Pub Date : 2024-02-09DOI: 10.5194/esurf-12-321-2024
Lindsay Marie Capito, Enrico Pandrin, Walter Bertoldi, Nicola Surian, Simone Bizzi
Abstract. The difficulties of measuring bedload transport in gravel-bed rivers have given rise to the morphological method wherein sediment transport can be inferred from changes in riverbed elevation and estimates of the distance traveled by sediment: its path length. Because current methods for estimating path length are time- and labor-intensive, we present a method to estimate a characteristic path length from repeat digital elevation models (DEMs of difference, i.e., DoDs). We propose an automated method to extract the spacing between erosional and depositional sites on the DoD by the application of variational mode decomposition (VMD), a signal processing method, to quantify the spacing as a proxy for path length. We developed this method using flume experiments where bed topography and sediment flux were measured and then applied it to published field data with physical path length measured from tracer measurements. Our sediment transport estimates were not significantly different than the measured sediment flux at lower discharges in the lab. However, we observed an underestimation of sediment flux at the higher discharges in the flume study. We interpret this as a limit of the method in confined settings, where sediment transport becomes decoupled from morphological changes. We also explore how the time between survey acquisitions, the morphological active width relative to the channel width, and DoD thresholding techniques affect the proposed method and the potential issues they pose for the morphological method in general.
摘要由于难以测量砾石床河流中的床面负荷迁移量，因此产生了一种形态学方法，即通过河床高程的变化和沉积物移动距离的估算（即路径长度）来推断沉积物的迁移量。由于目前估算路径长度的方法耗时耗力，我们提出了一种从重复数字高程模型（DEMs of difference，即 DoDs）中估算特征路径长度的方法。我们提出了一种自动方法，通过应用信号处理方法变异模态分解（VMD）来提取差异数字高程模型上侵蚀点和沉积点之间的间距，从而量化间距作为路径长度的替代值。我们利用测量床面地形和沉积通量的水槽实验开发了这一方法，然后将其应用于通过示踪测量测量物理路径长度的已公布实地数据。我们的沉积物输运估算值与实验室测量的较低排水量下的沉积物通量没有明显差异。不过，在水槽研究中，我们观察到较高排水量下的沉积物通量被低估了。我们将此解释为该方法在封闭环境中的局限性，在这种环境中，沉积物运移与形态变化脱钩。我们还探讨了勘测采集之间的时间间隔、形态活动宽度与河道宽度的相对关系以及 DoD 临界值技术对拟议方法的影响，以及它们对一般形态学方法造成的潜在问题。
{"title":"Path length and sediment transport estimation from DEMs of difference: a signal processing approach","authors":"Lindsay Marie Capito, Enrico Pandrin, Walter Bertoldi, Nicola Surian, Simone Bizzi","doi":"10.5194/esurf-12-321-2024","DOIUrl":"https://doi.org/10.5194/esurf-12-321-2024","url":null,"abstract":"Abstract. The difficulties of measuring bedload transport in gravel-bed rivers have given rise to the morphological method wherein sediment transport can be inferred from changes in riverbed elevation and estimates of the distance traveled by sediment: its path length. Because current methods for estimating path length are time- and labor-intensive, we present a method to estimate a characteristic path length from repeat digital elevation models (DEMs of difference, i.e., DoDs). We propose an automated method to extract the spacing between erosional and depositional sites on the DoD by the application of variational mode decomposition (VMD), a signal processing method, to quantify the spacing as a proxy for path length. We developed this method using flume experiments where bed topography and sediment flux were measured and then applied it to published field data with physical path length measured from tracer measurements. Our sediment transport estimates were not significantly different than the measured sediment flux at lower discharges in the lab. However, we observed an underestimation of sediment flux at the higher discharges in the flume study. We interpret this as a limit of the method in confined settings, where sediment transport becomes decoupled from morphological changes. We also explore how the time between survey acquisitions, the morphological active width relative to the channel width, and DoD thresholding techniques affect the proposed method and the potential issues they pose for the morphological method in general.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"80 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139759279","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-07DOI: 10.5194/egusphere-2024-71
Aaron T. Steelquist, Gustav B. Seixas, Mary L. Gillam, Sourav Saha, Seulgi Moon, George E. Hilley
Abstract. Incision rates of major rivers may reflect the effects of drainage reorganization, hillslope processes, tectonic uplift, climate, the properties of rocks into which rivers incise, and other autogenic processes. On the Colorado Plateau, incision rates along the Colorado River have been interpreted as resulting from abrupt base-level changes produced by the integration of the Colorado River system. Specifically, the integration of the Colorado River in the location of Grand Canyon is thought to have created a knickpoint, enhanced by lithologic contrasts, which is retreating upstream. While evidence exists for a <1 Ma acceleration of incision on parts of the Colorado River, uncertainty about the processes reflected in shorter-term incision rates muddies comparison with longer-term averages. In this work, we combine a cosmogenic radionuclide depth profile exposure age and post-Infrared Infrared Stimulated Luminescence (p-IR IRSL) to date fluvial deposits adjacent to the San Juan River, a major tributary of the Colorado River, near Mexican Hat, Utah. The deposits, resting on a 32 m strath surface, are constrained to be ∼28–40 ka, suggesting an incision rate of 804–1151 m Myr-1, nearly an order of magnitude higher than the long-term rate of ∼140 m Myr-1 over the past ∼1.2 Ma. We observe fluvial deposits that were abandoned due to a bedrock meander cutoff, which partially explains our accelerated incision rate. We use a simple geometric model, informed by our field data, to demonstrate how planform river evolution may, in some circumstances, increase short-term incision rates, relative to long-term incision rates. These short-term rates may also reflect a combination of autocyclic and climatic processes, which limits their ability to resolve longer-term changes in incision rate that may be related to changes in base-level or tectonics.
