Pub Date : 2024-03-28DOI: 10.5194/esurf-12-493-2024
Jens Martin Turowski, Aaron Bufe, Stefanie Tofelde
Abstract. The width of fluvial valley floors is a key parameter to quantifying the morphology of mountain regions. Valley floor width is relevant to diverse fields including sedimentology, fluvial geomorphology, and archaeology. The width of valleys has been argued to depend on climatic and tectonic conditions, on the hydraulics and hydrology of the river channel that forms the valley, and on sediment supply from valley walls. Here, we derive a physically based model that can be used to predict valley width and test it against three different datasets. The model applies to valleys that are carved by a river migrating laterally across the valley floor. We conceptualize river migration as a Poisson process, in which the river changes its direction stochastically at a mean rate determined by hydraulic boundary conditions. This approach yields a characteristic timescale for the river to cross the valley floor from one wall to the other. The valley width can then be determined by integrating the speed of migration over this timescale. For a laterally unconfined river that is not uplifting, the model predicts that the channel-belt width scales with river flow depth. Channel-belt width corresponds to the maximum width of a fluvial valley. We expand the model to include the effects of uplift and lateral sediment supply from valley walls. Both of these effects lead to a decrease in valley width in comparison to the maximum width. We identify a dimensionless number, termed the mobility–uplift number, which is the ratio between the lateral mobility of the river channel and uplift rate. The model predicts two limits: at high values of the mobility–uplift number, the valley evolves to the channel-belt width, whereas it corresponds to the channel width at low values. Between these limits, valley width is linked to the mobility–uplift number by a logarithmic function. As a consequence of the model, valley width increases with increasing drainage area, with a scaling exponent that typically has a value between 0.4 and 0.5, but can also be lower or higher. We compare the model to three independent datasets of valleys in experimental and natural uplifting landscapes and show that it closely predicts the first-order relationship between valley width and the mobility–uplift number.
{"title":"A physics-based model for fluvial valley width","authors":"Jens Martin Turowski, Aaron Bufe, Stefanie Tofelde","doi":"10.5194/esurf-12-493-2024","DOIUrl":"https://doi.org/10.5194/esurf-12-493-2024","url":null,"abstract":"Abstract. The width of fluvial valley floors is a key parameter to quantifying the morphology of mountain regions. Valley floor width is relevant to diverse fields including sedimentology, fluvial geomorphology, and archaeology. The width of valleys has been argued to depend on climatic and tectonic conditions, on the hydraulics and hydrology of the river channel that forms the valley, and on sediment supply from valley walls. Here, we derive a physically based model that can be used to predict valley width and test it against three different datasets. The model applies to valleys that are carved by a river migrating laterally across the valley floor. We conceptualize river migration as a Poisson process, in which the river changes its direction stochastically at a mean rate determined by hydraulic boundary conditions. This approach yields a characteristic timescale for the river to cross the valley floor from one wall to the other. The valley width can then be determined by integrating the speed of migration over this timescale. For a laterally unconfined river that is not uplifting, the model predicts that the channel-belt width scales with river flow depth. Channel-belt width corresponds to the maximum width of a fluvial valley. We expand the model to include the effects of uplift and lateral sediment supply from valley walls. Both of these effects lead to a decrease in valley width in comparison to the maximum width. We identify a dimensionless number, termed the mobility–uplift number, which is the ratio between the lateral mobility of the river channel and uplift rate. The model predicts two limits: at high values of the mobility–uplift number, the valley evolves to the channel-belt width, whereas it corresponds to the channel width at low values. Between these limits, valley width is linked to the mobility–uplift number by a logarithmic function. As a consequence of the model, valley width increases with increasing drainage area, with a scaling exponent that typically has a value between 0.4 and 0.5, but can also be lower or higher. We compare the model to three independent datasets of valleys in experimental and natural uplifting landscapes and show that it closely predicts the first-order relationship between valley width and the mobility–uplift number.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"53 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140313382","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 : 2024-03-26DOI: 10.5194/esurf-12-477-2024
Yuntao Tian, Lili Pan, Guihong Zhang, Xinbo Yao
