Fan Surface Research Articles

Stress Analysis of Ice Layers on Fan Rotor Blades in Aeroengines

Fan rotor blades are critical components of aeroengines. When an aircraft flies in icing conditions, ice accumulation on the fan surface may lead to periodic shedding. Severe ice shedding can cause mechanical damage to the engine, posing significant safety risks. This study investigates ice accretion on the surface of ROTOR 67 rotor blades and their stress distribution. This paper presents an in-depth analysis of the internal stress distribution of ice layers on the surface of rotating blades under different icing times and rotational speeds, especially the stress concentration of the areas at the contact surface between the ice layer and the blade. This study predicts the stress distribution of ice layers under different working conditions more accurately, which helps to identify potential ice layer fracture risks in advance. Moreover, it integrates the icing process, stress distribution, and shedding mechanism for analysis, providing a comprehensive perspective. It considers the interaction of various environmental factors and operating conditions, offering an in-depth understanding of ice layer behavior under complex working conditions.

Morphological characteristics and controlling factors of the piedmont fan systems in the Zanskar region, Northwest Himalaya, India

Piedmont fans are prominent geomorphic features formed at the transition between mountain slopes and valley floors. This study investigates the morphology of alluvial fans in the Zanskar Basin (ZB) to uncover the key variables influencing their development and morphodynamics. Utilizing advanced GIS and remote sensing techniques, along with field investigations, we conducted a detailed spatial analysis of 103 alluvial fans along the Doda, Tsarap, and Zanskar rivers. This approach allowed for precise mapping and characterization of these fans within complex depositional settings of ZB, particularly where fans merge into bajadas. Our analysis revealed distinct characteristics for the fans, including Fan Area (FA), Fan Slope (SF), Radius (R), Base Length of Fan (BF), Fan Maximum Entrenchment (FME), and Flow Expansion Angle (FEA). A morphometric analysis was then conducted to evaluate the correlation between the fans and their upstream basins. The linear regression analysis demonstrated both positive and negative correlations between these parameters, highlighting the important role of the upstream basins in controlling sediment delivery to fans. The findings suggest that larger basins contribute to the morphological development of fan systems, with larger, less steep fans forming as a result of greater flows and increased sediment supply from basins with denser drainage networks. Lower values of Mountain Front Sinuosity, Valley Floor Width to Valley Height ratio and Basin Elongation suggest that upstream basins in the ZB are significantly influenced by tectonic forces, resulting in linear mountain fronts, V-shaped valleys and elongated upstream basins. The F-99 fan, in particular, has developed a prominent stepped-fan morphology, attributed to differential uplift, vertical incision, and lateral migration of channels across the fan surface. Along the various fronts of the Zanskar, fan morphology is controlled by a complex interplay of long-term tectonic processes, climate, upstream lithology, and basin characteristics. Tectonic forces, particularly the NW-SE-trending ZSZ/STD and ZCT, exert first-order control on fan morphology by influencing sediment-flux and accommodation space. This influence is evident in tectonically modified landforms such as active mountain fronts, fan terraces, elongated basin shapes, wine-glass valleys and triangular facets, all indicating recent uplift and active tectonics in the region. Our results indicate that ZSZ and ZCT exert significant tectonic control over the geometry and evolution of fans, alongside substantial climatic influences.

Debris‐flow fan channel avulsions: An important secondary erosional process along the Ichino‐sawa torrent, Japan

