Pub Date : 2024-02-26DOI: 10.5194/esurf-12-399-2024
Moritz Altmann, Madlene Pfeiffer, Florian Haas, Jakob Rom, Fabian Fleischer, Tobias Heckmann, Livia Piermattei, Michael Wimmer, Lukas Braun, Manuel Stark, Sarah Betz-Nutz, Michael Becht
Abstract. We show a long-term erosion monitoring of several geomorphologically active gully systems on Little Ice Age lateral moraines in the European Central–Eastern Alps, covering a total time period from 1953 to 2019 and including several survey periods in order to identify corresponding morphodynamic trends. For the implementation, DEM (digital elevation model) of Differences (DoDs) were calculated, based on multitemporal high-resolution digital elevation models from historical aerial images (generated by structure from motion photogrammetry with multi-view stereo) and light detection and ranging from airborne platforms. Two approaches were implemented to achieve the corresponding objectives. First, by calculating linear regression models using the accumulated sediment yield and the corresponding catchment area (on a log–log scale), the range of the variability in the spatial distribution of erosion values within the sites. Second, we use volume calculations to determine the total and the mean sediment yield (as well as erosion rates) of the entire sites. Subsequently, both the sites and the different time periods of both approaches are compared. Based on the slopes of the calculated regression lines, it can be shown that the highest variability in the sediment yield at the sites occurs in the first time period (mainly 1950s to 1970s). This can be attributed to the fact that within some sites the sediment yield per square metre increases clearly more strongly (regression lines with slopes up to 1.5). In contrast, in the later time periods (1970s to mid-2000s and mid-2000s to 2017/2019), there is generally a decrease in 10 out of 12 cases (regression lines with slopes around 1). However, even at sites with an increase in the variability in the sediment yield over time, the earlier high variabilities are no longer reached. This means that the spatial pattern of erosion in the gully heads changes over time as it becomes more uniform. Furthermore, using sediment volume calculations and corresponding erosion rates, we show a generally decreasing trend in geomorphic activity (amount of sediment yield) between the different time periods in 10 out of 12 sites, while 2 sites show an opposite trend, where morphodynamics increase and remain at the same level. Finally, we summarise the results of long-term changes in the morphodynamics of geomorphologically active areas on lateral moraines by presenting the “sediment activity concept”, which, in contrast to theoretical models, is based on actually calculated erosion. The level of geomorphic activity depends strongly on the characteristics of the sites, such as size, slope length, and slope gradient, some of which are associated with deeply incised gullies. It is noticeable that especially areas with influence of dead ice over decades in the lower slope area show high geomorphic activity. Furthermore, we show that system internal factors, as well as the general paraglacial adjustment process, have a great
{"title":"Long-term monitoring (1953–2019) of geomorphologically active sections of Little Ice Age lateral moraines in the context of changing meteorological conditions","authors":"Moritz Altmann, Madlene Pfeiffer, Florian Haas, Jakob Rom, Fabian Fleischer, Tobias Heckmann, Livia Piermattei, Michael Wimmer, Lukas Braun, Manuel Stark, Sarah Betz-Nutz, Michael Becht","doi":"10.5194/esurf-12-399-2024","DOIUrl":"https://doi.org/10.5194/esurf-12-399-2024","url":null,"abstract":"Abstract. We show a long-term erosion monitoring of several geomorphologically active gully systems on Little Ice Age lateral moraines in the European Central–Eastern Alps, covering a total time period from 1953 to 2019 and including several survey periods in order to identify corresponding morphodynamic trends. For the implementation, DEM (digital elevation model) of Differences (DoDs) were calculated, based on multitemporal high-resolution digital elevation models from historical aerial images (generated by structure from motion photogrammetry with multi-view stereo) and light detection and ranging from airborne platforms. Two approaches were implemented to achieve the corresponding objectives. First, by calculating linear regression models using the accumulated sediment yield and the corresponding catchment area (on a log–log scale), the range of the variability in the spatial distribution of erosion values within the sites. Second, we use volume calculations to determine the total and the mean sediment yield (as well as erosion rates) of the entire sites. Subsequently, both the sites and the different time periods of both approaches are compared. Based on the slopes of the calculated regression lines, it can be shown that the highest variability in the sediment yield at the sites occurs in the first time period (mainly 1950s to 1970s). This can be attributed to the fact that within some sites the sediment yield per square metre increases clearly more strongly (regression lines with slopes up to 1.5). In contrast, in the later time periods (1970s to mid-2000s and mid-2000s to 2017/2019), there is generally a decrease in 10 out of 12 cases (regression lines with slopes around 1). However, even at sites with an increase in the variability in the sediment yield over time, the earlier high variabilities are no longer reached. This means that the spatial pattern of erosion in the gully heads changes over time as it becomes more uniform. Furthermore, using sediment volume calculations and corresponding erosion rates, we show a generally decreasing trend in geomorphic activity (amount of sediment yield) between the different time periods in 10 out of 12 sites, while 2 sites show an opposite trend, where morphodynamics increase and remain at the same level. Finally, we summarise the results of long-term changes in the morphodynamics of geomorphologically active areas on lateral moraines by presenting the “sediment activity concept”, which, in contrast to theoretical models, is based on actually calculated erosion. The level of geomorphic activity depends strongly on the characteristics of the sites, such as size, slope length, and slope gradient, some of which are associated with deeply incised gullies. It is noticeable that especially areas with influence of dead ice over decades in the lower slope area show high geomorphic activity. Furthermore, we show that system internal factors, as well as the general paraglacial adjustment process, have a great","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"15 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-02-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139968321","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 : 2024-02-26DOI: 10.5194/esurf-12-381-2024