Abstract. This study implements the least-squares inversion method for solving the exhumation history from the thermochronologic age–elevation relationship (AER) based on the linear equation among exhumation rate, age and total exhumation from the closure depth to the Earth surface. Modeling experiments suggest significant and systematic influence of initial geothermal model, the a priori exhumation rate and the time interval length on the a posteriori exhumation history. Lessons learned from the experiments include that (i) the modern geothermal gradient can be used for constraining the initial geothermal model, (ii) a relatively high a priori exhumation rate would lead to systematically lower a posteriori exhumation and vice versa, (iii) the variance of the a priori exhumation rate controls the variation in the inverted exhumation history, and (iv) the choice of time interval length should be optimized for resolving the potential temporal changes in exhumation. To mitigate the dependence of inverted erosion history on these initial parameters, we implemented a new stepwise inverse modeling method for optimizing the model parameters by comparing the observed and predicted thermochronologic data and modern geothermal gradients. Finally, method demonstration was performed using four synthetic datasets and three natural examples of different exhumation rates and histories. It is shown that the inverted rock exhumation histories from the synthetic datasets match the whole picture of the “truth”, although the temporal changes in the magnitude of exhumation are underestimated. Modeling of the datasets from natural samples produces geologically reasonable exhumation histories. The code and data used in this work are available on Zenodo (https://doi.org/10.5281/zenodo.10839275).
{"title":"An efficient approach for inverting rock exhumation from thermochronologic age–elevation relationship","authors":"Yuntao Tian, Lili Pan, Guihong Zhang, Xinbo Yao","doi":"10.5194/esurf-12-477-2024","DOIUrl":"https://doi.org/10.5194/esurf-12-477-2024","url":null,"abstract":"Abstract. This study implements the least-squares inversion method for solving the exhumation history from the thermochronologic age–elevation relationship (AER) based on the linear equation among exhumation rate, age and total exhumation from the closure depth to the Earth surface. Modeling experiments suggest significant and systematic influence of initial geothermal model, the a priori exhumation rate and the time interval length on the a posteriori exhumation history. Lessons learned from the experiments include that (i) the modern geothermal gradient can be used for constraining the initial geothermal model, (ii) a relatively high a priori exhumation rate would lead to systematically lower a posteriori exhumation and vice versa, (iii) the variance of the a priori exhumation rate controls the variation in the inverted exhumation history, and (iv) the choice of time interval length should be optimized for resolving the potential temporal changes in exhumation. To mitigate the dependence of inverted erosion history on these initial parameters, we implemented a new stepwise inverse modeling method for optimizing the model parameters by comparing the observed and predicted thermochronologic data and modern geothermal gradients. Finally, method demonstration was performed using four synthetic datasets and three natural examples of different exhumation rates and histories. It is shown that the inverted rock exhumation histories from the synthetic datasets match the whole picture of the “truth”, although the temporal changes in the magnitude of exhumation are underestimated. Modeling of the datasets from natural samples produces geologically reasonable exhumation histories. The code and data used in this work are available on Zenodo (https://doi.org/10.5281/zenodo.10839275).","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"50 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140313182","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 : 2024-03-25DOI: 10.5194/egusphere-2024-172
Dominik Amschwand, Jonas Wicky, Martin Scherler, Martin Hoelzle, Bernhard Krummenacher, Anna Haberkorn, Christian Kienholz, Hansueli Gubler
Abstract. We estimate the sub-surface energy budget and heat fluxes in the coarse-blocky active layer (AL) of the Murtèl rock glacier, a seasonally snow-covered permafrost landform located in the eastern Swiss Alps. In the highly permeable AL, conductive/diffusive heat transfer including thermal radiation, non-conductive heat transfer by air circulation (convection), and heat storage changes from seasonal accretion and melting of ground ice shape the ground thermal regime. We quantify individual heat fluxes based on a novel in-situ sensor array in the AL and direct observations of the ground ice melt in the years 2020–2022. Two thaw-season mechanisms render Murtèl rock glacier comparatively climate-resilient. First, the AL intercepts ~70 % (55–85 MJ m−2) of the thaw-season ground heat flux by melting ground ice that runs off as meltwater, ~20 % (10–20 MJ m−2) is spent on heating the blocks, and only ~10 % (7–13 MJ m−2) is transferred into the permafrost body beneath and causes slow permafrost degradation. Second, the effective thermal conductivity in the ventilated AL increases from 1.2 W m−1 K−1 under strongly stable temperature gradients to episodically over 10 W m−1 K−1 under unstable temperature gradients, favouring convective cooling by buoyancy-driven Rayleigh ventilation (thermal semiconductor effect). In winter, radiatively cooled air infiltrating through a discontinuous, semi-closed snowcover leads to strong AL cooling. The two characteristic parameters (effective thermal conductivity and intrinsic permeability) are sensitive to debris texture, hence these convective undercooling processes are specific to highly permeable coarse-blocky material.
