environment coupled with the fluctuating strength of Indian summer monsoon (ISM) and regression phase of sea-level since 6000 years before present (YBP). However, the borehole lithostratigraphic records reveal that the ancient delta fan was formed under the different fluvio-marine depositional environments of the marine transgression, regression and stillstand phases since 32,200 YBP. The riverbed of the recent course is ascended than the palaeo-courses due to declining trends of water discharge and sediment load in the last four decades as well as during the late Holocene mega-drought event. The channel unit and abandoned unit have been transformed into the aggradational unit with micro-morphologies of point bar, fill-terrace, and natural levee under the influence of channel avulsion and bulk of sediment deposition related to the fluctuating flow regime and base level of erosion. The micro-morphological features (marshes, oxbow lakes and meander neck-cuts) of the abandoned unit have been modified from the channel unit after diversion of the recent course from the palaeo-course owing to extreme discharge and valley drowning during lowstand.

Inversion of bedrock channel profiles in the Daqing Shan in Inner Mongolia, northern China: Implications for late Cenozoic tectonic history in the Hetao Basin and the Yellow River evolution

Many studies indicate the Hetao Basin in Inner Mongolia, northern China, controlled the erosion base level of the upper Yellow River before 1.5 Ma. The late Cenozoic extensional rifting in the Hetao Basin in response to the northeastward growth of the Tibetan Plateau may be an plausible mechanism that initiated the headward erosional signal along the Yellow River at the northeastern margin of Tibetan Plateau ~1.8 Ma ago. However, little attention has been paid to establish the relationship between the late Cenozoic tectonic evolution in the Hetao Basin and integration of the upper Yellow River. In this paper, we explore the tectonic mechanism that can drive headward erosion along the Yellow River and the timescales over which it occurred by reconstructing the late Cenozoic tectonic history in the Hetao Basin. We applied linear inversion of bedrock channel profiles and late Cenozoic sedimentary strata in the Daqing Shan to explore the late Cenozoic tectonic evolution in the Hetao Basin. Results show that the accelerated vertical slip between the Daqing Shan and the Hetao Basin initiated at 2.8 ± 0.8 Ma, and the average relative uplift rate was 0.18 ± 0.04 mm/yr since 2.8 Ma. The lowering of erosion base level in the Hetao Basin since 2.8 ± 0.8 Ma produced a headward erosional signal along the Yellow River that initiated fluvial incision at the northeastern margin of the Tibetan Plateau ~1.8 Ma ago. That indicates the accelerated extensional rifting in the Hetao Basin has been responsible for the integration of the upper Yellow River since the late Pliocene. Our study improved understanding how the Yellow River responds to the late Cenozoic rifting around the Ordos Block, as well as the northeastward growth of the Tibetan Plateau. Meanwhile, these tectonic processes were also linked together by the Yellow River evolution.

Prof. PhD Dinyo Dimitrov Kanev (1922-1997) – A Distinguished Scientist and University Lecturer in Geomorphology of Bulgaria and Balkan Peninsula

Prof. PhD Dinyo Dimitrov Kanev was one of the most distinguished Bulgarian scientists and university lecturers in geomorphology of Bulgaria and the Balkan Peninsula. The paper presents prof. Kanev’s main scientific works. On the basis of their analysis, they have been grouped into books, maps and atlases, as well as publications related to various thematic topics, e.g. investigations of denudation surfaces, the impact of the base level of erosion on the relief development, studies of the geomorphological evolution of various areas in Bulgaria, morphostructures and morphostructural development of Bulgaria’s relief, the neotectonic movements and their geomorphological response, studies of the volcanic relief in Bulgaria, as well as analysis of the seismic activity and the impact of the relief on the seismic effects, etc. Other works, such as ones related to the problems of the geomorphological investigations in Bulgaria, the geomorphological specifics of the Main Watershed of the Balkan Peninsula, the relation between relief and recreational resources, etc., have also been presented in the paper. Additionaly, the contributions of Prof. PhD Dinyo Kanev to the establishment of section “Geomorphology and Cartography” (now “Climatology, Hydrology and Geomorphology”) in the Faculty of Geology and Geography at the Sofioter University “St. Kl. Ohridski”, Sofia and to the development of geomorphology and cartography as scientific fields in Bulgaria are highlighted.