Paul A. Carling
Abstract. The size distributions and the shapes of detrital rock clasts can shed light on the environmental history of the clast assemblages and the processes responsible for clast comminution. For example, mechanical fracture due to the stresses imposed on a basal rock surface by a body of flowing glacial ice releases initial “parent” shapes of large blocks of rock from an outcrop, which then are modified by the mechanics of abrasion and fracture during subglacial transport. The latter processes produce subsequent generations of shapes, possibly distinct in form from the parent blocks. A complete understanding of both the processes responsible for block shape changes and the trends in shape adjustment with time and distance away from the source outcrop is lacking. Field data on edge rounding and shape changes of Shap granite blocks (dispersed by Devensian ice eastwards from the outcrop) are used herein to explore the systematic changes in block form with distance from the outcrop. The degree of edge rounding for individual blocks increases in a punctuated fashion with the distance from the outcrop as blocks fracture repeatedly to introduce new fresh unrounded edges. In contrast, block shape is conservative, with parent blocks fracturing to produce self-similar “child” shapes with distance. Measured block shapes evolve in accord with two well-known models for block fracture mechanics – (1) stochastic and (2) silver ratio models – towards one or the other of these two attractor states. Progressive reduction in block size, in accord with fracture mechanics, reflects the fact that most blocks were transported at the sole of the ice mass and were subject to the compressive and tensile forces of the ice acting on the stoss surfaces of blocks lying against a bedrock or till surface. The interpretations might apply to a range of homogeneous hard rock lithologies.
{"title":"Coevolving edge rounding and shape of glacial erratics: the case of Shap granite, UK","authors":"Paul A. Carling","doi":"10.5194/esurf-12-381-2024","DOIUrl":"https://doi.org/10.5194/esurf-12-381-2024","url":null,"abstract":"Abstract. The size distributions and the shapes of detrital rock clasts can shed light on the environmental history of the clast assemblages and the processes responsible for clast comminution. For example, mechanical fracture due to the stresses imposed on a basal rock surface by a body of flowing glacial ice releases initial “parent” shapes of large blocks of rock from an outcrop, which then are modified by the mechanics of abrasion and fracture during subglacial transport. The latter processes produce subsequent generations of shapes, possibly distinct in form from the parent blocks. A complete understanding of both the processes responsible for block shape changes and the trends in shape adjustment with time and distance away from the source outcrop is lacking. Field data on edge rounding and shape changes of Shap granite blocks (dispersed by Devensian ice eastwards from the outcrop) are used herein to explore the systematic changes in block form with distance from the outcrop. The degree of edge rounding for individual blocks increases in a punctuated fashion with the distance from the outcrop as blocks fracture repeatedly to introduce new fresh unrounded edges. In contrast, block shape is conservative, with parent blocks fracturing to produce self-similar “child” shapes with distance. Measured block shapes evolve in accord with two well-known models for block fracture mechanics – (1) stochastic and (2) silver ratio models – towards one or the other of these two attractor states. Progressive reduction in block size, in accord with fracture mechanics, reflects the fact that most blocks were transported at the sole of the ice mass and were subject to the compressive and tensile forces of the ice acting on the stoss surfaces of blocks lying against a bedrock or till surface. The interpretations might apply to a range of homogeneous hard rock lithologies.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"27 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-02-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139967556","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 : 2024-02-26DOI: 10.5194/egusphere-2024-336
Stefan Hergarten
Abstract. Faceted topographies at normal faults have been studied for more than a century. Since the dip angle of the facets is typically much lower than the dip angle of the fault, it is clear that the facets are not just the exhumed footwall, but have been eroded considerably. It has also been shown that a constant erosion rate in combination with a constant rate of displacement can explain the occurrence of planar facets. Quantitatively, however, the formation of faceted topographies is still not fully understood. In this study, the shared stream-power model for fluvial erosion and sediment transport is used in combination with a recently published extension for hillslopes. As a major theoretical result, it is found that the ratio of the tangent of the facet angle and the dip angle of the fault as well as the ratio of baseline length and horizontal width of perfect triangular facets mainly depends on the ratio of the horizontal rate of displacement and the hillslope erodibility. Numerical simulations reveal that horizontal displacement is crucial for the formation of triangular facets. For vertical faults, facets are rather polygonal and much longer than wide. While the sizes of individual facets vary strongly, the average size is controlled by the ratio of hillslope erodibility and fluvial erodibility.