摘要主要河流的切入率可能反映了排水系统重组、山坡过程、构造隆起、气候、河流切入岩石的特性以及其他自生过程的影响。在科罗拉多高原，科罗拉多河沿岸的切入率被解释为科罗拉多河水系整合所产生的突然基底变化所致。具体来说，科罗拉多河在大峡谷位置的汇合被认为形成了一个因岩性对比而增强的节理点，该节理点正在向上游后退。虽然有证据表明科罗拉多河的部分河段在 1 亿年前加速了侵蚀，但短期侵蚀速率所反映的过程的不确定性使得与长期平均侵蚀速率的比较变得模糊不清。在这项研究中，我们结合了宇宙放射性核素深度剖面暴露年龄和后红外激发发光法（p-IR IRSL），对犹他州墨西哥帽附近科罗拉多河主要支流圣胡安河附近的河流沉积物进行了年代测定。这些沉积物位于 32 米长的地层表面，年代为 28-40 ka，表明侵蚀速率为 804-1151 m Myr-1，比过去 1.2 Ma 的长期侵蚀速率 140 m Myr-1 高出近一个数量级。我们观察到由于基岩河曲断裂而被遗弃的河道沉积，这部分解释了我们的加速侵蚀速率。我们利用一个简单的几何模型，并结合我们的实地数据，证明了在某些情况下，相对于长期侵蚀速率，平面河流的演化可能会增加短期侵蚀速率。这些短期速率也可能反映了自循环和气候过程的综合作用，这限制了它们解决可能与基底或构造变化有关的长期侵蚀速率变化的能力。
{"title":"The impact of bedrock meander cutoffs on 50 ka-year-scale incision rates, San Juan River, Utah","authors":"Aaron T. Steelquist, Gustav B. Seixas, Mary L. Gillam, Sourav Saha, Seulgi Moon, George E. Hilley","doi":"10.5194/egusphere-2024-71","DOIUrl":"https://doi.org/10.5194/egusphere-2024-71","url":null,"abstract":"<strong>Abstract.</strong> Incision rates of major rivers may reflect the effects of drainage reorganization, hillslope processes, tectonic uplift, climate, the properties of rocks into which rivers incise, and other autogenic processes. On the Colorado Plateau, incision rates along the Colorado River have been interpreted as resulting from abrupt base-level changes produced by the integration of the Colorado River system. Specifically, the integration of the Colorado River in the location of Grand Canyon is thought to have created a knickpoint, enhanced by lithologic contrasts, which is retreating upstream. While evidence exists for a <1 Ma acceleration of incision on parts of the Colorado River, uncertainty about the processes reflected in shorter-term incision rates muddies comparison with longer-term averages. In this work, we combine a cosmogenic radionuclide depth profile exposure age and post-Infrared Infrared Stimulated Luminescence (p-IR IRSL) to date fluvial deposits adjacent to the San Juan River, a major tributary of the Colorado River, near Mexican Hat, Utah. The deposits, resting on a 32 m strath surface, are constrained to be ∼28–40 ka, suggesting an incision rate of 804–1151 m Myr<sup>-1</sup>, nearly an order of magnitude higher than the long-term rate of ∼140 m Myr<sup>-1</sup> over the past ∼1.2 Ma. We observe fluvial deposits that were abandoned due to a bedrock meander cutoff, which partially explains our accelerated incision rate. We use a simple geometric model, informed by our field data, to demonstrate how planform river evolution may, in some circumstances, increase short-term incision rates, relative to long-term incision rates. These short-term rates may also reflect a combination of autocyclic and climatic processes, which limits their ability to resolve longer-term changes in incision rate that may be related to changes in base-level or tectonics.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"5 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139759542","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-06DOI: 10.5194/egusphere-2024-160
Caroline Fenske, Jean Braun, François Guillocheau, Cécile Robin
Abstract. Duricrusts are hard elemental layers forming in climatically contrasted environments. Ferricretes (or iron duricrusts) are a type of duricrust, made of indurated iron layers. They form in tropical to semi-arid environments, but can be currently observed all around the world, in areas such as Africa, South America, India, and Australia. In most cases, they cap hills and appear to protect softer layers beneath. Two hypotheses have been proposed for the formation of duricrusts, i.e., the hydrological or horizontal model where the enrichment in the hardening element (iron for ferricretes) is the product of leaching and precipitation through the beating of the water table during contrasted seasonal cycles, and the laterisation or vertical model, where the formation of iron duricrusts is the final stage of laterisation. In this article, we present the first numerical model for the formation of iron duricrusts based on the hydrological hypothesis. The model is an extension to an existing regolith formation model where the position of the water table is used to predict the formation of a hardened layer at a rate set by a characteristic time scale τ and over a depth set by the beating range of the water table, λ. Hardening causes a decrease in surface erodibility, which we introduce in the model as a dimensionless factor κ that multiplies the surface transport coefficient of the model. Using the model we show under which circumstances duricrusts form by introducing two dimensionless numbers that combine the model parameters (λ and τ) as well as parameters representing external forcing like precipitation rate and uplift rate. We demonstrate that by using model parameter values obtained by independent constraints from field observations, hydrology and geochronology, the model predictions reproduce the observed conditions for duricrust formation. We also show that there exists a strong feedback from duricrust formation on the shape of the regolith and the position of the water table. Finally we demonstrate that the commonly accepted view that, because they are commonly found at the top of hills, duricrusts protect elements of the landscape is most likely an over-interpretation and that caution must be taken before using duricrusts as markers of uplift and/or base level falls.