AbstractSediment transported from debris‐flow initiation zones is typically stored in a topographic feature called a debris‐flow fan, the formation process of which governs secondary sediment transport further downstream. Although sediment transport from debris‐flow fans can impact sediment regimes and change landforms, the determinants of progressive fan formation are not well constrained. To identify such determinants, this study monitored debris flows and performed topographic surveys of debris‐flow fans in the Ichino‐sawa torrent (Japan) during 2016–2017. In this period, eight debris flows occurred, two of which eroded the existing fan and formed a new channel with a short recurrence interval (~40 days). Consequently, these two cases induced substantial sediment transport further downstream from the fan. The examined rainfall indices did not provide a threshold for diagnosing the occurrence of such sediment transport. Debris flows with a large flow depth and a long duration led to changes in the runout direction and subsequently formed new channels. Before these processes, the existing channel was backfilled and plugged by previous debris flows, forming a steep fan surface around the fan apex. The results suggest that increasing the magnitude and the duration of debris flows potentially triggers sediment transport from fans coupled with channel plugging. The annual sediment transport from the fan exceeded almost all sediment yields of the world rivers and was found comparable with that linked with volcanic eruptions and their aftermath. Thus, the fan‐formation process can induce substantial sediment transport, independent of volcanic perturbations and extreme climatic events, and is dependent on the sediment supply from repeated occurrence of debris flows in the initiation zones.

High-resolution observations of recurrent jets from an arch filament system

Solar jets are collimated plasma ejections along magnetic field lines observed in hot (extreme-ultraviolet (EUV) jets) and cool (chromospheric surges) temperature diagnostics. Their trigger mechanisms and the relationship between hot and cool jets are still not completely understood. We aim to investigate the generation of a sequence of active-region solar jets and their evolution from the photospheric to the coronal heights using multithermal observations from ground-based and space-borne instruments. Using the synergy of high-spatial-resolution and high-temporal-resolution observations by the Swedish 1-m Solar Telescope (SST), along with the Solar Dynamics Observatory (SDO), we analyzed a sequence of solar jets originating in a mixed-polarity region between the leading and following sunspots of an active region. We investigated the kinematics of these jets using the spectra from the SST observations. We used a non-force-free field (NFFF) extrapolation technique to derive the magnetic field topology of the active region. A mixed-polarity region is formed over a long period (24 hours) with persistent magnetic flux emergence. This region has been observed as an arch filament system (AFS) in chromospheric SST observations. In this region, negative polarities surrounded by positive polarities create a fan surface with a null point at a height of 6 Mm detected in the NFFF extrapolation. SST observations in the Hbeta spectral line reveal a large flux rope over the AFS moving from north to south, causing successive EUV and cool jets to move in the east--west direction and later towards the south along the long open loops. The high-resolution SST observations (0 per pixel) resolve the dark area observed at the jet base and reveal the existence of an AFS with an extended cool jet, which may be the result of a peeling-like mechanism of the AFS. Based on the combined analysis of SST and AIA observations along with extrapolated magnetic topology, it is suggested that the magnetic reconnection site may move southward by approximately 20 Mm until it reaches a region where the open magnetic field lines are oriented north--south.

Hybrid of non-dominated sorting genetic algorithm II and invasive weed optimization for fan duct surface heat exchanger configuration optimization design

In this research, configuration optimization was conducted for FDSHX (fan duct surface heat exchanger) that is a new type of heat exchanger adopted in aero-engine heat management in recent years. Firstly, a method of Taguchi-ANFIS (Taguchi-Adaptive Neuro-Fuzzy Inference System), which can reduce training data volume utilizing orthogonal experimental matrix, was proposed to construct a rapid response mathematical model between three configuration parameters, including fin pitch, fin thickness, and oil passages number, and two design indicators, including heat transfer capacity and operating weight, based on the data prepared by an experimental validated FDSHX heat transfer capacity calculation method using heat transfer unit simulation. Secondly, a hybrid method of NSGA II-IWO (Non-dominated Sorting Genetic Algorithm II-Invasive Weed Optimization), which can simultaneously obtain the strong abilities of exploration and escaping from trap into local optima, was proposed to drive the constructed response mathematical model to enhance heat transfer through adjusting the three configuration parameters. Optimization comparison was performed between NSGA II-IWO and four classic optimization algorithms including GA (Genetic Algorithm), IWO (Invasive Weed Optimization), CA (Cultural Algorithm), and HS (Harmony Search). This research provides an integrated solution to help mechanical engineers improve the applicability and reasonableness of FDSHX design.