{"title":"A simple model for faceted topographies at normal faults based on an extended stream-power law","authors":"Stefan Hergarten","doi":"10.5194/egusphere-2024-336","DOIUrl":"https://doi.org/10.5194/egusphere-2024-336","url":null,"abstract":"<strong>Abstract.</strong> Faceted topographies at normal faults have been studied for more than a century. Since the dip angle of the facets is typically much lower than the dip angle of the fault, it is clear that the facets are not just the exhumed footwall, but have been eroded considerably. It has also been shown that a constant erosion rate in combination with a constant rate of displacement can explain the occurrence of planar facets. Quantitatively, however, the formation of faceted topographies is still not fully understood. In this study, the shared stream-power model for fluvial erosion and sediment transport is used in combination with a recently published extension for hillslopes. As a major theoretical result, it is found that the ratio of the tangent of the facet angle and the dip angle of the fault as well as the ratio of baseline length and horizontal width of perfect triangular facets mainly depends on the ratio of the horizontal rate of displacement and the hillslope erodibility. Numerical simulations reveal that horizontal displacement is crucial for the formation of triangular facets. For vertical faults, facets are rather polygonal and much longer than wide. While the sizes of individual facets vary strongly, the average size is controlled by the ratio of hillslope erodibility and fluvial erodibility.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"30 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-02-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139967910","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 : 2024-02-23DOI: 10.5194/egusphere-2023-2099
Andrew Hollyday, Maureen E. Raymo, Jacqueline Austermann, Fred Richards, Mark Hoggard, Alessio Rovere
Abstract. Global mean sea level during the mid-Pliocene Epoch (~3 Ma), when CO2 and temperatures were above present levels, was notably higher than today due to reduced global ice sheet coverage. Nevertheless, the extent to which ice sheets responded to Pliocene warmth remains in question, owing to high levels of uncertainty in proxy-based sea-level reconstructions as well as solid Earth dynamic models that have been used to evaluate a limited number of data constraints. Here, we present a global dataset of ten wavecut scarps that formed by successive Pliocene sea-level oscillations and which are observed today at elevations ranging from ~6 to 109 m above sea level. The present-day elevations of these features have been identified using a combination of high-resolution digital elevation models and field mapping. Using the MATLAB interface TerraceM, we extrapolate the cliff and platform surfaces to determine the elevation of the scarp toe, which in most settings is buried under meters of talus. We correct the scarp-toe elevations for glacial isostatic adjustment and find that this process alone cannot explain observed differences in Pliocene paleoshoreline elevations around the globe. We next determine the signal associated with mantle dynamic topography by back-advecting the present-day three-dimensional buoyancy structure of the mantle and calculating the difference in radial surface stresses over the last 3 Myr using the convection code ASPECT. We include a wide range of present-day mantle structures (buoyancy and viscosity) constrained by seismic tomography models, geodynamic observations, and rock mechanics laboratory experiments. Finally, we identify preferred dynamic topography change predictions based on their agreement with scarp elevations and use our most confident result to estimate a Pliocene global mean sea level based on one scarp from De Hoop, South Africa. This inference (11.6 ± 5.2 m) is a downward revision and may imply ice sheets were relatively resistant to warm Pliocene climate conditions. We also conclude, however, that more targeted model development is needed to more reliably infer mid-Pliocene global mean sea level based on all scarps mapped in this study.
{"title":"Pliocene shorelines and the epeirogenic motion of continental margins: A target dataset for dynamic topography models","authors":"Andrew Hollyday, Maureen E. Raymo, Jacqueline Austermann, Fred Richards, Mark Hoggard, Alessio Rovere","doi":"10.5194/egusphere-2023-2099","DOIUrl":"https://doi.org/10.5194/egusphere-2023-2099","url":null,"abstract":"<strong>Abstract.</strong> Global mean sea level during the mid-Pliocene Epoch (~3 Ma), when CO<sub>2</sub> and temperatures were above present levels, was notably higher than today due to reduced global ice sheet coverage. Nevertheless, the extent to which ice sheets responded to Pliocene warmth remains in question, owing to high levels of uncertainty in proxy-based sea-level reconstructions as well as solid Earth dynamic models that have been used to evaluate a limited number of data constraints. Here, we present a global dataset of ten wavecut scarps that formed by successive Pliocene sea-level oscillations and which are observed today at elevations ranging from ~6 to 109 m above sea level. The present-day elevations of these features have been identified using a combination of high-resolution digital elevation models and field mapping. Using the MATLAB interface TerraceM, we extrapolate the cliff and platform surfaces to determine the elevation of the scarp toe, which in most settings is buried under meters of talus. We correct the scarp-toe elevations for glacial isostatic adjustment and find that this process alone cannot explain observed differences in Pliocene paleoshoreline elevations around the globe. We next determine the signal associated with mantle dynamic topography by back-advecting the present-day three-dimensional buoyancy structure of the mantle and calculating the difference in radial surface stresses over the last 3 Myr using the convection code ASPECT. We include a wide range of present-day mantle structures (buoyancy and viscosity) constrained by seismic tomography models, geodynamic observations, and rock mechanics laboratory experiments. Finally, we identify preferred dynamic topography change predictions based on their agreement with scarp elevations and use our most confident result to estimate a Pliocene global mean sea level based on one scarp from De Hoop, South Africa. This inference (11.6 ± 5.2 m) is a downward revision and may imply ice sheets were relatively resistant to warm Pliocene climate conditions. We also conclude, however, that more targeted model development is needed to more reliably infer mid-Pliocene global mean sea level based on all scarps mapped in this study.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"45 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-02-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139956956","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 : 2024-02-22DOI: 10.5194/egusphere-2024-198
Cho-Hee Lee, Yeong Bae Seong, John Weber, Sangmin Ha, Dong-Eun Kim, Byung Yong Yu