摘要我们估算了位于瑞士阿尔卑斯山东部的穆尔泰尔岩石冰川（一种季节性积雪覆盖的永久冻土地貌）粗块状活动层（AL）的次表层能量预算和热通量。在高渗透性的活动层中，包括热辐射在内的传导性/扩散性热传递、空气循环（对流）产生的非传导性热传递以及地冰季节性增厚和融化产生的热储量变化决定了地热状态。我们根据 AL 中的新型原位传感器阵列和 2020-2022 年对地冰融化的直接观测，对各个热通量进行了量化。两种解冻季节机制使穆尔泰勒岩石冰川具有相对较强的气候适应能力。首先，融化季的地面热通量中，约 70% （55-85 兆焦耳/平方米-2）由融化的地冰截取，以融水形式流走，约 20% （10-20 兆焦耳/平方米-2）用于加热块体，只有约 10% （7-13 兆焦耳/平方米-2）转移到下面的永久冻土体中，导致永久冻土缓慢降解。其次，在温度梯度非常稳定的情况下，通风冻土层的有效热传导率从 1.2 W m-1 K-1 增加到温度梯度不稳定时的 10 W m-1 K-1 以上，有利于通过浮力驱动的雷利通风进行对流冷却（热半导体效应）。在冬季，辐射冷却空气通过不连续的半封闭雪盖渗入，导致强烈的 AL 冷却。这两个特征参数（有效热导率和固有渗透率）对碎屑质地非常敏感，因此这些对流过冷过程是高渗透性粗块状物质所特有的。
{"title":"Sub-surface processes and heat fluxes at coarse-blocky Murtèl rock glacier (Engadine, eastern Swiss Alps)","authors":"Dominik Amschwand, Jonas Wicky, Martin Scherler, Martin Hoelzle, Bernhard Krummenacher, Anna Haberkorn, Christian Kienholz, Hansueli Gubler","doi":"10.5194/egusphere-2024-172","DOIUrl":"https://doi.org/10.5194/egusphere-2024-172","url":null,"abstract":"<strong>Abstract.</strong> We estimate the sub-surface energy budget and heat fluxes in the coarse-blocky active layer (AL) of the Murtèl rock glacier, a seasonally snow-covered permafrost landform located in the eastern Swiss Alps. In the highly permeable AL, conductive/diffusive heat transfer including thermal radiation, non-conductive heat transfer by air circulation (convection), and heat storage changes from seasonal accretion and melting of ground ice shape the ground thermal regime. We quantify individual heat fluxes based on a novel in-situ sensor array in the AL and direct observations of the ground ice melt in the years 2020–2022. Two thaw-season mechanisms render Murtèl rock glacier comparatively climate-resilient. First, the AL intercepts ~70 % (55–85 MJ m<sup>−2</sup>) of the thaw-season ground heat flux by melting ground ice that runs off as meltwater, ~20 % (10–20 MJ m<sup>−</sup><sup>2</sup>) is spent on heating the blocks, and only ~10 % (7–13 MJ m<sup>−</sup><sup>2</sup>) is transferred into the permafrost body beneath and causes slow permafrost degradation. Second, the effective thermal conductivity in the ventilated AL increases from 1.2 W m<sup>−</sup><sup>1</sup> K<sup>−</sup><sup>1</sup> under strongly stable temperature gradients to episodically over 10 W m<sup>−</sup><sup>1</sup> K<sup>−</sup><sup>1</sup> under unstable temperature gradients, favouring convective cooling by buoyancy-driven Rayleigh ventilation (thermal semiconductor effect). In winter, radiatively cooled air infiltrating through a discontinuous, semi-closed snowcover leads to strong AL cooling. The two characteristic parameters (effective thermal conductivity and intrinsic permeability) are sensitive to debris texture, hence these convective undercooling processes are specific to highly permeable coarse-blocky material.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"2016 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140299230","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 : 2024-03-19DOI: 10.5194/egusphere-2024-656
Rachele Dominguez, Michael Fenster, John McManus
Abstract. This study extracted historical water level data from 12 National Oceanographic and Atmospheric Administration tide gauge stations, spanning the period from the early 20th century to 2022 from central Maine to southern Florida, in order to determine if temporal and spatial trends existed in frequency and magnitude of storms along the U.S. Atlantic Ocean coast. We used the Storm Erosion Potential Index (SEPI) to identify and quantify storms. We then use the timing and magnitude of those storms to determine the cumulative effect of storm clustering and large magnitude storms on sandy beaches using the cumulative storm impact index (CSII) empirical model. The results from this study showed (1) no appreciable increase in storm frequency at any of the stations (except for sheltered stations susceptible to storm tide augmentation); (2) statistically significant, but modest increases in storm magnitudes over time for eight of the 12 tidal stations; (3) regional differences in storm magnitudes (SEPI) and cumulative storm impacts (CSII) characteristic of more frequent extratropical storms (temporal clustering) in the north and less frequent tropical storms in the south; and (4) a four to 10 year recovery period for regional beach recovery.