Coefficient Analysis of the Alluvial Fan Surface Geometry: A Methodological Approach to Applied Geomorphology

The alluvial fan is a depositional geomorphic surface at the foothills. Most of the alluvial fans in tropical regions are highly dynamic under wet climatic conditions and neotectonic environments. The fans of this region are covered with fertile top soils and deep forests. The soils attack people for agriculture in this region. Presently the continuously growing population pressure causes huge deforestation in these alluvial fan areas for cultivation which causes an accelerating rate of natural hazards like flash floods, landslides, and soil erosion that accelerate the dynamic nature of the fan surfaces. The coefficient analysis helps to understand the dynamic nature of the alluvial fan surface and thus helps to identify the hazard-prone area for planning purposes.

Searching for Chinese Song Dynasty fans related to cultural dimensions

This study examines the formation of fan culture in China during the Song Dynasty, focusing on the cultural expressions inherent in fan making. With the aim of exploring the fan culture of the Song Dynasty, qualitative research methods and descriptive analysis were employed. The cultural dimensions under investigation include connotations, beliefs, lifestyles, aesthetics, materials, and craftsmanship. To conduct this investigation, the researcher visited the Guangdong Provincial Museum and the Guangdong Provincial Arts and Crafts Mall, where a variety of fans were studied and analyzed for their design and usage patterns. The Song Dynasty in China integrated fan-making with the prevailing culture of the era. Through both practical function and distinctive design, the art adorning the fan faces showcased a wealth of calligraphy and painting from Song Dynasty culture. Over generations, this amalgamation evolved into a unique art form. During the Song Dynasty, fan culture thrived, with fan painting transcending mere decoration to become a distinct genre of painting and calligraphy. Artists of the period often utilized the fan's shape as a canvas, showcasing a diverse array of subjects and an exquisite artistic style. Both in design and production, fan makers of the Song Dynasty achieved remarkable levels of artistry. Fans were crafted from a variety of materials and in different shapes, including Paper Fans, KeSiTuan Fans, and Round Silk Fans, each exhibiting round, square, or hexagonal forms, respectively. The paintings and calligraphy adorning these fans were exceptionally refined, frequently executed by renowned artists such as Su Shi, Mi Fu, and Wen Tong, whose works adorned fan surfaces commonly. These artworks not only demonstrated the artists' skill but also reflected the aesthetic and cultural ethos of Song Dynasty society.

Evolutionary model for glacial lake-outburst fans at the ice-sheet front: Development of meltwater outlets and origins of bedforms

Large-scale landforms originated from jökulhlaups or glacial lake-outburst floods (GLOFs), and their small-scale components help in recognising the sedimentary environment of the flood. The GLOF fans that developed along the Pleistocene ice-sheet margin have not been investigated in detail, and north-eastern Poland, with its Megaflood Landform System and Bachanowo and Szeszupka fans, seems ideal for landform and sedimentary studies. This paper provides (1) an important opportunity to recognise the origins of glacier lake-outburst flood outlets and their evolution during two GLOFs and (2) a model of the origin of ice-marginal fans considering changes in sedimentary environment reflecting flood stages. During the first GLOF (GLOF1), the rising stage of meltwater burst triggered the formation of a supraglacial outlet and the development of the Szeszupka outburst fan. During the pulsed peak discharge, subglacial multi-channelised meltwater outburst caused the formation of the Bachanowo Gate, which was finally transformed at the flood waning stage. Such processes were associated with the widening of the floodwater subglacial routeway, when floodwater outlets rapidly spread across the glacier snout. In contrast, GLOF2 was responsible only for the Szeszupka fan erosion and development of outburst terraces. The small-scale bedforms continuum, recognised on the outburst fan surface, is associated with the development of streamlined erosional residuals, scours and their trains during the rising stage and peak discharge, while the waning stage and very end of flood conditions were favourable to the formation of pendant bars, distributive channels with erosional bars and chute bars, regardless of the feeding systems of the outburst fans.The fan deposits were OSL-dated and revealed either, likely, overly old ages or an age of 13.2 ± 0.9 ka. The latter age would imply the ‘normal’ meltwater outflow having a correlation with the events in the region. Nevertheless, this age might be considered a minimum age of the flood.