Abstract. Quantifying present topography can provide insights into landscape evolution and its controls, as the present topography is a cumulative expression of the types, distributions, and intensities of past and present processes. The Ulsan Fault Zone (UFZ) is an active fault zone on the southeastern Korean Peninsula that has been reactivated as a reverse fault around 5 Ma. This NNW–SSE-trending fault zone exhibits a predominantly reverse sense of movement today and dips towards the east. This study investigates the history of tectonic activity along the UFZ and the landscape evolution of the hanging wall side of the UFZ, focusing on neotectonic perturbations using 10Be-derived catchment-wide denudation rate and bedrock incision rates, geomorphic indices, and a landscape evolution model. We evaluated the spatial variation in the relative tectonic intensity from the variation in geomorphic indices along the UFZ. Five geological segments were identified along the fault based on the relative tectonic intensity and fault geometry. We then simulated four cases of landscape evolution using modelling to investigate the geomorphic processes and topographic changes in the study area in response to fault slip. The model results reveal that the geomorphic processes and the patterns of geomorphic indices (e.g., χ anomalies) depend on the inherited topography (i.e., the topography that existed prior to reverse faulting on the UFZ). On the basis of this important finding, we interpret the tectono-geomorphic history of the study area as follows: (1) the northern part of the UFZ has been in a transient state and is in topographic and geometric disequilibrium, as this part underwent asymmetric uplift (westward tilting) prior to reverse faulting on the UFZ around 5 Ma; and (2) its southern part was negligibly influenced by the asymmetric uplift before reverse faulting. Our study demonstrates geomorphic indices as reliable criteria for dividing faults into segments and, together with landscape evolution modelling, to investigate the influence of inherited topography on present topography and to help determine tectono-geomorphic histories.
{"title":"Geomorphic indices for unveiling fault segmentation and tectono-geomorphic evolution with insights into the impact of inherited topography, Ulsan Fault Zone, Korea","authors":"Cho-Hee Lee, Yeong Bae Seong, John Weber, Sangmin Ha, Dong-Eun Kim, Byung Yong Yu","doi":"10.5194/egusphere-2024-198","DOIUrl":"https://doi.org/10.5194/egusphere-2024-198","url":null,"abstract":"<strong>Abstract.</strong> Quantifying present topography can provide insights into landscape evolution and its controls, as the present topography is a cumulative expression of the types, distributions, and intensities of past and present processes. The Ulsan Fault Zone (UFZ) is an active fault zone on the southeastern Korean Peninsula that has been reactivated as a reverse fault around 5 Ma. This NNW–SSE-trending fault zone exhibits a predominantly reverse sense of movement today and dips towards the east. This study investigates the history of tectonic activity along the UFZ and the landscape evolution of the hanging wall side of the UFZ, focusing on neotectonic perturbations using <sup>10</sup>Be-derived catchment-wide denudation rate and bedrock incision rates, geomorphic indices, and a landscape evolution model. We evaluated the spatial variation in the relative tectonic intensity from the variation in geomorphic indices along the UFZ. Five geological segments were identified along the fault based on the relative tectonic intensity and fault geometry. We then simulated four cases of landscape evolution using modelling to investigate the geomorphic processes and topographic changes in the study area in response to fault slip. The model results reveal that the geomorphic processes and the patterns of geomorphic indices (e.g., χ anomalies) depend on the inherited topography (i.e., the topography that existed prior to reverse faulting on the UFZ). On the basis of this important finding, we interpret the tectono-geomorphic history of the study area as follows: (1) the northern part of the UFZ has been in a transient state and is in topographic and geometric disequilibrium, as this part underwent asymmetric uplift (westward tilting) prior to reverse faulting on the UFZ around 5 Ma; and (2) its southern part was negligibly influenced by the asymmetric uplift before reverse faulting. Our study demonstrates geomorphic indices as reliable criteria for dividing faults into segments and, together with landscape evolution modelling, to investigate the influence of inherited topography on present topography and to help determine tectono-geomorphic histories.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"7 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-02-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139921565","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 : 2024-02-21DOI: 10.5194/egusphere-2024-351
Amanda Lily Wild, Jean Braun, Alexander C. Whittaker, Sebastien Castelltort
Abstract. Within the stratigraphic record, changes in grain size are often interpreted as a signature of external forcing events. However, it is not yet well constrained how autogenic processes (such as channel mobility) influence grain size signatures within the fluvial system. Here, we combine a landscape evolution model based on the Stream Power Law but modified for sedimentation (Yuan et al., 2019) with an extension of the self-similar grain size model Fedele and Paola (2007) to multiple dimensions (i.e., along dynamically evolving river channels) to study the relative importance of autogenic processes in con- trolling grain size fining. We first show how our new model can reproduce the results obtained by classical analytical solutions assuming that fining is controlled by subsidence only, in a single or amalgamated channel. We then show that deviations from past (subsidence and single channel only) predictions arise when varying two main parameters: first the ratio between the incoming sediment flux and integrated subsidence rate (F ), which increases with the degree of bypass of the system; and second, the ratio of the discharge leaving the mountain to the discharge generated within the subsiding basin (β), which controls the shape of the topography of the basin. We demonstrate that there exists two regimes, one corresponding to low values of F or high values of β, where the grain size fining is controlled by subsidence, and one corresponding to high F and low β values, where grain size fining is controlled by autogenic processes under steep topographic slopes that propagate sedimentary waves through the basin. Coupling the LEM to a flexural model predicts that grain size fining evolves from subsidence to autogeniccontrol in basins characterized by a progressive increase of F (under-filled to over-filled foreland), as seen in the case example of the Alberta Foreland Basin. Our results indicate that grain size fining during low filling conditions (e.g. early stage as the basin is forming) can indicate the dominantly tectonic controlled parameter of the flux relative to underlying subsidence ratio (F ); whereas, any fining under high bypass conditions (e.g. late stage once the basin is overfilled) can indicate the climate controlled upstream vs downstream ratio (β).