{"title":"A numerical model for duricrust formation by water table fluctuations","authors":"Caroline Fenske, Jean Braun, François Guillocheau, Cécile Robin","doi":"10.5194/egusphere-2024-160","DOIUrl":"https://doi.org/10.5194/egusphere-2024-160","url":null,"abstract":"<strong>Abstract.</strong> Duricrusts are hard elemental layers forming in climatically contrasted environments. Ferricretes (or iron duricrusts) are a type of duricrust, made of indurated iron layers. They form in tropical to semi-arid environments, but can be currently observed all around the world, in areas such as Africa, South America, India, and Australia. In most cases, they cap hills and appear to protect softer layers beneath. Two hypotheses have been proposed for the formation of duricrusts, i.e., the hydrological or horizontal model where the enrichment in the hardening element (iron for ferricretes) is the product of leaching and precipitation through the beating of the water table during contrasted seasonal cycles, and the laterisation or vertical model, where the formation of iron duricrusts is the final stage of laterisation. In this article, we present the first numerical model for the formation of iron duricrusts based on the hydrological hypothesis. The model is an extension to an existing regolith formation model where the position of the water table is used to predict the formation of a hardened layer at a rate set by a characteristic time scale τ and over a depth set by the beating range of the water table, λ. Hardening causes a decrease in surface erodibility, which we introduce in the model as a dimensionless factor κ that multiplies the surface transport coefficient of the model. Using the model we show under which circumstances duricrusts form by introducing two dimensionless numbers that combine the model parameters (λ and τ) as well as parameters representing external forcing like precipitation rate and uplift rate. We demonstrate that by using model parameter values obtained by independent constraints from field observations, hydrology and geochronology, the model predictions reproduce the observed conditions for duricrust formation. We also show that there exists a strong feedback from duricrust formation on the shape of the regolith and the position of the water table. Finally we demonstrate that the commonly accepted view that, because they are commonly found at the top of hills, duricrusts protect elements of the landscape is most likely an over-interpretation and that caution must be taken before using duricrusts as markers of uplift and/or base level falls.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"9 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139759568","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-02-01DOI: 10.5194/esurf-12-301-2024
Sara Polanco, Mike Blum, Tristan Salles, Bruce C. Frederick, Rebecca Farrington, Xuesong Ding, Ben Mather, Claire Mallard, Louis Moresi
Abstract. The interplay between climate-forced sea level change, erosional and depositional processes, and flexural isostasy in deep time on passive margin deltas remains poorly understood. We performed a series of conceptual simulations to investigate flexural isostatic responses to high-frequency fluctuations in water and sediment load associated with climatically driven sea level changes. We model a large drainage basin that discharges to a continental margin and produces a large deltaic depocenter, then prescribe synthetic and climatic-driven sea level curves of different frequencies to assess flexural response. Results show that flexural isostatic responses are bidirectional over 100–1000 kyr timescales and are in sync with the magnitude, frequency, and direction of sea level fluctuations and that isostatic adjustments play an important role in driving along-strike and cross-shelf river mouth migration and sediment accumulation. Our findings demonstrate that climate-forced sea level changes produce a feedback mechanism that results in self-sustaining creation of accommodation into which sediment is deposited and plays a major role in delta morphology and stratigraphic architecture.