Surface grain size of alluvial fans on Mars from thermal inertia, as an indicator of depositional style

The depositional history of alluvial fans on Mars provides insight into the climatic conditions during the time of fan formation in the late Hesperian to early Amazonian. However, traditional stratigraphic analysis of the alluvial fan deposits is not possible across most of Mars. This study assesses the use of thermal inertia data as a tool for sedimentologic interpretation of 437 Mars alluvial fans. Based on previous work demonstrating the relationship between depositional style, grain size, and thermophysical properties, this study uses analysis of the thermal inertia of alluvial fan surfaces across the global population of fans on Mars to make an assessment of depositional styles that built the alluvial fans. The thermal inertia values across the global population of fans are indicative of sand- to pebble-sized sediment. The variability of grain sizes across the global population is more homogenous than expected based on comparisons to terrestrial alluvial fans. Nearly all Mars alluvial fans have an average thermal inertia that corresponds to pebble and smaller grain size, and < 1% of Mars alluvial fans have an average thermal inertia that corresponds to cobble-sized grains. Spatial patterns of thermal inertia variability on alluvial fan surfaces show a small number of fans with evidence for either downslope fining or channelization, but the majority of fans show no recognizable geologic patterns in surface thermal inertia. The interpretation of the thermal inertia-derived grain size suggests that either there is widespread mantling of unconsolidated sand across the surface, or that Mars alluvial fans were built by primarily sand-sized sediment, which may be indicative of lower energy sediment transport events.

Fossilized autogenic responses of grain‐size transition to sediment supply and water discharge: Alluvial fan experiments

ABSTRACTAutogenic feedbacks can produce large‐scale, organized stratigraphic patterns in alluvial fans, but autogenic depositional signatures of specific upstream boundary conditions remain challenging to interpret. Here, a combination of theory, experiment and field application is used to explore how autogenic lithofacies changes can be interpreted as stratigraphic indicators of upstream boundary conditions. Six experiments were conducted to test the effects of sediment supply and water discharge rates on autogenic advance and retreat of the lithofacies boundary (grain‐size transition) in an alluvial fan with two dominant grain sizes. Migration of the grain‐size transition caused a short‐term zigzag pattern in the grain‐size transition position in the dip‐directional deposit section. For each experiment, time‐lapse images and laser topographic scans of the fan surface and stratigraphic cross‐sections of the final deposits were used to quantify characteristic timescales of autogenic processes. Timescales for fan‐margin migration, surface wet‐fraction change and grain‐size transition migration generally shorten as sediment supply rate increases and water discharge rate decreases. Increasing the sediment supply rate shortens the duration of the fluvial sediment storage and release cycle, producing higher frequency zigzags in the grain‐size transition trajectory. Increasing the water discharge tends to widen channels and lengthens the duration of the fluvial sediment storage and release cycle, constructing lower frequency zigzags in the grain‐size transition trajectory. Increasing the water discharge also enables more sediment to transport further downstream during release events, leading to higher magnitude zigzags in the grain‐size transition trajectory. These relationships between upstream boundary conditions and the grain‐size transition trajectory demonstrate how autogenic stratigraphic signals could be used as a tool to infer relative changes in boundary conditions.

Numerical investigations on aero-engine icing characteristics at mixed phase conditions