{"title":"Storm surge frequency, magnitude, and cumulative storm beach impact along the U.S. east coast","authors":"Rachele Dominguez, Michael Fenster, John McManus","doi":"10.5194/egusphere-2024-656","DOIUrl":"https://doi.org/10.5194/egusphere-2024-656","url":null,"abstract":"<strong>Abstract.</strong> This study extracted historical water level data from 12 National Oceanographic and Atmospheric Administration tide gauge stations, spanning the period from the early 20th century to 2022 from central Maine to southern Florida, in order to determine if temporal and spatial trends existed in frequency and magnitude of storms along the U.S. Atlantic Ocean coast. We used the Storm Erosion Potential Index (SEPI) to identify and quantify storms. We then use the timing and magnitude of those storms to determine the cumulative effect of storm clustering and large magnitude storms on sandy beaches using the cumulative storm impact index (CSII) empirical model. The results from this study showed (1) no appreciable increase in storm frequency at any of the stations (except for sheltered stations susceptible to storm tide augmentation); (2) statistically significant, but modest increases in storm magnitudes over time for eight of the 12 tidal stations; (3) regional differences in storm magnitudes (SEPI) and cumulative storm impacts (CSII) characteristic of more frequent extratropical storms (temporal clustering) in the north and less frequent tropical storms in the south; and (4) a four to 10 year recovery period for regional beach recovery.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"36 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140170762","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 : 2024-03-14DOI: 10.5194/esurf-12-449-2024
Daniel J. Ciarletta, Jennifer L. Miselis, Julie C. Bernier, Arnell S. Forde
Abstract. Understanding the response of coastal barriers to future changes in rates of sea level rise, sediment availability, and storm intensity/frequency is essential for coastal planning, including socioeconomic and ecological management. Identifying drivers of past changes in barrier morphology, as well as barrier sensitivity to these forces, is necessary to accomplish this. Using remote sensing, field, and laboratory analyses, we reconstruct the mesoscale (decades–centuries) evolution of central Fire Island, a portion of a 50 km barrier island fronting Long Island, New York, USA. We find that the configuration of the modern beach and foredune at Fire Island is radically different from the system's relict morphostratigraphy. Central Fire Island is comprised of at least three formerly inlet-divided rotational barriers with distinct subaerial beach and dune–ridge systems that were active prior to the mid-19th century. Varying morphologic states reflected in the relict barriers (e.g., progradational and transgressive) contrast with the modern barrier, which is dominated by a tall and nearly continuous foredune and is relatively static, except for erosion and drowning of its fringing marsh. We suggest that this state shift indicates a transition from a regime dominated by inlet-mediated gradients in alongshore sediment availability to one where human impacts exerted greater influence on island evolution from the late 19th century onward. The retention of some geomorphic capital in Fire Island's relict subaerial features combined with its static nature renders the barrier increasingly susceptible to narrowing and passive submergence. This may lead to an abrupt geomorphic state shift in the future, a veiled vulnerability that may also exist in other stabilized barriers.