Erosion characteristics of loess tunnels on the Loess Plateau: A field investigation and experimental study

AbstractLoess tunnels are a common geo‐hazard in the Loess Plateau and not only cause considerable soil and water loss, but also aggravate and even induce the occurrence and development of other disasters such as ground fissures, mudflows, collapses, and landslides. To date, research on the hydrological characteristics and erosion behaviour of loess tunnel systems has focused on field investigation data and limited river basin observation data, whereas field test information and data are very scarce. In this study, field surveys, observations, field scouring experiments, and laboratory‐based sediment percentage tests were conducted to analyse the erosion characteristics, spatial distribution, and hydrological characteristics of a large‐scale loess tunnel system in the hilly Loess Plateau southeast region of northern China. The results showed that the loess tunnel erosion exhibited periodicity. Tunnel erosion in each period shows a similar erosion process, that is, thin‐layer water flow erosion and lateral expansion, tunnel wall collapse and deposit due to the loss of support from the lateral erosion, and erosion and transport of deposits by water flow. Waterfall erosion, lateral erosion, headward erosion, and the resulting collapses were the main forms of tunnel erosion. Besides this, the base level of erosion significantly affects the erosion characteristics of the loess tunnel. The hydrological characteristics during field scouring experiments exhibited three different stages: a lag effect, attributed to the temporary loss of water velocity in the first stage; small water flow fluctuations in the second stage; and an increase in total seepage loss with increased water injection flow in the third stage. The erosion rate was positively correlated with the flow quantity. The results of this study not only provide valuable reference data for research on the mechanism and velocity of erosion events in loess, but also provide a theoretical basis for the prevention of loess tunnel disasters in engineering construction. © 2020 John Wiley & Sons, Ltd.

The Influence of Knickpoints on the Erosion in Songlin River Basin

Based on fieldwork and the longitudinal section obtained by ArcGIS, seven major knickpoints in Songlin River Basin are located. It is found that the regions with a great average elevation difference between ridge and valley suffer more from disasters such as collapse, landslides, and debris flows. Dimensionless number Vindex is used to quantitatively describe the cross-section of the Songlin River Valley. The Vindex coefficient is below 0 outside the upstream influence of knickpoint and in downstream of knickpoint and it is over 0 in the upstream of knickpoint and at the knickpoint. The overall change trend is “super V shape-U shape-super V shape”. The formation and development of knickpoints strongly influence the geomorphological characteristics of the Songlin River Basin. Due to the rising erosion base level of the upstream of knickpoint, sediment is deposited and the incision rate of riverbed decreases or it even stops down cutting. In this way, the average elevation difference between ridge and valley is tend to reduce, which lowers the energy that causes geological hazards and improves the stability of the upstream. The gradient of both riverbanks decreases, forming a flat and wide U-shaped river valley. Although the elevation difference between the river and the downstream watershed of the knickpoint remains constant, the current energy increases and the erosion is still severe, keeping the valley in a V shape.

Late Holocene Pollen Record of Environmental Changes in Karimata Strait, Sunda Shelf Region

DOI: 10.17014/ijog.6.1.41-55Pollen analysis has been conducted on a 90 cm gravity core taken from the Karimata Strait to reveal pollen facies in marine sediment and Late Holocene environmental changes in the central Sunda Shelf region. The core site is at 32 m water depth and located about 170 km northwest of Bangka Island, Indonesia. Ten samples were collected at 10 cm intervals through the core. The total number of pollen grains counted in the samples varies between very low (<50 grains) to abundant (>200 grains). High frequencies (50 - 70%) of mangrove pollen are found at 90 to 40 cm indicating that pollen facies in offshore marine sediment may be comparable with those in mangrove forest floor sediment. The core site has been in a neritic environment since its early deposition ca. 1,800 yr B.P. (~150 A.D.) when mangroves vastly grew on the tidal flats of the surrounding islands and they persisted to ca. 700 yr B.P. (~1,250 A.D.). In the middle of this period, a catastrophic event speculatively due to the 535 A.D. Krakatau eruption might have responsible for the decrease of mangroves and the disappearance of benthic foraminifers. The deposition of silicious materials (tephra) due to this eruption might have provided an opportunity for benthic foraminifers to increase their population subsequently. From ca. 700 yr B.P. (~1,250 A.D.) mangroves declined, as indicated by lower frequencies of pollen grain in samples from 30 cm deep upward. It occurred simultaneously with the deposition of coarser sediment and the increase of benthic foraminifer abundance. Interplay of anthropogenic activities, strengthening ENSO cycle, and lowering erosion base level might have been responsible for these environmental changes.

Multi-level Domica–Baradla cave system (Slovakia, Hungary): Middle Pliocene–Pleistocene evolution and implications for the denudation chronology of the Western Carpathians