Ice crystal/mixed phase icing in aero-engine will cause engine surge, stalling, thrust reduction, and even stop in extreme cases, which seriously endangers flight safety. In this paper, the characteristics of mixed phase ice accretion in aero-engines are numerically studied. The air flow field model, mixed phase trajectory model, impact model, sticking model and ice accretion model are established. Meanwhile, the sensitivity parameters of ice accretion, such as flight speed, icing time, melting rate (LWC/TWC), and relative humidity (RH), were investigated in detail. The results show that the ice thickness of nacelle surface and nosecone surface increases with the increase of flight speed. With the increase of fan span, the icing thickness of the fan surface increases significantly. The icing of the fan is mainly concentrated on the pressure side of the fan, while the suction side of the fan only has a small amount of icing in the leading edge. In the early stage of icing, the icing thickness of nacelle increases rapidly, and with the increase of icing time, the icing thickness increases, but the icing growth rate becomes slower. With the increase of the melting rate, the ice thickness of the nacelle, the nosecone and the fan pressure side surface increased significantly. When the fan span is 90 % and the melting rate is 0.05, 0.15, and 0.25, the maximum icing amount on the fan surface is 1.56, 3.85, and 5.71 mm, respectively. When the RH is high, there is more ice accumulation on the nacelle surface. At RH is 80 %, the ice thickness at the nosecone tip reaches 5.48 mm. Finally, when using the hot air deicing method, the hot air flow needs to be reasonably distributed according to the amount of icing, and the parts with less icing can appropriately reduce the distribution of hot air for rational use of energy and energy conservation.

The formation of fan‐deltas in mountain lakes: Findings from Zelené Kežmarské Lake (Slovakia)

AbstractFan‐deltas are formed in mountain lakes, contributing to changes in shorelines' shapes and filling lake basins with sediments. Factors that condition sediment delivery to the lakes and the formation of fan‐deltas are not fully understood. This study aims to identify processes forming fan‐deltas in mountain lakes based on the sedimentary architecture of a fan‐delta filling Zelené Kežmarské Lake (Slovakia). Our study is based on ground‐penetrating radar and seismic refraction surveys conducted over the lake and debris‐flow fans in its vicinity, and grain‐size analyses of the surface deposits. The internal structure of the fan‐delta comprises foreset deposits representing the fan‐delta lobes. Mouth bars were identified in the near‐shore zone. The fan‐delta is built of sands and silty sands whereas an alluvial debris‐flow dominated fan west of the lake contains gravels. A general trend of downslope fining of the fan surface sediments, disturbed by zones of coarse gravels, was identified in the surficial sediments forming the fan. The fan‐delta was formed by depositional events in humid periods, alternating with dry periods featured with a small or no deposition. The lake‐level steadily rose in the humid periods and remained stable in dry periods. The contrast between the coarse sediments forming the alluvial debris‐flow dominated fan, and sands forming the fan‐delta was caused by a selective deposition. Coarse gravels in the fan were mobilized in humid periods but did not reach the lake‐shore. The reason was a basement rock ridge situated parallel to the lake shore. Sands were delivered to the fan‐delta in humid periods owing to frequent high‐energy flows. A deposition of silts took place in dry periods. The studied fan‐delta might preserve the sedimentary record of three humid periods from the last 200 years. However, further studies are needed to establish the timing of the fan‐delta formation.

Diachronous Quaternary Development of the Jiayuguan Fault and Implications for Strain Compartmentalization and Modern Earthquake Hazards in the NW Hexi Corridor, China

AbstractThe NNW‐trending Jiayuguan Fault (JYGF) is an actively developing thrust fault that delimits the SW margin of Jiayuguan, a major industrial city in the northwestern Hexi Corridor, China. In this study, we document the geometry, kinematics, and slip rates of the JYGF based on analysis of satellite imagery, low‐altitude photogrammetry, field observations, paleo‐seismic trenching, and Quaternary dating. The JYGF hanging‐wall contains a NE‐vergent asymmetric anticline of Cretaceous redbeds unconformably overlain by faulted, tilted and folded alluvial fan and fluvial terrace surfaces. Subsidiary fault scarps are associated with anticlinal flexure and contractional strain. The vertical uplift and crustal shortening rates are both ∼0.1 mm/a since ∼420 ka and geomorphic markers and dated landforms indicate southeastward fault propagation and hanging‐wall uplift from the Heishan toward the modern Beida River channel. The NW end of the fault appears to connect with the Altyn‐Tagh‐Heishan‐Jinta'Nanshan sinistral strike‐slip fault array suggesting that the JYGF is one of several parallel, splay faults that transfer strike‐slip motion to active folding and thrusting in the region. We relocate the 1992 Ms 5.4 earthquake epicenter using the NonLinLoc method and suggest that the JYGF may link southeastward with Quaternary‐active faults and folds in the Wenshushan. A seismic rupture along the total fault length of 25–40 km for the JYGF‐Wenshushan deforming belt corresponds to a potential earthquake magnitude in the 6.6–7.0 range. Compartmentalized faulting and folding in the NW–most Hexi Corridor defines a triangular block of active deformation where NE‐directed contractional deformation of the Qilian Shan foreland interacts with E‐W left‐lateral displacement along the Altyn‐Tagh‐Heishan‐Jinta'Nanshan sinistral strike‐slip system.