{"title":"Implications for the resilience of modern coastal systems derived from mesoscale barrier dynamics at Fire Island, New York","authors":"Daniel J. Ciarletta, Jennifer L. Miselis, Julie C. Bernier, Arnell S. Forde","doi":"10.5194/esurf-12-449-2024","DOIUrl":"https://doi.org/10.5194/esurf-12-449-2024","url":null,"abstract":"Abstract. Understanding the response of coastal barriers to future changes in rates of sea level rise, sediment availability, and storm intensity/frequency is essential for coastal planning, including socioeconomic and ecological management. Identifying drivers of past changes in barrier morphology, as well as barrier sensitivity to these forces, is necessary to accomplish this. Using remote sensing, field, and laboratory analyses, we reconstruct the mesoscale (decades–centuries) evolution of central Fire Island, a portion of a 50 km barrier island fronting Long Island, New York, USA. We find that the configuration of the modern beach and foredune at Fire Island is radically different from the system's relict morphostratigraphy. Central Fire Island is comprised of at least three formerly inlet-divided rotational barriers with distinct subaerial beach and dune–ridge systems that were active prior to the mid-19th century. Varying morphologic states reflected in the relict barriers (e.g., progradational and transgressive) contrast with the modern barrier, which is dominated by a tall and nearly continuous foredune and is relatively static, except for erosion and drowning of its fringing marsh. We suggest that this state shift indicates a transition from a regime dominated by inlet-mediated gradients in alongshore sediment availability to one where human impacts exerted greater influence on island evolution from the late 19th century onward. The retention of some geomorphic capital in Fire Island's relict subaerial features combined with its static nature renders the barrier increasingly susceptible to narrowing and passive submergence. This may lead to an abrupt geomorphic state shift in the future, a veiled vulnerability that may also exist in other stabilized barriers.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"5 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140170864","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 : 2024-03-14DOI: 10.5194/egusphere-2024-467
Pierre Dietrich, François Guillocheau, Guilhem Amin Douillet, Neil Patrick Griffis, Guillaume Baby, Daniel Paul Le Heron, Laurie Barrier, Maximilien Mathian, Isabel Patricia Montañez, Cécile Robin, Thomas Gyomlai, Christoph Kettler, Axel Hofmann
<strong>Abstract.</strong> The modern relief of Southern Africa is characterised by stepped plateaus bordered by escarpments. This morphology is thought to result from stepwise uplift and ensuing continental-scale erosion of the region as it rode over Africa’s mantle ‘superplume’ following the break-up of Gondwana, i.e. since the mid-Mesozoic. We demonstrate in this contribution that this modern morphology of Southern Africa is in fact largely inherited from glacial erosion associated to the Late Paleozoic Ice Age (LPIA) that occurred between 370 and 260 Myr ago, during which Gondwana – which included Southern Africa – was covered in thick ice masses. Southern Africa hosts vast (up to 10<sup>6</sup> km²) and thick (up to 5 km) sedimentary basins ranging from the Carboniferous, represented by glaciogenic sediments tied to the LPIA, to the Jurassic-Cretaceous. These basins are separated by intervening regions largely underlain by Archean to Paleoproterozoic cratonic areas that correspond to paleohighlands that preserve much of the morphology that existed when sedimentary basins formed, and particularly glacial landforms. In this contribution, we review published field and remote data