Earth Surface Processes and Landforms最新文献

The Thar Desert, India has desert pavements comprising angular-subangular to well-rounded gravels at marginally higher elevations than the surrounding terrain. Sedimentological and geomorphic analyses suggest that the pavements are lags of weathered Mesozoic and older bedrock. The presence of Palaeolithic artefacts on the pavement surfaces and occasionally within their matrix was used to infer their antiquity and landscape stability.

This study presents the first surface exposure ages based on cosmic-ray-produced ¹⁰Be and ²¹Ne for pavements at four sites in the Thar Desert, viz. Bhojka, Hamira, Solanki and Jayal. The computation of model exposure ages assumed that (a) the gravels were derived from cemented conglomerates, uplifted by tectonics and thereafter disintegrated by climate, and (b) cosmogenic nuclide production in the gravels began when the conglomerates approached the surface and, continued during their disintegration, gravity sliding of individual gravels and storage, until the present. Assuming an average burial depth of 50 cm, ²¹Ne and ¹⁰Be data provide ages ranging from 1.30 to 2.92 Ma and 1.11 to 5.4 Ma, respectively, for the two nuclides.

Published electron spin resonance ages of Thar calcretes suggest the presence of water and extreme seasonality since 1.54 Ma. Such conditions facilitated the mobilization and precipitation of carbonates. The pavement ages and the minimum age of the conglomerate at 2.51 Ma extend the time of such desertic conditions to > 2.51 Ma and suggest that the initiation of desertic conditions in the Thar was possibly linked to global aridity beginning around 3.6 Ma.

Depending on assumptions, cosmic ray surface exposure (¹⁰Be) ages at Jayal range between 0.76 and 2.43 Ma. In the context of the Indian Palaeolithic, the presence of tools on the gravel surfaces and within dunes, suggests frequent occupation of this region from at least 0.76 Ma and, parallels Early to Middle Pleistocene Acheulian assemblages from Southern India.

Moles—small insectivorous mammals of the family Talpidae—are widespread across the Northern Hemisphere. These subterranean mammals are easily detected through the mounds, or molehills, they construct as surface bioproducts of tunnel systems excavated underground. The dense aggregation of these bioconstructions in a range of environments (e.g., floodplains, woodland, coastal dunes and upland regions) indicates that moles may play an important role in sediment systems. However, compared with other fossorial mammals (e.g., gophers and rabbits), the impact of moles as direct and indirect biogeomorphic agents is poorly understood. Furthermore, little is known about how molehills develop and degrade over time or how long they persist as landscape features. By examining molehills created by the European mole (Talpa europaea) over 4 months on a floodplain in Oxfordshire, UK, we provide a quantitative assessment of how these landforms evolve over time and space. Through the creation of high-resolution digital elevation models (DEMs) using structure-from-motion (SfM) photogrammetry, we derive a variety of metrics describing molehill morphology and produce a detailed record of how molehills change at weekly time intervals. In addition, measurements of molehill volume are used to estimate the excavation rate of moles over a month. Findings show that (i) molehills are dynamic landforms that change in size and shape in response to phases of construction, collapse, erosion and rebuilding; (ii) rates of degradation are influenced by soil characteristics and seasonal weather conditions; (iii) molehills can persist as landscape features for several months; and (iv) moles are capable of moving a substantial volume of sediment in highly active areas (3.89 m³ ha⁻¹ month⁻¹). Future work is now needed to determine the geomorphic impact of T. europaea over larger spatial scales (e.g., river catchments) and longer timescales (e.g., years–decades) to determine its importance in relation to other bioturbators and within the wider sediment system.