Alluvial fan response to Alpine Fault earthquakes on the Westland piedmont, Whataroa, Aotearoa‐New Zealand

AbstractWe examined the stratigraphy of alluvial fans formed at the steep range front of the Southern Alps at Te Taho, on the north bank of the Whataroa River in central West Coast, South Island, New Zealand. The range front coincides with the Alpine Fault, an Australian‐Pacific plate boundary fault, which produces regular earthquakes. Our study of range front fans revealed aggradation at 100‐ to 300‐year intervals. Radiocarbon ages and soil residence times (SRTs) estimated by a quantitative profile development index allowed us to elucidate the characteristics of four episodes of aggradation since 1000 CE. We postulate a repeating mode of fan behaviour (fan response cycle [FRC]) linked to earthquake cycles via earthquake‐triggered landslides. FRCs are characterised by short response time (aggradation followed by incision) and a long phase when channels are entrenched and fan surfaces are stable (persistence time). Currently, the Te Taho and Whataroa River fans are in the latter phase. The four episodes of fan building we determined from an OxCal sequence model correlate to Alpine Fault earthquakes (or other subsidiary events) and support prior landscape evolution studies indicating ≥M7.5 earthquakes as the main driver of episodic sedimentation. Our findings are consistent with other historic non‐earthquake events on the West Coast but indicate faster responses than other earthquake sites in New Zealand and elsewhere where rainfall and stream gradients (the basis for stream power) are lower. Judging from the thickness of fan deposits and the short response times, we conclude that pastoral farming (current land‐use) on the fans and probably across much of the Whataroa River fan would be impossible for several decades after a major earthquake. The sustainability of regional tourism and agriculture is at risk, more so because of the vulnerability of the single through road in the region (State Highway 6).

Ultra-high-resolution observations of persistent null-point reconnection in the solar corona

Magnetic reconnection is a key mechanism involved in solar eruptions and is also a prime possibility to heat the low corona to millions of degrees. Here, we present ultra-high-resolution extreme ultraviolet observations of persistent null-point reconnection in the corona at a scale of about 390 km over one hour observations of the Extreme-Ultraviolet Imager on board Solar Orbiter spacecraft. The observations show formation of a null-point configuration above a minor positive polarity embedded within a region of dominant negative polarity near a sunspot. The gentle phase of the persistent null-point reconnection is evidenced by sustained point-like high-temperature plasma (about 10 MK) near the null-point and constant outflow blobs not only along the outer spine but also along the fan surface. The blobs appear at a higher frequency than previously observed with an average velocity of about 80 km s−1 and life-times of about 40 s. The null-point reconnection also occurs explosively but only for 4 minutes, its coupling with a mini-filament eruption generates a spiral jet. These results suggest that magnetic reconnection, at previously unresolved scales, proceeds continually in a gentle and/or explosive way to persistently transfer mass and energy to the overlying corona.