{"title":"Flexural isostatic response of continental-scale deltas to climatically driven sea level changes","authors":"Sara Polanco, Mike Blum, Tristan Salles, Bruce C. Frederick, Rebecca Farrington, Xuesong Ding, Ben Mather, Claire Mallard, Louis Moresi","doi":"10.5194/esurf-12-301-2024","DOIUrl":"https://doi.org/10.5194/esurf-12-301-2024","url":null,"abstract":"Abstract. The interplay between climate-forced sea level change, erosional and depositional processes, and flexural isostasy in deep time on passive margin deltas remains poorly understood. We performed a series of conceptual simulations to investigate flexural isostatic responses to high-frequency fluctuations in water and sediment load associated with climatically driven sea level changes. We model a large drainage basin that discharges to a continental margin and produces a large deltaic depocenter, then prescribe synthetic and climatic-driven sea level curves of different frequencies to assess flexural response. Results show that flexural isostatic responses are bidirectional over 100–1000 kyr timescales and are in sync with the magnitude, frequency, and direction of sea level fluctuations and that isostatic adjustments play an important role in driving along-strike and cross-shelf river mouth migration and sediment accumulation. Our findings demonstrate that climate-forced sea level changes produce a feedback mechanism that results in self-sustaining creation of accommodation into which sediment is deposited and plays a major role in delta morphology and stratigraphic architecture.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"61 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139661571","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-31DOI: 10.5194/esurf-12-271-2024
Tobias Roylands, Robert G. Hilton, Erin L. McClymont, Mark H. Garnett, Guillaume Soulet, Sébastien Klotz, Mathis Degler, Felipe Napoleoni, Caroline Le Bouteiller
Abstract. Chemical weathering of sedimentary rocks can release carbon dioxide (CO2) and consume oxygen (O2) via the oxidation of petrogenic organic carbon and sulfide minerals. These pathways govern Earth's surface system and climate over geological timescales, but the present-day weathering fluxes and their environmental controls are only partly constrained due to a lack of in situ measurements. Here, we investigate the gaseous exchange of CO2 and O2 during the oxidative weathering of black shales and marls exposed in the French southern Alps. On six field trips over 1 year, we use drilled headspace chambers to measure the CO2 concentrations in the shallow critical zone and quantify CO2 fluxes in real time. Importantly, we develop a new approach to estimate the volume of rock that contributes CO2 to a chamber, and assess effective diffusive gas exchange, by first quantifying the mass of CO2 that is stored in a chamber and connected rock pores. Both rock types are characterized by similar contributing rock volumes and diffusive movement of CO2. However, CO2 emissions differed between the rock types, with yields over rock outcrop surfaces (inferred from the contributing rock volume and the local weathering depths) ranging on average between 73 and 1108 tCkm-2yr-1 for black shales and between 43 and 873 tCkm-2yr-1 for marls over the study period. Having quantified diffusive processes, chamber-based O2 concentration measurements are used to calculate O2 fluxes. The rate of O2 consumption increased with production of CO2, and with increased temperature, with an average O2:CO2 molar ratio of 10:1. If O2 consumption occurs by both rock organic carbon oxidation and carbonate dissolution coupled to sulfide oxidation, either an additional O2 sink needs to be identified or significant export of dissolved inorganic carbon occurs from the weathering zone. Together, our findings refine the tools we have to probe CO2 and O2 exchange in rocks at Earth's surface and shed new light on CO2 and O2 fluxes, their drivers, and the fate of rock-derived carbon.
{"title":"Probing the exchange of CO2 and O2 in the shallow critical zone during weathering of marl and black shale","authors":"Tobias Roylands, Robert G. Hilton, Erin L. McClymont, Mark H. Garnett, Guillaume Soulet, Sébastien Klotz, Mathis Degler, Felipe Napoleoni, Caroline Le Bouteiller","doi":"10.5194/esurf-12-271-2024","DOIUrl":"https://doi.org/10.5194/esurf-12-271-2024","url":null,"abstract":"Abstract. Chemical weathering of sedimentary rocks can release carbon dioxide (CO2) and consume oxygen (O2) via the oxidation of petrogenic organic carbon and sulfide minerals. These pathways govern Earth's surface system and climate over geological timescales, but the present-day weathering fluxes and their environmental controls are only partly constrained due to a lack of in situ measurements. Here, we investigate the gaseous exchange of CO2 and O2 during the oxidative weathering of black shales and marls exposed in the French southern Alps. On six field trips over 1 year, we use drilled headspace chambers to measure the CO2 concentrations in the shallow critical zone and quantify CO2 fluxes in real time. Importantly, we develop a new approach to estimate the volume of rock that contributes CO2 to a chamber, and assess effective diffusive gas exchange, by first quantifying the mass of CO2 that is stored in a chamber and connected rock pores. Both rock types are characterized by similar contributing rock volumes and diffusive movement of CO2. However, CO2 emissions differed between the rock types, with yields over rock outcrop surfaces (inferred from the contributing rock volume and the local weathering depths) ranging on average between 73 and 1108 tCkm-2yr-1 for black shales and between 43 and 873 tCkm-2yr-1 for marls over the study period. Having quantified diffusive processes, chamber-based O2 concentration measurements are used to calculate O2 fluxes. The rate of O2 consumption increased with production of CO2, and with increased temperature, with an average O2:CO2 molar ratio of 10:1. If O2 consumption occurs by both rock organic carbon oxidation and carbonate dissolution coupled to sulfide oxidation, either an additional O2 sink needs to be identified or significant export of dissolved inorganic carbon occurs from the weathering zone. Together, our findings refine the tools we have to probe CO2 and O2 exchange in rocks at Earth's surface and shed new light on CO2 and O2 fluxes, their drivers, and the fate of rock-derived carbon.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"37 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139646612","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-30DOI: 10.5194/esurf-12-231-2024
Xuxu Wu, Jonathan Malarkey, Roberto Fernández, Jaco H. Baas, Ellen Pollard, Daniel R. Parsons