摘要在地层记录中，粒度变化通常被解释为外部作用事件的特征。然而，目前还不能很好地解释自生过程（如河道流动性）如何影响河道系统内的粒度特征。在此，我们将基于溪流幂律但针对沉积进行了修改的景观演化模型（Yuan 等，2019 年）与 Fedele 和 Paola（2007 年）的自相似粒度模型扩展到多个维度（即沿动态演化的河道）相结合，研究自生过程在控制粒度细化中的相对重要性。我们首先展示了我们的新模型是如何在单一或混合河道中重现经典分析方法得出的结果的，即假设细化仅由沉降控制。然后，我们展示了当改变以下两个主要参数时，过去（仅由沉降和单一河道控制）的预测结果会出现偏差：首先是进入的沉积通量与综合沉降速率（F）之间的比率，该比率会随着系统旁路程度的增加而增加；其次是离开山体的排水量与沉降盆地内产生的排水量之间的比率（β），该比率控制着盆地地形的形状。我们证明存在两种情况，一种是 F 值低或 β 值高，晶粒细化受沉降控制；另一种是 F 值高、β 值低，晶粒细化受陡峭地形斜坡下的自生过程控制，沉积波在盆地中传播。将 LEM 与挠曲模型耦合可预测，在以 F 值逐渐增加（前陆充填不足到前陆充填过度）为特征的盆地中，粒度细化会从沉降演变为自生控制，这在阿尔伯塔前陆盆地的案例中可以看到。我们的研究结果表明，在低充盈条件下（如盆地形成的早期阶段）的粒度细化可以表明通量相对于基本沉降比（F）的参数主要受构造控制；而在高旁通条件下（如盆地过度充盈的晚期阶段）的任何细化可以表明受气候控制的上游与下游比（β）。
{"title":"Autogenic vs Subsidence Controls on Grain Size Fining through Multi-Channel Landscape Evolution Modelling","authors":"Amanda Lily Wild, Jean Braun, Alexander C. Whittaker, Sebastien Castelltort","doi":"10.5194/egusphere-2024-351","DOIUrl":"https://doi.org/10.5194/egusphere-2024-351","url":null,"abstract":"<strong>Abstract.</strong> Within the stratigraphic record, changes in grain size are often interpreted as a signature of external forcing events. However, it is not yet well constrained how autogenic processes (such as channel mobility) influence grain size signatures within the fluvial system. Here, we combine a landscape evolution model based on the Stream Power Law but modified for sedimentation (Yuan et al., 2019) with an extension of the self-similar grain size model Fedele and Paola (2007) to multiple dimensions (i.e., along dynamically evolving river channels) to study the relative importance of autogenic processes in con- trolling grain size fining. We first show how our new model can reproduce the results obtained by classical analytical solutions assuming that fining is controlled by subsidence only, in a single or amalgamated channel. We then show that deviations from past (subsidence and single channel only) predictions arise when varying two main parameters: first the ratio between the incoming sediment flux and integrated subsidence rate (<em>F</em> ), which increases with the degree of bypass of the system; and second, the ratio of the discharge leaving the mountain to the discharge generated within the subsiding basin (<em>β</em>), which controls the shape of the topography of the basin. We demonstrate that there exists two regimes, one corresponding to low values of <em>F</em> or high values of <em>β</em>, where the grain size fining is controlled by subsidence, and one corresponding to high <em>F</em> and low <em>β</em> values, where grain size fining is controlled by autogenic processes under steep topographic slopes that propagate sedimentary waves through the basin. Coupling the LEM to a flexural model predicts that grain size fining evolves from subsidence to autogeniccontrol in basins characterized by a progressive increase of <em>F</em> (under-filled to over-filled foreland), as seen in the case example of the Alberta Foreland Basin. Our results indicate that grain size fining during low filling conditions (e.g. early stage as the basin is forming) can indicate the dominantly tectonic controlled parameter of the flux relative to underlying subsidence ratio (<em>F</em> ); whereas, any fining under high bypass conditions (e.g. late stage once the basin is overfilled) can indicate the climate controlled upstream vs downstream ratio (<em>β</em>).","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"18 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139921569","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 : 2024-02-16DOI: 10.5194/egusphere-2024-231
Johannes Leinauer, Michael Dietze, Sibylle Knapp, Riccardo Scandroglio, Maximilian Jokel, Michael Krautblatter
Abstract. The increasing hazard of major rock slope failures, exacerbated by climate change, underscores the importance of anticipating pre-failure process dynamics. While standard triggers are recognized for small rockfalls, few comprehensive driver quantifications exist for massive pre-failure rock slopes. Here we exploit >4 years multi-method high-resolution monitoring data from a well-prepared high-magnitude rock slope instability. To quantify and understand the effect of possible drivers – water from rain and snowmelt, internal rock fracturing and earthquakes – we correlate slope displacements with environmental data, local seismic recordings and earthquake catalogues. During the snowmelt phase, displacements are controlled by meltwater infiltration with high correlation and a time lag of 4–9 days. During the snow-free summer, rainfall drives the system with a time lag of 1–16 h for up to several days without a minimum activation rain sum threshold. Detected rock fracturing, linked to temperature and freeze-thaw cycles, is predominantly surface-near and unrelated to displacement rates. A classic Newmark analysis of recent and historic earthquakes indicates a low potential for immediate triggering of a major failure at the case site, unless it is already very close to failure. Seismic topographic amplification of the peak ground velocity at the summit ranges from a factor of 2–11 and is spatially heterogeneous, indicating a high criticality of the slope. The presented methodological approach enables a comprehensive rockfall driver evaluation and indicates where future climatic changes, e.g. in precipitation intensity and frequency, may alter the preparation of major rock slope failures.