The trans-boundary Slovak-Hungarian Domica–Baradla cave system (Slovak and Aggtelek karsts), >26 km in length, consists of evolution levels that have been formed in relation to the incision phases of the Jósva Valley. Existing opinions on the age of the well-known cave system have not been based on the dating of cave sediments deposited during older evolution phases. Previous U-series dating and the first paleomagnetic analyses of dripstones, flowstones and fine-grained allochthonous sediments identified only younger accumulative phases of the cave evolution in Late Pleistocene. Our cosmogenic nuclide dating (10Be and 26Al) of allochthonous fluvial gravels from the upper and lower levels of the Domica Cave (Slovakia) reveal much older evolution phases. Two burial ages at 3.47 ± 0.78 Ma and 2.94 ± 0.50 Ma show that the upper level of the cave system originated in, or before, the Middle Pliocene. Its younger accumulation phases (Early–Middle Pleistocene) are documented based on magnetostratigraphy and U-series dating of fine-grained sediments and flowstones. The Brunhes/Matuyama boundary (780 ka), Kamikatsura excursion (~900 ka), Santa Rosa excursion (~932 ka) and Jaramillo magnetozone (~1.001–1.069 Ma) were identified from the newly studied profile in the Suchá chodba Passage (the ages of flowstones in upper part of this profile are ~130 ka, 173 ka and 199 ka). In some places, several small older (paleokarst?) solutional phreatic cavities are cut by this cave level. The lower evolution level, located 12–18 m below the upper level, originated in the Early Pleistocene (the burial age of allochthonous fluvial gravels is 1.92 ± 0.25 Ma). Low pre-burial denudation rates (3.1–5.6 m/Ma) correspond with the slowdown or interruption of tectonic uplift of the area and the long-term stabilized erosion base level during the formation of these cave levels. Their origin was linked with the formation of large pediments, of which remnants are preserved on both sides of the Jósva Valley (Hungary). The pediments probably correlate to the ‘foothill’ (Middle Pliocene) and ‘river-side’ (Late Pliocene–Early Pleistocene) levels in the denudation chronology of the Western Carpathians.

Influence of the Dnipro cascade of reservoirs on the current geomorphogenesis of adjoining territories

The construction of the Dnipro cascade of reservoirs caused one of the largest transformations of natural relief in Ukraine. The result of which was the following: regional activation of land flooding (an area of over 1 million hectares); strengthening of erosion processes, abrasion of shores of reservoirs; the development of dangerous exogenous relief-forming processes (landslide, sinking and suffosion). An increase of the water-edge in the Dnipro river has led to a sharp and significant increase of the local base level of erosion. As a result, a new coastline with a total length of about 3,5 thousand km was formed. More than a third of which is actively damaged by denudation, especially abrasive and erosive processes, and needs protection. In this area there are more than 190 settlements where more than 600 thousand inhabitants live. Such excessive anthropogenic loading on the Dnipro basin disturbed its natural balance and greatly increased the risk of developing dangerous exogenous processes, caused the ecological state crisis of many territories. The features of the formation of the banks of reservoirs are influenced by a number of factors, the most important of which are: geomorphological conditions (confinement to certain forms of relief, dissection of the coast, slope steepness, spectrum and intensity of manifestation of exogenous processes); the lithologic composition of the rocks involved in the structure of the shores; wave mode and level reservoir regime. The combined influence of these and other factors is determined by: the local features of the reformation of the banks, the development of complexes of exogenous processes with distinctions of their activity and formation of certain forms of relief. In conditions of increasing technogenic loading on the relief monitoring and forecast of the development of exogenous processes are among the most important applied objectives of geomorphology.

The evolutionary changes of channel morphology in initial stage of water flow and sediment transport in shallow water

When sediment laden flow enters the broad areas from a narrow river channel, the flow velocity declines abruptly, due to the enlarging width. As a result, the sediment silts in the region. This phenomenon occurs when the sediment laden flow enters a plain from a mountainous river, or when it flows into lakes and oceans from rivers. The former condition results in the development of an alluvial fan, while the latter leads to the formation of a delta, and then again gradually evolved into an alluvial river which by the developing process of water flow and sediment transport, and it appears various pattern along with its growth. The river pattern can divide into many types, the classics types are straight channel, meandering channel, branching channel and braided channel. Model test is one of the most important technical means researching water flow and sediment transport and predicting riverbed evolution. At present, many scholars, domestic and overseas, excavate straight river in the foundation bed to research channel morphology changes, and do less research on non-straight river in the foundation channel morphological changes. The formation and development process of alluvial river is a continuous variation, the essay will mainly discuss the evolution change of river channel from nothing on the surface of rivers into the lake delta, under the constant coming water and sediment and constant erosion base level. In this study, in order to study the evolutionary changes of channel morphology in initial stage of water flow and sediment transport in shallow water, non-uniform sediment was used, for a model generalization test, under the conditions of a constant inflow water and sediment, gradient, as well as an outlet base level. The sediment test results showed that the evolutionary changes of channel morphology experienced three stages. At the first stage, straight channel and branching channel were appeared alternately. At the second stage, a single micro-bend channel morphology swing development on the surface of delta deposition occurred with the branching channel of tributary shunt gradually decrease and die. At the third stage, there’s mainly meandering channel occurred with the coefficient of twists become larger with the concave bank continuously scouring regressive in the micro-bend channel. Through analysis and experiment, results show that the channel morphology of the second stage and the third stage present as sine curve characteristics: the upper channel located in the inlet of the sine curve, the middle and lower of the bend channel are located in the peaks and troughs of sine curve. With time going on, the amplitude and direction of sine curve become large gradually, and the coefficient of channel tends to be stable. Finally, the evolutionary changes of channel morphology is analyzed from the bed load and boundary conditions. This study is of great theoretical significance, and the achievements will enrich the theory of river dynamics and riverbed evolution.