Environmental flows are commonly provided in regulated rivers to maintain and restore riverine environments, including riverbank vegetation. Given the expense and political sensitivity of providing water for the environment, greater certainty regarding the expected benefits of environmental flows is required. We assessed the role of managed flows (for both environmental and consumptive purposes) in delivering sediment and plant propagules to facilitate riverbank recovery. Using artificial turf mats, we determined sediment and seed deposition from 11 flow events over 3 years of varying magnitudes, durations and timing in a heavily regulated lowland river in south-east Australia. At three sites on the Goulburn River, Victoria, mats were placed on different geomorphic features along an elevation gradient (bars, benches, banks and ledges) before a flow event, and the sediment deposited during the event was analysed and assessed for seedling emergence. A total of 401 kg of sediment and 110 980 seeds were sampled. Mats that were inundated via managed flow releases had an order of magnitude more sediment, and around twice the richness of seed taxa, than mats that were not inundated. More sediment and seed taxa were deposited on low-lying bars than on more elevated features, while seed composition but not abundance varied across features. A longer duration of inundation was associated with the deposition of more sediment, but not seed taxa or abundance. Unexpectedly, there was no evidence that managed flows delivered less sediment and seeds compared with unregulated tributary inflows. Our findings suggest that in regulated rivers, environmental flows are likely to be critical for providing the sediment and seed necessary to restore geomorphic conditions and promote plant recruitment. Longer flow durations are likely to provide more sediment, while high-flow events may be particularly important for promoting diverse native riparian plant communities across the full range of in-channel geomorphic features.

This study presents case studies conducted in northeast Thailand, where sinkhole collapses have continuously occurred in certain areas. Rapid descent of groundwater in a karst aquifer has the potential to induce sinkhole collapses within the karst morphology. Field investigations have revealed surface expressions of potentially hazardous sinkholes associated with zones of groundwater depression and abandoned groundwater wells. 2D electrical resistivity tomography (ERT) profiles were executed along the trend of such sinkhole collapses. The ERT results were combined to outline potentially dangerous cavities and continuous fractures. Sinkhole collapses in this scenario are primarily induced by groundwater depression and rainfall. Groundwater flows through conduits connecting a quarry with a karst cavern network, and dewatering of the quarry reduces the surrounding groundwater level. Runoff from rainfall percolates within overburden and enters air-filled cavities. Additionally, quarry blasting activities may cause vibrations that trigger the formation of sinkholes. Observations of surficial collapse features were generally consistent with geophysical ERT-interpreted subsurface cavities and fractures. Consequently, implementing regulatory measures to restrict the depth of limestone quarrying that affects groundwater levels may be necessary to prevent sinkhole collapses. The sinkhole formation phenomenon underscores a critical link between groundwater fluctuations and the stability of karst landscapes.

River classification is a necessary starting point for understanding river ecosystems and developing management guidelines. Using GIS to analyse an Andean river basin, we compare the application of two geomorphic classification methods at the segment scale: The Geomorphic Units Survey Classification System (GUS) and the Functional Process Zones (FPZ). Segment definition follows a manual procedure in GUS and a semi-automated procedure in FPZ. Our objective was to assess the relationship between geomorphology and fish assemblages' structure. Fish sampling was carried out in collaboration with participants from local indigenous Mapuche-Pewenche communities. Non-parametric multivariate statistical analyses were conducted in order to quantify and describe geomorphic patterns and whether fish assemblages responded consistently with river classifications. Both classifications give insight into the physical characteristics of rivers, such as slope and floodplain width, that make habitat available for different fish assemblages. The two methods provide results that consistently coincide in their identification of geographic distribution and main geomorphic variables of different river types (geomorphic types) throughout the river network. The variation of different river geomorphologies was associated with variation in fish assemblage structure. Geomorphic variables that best characterize the distribution pattern of fish assemblages were elevation, confinement and valley floor width. Confined rivers accommodated highly similar fish assemblages dominated by invasive trout (Salmo trutta and Oncorhynchus mykiss). Unconfined rivers located at higher elevations had greater temporal variability and were mainly composed of trout and native catfish Trichomycterus areolatus. Semiconfined rivers presented the highest geomorphic variability and were associated with high spatial and temporal variability of fish assemblages characterized by both native and non-native species. The association between fish assemblages and fluvial geomorphology could help in prioritizing rivers for exotic fish species control. These findings should aid in restoring highly intervened Andean rivers and improving management techniques in basins with a variety of human activities.