Abstract. Wave–current ripples that develop on seabeds of mixed non-cohesive sand and cohesive clay are commonplace in coastal and estuarine environments. While laboratory research on ripples forming in these types of mixed-bed environments is relatively limited, it has identified deep cleaning, the removal of clay below the ripple troughs, as an important factor controlling ripple development. New large-scale flume experiments seek to address this sparsity in data by considering two wave–current conditions with initial clay content, C0, ranging from 0 % to 18.3 %. The experiments record ripple development and pre- and post-experiment bed clay contents to quantify clay winnowing. The present experiments are combined with previous wave-only, wave–current, and current-only experiments to produce a consistent picture of larger and smaller flatter ripples over a range of wave–current conditions and C0. Specifically, the results reveal a sudden decrease in the ripple steepness for C0 > 10.6 %, likely associated with a decrease in hydraulic conductivity of 3 orders of magnitude. Accompanying the sudden change in steepness is a gradual linear decrease in wavelength with C0 for C0 > 7.4 %. Ultimately, for the highest values of C0, the bed remains flat, but clay winnowing still takes place, albeit at a rate 2 orders of magnitude lower than for rippled beds. For a given flow, the initiation time, when ripples first appear on a flat bed, increases with increasing C0. This, together with the fact that the bed remains flat for the highest values of C0, demonstrates that the threshold of motion increases with C0. The inferred threshold enhancement, and the occurrence of large and small ripples, is used to construct a new three-dimensional phase diagram of bed characteristics involving the wave and current Shields parameters and C0, which has important implications for morphodynamic modelling.
{"title":"Influence of cohesive clay on wave–current ripple dynamics captured in a 3D phase diagram","authors":"Xuxu Wu, Jonathan Malarkey, Roberto Fernández, Jaco H. Baas, Ellen Pollard, Daniel R. Parsons","doi":"10.5194/esurf-12-231-2024","DOIUrl":"https://doi.org/10.5194/esurf-12-231-2024","url":null,"abstract":"Abstract. Wave–current ripples that develop on seabeds of mixed non-cohesive sand and cohesive clay are commonplace in coastal and estuarine environments. While laboratory research on ripples forming in these types of mixed-bed environments is relatively limited, it has identified deep cleaning, the removal of clay below the ripple troughs, as an important factor controlling ripple development. New large-scale flume experiments seek to address this sparsity in data by considering two wave–current conditions with initial clay content, C0, ranging from 0 % to 18.3 %. The experiments record ripple development and pre- and post-experiment bed clay contents to quantify clay winnowing. The present experiments are combined with previous wave-only, wave–current, and current-only experiments to produce a consistent picture of larger and smaller flatter ripples over a range of wave–current conditions and C0. Specifically, the results reveal a sudden decrease in the ripple steepness for C0 > 10.6 %, likely associated with a decrease in hydraulic conductivity of 3 orders of magnitude. Accompanying the sudden change in steepness is a gradual linear decrease in wavelength with C0 for C0 > 7.4 %. Ultimately, for the highest values of C0, the bed remains flat, but clay winnowing still takes place, albeit at a rate 2 orders of magnitude lower than for rippled beds. For a given flow, the initiation time, when ripples first appear on a flat bed, increases with increasing C0. This, together with the fact that the bed remains flat for the highest values of C0, demonstrates that the threshold of motion increases with C0. The inferred threshold enhancement, and the occurrence of large and small ripples, is used to construct a new three-dimensional phase diagram of bed characteristics involving the wave and current Shields parameters and C0, which has important implications for morphodynamic modelling.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"36 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139588684","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-30DOI: 10.5194/esurf-12-249-2024
Natalie Barbosa, Johannes Leinauer, Juilson Jubanski, Michael Dietze, Ulrich Münzer, Florian Siegert, Michael Krautblatter
Abstract. Massive sediment pulses in catchments are a key alpine multi-risk component. Substantial sediment redistribution in alpine catchments frequently causes flooding, river erosion, and landsliding and affects infrastructure such as dam reservoirs as well as aquatic ecosystems and water quality. While systematic rock slope failure inventories have been collected in several countries, the subsequent cascading sediment redistribution is virtually unaccessed. For the first time, this contribution reports the massive sediment redistribution triggered by the multi-stage failure of more than 130 000 m3 from the Hochvogel dolomite peak during the summer of 2016. We applied change detection techniques to seven 3D-coregistered high-resolution true orthophotos and digital surface models (DSMs) obtained through digital aerial photogrammetry later optimized for precise volume calculation in steep terrain. The analysis of seismic information from surrounding stations revealed the temporal evolution of the cliff fall. We identified the proportional contribution of > 600 rockfall events (> 1 m3) from four rock slope catchments with different slope aspects and their volume estimates. In a sediment cascade approach, we evaluated erosion, transport, and deposition from the rock face to the upper channelized erosive debris flow channel, then to the widened dispersive debris flow channel, and finally to the outlet into the braided sediment-supercharged Jochbach river. We observe the decadal flux of more than 400 000 m3 of sediment, characterized by massive sediment waves that (i) exhibit reaction times of 0–4 years in response to a cliff fall sediment input and relaxation times beyond 10 years. The sediment waves (ii) manifest with faster response times of 0–2 years in the upper catchment and over 2 years in the lower catchments. The entire catchment (iii) undergoes a rapid shift from sedimentary (102–103 mm a−1) to massive erosive regimes (102 mm a−1) within single years, and the massive sediment redistribution (iv) shows limited dependency on rainfall frequency and intensity. This study provides generic information on spatial and temporal patterns of massive sediment pulses in highly sediment-charged alpine catchments.