Subsidence and conversion of the Dead Sea basin to an inland erosion base level in the early middle Miocene as inferred from geomorphological analysis of its ancient western fluvial outlet

The first major subsidence of the Dead Sea pull-apart basin (DSB) is evidenced by the thick Hufeira Member of the terrestrial Hazeva Formation. The age of the Hufeira Member and the conversion of the DSB to an inland erosion base level are not well constrained. For this purpose we studied the effect of the evolving basin on its ancient fluvial outlet to the Arad-Be'er Sheva Valley (ABSV), which served as a Miocene corridor between the embryonic DSB region in the east and the Mediterranean Sea in the west. We mapped and analyzed the morphostratigraphy of four series of rock-cut erosion surfaces (from top to bottom: the Barir, Kuseifa, Ar'ara, and Shemen surfaces). They are manifested in the east as fluvial erosion surfaces, capped by conglomerates, passing laterally westward to marine wave-cut surfaces, capped by a shallow marine limestone of the early middle Miocene Ziqlag Formation. The age of these surfaces is constrained to the early middle Miocene (Langhian) based on morphostratigraphy correlation with the Ziqlag Formation. Paleogeographic reconstruction of the two higher and older surfaces reveals transverse valleys, which drained the DSB region and crossed the present route of the regional water divide. These transverse valleys were presumably the western outlets to the Mediterranean Sea of the newly subsiding basin. Precambrian components in the assemblage of the clasts that cover the Kuseifa surface were not found in the Hufeira Member and thus reflect an ongoing post-Hufeira exumation of the DSB drainage basin. Hence, this early middle Miocene surface postdates the Hufeira Member, assigning an age of late early Miocene to the first major subsidence of the DSB. The two lower and younger surfaces represent local drainage systems confined to the ABSV. This transition from regional to local drainage system marks the establishment of the present regional water divide and the conversion of the DSB to an inland erosion base level during the early middle Miocene.

Formation of river terraces in conditions of high seismicity

We have investigated the river terraces on the left bank of the Irkut river in the Torskaya depression a short distance from the village of Guzhiry. On the basis of lithological-geological findings and radiocarbon datings of buried soils from two sections of the second terrace (12–14 m), we identified nine formation stages of the terrace in the latter half of the Late Neopleistocene and in the Holocene. They reflect multiple changes of the leading exogenous process, implying a variety of the genetic types of deposits (soils, and aeolian and alluvial sediments) during the Early and Mid-Holocene. The formation stages of alluvium are correlated with periods of high water. It is found that the final transition of alluvial to cover deposits is associated with incision of the river to 2–4 m and is dated to 5.2–4.5 cal. ka. We examine the alternation of the natural factors for the formation of deposits of the second terrace of the Irkut river in the Late Neopleistocene and Holocene. One (hydroclimatic) factor implies accumulation of deposits of the alluvial and cover complex depending on climate and water runoff fluctuations, landscape changes, and on variation in the base level of erosion. The other (seismic) factor is correlated with data on high activity of the Tory paleoseismogenic structure, which seems to have caused the lowering as well as the rise of the bottom of the depression at the time of strong earthquakes and, as a consequence, erosion or accumulation of deposits of the channel facies of alluvium. It is established that the chief causes for the change of the terrace’s deposit types were the natural-climatic changes, the character and directedness of tectonic movements, the variations in the base levels of erosion, and the height of floo ds.

Development of Ground Fissures: A Case Study from Southern Parts of Uttar Pradesh, India

Abstract In recent past several incidences of ground fissures have been reported from different parts of Uttar Pradesh. The area had witnessed several drought years followed by heavy rainfall, immediately after which the fissures were noticed. This had been a cause of concern for the public and planners in general and the scientific community in particular. The authors carried out investigation of these fissures for identifying possible mechanism for their development. The studies have indicated that sudden heavy rainfall after several drought years along with the composition of the soil profile, lowering of base level of erosion in the nearby major streams are the triggering factor in the development of the cracks. The sub-surface piping inside the ground at shallow depth and collapse of the overburden inside the pipe is the possible mechanism for their formation. The development of ground fissures/cracks is a local phenomenon, related to aseismic causes and as such there does not appear to create a panic situation. As the large trees with branching roots, were not affected by the ground fissures, the plantation of such trees may prevent the areas from further extension and development of ground cracks.