The São Francisco River in Northeast Brazil has seen hydrological and morphological changes due to extensive damming and climate change over the past century. In this study, we examine the influence of human activities and natural fluctuations in precipitation on the hydrological patterns of the basin and the morphological responses of the lower course of the river (LOW-SF) to these alterations over a span of several decades. The findings indicate a decrease in water release by 41% from 1995 to 2013 and 54% from 2013 to 2018, solely attributed to human actions. Furthermore, the operation of the reservoirs of the large dams resulted in a reduction in hydrological seasonality. The changing hydrological regime caused morphological changes that resulted in an expansion of the exposed subaerial fluvial bars in the LOW-SF and a reduction in channel width. As a result, the abandonment of small secondary channels occurred, leading to the cessation of inundation in previously buried elevated portions of bars, even during certain seasons. Another important factor was the spread of morphological changes in the LOW-SF, which started from the areas farthest from the last dam in the series of large dams, the Xingó Dam, and spread to the nearby regions. This is due to the lack of major tributaries in the semiarid region of the LOW-SF. The integrated assessment presented in this study illustrates both natural and anthropogenic influences. Moreover, in light of projected declines in precipitation, it is anticipated that natural phenomena could result in a substantial 73% decrease in water flow by the mid-20th century. This climatic scenario will lead to increased utilization of hydroelectric plants and more stringent control of water flow downstream of the dam cascade, intensifying the already documented adverse effects and posing the possibility of novel morphological adaptations.

Glacial lake outburst floods (GLOFs) are sudden, and often hazardous, floods occurring upon the failure of a glacial lake dam or moraine. A GLOF occurred at Sulzenau Lake (Tyrol, Austria) in August 2017 due to a partial moraine and dam failure, damaging nearby infrastructure. Due to the ongoing retreat of Sulzenau Glacier, the areal extent, depth, water volume, and shoreline configuration of Sulzenau Lake fluctuate over both short- and long-term periods. Here, we used remote sensing data to create a detailed geomorphological overview of the valley, analyse the lake's evolution since 2009, and characterize the conditions leading to the 2017 dam failure. Using optical remote sensing imagery, we generated detailed pre- and post-event geomorphological maps of Sulzenau Lake and areas impacted by the GLOF to characterize erosional and depositional zones. We employed the Normalized Difference Water Index (NDWI) and mapped the post-event boulder distribution. Based on multi-temporal mapping, we calculated water volumes, analysed changes in lake and glacier surfaces since 1970, and compared them with ERA-5 meteorological data. Lake growth was primarily due to rising temperatures and glacier retreat. In 2017, both precipitation and air temperatures in the Sulzenau Valley exceeded the 1991–2021 averages, with precipitation 14.8% higher and air temperatures 0.35°C above the 30-year mean. Ice velocities for Sulzenau Glacier reached 170 m/year during 2015–2022. By modelling flow conditions required for observed boulder movements during the GLOF, we constrained the peak discharge to 150–200 m³/s. No significant pre-2017 GLOF activity or meteorological anomalies were detected. Accordingly, we attribute the GLOF and dam failure to an increased meltwater flux and increased precipitation, possibly augmented by subglacial/englacial lake drainage. The 2017 Sulzenau Valley GLOF is a pertinent example of environmental changes and associated hazards in high-mountain glacial environments due to global warming.