Geomorphic Changes of the Scott River Alluvial Fan in Relation to a Four-Day Flood Event

A four-day glacier-melt flood (13–16 August 2013) caused abrupt geomorphic changes in the proglacial gravel-bed Scott River, which drains the small (10 km2) Scott Glacier catchment (SW Svalbard). This type of flood occurs on Svalbard increasingly during periods of abnormally warm or rainy weather in summer or early autumn, and the probability of occurrence grows in direct proportion to the increase in temperature and/or precipitation intensity. In the summer of 2013, during the measurement season, the highest daily precipitation (17 mm) occurred on 13 August. During the following four days, it constituted in total 47 mm, i.e., 50% of the precipitation total for the measurement period of 2013. The largest flood in 20 years was caused by high precipitation with a synchronous rise in temperature from about 1.0 to 8.6 °C. These values exceeded multi-year averages (32 mm and 5.0 °C, respectively) at an average discharge of 0.9 m3/s (melt season mean 1986–2011). These conditions caused a rapid and abrupt response of the river with the dominant (90%) glacier-fed. The increase in discharge to 4.6 m3/s, initiated by the glacial flood, mobilized significant amounts of sediment in the river bed and channel. Geomorphic changes within the alluvial fan as an area of 58,940 m2, located at the mouth of the Scott River, were detected by multi-sites terrestrial laser scanning using a Leica Scan Station C10 and then estimated using Geomorphic Change Detection (GCD) software. The changes found involved 39% of the alluvial fan area (23,231 m2). The flood-induced total area of lowering (erosion) covered 26% of the alluvial fan (6035 m2), resulting in the removal of 1183 ± 121 m3 of sediment volume. During the final phase of the flood, two times more sediment (1919 ± 344 m3) was re-deposited within the alluvial fan surface, causing significant aggradation on 74% of its area (17,196 m2). These geomorphic changes resulted in an average lowering (erosion) of the alluvial fan surface of 0.2 m and an average rising (deposition) of 0.1 m.

Lithofacies and Depositional Environments of the Garubathan Alluvial Fan, North Bengal, India

Abstract The sedimentology of the Garubathan alluvial fan of north Bengal foothills is a product of Himalayan neotectonics and monsoon climate. The active neo-tectonics of the Main Central Thrust (MCT), Ramgarh Thrust (RT) and Ghis Transverse Fault (GTF) produce a huge amount of angular clasts in the upper reaches of the river Chel and Mal. During the wet season, either sediment flow by gravity or turbulent stream flow or both, move the clasts to the downhill. The tectonic zone of Main Boundary Thrust (MBT) and Main Frontal Thrust (MFT) are relative passive thrusts than the MCT, RT and GTF in the study area. A very low angle slope is observed in the area of MBT and MFT of the study area. So, the downhill deposition occurred in MBT and MFT zones of the study area. The river Chel and Mal are perinial rivers. During dry periods (pre-monsoon and post-monsoon), in the absence of sediment flow by gravity or turbulent stream flow, the low stream competency deposit the fine sediments. To identify the depositional environments three, seven and six lithofacies varieties were identified in the upper, middle and lower fan surfaces, respectively. The non-cohesive sediment flows by gravity deposited large angular boulders, cobbles and pebbles in the upper fan area. These deposits are either chaotic, unsorted, un-imbricated or graded and imbricated. Deposition of sand is scanty. Both, sediment flow by gravity and fluvial processes deposited angular to round clasts with matrix in the middle fan area. In this area the deposits are reverse graded, reverse to normally graded, laminated and cross-bedded. The high facies diversity of this area indicates highly variable nature of the depositional environments. In the lower fan area, presence of both clast-supported chaotic and matrix-supported laminated or cross-bedded layers suggests a complex nature of the depositional environment of sediment flow by gravity and fluvial processes.

Spatial and Temporal Analysis of Geologic Slip Rates, Cucamonga Fault, California, USA: Implications for Along‐Strike Applications and Multi‐Fault Rupture