摘要集水区的大量泥沙脉冲是高山多重风险的关键组成部分。高山集水区的大量沉积物再分布经常会导致洪水、河流侵蚀和滑坡，并影响大坝水库等基础设施以及水生生态系统和水质。虽然一些国家已经收集了系统的岩石斜坡崩塌清单，但对随后的级联沉积物再分布却几乎一无所知。本文首次报告了 2016 年夏季霍赫沃格尔白云岩山峰超过 13 万立方米的多级崩塌引发的大规模沉积物再分布。我们对通过数字航空摄影测量获得的七张三维重建高分辨率真实正射影像图和数字地表模型（DSM）应用了变化检测技术，随后对其进行了优化，以便在陡峭地形中进行精确的体积计算。对周边台站地震信息的分析揭示了悬崖坠落的时间演变过程。我们确定了来自四个不同坡度的岩坡集水区的大于 600 次落石事件（大于 1 立方米）的比例贡献及其体积估算。通过沉积物级联法，我们评估了从岩壁到上部渠化侵蚀性泥石流河道，再到拓宽的分散性泥石流河道，最后到进入辫状沉积物增压的约赫巴赫河出口的侵蚀、迁移和沉积情况。我们观测到十年一次的超过 400 000 立方米的沉积物流量，其特点是巨大的沉积物波浪：(i) 对崖降沉积物输入的反应时间为 0-4 年，弛豫时间超过 10 年。沉积物波 (ii) 在上游集水区的反应时间较快，为 0-2 年，在下游集水区则超过 2 年。整个集水区（iii）在数年内从沉积（102-103 mm a-1）快速转变为大规模侵蚀（102 mm a-1），而大规模沉积物再分布（iv）对降雨频率和强度的依赖性有限。这项研究提供了有关高沉积高山集水区大量泥沙脉冲时空模式的通用信息。
{"title":"Massive sediment pulses triggered by a multi-stage 130 000 m3 alpine cliff fall (Hochvogel, DE–AT)","authors":"Natalie Barbosa, Johannes Leinauer, Juilson Jubanski, Michael Dietze, Ulrich Münzer, Florian Siegert, Michael Krautblatter","doi":"10.5194/esurf-12-249-2024","DOIUrl":"https://doi.org/10.5194/esurf-12-249-2024","url":null,"abstract":"Abstract. Massive sediment pulses in catchments are a key alpine multi-risk component. Substantial sediment redistribution in alpine catchments frequently causes flooding, river erosion, and landsliding and affects infrastructure such as dam reservoirs as well as aquatic ecosystems and water quality. While systematic rock slope failure inventories have been collected in several countries, the subsequent cascading sediment redistribution is virtually unaccessed. For the first time, this contribution reports the massive sediment redistribution triggered by the multi-stage failure of more than 130 000 m3 from the Hochvogel dolomite peak during the summer of 2016. We applied change detection techniques to seven 3D-coregistered high-resolution true orthophotos and digital surface models (DSMs) obtained through digital aerial photogrammetry later optimized for precise volume calculation in steep terrain. The analysis of seismic information from surrounding stations revealed the temporal evolution of the cliff fall. We identified the proportional contribution of > 600 rockfall events (> 1 m3) from four rock slope catchments with different slope aspects and their volume estimates. In a sediment cascade approach, we evaluated erosion, transport, and deposition from the rock face to the upper channelized erosive debris flow channel, then to the widened dispersive debris flow channel, and finally to the outlet into the braided sediment-supercharged Jochbach river. We observe the decadal flux of more than 400 000 m3 of sediment, characterized by massive sediment waves that (i) exhibit reaction times of 0–4 years in response to a cliff fall sediment input and relaxation times beyond 10 years. The sediment waves (ii) manifest with faster response times of 0–2 years in the upper catchment and over 2 years in the lower catchments. The entire catchment (iii) undergoes a rapid shift from sedimentary (102–103 mm a−1) to massive erosive regimes (102 mm a−1) within single years, and the massive sediment redistribution (iv) shows limited dependency on rainfall frequency and intensity. This study provides generic information on spatial and temporal patterns of massive sediment pulses in highly sediment-charged alpine catchments.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"40 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139670015","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-23DOI: 10.5194/esurf-12-219-2024
Stefan Hergarten
Abstract. Rock avalanches reach considerably greater runout lengths than predicted by Coulomb friction. While it has been known for a long time that runout length increases with volume, explaining the increase qualitatively is still a challenge. In this study, the widely used Voellmy rheology is reinterpreted and modified. Instead of adding a Coulomb friction term and a velocity-dependent term, the modified rheology assigns the two terms to different regimes of velocity. While assuming a transition between Coulomb friction and flow at a given velocity is the simplest approach, a reinterpretation of an existing model for the kinetic energy of random particle motion predicts a dependence of the crossover velocity on the thickness of the rock avalanche. Analytical solutions for a lumped mass on a simple 1D topography reveal the existence of a slope-dominated and a height-dominated regime within the regime of flow. In the slope-dominated regime, the kinetic energy at the foot of the slope depends mainly on the slope angle, while the absolute height relative to the valley floor has little effect, and vice versa. Both regimes can be distinguished by the ratio of a length scale derived from the rheology and the length scale of the topography. Long runout occurs in the height-dominated regime. In combination with empirical relations between volume, thickness, and height, the approach based on the random kinetic energy model reproduces the scaling of runout length with volume observed in nature very well.