and provide new large-scale interpretation of the geomorphology of these paleohighlands of Southern Africa. Our foremost finding is that over Southern Africa, vast surfaces, tens to hundreds of thousands km² (71.000–360.000 km²) are exhumed glacial landscapes tied to the LPIA. These glacial landscapes manifest in the form of cm-scale striated pavements, m-scale fields of <em>roches moutonnées</em>, whalebacks and crag-and-tails, narrow gorges cut into high-standing mountain ranges, and km-scale planation surfaces and large U-shaped valleys, overdeepenings, fjords and troughs up to 200 km in length. Many modern savannahs and desertic landscapes of Southern Africa are therefore relict glacial landscapes and relief ca. 300 Myr old. These exhumed glacial relief moreover exerts a strong control on the modern-day aspect of the geomorphology of Southern Africa as (1) some escarpments that delineate high-standing plateaux from valleys and coastal plains are inherited glacial relief in which glacial valleys are carved, (2) some hill or mountain ranges already existed by LPIA times and were likely modelled by glacial erosion, and (3) the drainage network of many of the main rivers of Southern Africa is funnelled through ancient glacial valleys. This remarkable preservation allowed us to reconstruct the paleogeography of Southern Africa in the aftermath of the LPIA, consisting of highlands over which ice masses nucleated and from which they flowed through the escarpments and toward lowlands that now correspond to sedimentary basins. Our findings therefore indicate that glacial landforms and relief of continental-scale can survive over tens to hundreds of million years. This preservation and modern exposure of the glacial paleolandscapes were achieved through burial under piles of
{"title":"The Glacial Paleolandscapes of Southern Africa: the Legacy of the Late Paleozoic Ice Age","authors":"Pierre Dietrich, François Guillocheau, Guilhem Amin Douillet, Neil Patrick Griffis, Guillaume Baby, Daniel Paul Le Heron, Laurie Barrier, Maximilien Mathian, Isabel Patricia Montañez, Cécile Robin, Thomas Gyomlai, Christoph Kettler, Axel Hofmann","doi":"10.5194/egusphere-2024-467","DOIUrl":"https://doi.org/10.5194/egusphere-2024-467","url":null,"abstract":"<strong>Abstract.</strong> The modern relief of Southern Africa is characterised by stepped plateaus bordered by escarpments. This morphology is thought to result from stepwise uplift and ensuing continental-scale erosion of the region as it rode over Africa’s mantle ‘superplume’ following the break-up of Gondwana, i.e. since the mid-Mesozoic. We demonstrate in this contribution that this modern morphology of Southern Africa is in fact largely inherited from glacial erosion associated to the Late Paleozoic Ice Age (LPIA) that occurred between 370 and 260 Myr ago, during which Gondwana – which included Southern Africa – was covered in thick ice masses. Southern Africa hosts vast (up to 10<sup>6</sup> km²) and thick (up to 5 km) sedimentary basins ranging from the Carboniferous, represented by glaciogenic sediments tied to the LPIA, to the Jurassic-Cretaceous. These basins are separated by intervening regions largely underlain by Archean to Paleoproterozoic cratonic areas that correspond to paleohighlands that preserve much of the morphology that existed when sedimentary basins formed, and particularly glacial landforms. In this contribution, we review published field and remote data and provide new large-scale interpretation of the geomorphology of these paleohighlands of Southern Africa. Our foremost finding is that over Southern Africa, vast surfaces, tens to hundreds of thousands km² (71.000–360.000 km²) are exhumed glacial landscapes tied to the LPIA. These glacial landscapes manifest in the form of cm-scale striated pavements, m-scale fields of <em>roches moutonnées</em>, whalebacks and crag-and-tails, narrow gorges