{"title":"How water, temperature and seismicity control the preparation of massive rock slope failure (Hochvogel, DE/AT)","authors":"Johannes Leinauer, Michael Dietze, Sibylle Knapp, Riccardo Scandroglio, Maximilian Jokel, Michael Krautblatter","doi":"10.5194/egusphere-2024-231","DOIUrl":"https://doi.org/10.5194/egusphere-2024-231","url":null,"abstract":"<strong>Abstract.</strong> The increasing hazard of major rock slope failures, exacerbated by climate change, underscores the importance of anticipating pre-failure process dynamics. While standard triggers are recognized for small rockfalls, few comprehensive driver quantifications exist for massive pre-failure rock slopes. Here we exploit >4 years multi-method high-resolution monitoring data from a well-prepared high-magnitude rock slope instability. To quantify and understand the effect of possible drivers – water from rain and snowmelt, internal rock fracturing and earthquakes – we correlate slope displacements with environmental data, local seismic recordings and earthquake catalogues. During the snowmelt phase, displacements are controlled by meltwater infiltration with high correlation and a time lag of 4–9 days. During the snow-free summer, rainfall drives the system with a time lag of 1–16 h for up to several days without a minimum activation rain sum threshold. Detected rock fracturing, linked to temperature and freeze-thaw cycles, is predominantly surface-near and unrelated to displacement rates. A classic Newmark analysis of recent and historic earthquakes indicates a low potential for immediate triggering of a major failure at the case site, unless it is already very close to failure. Seismic topographic amplification of the peak ground velocity at the summit ranges from a factor of 2–11 and is spatially heterogeneous, indicating a high criticality of the slope. The presented methodological approach enables a comprehensive rockfall driver evaluation and indicates where future climatic changes, e.g. in precipitation intensity and frequency, may alter the preparation of major rock slope failures.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"19 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-02-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139759278","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 : 2024-02-15DOI: 10.5194/esurf-12-347-2024
Yutian Ke, Damien Calmels, Julien Bouchez, Marc Massault, Benjamin Chetelat, Aurélie Noret, Hongming Cai, Jiubin Chen, Jérôme Gaillardet, Cécile Quantin
Abstract. The Huanghe (Yellow River), one of the largest turbid river systems in the world, has long been recognized as a major contributor of suspended particulate matter (SPM) to the ocean. However, over the last few decades, the SPM export flux of the Huanghe has decreased over 90 % due to the high management, impacting the global export of particulate organic carbon (POC). To better constrain sources and modes of transport of POC beyond the previously investigated transportation of POC near the channel surface, SPM samples were for the first time collected over a whole channel cross-section in the lower Huanghe. Riverine SPM samples were analyzed for particle size and major element contents, as well as for POC content and dual carbon isotopes (13C and 14C). Clear vertical and lateral heterogeneities of the physical and chemical properties of SPM are observed within the river cross-section. For instance, finer SPM carry more POC in general with higher 14C activity near the surface of the right bank. Notably, we discuss how bank erosion in the alluvial plain is likely to generate lateral heterogeneity in POC composition. The Huanghe POC is millennial-aged (4020 ± 500 radiocarbon years) and dominated by organic carbon (OC) from the biosphere, while the lithospheric fraction is ca. 12 %. The mobilization of aged and refractory OC, including radiocarbon-dead biospheric OC, from deeper soil horizons of the loess–paleosol sequence through erosion in the Chinese Loess Plateau is an important mechanism contributing to fluvial POC in the Huanghe drainage basin. Altogether, anthropogenic activities can drastically change the compositions and transport dynamics of fluvial POC, consequentially altering the feedback of the source-to-sink trajectory of a river system to regional and global carbon cycles.