{"title":"Scaling between volume and runout of rock avalanches explained by a modified Voellmy rheology","authors":"Stefan Hergarten","doi":"10.5194/esurf-12-219-2024","DOIUrl":"https://doi.org/10.5194/esurf-12-219-2024","url":null,"abstract":"Abstract. Rock avalanches reach considerably greater runout lengths than predicted by Coulomb friction. While it has been known for a long time that runout length increases with volume, explaining the increase qualitatively is still a challenge. In this study, the widely used Voellmy rheology is reinterpreted and modified. Instead of adding a Coulomb friction term and a velocity-dependent term, the modified rheology assigns the two terms to different regimes of velocity. While assuming a transition between Coulomb friction and flow at a given velocity is the simplest approach, a reinterpretation of an existing model for the kinetic energy of random particle motion predicts a dependence of the crossover velocity on the thickness of the rock avalanche. Analytical solutions for a lumped mass on a simple 1D topography reveal the existence of a slope-dominated and a height-dominated regime within the regime of flow. In the slope-dominated regime, the kinetic energy at the foot of the slope depends mainly on the slope angle, while the absolute height relative to the valley floor has little effect, and vice versa. Both regimes can be distinguished by the ratio of a length scale derived from the rheology and the length scale of the topography. Long runout occurs in the height-dominated regime. In combination with empirical relations between volume, thickness, and height, the approach based on the random kinetic energy model reproduces the scaling of runout length with volume observed in nature very well.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"51 2 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139558917","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-19DOI: 10.5194/egusphere-2023-2651
Lingxiao Gong, Peter van der Beek, Taylor F. Schildgen, Edward R. Sobel, Simone Racano, Apolline Mariotti
Abstract. Fluvial drainage patterns in orogenic belts reflect the interaction between tectonics, climate, and lithology. The central South Tian Shan displays a complex fluvial drainage pattern that shifts from longitudinal (flowing parallel to mountain ranges) in the west to transverse (flowing across ranges) in the east. Whether such drainage patterns reflect underlying patterns of tectonic deformation, lithology, climatic changes, or the influence of surface processes within a drainage basin is often unclear. We focus here on the anomalously large Saryjaz catchment of SE Kyrgyzstan, which marks the transition between longitudinal and transverse drainage. We analyse topographic and fluvial metrics including slope, river steepness (ksn) and the integral proxy χ along the river profile, and map the spatial distribution and characteristics of knickpoints to discern the possible controls on the observed drainage pattern. We discriminate between knickpoints of different origin: tectonic, lithologic, glacial, and those linked to transient waves of incision. We find a series of transient knickpoints in tributaries downstream of a sharp 180ᵒ bend in the main stem of the Saryjaz River, which also marks a striking increase in channel steepness. Both observations indicate accelerated incision along this lower reach of the catchment. Knickpoint elevations decrease downstream, whereas incision depth, χ values of knickpoints (measured from the tributary junctions) and ksn values and ratios are constant among tributaries. These results suggest that incision is driven “top-down” by a large-magnitude river-capture event rather than “bottom-up” by base-level fall. We estimate an erodibility parameter from 10Be derived catchment-average denudation rates and use this to estimate the celerity of knickpoints. We find that the knickpoints started retreating at a similar time, between ca. 1.5 and 4.4 Myr ago. Considering the river patterns and the timing constraints, we suggest that this capture event was likely driven by the overfill of Neogene intermontane basins, potentially affected by both tectonic and climate factors.