AbstractTo constrain fault processes and hazard, fault slip rates may be extrapolated over different fault lengths or time intervals. Here, we investigate slip rates for the Cucamonga Fault (CF). The CF is located at the junction of the Transverse Range fault system with the San Andreas and San Jacinto Faults, and it is hypothesized to connect with these faults, promoting the propagation of large, multi‐fault earthquakes. Previous work has shown that CF displacements on late Quaternary alluvial fan surfaces are highly variable along strike. We present two new 10Be surface exposure ages from depth profiles on the alluvial fans. Slip rates are consistent with a rate of 1.4 ± 0.3 m/kyr over time intervals of ∼20, ∼30, and ∼40 kyr. If the CF participates in multi‐fault ruptures, then these earthquakes occur either rarely or with sufficient regularity to maintain apparently steady rates over multiple intervals. We also explore along‐strike fault displacement variability using a calibrated morphological model. The model successfully reproduces scarp profiles and indicates that fault displacement variability can be explained in part by scarp age but not uplift rate. We infer that both erosion by ephemeral gullying and distributed deformation contribute to fault displacement variability, although both are difficult to detect confidently without excavations across the scarp. These investigations show that better characterization of cumulative‐slip variability along strike may improve accuracy and precision of slip rates. Slip rates that do not consider epistemic uncertainties may not be suitable for extrapolation over longer fault sections.

Response of termite mounds to changes of geomorphic forms and processes and associated edaphic variations

Despite extensive research on edaphic variations due to termitaria development, there have been no studies dedicated toward showing how changes in geomorphological components affect the lifecycle stages of termitaria. In this study, we assessed (1) the responses of termite mounds (in terms of their life stages) to changes in geomorphic forms and processes in northeastern Iran; and (2) how extinction of termite mounds encourages a trend of land degradation in semi-arid ecosystems. Samples of soil around active, abandoned, and extinct termite mounds located on young, intermediate, and old alluvial fan surfaces were gathered. Twenty soil physicochemical properties were selected and measured to determine the comparative soil quality indices (SQI). The highest mean SQI value was observed among intermediate fans, where the greatest proportion of active mounds was located. The mean SQI for young and old fans, where the greatest proportion of abandoned mounds was located, displayed a statistically significant decrease. The SQI of areas with extinct mounds exhibited the lowest statistical value. The lower soil quality values for the old and young fans is due to seasonal and annual flooding and associated depositional processes, leading to surface instability on these landforms. The development of gully erosion processes in old fans inhibits soil development and encourages the abandoning of termite mounds. By contrast, the relative stability of the intermediate fan surfaces enables soils to develop, due to the fewer flooding, inundation, and gullying processes, prompting more stability of the termite mounds. These findings describe how environmental changes stimulated by the different geomorphic forms and processes affect the stability trend of termite mounds and lead to changes in their lifecycle stages.

Tectonic geomorphology and Quaternary fault slip rates in the Tsambagarav Massif, Mongolian Altai

AbstractThe NNW‐striking Mongolian Altai is a Late Cenozoic dextral strike–slip deformation belt affected by the far‐field stress caused by the collision between India and Eurasia. The Tsambagarav Massif is bounded by faults, has a triangular plan shape, and attains the highest elevation of the belt. This massif is adjacent to the central segment of the Hovd fault, which is the largest fault in the Mongolian Altai. Here, we use 10Be surface exposure dating, radiocarbon dating, and paleoseismic trenching to reveal deformation patterns and Quaternary slip rates for two range‐bounding faults: the Tsambagarav dextral reverse fault and the Lower thrust fault. The Lower thrust exhibits thrusting motion along the low‐angle structural fabric of the basement rock and cuts Quaternary alluvial fan deposits, vertically offsetting their surfaces by 3.9–5.1 m, with fault scarps extending several kilometres along‐strike. The Tsambagarav dextral reverse fault is characterized by strike–slip motion along the high‐angle structural fabric of basement rock. Various surface deformation features indicate recent dextral strike–slip, including displacements of Late Quaternary moraine by ~50 m. Dividing the measured displacements by 10Be surface exposure ages of alluvial fan surfaces (for the Lower thrust) and moraine (for the Tsambagarav dextral reverse fault) gives a reverse slip rate of 0.3–1.7 mm/yr for the Lower thrust and a horizontal slip rate of 1.7–2.6 mm/yr for the dextral reverse fault. Radiocarbon ages of animal bones in a pond deposit accumulated along an associated tensional crack indicate that the last earthquake that caused a surface rupture occurred between 1924 and 1708 cal yr BP. Our study suggests that strain partitioning has occurred on the faults of the Tsambagarav Massif.