{"title":"Channel cross-section heterogeneity of particulate organic carbon transport in the Huanghe","authors":"Yutian Ke, Damien Calmels, Julien Bouchez, Marc Massault, Benjamin Chetelat, Aurélie Noret, Hongming Cai, Jiubin Chen, Jérôme Gaillardet, Cécile Quantin","doi":"10.5194/esurf-12-347-2024","DOIUrl":"https://doi.org/10.5194/esurf-12-347-2024","url":null,"abstract":"Abstract. The Huanghe (Yellow River), one of the largest turbid river systems in the world, has long been recognized as a major contributor of suspended particulate matter (SPM) to the ocean. However, over the last few decades, the SPM export flux of the Huanghe has decreased over 90 % due to the high management, impacting the global export of particulate organic carbon (POC). To better constrain sources and modes of transport of POC beyond the previously investigated transportation of POC near the channel surface, SPM samples were for the first time collected over a whole channel cross-section in the lower Huanghe. Riverine SPM samples were analyzed for particle size and major element contents, as well as for POC content and dual carbon isotopes (13C and 14C). Clear vertical and lateral heterogeneities of the physical and chemical properties of SPM are observed within the river cross-section. For instance, finer SPM carry more POC in general with higher 14C activity near the surface of the right bank. Notably, we discuss how bank erosion in the alluvial plain is likely to generate lateral heterogeneity in POC composition. The Huanghe POC is millennial-aged (4020 ± 500 radiocarbon years) and dominated by organic carbon (OC) from the biosphere, while the lithospheric fraction is ca. 12 %. The mobilization of aged and refractory OC, including radiocarbon-dead biospheric OC, from deeper soil horizons of the loess–paleosol sequence through erosion in the Chinese Loess Plateau is an important mechanism contributing to fluvial POC in the Huanghe drainage basin. Altogether, anthropogenic activities can drastically change the compositions and transport dynamics of fluvial POC, consequentially altering the feedback of the source-to-sink trajectory of a river system to regional and global carbon cycles.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"5 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139759260","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 : 2024-02-15DOI: 10.5194/esurf-12-367-2024
Gary Parker, Chenge An, Michael P. Lamb, Marcelo H. Garcia, Elizabeth H. Dingle, Jeremy G. Venditti
Abstract. The grain size 2 mm is the conventional border between sand and gravel. This size is used extensively, and generally without much physical justification, to discriminate between such features as sedimentary deposit type (clast-supported versus matrix-supported), river type (gravel bed versus sand bed), and sediment transport relation (gravel versus sand). Here we inquire as to whether this 2 mm boundary is simply a social construct upon which the research community has decided to agree or whether there is some underlying physics. We use dimensionless arguments to show the following for typical conditions on Earth, i.e., natural clasts (e.g., granitic or limestone) in 20 ∘C water. As grain size ranges from 1 to 5 mm (a narrow band including 2 mm), sediment suspension becomes vanishingly small at normal flood conditions in alluvial rivers. We refer to this range as pea gravel. We further show that bedload movement of a clast in the pea gravel range with, for example, a size of 4 mm moving over a bed of 0.4 mm particles has an enhanced relative mobility compared to a clast with a size of 40 mm moving over a bed of the same 4 mm particles. With this in mind, we use 2 mm here as shorthand for the narrow pea gravel range of 1–5 mm over which transport behavior is distinct from both coarser and finer material. The use of viscosity allows the delineation of a generalized dimensionless bed grain size discriminator between “sand-like” and “gravel-like” rivers. The discriminator is applicable to sediment transport on Titan (ice clasts in flowing methane/ethane liquid at reduced gravity) and Mars (mafic clasts in flowing water at reduced gravity), as well as Earth.