{"title":"Drainage rearrangement in an intra-continental mountain belt: A case study from the central South Tian Shan, Kyrgyzstan","authors":"Lingxiao Gong, Peter van der Beek, Taylor F. Schildgen, Edward R. Sobel, Simone Racano, Apolline Mariotti","doi":"10.5194/egusphere-2023-2651","DOIUrl":"https://doi.org/10.5194/egusphere-2023-2651","url":null,"abstract":"<strong>Abstract.</strong> Fluvial drainage patterns in orogenic belts reflect the interaction between tectonics, climate, and lithology. The central South Tian Shan displays a complex fluvial drainage pattern that shifts from longitudinal (flowing parallel to mountain ranges) in the west to transverse (flowing across ranges) in the east. Whether such drainage patterns reflect underlying patterns of tectonic deformation, lithology, climatic changes, or the influence of surface processes within a drainage basin is often unclear. We focus here on the anomalously large Saryjaz catchment of SE Kyrgyzstan, which marks the transition between longitudinal and transverse drainage. We analyse topographic and fluvial metrics including slope, river steepness (<em>k<sub>sn</sub></em>) and the integral proxy <em>χ</em> along the river profile, and map the spatial distribution and characteristics of knickpoints to discern the possible controls on the observed drainage pattern. We discriminate between knickpoints of different origin: tectonic, lithologic, glacial, and those linked to transient waves of incision. We find a series of transient knickpoints in tributaries downstream of a sharp 180ᵒ bend in the main stem of the Saryjaz River, which also marks a striking increase in channel steepness. Both observations indicate accelerated incision along this lower reach of the catchment. Knickpoint elevations decrease downstream, whereas incision depth, <em>χ</em> values of knickpoints (measured from the tributary junctions) and <em>k<sub>sn</sub></em> values and ratios are constant among tributaries. These results suggest that incision is driven “top-down” by a large-magnitude river-capture event rather than “bottom-up” by base-level fall. We estimate an erodibility parameter from <sup>10</sup>Be derived catchment-average denudation rates and use this to estimate the celerity of knickpoints. We find that the knickpoints started retreating at a similar time, between ca. 1.5 and 4.4 Myr ago. Considering the river patterns and the timing constraints, we suggest that this capture event was likely driven by the overfill of Neogene intermontane basins, potentially affected by both tectonic and climate factors.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"15 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139508548","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-18DOI: 10.5194/esurf-12-201-2024
Davide Tognin, Andrea D'Alpaos, Luigi D'Alpaos, Andrea Rinaldo, Luca Carniello
Abstract. A proper understanding of sediment resuspension and transport processes is key to the morphodynamics of shallow tidal environments. However, a complete spatial and temporal coverage of suspended sediment concentration (SSC) to describe these processes is hardly available, preventing the effective representation of depositional dynamics in long-term modelling approaches. Through aiming to couple erosion and deposition dynamics in a unique synthetic theoretical framework, we here investigate SSC dynamics, following a similar approach to that adopted for erosion (D'Alpaos et al., 2024). The analysis with the peak-over-threshold theory of SSC time series computed using a fully coupled, bi-dimensional model allows us to identify interarrival times, intensities, and durations of over-threshold events and test the hypothesis of modelling SSC dynamics as a Poisson process. The effects of morphological modifications on spatial and temporal SSC patterns are investigated in the Venice Lagoon, for which several historical configurations in the last 4 centuries are available. Our results show that, similar to erosion events, SSC can be modelled as a marked Poisson process in the intertidal flats for all the analysed morphological lagoon configurations because exponentially distributed random variables describe over-threshold events well. Although erosion and resuspension are intimately intertwined, erosion alone does not suffice to describe also SSC because of the non-local dynamics due to advection and dispersion processes. The statistical characterization of SSC events completes the framework introduced for erosion mechanics, and together, they represent a promising tool to generate synthetic, yet realistic, time series of shear stress and SSC for the long-term modelling of tidal environments.
{"title":"Statistical characterization of erosion and sediment transport mechanics in shallow tidal environments – Part 2: Suspended sediment dynamics","authors":"Davide Tognin, Andrea D'Alpaos, Luigi D'Alpaos, Andrea Rinaldo, Luca Carniello","doi":"10.5194/esurf-12-201-2024","DOIUrl":"https://doi.org/10.5194/esurf-12-201-2024","url":null,"abstract":"Abstract. A proper understanding of sediment resuspension and transport processes is key to the morphodynamics of shallow tidal environments. However, a complete spatial and temporal coverage of suspended sediment concentration (SSC) to describe these processes is hardly available, preventing the effective representation of depositional dynamics in long-term modelling approaches. Through aiming to couple erosion and deposition dynamics in a unique synthetic theoretical framework, we here investigate SSC dynamics, following a similar approach to that adopted for erosion (D'Alpaos et al., 2024). The analysis with the peak-over-threshold theory of SSC time series computed using a fully coupled, bi-dimensional model allows us to identify interarrival times, intensities, and durations of over-threshold events and test the hypothesis of modelling SSC dynamics as a Poisson process. The effects of morphological modifications on spatial and temporal SSC patterns are investigated in the Venice Lagoon, for which several historical configurations in the last 4 centuries are available. Our results show that, similar to erosion events, SSC can be modelled as a marked Poisson process in the intertidal flats for all the analysed morphological lagoon configurations because exponentially distributed random variables describe over-threshold events well. Although erosion and resuspension are intimately intertwined, erosion alone does not suffice to describe also SSC because of the non-local dynamics due to advection and dispersion processes. The statistical characterization of SSC events completes the framework introduced for erosion mechanics, and together, they represent a promising tool to generate synthetic, yet realistic, time series of shear stress and SSC for the long-term modelling of tidal environments.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"41 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139497341","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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