Severe wildfire may alter steep mountain streams by increasing peak discharges, elevating sediment and wood inputs into channels, and increasing susceptibility to landslides and debris flows. In the Pacific Northwest, where mean annual precipitation is high and mean fire-return intervals range from decades to centuries, understanding of steep stream response to fire is limited. We evaluate the hydrologic and geomorphic response of ~100-m-long steep stream reaches to the large-scale and severe 2020 fires in the Western Cascade Range, Oregon. In the two runoff seasons after the fires, peak flows in burned reaches were below the 2-year recurrence interval flood, a level sufficient to mobilize the median grain size of bed material, but not large enough to mobilize coarser material and reorganize channel morphology. Sediment inputs to study streams consisted of two road-fill failure landslides, slumps, sheetwash, and minor bank erosion; precipitation thresholds to trigger debris flows were not exceeded in our sites. There was a 50% increase in the number of large wood pieces in burned reaches after the fires. Changes in fluxes of water, sediment, and wood induced shifts in the balance of sediment supply to transport capacity, initiating a sequence of sediment aggradation and bed-material fining followed by erosion and bed-material coarsening. Gross channel form showed resilience to change, and an unburned reference reach exhibited little morphologic change. Post-fire recruitment of large wood will likely have long-term implications for channel morphology and habitat heterogeneity. Below-average precipitation during the study period, combined with an absence of extreme precipitation events, was an important control on channel responses. Climate change may have a complex effect on stream response to wildfire by increasing the propensity for both drought and extreme rain events and by altering vegetation recovery patterns.

Earthquakes are vibrations that occur on the surface of earth, generating fires, ground shaking, tsunamis, landslides and cracks. These incidents can cause severe damage and loss of life. Accurate earthquake forecasts are critical for anticipating and mitigating these hazards, which can avoid damage to buildings and infrastructure and save lives. To address the challenges given by earthquakes probabilistic nature, this paper presents a hybrid SARIMA–XGBoost approach to earthquake magnitude prediction. The suggested technique consists of a two-step process: an exploration phase that uses exploratory data analysis, which includes descriptive statistics and data visualisation, and a prediction phase that focusses on forecasting future earthquakes. Using a large significant earthquake dataset spanning 1965–2023, the study intends to gain insights and lessons for more effective earthquake prediction methods. Further, in a comparison analysis, the results of SARIMA-XGBoost model are compared to those of traditional ARIMA and SARIMA models. The results highlight the superior performance of the hybrid SARIMA–XGBoost model, showcasing a mean absolute error (MAE) of 0.038, a mean squared error (MSE) of 0.0040, and a root mean squared error (RMSE) of 0.068. These metrics collectively underscore the model's enhanced accuracy in forecasting earthquake magnitudes. The notably low values of MAE, MSE and RMSE indicate that our hybrid approach significantly improves prediction accuracy compared to alternative models. By integrating SARIMA's time series (TS) analysis with XGBoost's machine learning (ML) capabilities, the hybrid model reduces forecasting errors more effectively, demonstrating its clear advantage in precision.

Rock glaciers are characteristic landforms in alpine environments originating from the movement of permanently frozen ground. Hereby, rock glacier velocity (RGV) is an important parameter for understanding the effects of climate change on mountain permafrost. Although understanding of rock glacier dynamics has increased during the last decades, linking small-scale surface kinematics to sub-surface properties and heterogeneities remains a challenge. To address this gap, we conducted geophysical surveys (electrical resistivity tomography [ERT] and ground-penetrating radar [GPR]) along two profile lines of 450 and 950 m in length on a rock glacier in the Central Swiss Alps. Additionally, RGV was derived from Sentinel-1 differential synthetic aperture radar interferometry (DInSAR) to quantify annual east–west displacement and elevation change as well as seasonal acceleration during the snow-free summer months with a ground sampling distance of 5 m. Our results show that movement angle and seasonality are highly associated with different patterns in sub-surface structure. These different movement patterns are linked to subunits of different morphological origins. Thereby, we can upscale the geophysical results based on the DInSAR surface movement parameters and outline an area within the study site probably affected by ice of glacial origin. Hence, DInSAR movement angle and seasonality can help to bring local sub-surface information derived from time-consuming geophysical investigations into the spatial domain. In this way, a better understanding of the current morphodynamics as well as the past and future evolution of the landform can be reached. Applying the approach to other sites with available geophysical investigations could enhance our knowledge about systematic links between surface kinematics and the internal structure of rock glaciers and other ice-rich glacial and peri-glacial landforms, as well as their response to a warming climate.