{"title":"Dimensionless argument: a narrow grain size range near 2 mm plays a special role in river sediment transport and morphodynamics","authors":"Gary Parker, Chenge An, Michael P. Lamb, Marcelo H. Garcia, Elizabeth H. Dingle, Jeremy G. Venditti","doi":"10.5194/esurf-12-367-2024","DOIUrl":"https://doi.org/10.5194/esurf-12-367-2024","url":null,"abstract":"Abstract. The grain size 2 mm is the conventional border between sand and gravel. This size is used extensively, and generally without much physical justification, to discriminate between such features as sedimentary deposit type (clast-supported versus matrix-supported), river type (gravel bed versus sand bed), and sediment transport relation (gravel versus sand). Here we inquire as to whether this 2 mm boundary is simply a social construct upon which the research community has decided to agree or whether there is some underlying physics. We use dimensionless arguments to show the following for typical conditions on Earth, i.e., natural clasts (e.g., granitic or limestone) in 20 ∘C water. As grain size ranges from 1 to 5 mm (a narrow band including 2 mm), sediment suspension becomes vanishingly small at normal flood conditions in alluvial rivers. We refer to this range as pea gravel. We further show that bedload movement of a clast in the pea gravel range with, for example, a size of 4 mm moving over a bed of 0.4 mm particles has an enhanced relative mobility compared to a clast with a size of 40 mm moving over a bed of the same 4 mm particles. With this in mind, we use 2 mm here as shorthand for the narrow pea gravel range of 1–5 mm over which transport behavior is distinct from both coarser and finer material. The use of viscosity allows the delineation of a generalized dimensionless bed grain size discriminator between “sand-like” and “gravel-like” rivers. The discriminator is applicable to sediment transport on Titan (ice clasts in flowing methane/ethane liquid at reduced gravity) and Mars (mafic clasts in flowing water at reduced gravity), as well as Earth.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"170 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139759262","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 : 2024-02-13DOI: 10.5194/egusphere-2023-2568
An Li, Michelle Koutnik, Stephen Brough, Matteo Spagnolo, Iestyn Barr
Abstract. While glacial remnants in the form of viscous flow features in the mid-latitudes of Mars are considered to be cold-based in the present-day, an increasing amount of geomorphic evidence suggests that at least some flow features were previously wet-based or had a mixed thermal state (polythermal) at during their evolution. Many of the viscous flow features known as glacier-like forms have been observed to emerge from alcoves that appear similar to cirques on Earth. Terrestrial cirques are typically characterized by a concave basin connected to a steep backwall. Cirques are expected to form from depressions in mountainsides that fill with snow/ice and over time support active glaciers that deepen the depressions by wet-based glacial erosion. To assess which alcoves on Mars are most “cirque-like”, we mapped a population of ~2000 alcoves in Deuteronilus Mensae, a region in the mid-latitudes of Mars characterized by mesas encompassed by glacial remnants. Based on visual characteristics and morphometrics, we refined our dataset to 386 “cirque-like alcoves”, which is five times the amount of glacier-like forms in the region, and used this to assess the past extent and style of glaciation on Mars. Using high resolution imagery, we find geomorphic evidence for glacial occupation associated with the cirque-like alcoves, including crevasse-like features, surface lineations, polygonal terrain, and moraine-like ridges. We propose that the cirque-like alcoves with icy remnants similar to rock glaciers on Earth represent a late stage of glacier-like form evolution. We also outline stages of cirque-like alcove evolution, linking a potential early stage of cirque-like alcoves to gully activity. On a population-wide scale, the cirque-like alcoves have a south to southeastward aspect bias, which may indicate a requirement for increased insolation for melting to occur and a connection to gullies on Mars. While the alcoves also have similarities to other features such as landslide scarps and amphitheater-headed valleys, the cirque-like alcoves have unique morphologies and morphometrics that differentiate their origin. Assuming warm-based erosion rates, the cirque-like alcoves have timescales consistent with both glacier-like forms and other viscous flow features like lobate debris aprons, whereas cold-based erosion rates would only allow the older timescales of lobate debris aprons. We propose that based on the geomorphic features and southward aspect, cirque-like alcove formation is more consistent with warm-based glaciation.
{"title":"Cirque-like alcoves in the northern mid-latitudes of Mars as evidence of glacial erosion","authors":"An Li, Michelle Koutnik, Stephen Brough, Matteo Spagnolo, Iestyn Barr","doi":"10.5194/egusphere-2023-2568","DOIUrl":"https://doi.org/10.5194/egusphere-2023-2568","url":null,"abstract":"<strong>Abstract.</strong> While glacial remnants in the form of viscous flow features in the mid-latitudes of Mars are considered to be cold-based in the present-day, an increasing amount of geomorphic evidence suggests that at least some flow features were previously wet-based or had a mixed thermal state (polythermal) at during their evolution. Many of the viscous flow features known as glacier-like forms have been observed to emerge from alcoves that appear similar to cirques on Earth. Terrestrial cirques are typically characterized by a concave basin connected to a steep backwall. Cirques are expected to form from depressions in mountainsides that fill with snow/ice and over time support active glaciers that deepen the depressions by wet-based glacial erosion. To assess which alcoves on Mars are most “cirque-like”, we mapped a population of ~2000 alcoves in Deuteronilus Mensae, a region in the mid-latitudes of Mars characterized by mesas encompassed by glacial remnants. Based on visual characteristics and morphometrics, we refined our dataset to 386 “cirque-like alcoves”, which is five times the amount of glacier-like forms in the region, and used this to assess the past extent and style of glaciation on Mars. Using high resolution imagery, we find geomorphic evidence for glacial occupation associated with the cirque-like alcoves, including crevasse-like features, surface lineations, polygonal terrain, and moraine-like ridges. We propose that the cirque-like alcoves with icy remnants similar to rock glaciers on Earth represent a late stage of glacier-like form evolution. We also outline stages of cirque-like alcove evolution, linking a potential early stage of cirque-like alcoves to gully activity. On a population-wide scale, the cirque-like alcoves have a south to southeastward aspect bias, which may indicate a requirement for increased insolation for melting to occur and a connection to gullies on Mars. While the alcoves also have similarities to other features such as landslide scarps and amphitheater-headed valleys, the cirque-like alcoves have unique morphologies and morphometrics that differentiate their origin. Assuming warm-based erosion rates, the cirque-like alcoves have timescales consistent with both glacier-like forms and other viscous flow features like lobate debris aprons, whereas cold-based erosion rates would only allow the older timescales of lobate debris aprons. We propose that based on the geomorphic features and southward aspect, cirque-like alcove formation is more consistent with warm-based glaciation.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"205 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139759277","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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