cut into high-standing mountain ranges, and km-scale planation surfaces and large U-shaped valleys, overdeepenings, fjords and troughs up to 200 km in length. Many modern savannahs and desertic landscapes of Southern Africa are therefore relict glacial landscapes and relief ca. 300 Myr old. These exhumed glacial relief moreover exerts a strong control on the modern-day aspect of the geomorphology of Southern Africa as (1) some escarpments that delineate high-standing plateaux from valleys and coastal plains are inherited glacial relief in which glacial valleys are carved, (2) some hill or mountain ranges already existed by LPIA times and were likely modelled by glacial erosion, and (3) the drainage network of many of the main rivers of Southern Africa is funnelled through ancient glacial valleys. This remarkable preservation allowed us to reconstruct the paleogeography of Southern Africa in the aftermath of the LPIA, consisting of highlands over which ice masses nucleated and from which they flowed through the escarpments and toward lowlands that now correspond to sedimentary basins. Our findings therefore indicate that glacial landforms and relief of continental-scale can survive over tens to hundreds of million years. This preservation and modern exposure of the glacial paleolandscapes were achieved through burial under piles of","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"82 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140127627","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 : 2024-03-11DOI: 10.5194/egusphere-2024-312
Kaiheng Hu, Hao Li, Shuang Liu, Li Wei, Xiaopeng Zhang, Limin Zhang, Bo Zhang, Manish Raj Gouli
Abstract. Periglacial debris flows boosted by strong earthquakes or climatic warming in alpine mountains play a crucial role in sediment delivery from hillslopes and downslope channels into rivers. Rapid and massive sediment supply to rivers by the debris flows has profoundly influenced the evolution of the alpine landscape. Nonetheless, there is a dearth of knowledge concerning the roles tectonic and climatic factors played in the intensified sediment erosion and transportation. In order to increase our awareness of the mass wasting processes and glacier changes, five debris flows that occurred at the Zelunglung catchment of the eastern syntaxis of the Himalayas since 1950 Assam earthquake are investigated in detail by field surveys and long-term remote sensing interpretation. Long-term seismic and meteorological data indicate that the four events of 1950–1984 were the legacies of the earthquake, and recent warming events drove the 2020 event. The transported sediment volume indexed with a non-vegetated area on the alluvial fan reduced by 91 % to a stable low level nearly 40 years after 1950. It is reasonable to hypothesize that tectonic and climatic factors alternately drive the sediment supplies caused by the debris flows. High concentrations of coarse grains, intense erosion, and extreme impact force of the 2020 debris flow raised concerns about the impacts of such excess sediment inputs on the downstream river evolution and infrastructure safety. In regard to the hydrometeorological conditions of the main river, the time to evacuate the transported coarse sediments is approximately two orders of magnitude of the recurrence period of periglacial debris flows.
{"title":"Variation of sediment supply by periglacial debris flows at Zelunglung in the eastern syntaxis of Himalayas since the 1950 Assam Earthquake","authors":"Kaiheng Hu, Hao Li, Shuang Liu, Li Wei, Xiaopeng Zhang, Limin Zhang, Bo Zhang, Manish Raj Gouli","doi":"10.5194/egusphere-2024-312","DOIUrl":"https://doi.org/10.5194/egusphere-2024-312","url":null,"abstract":"<strong>Abstract.</strong> Periglacial debris flows boosted by strong earthquakes or climatic warming in alpine mountains play a crucial role in sediment delivery from hillslopes and downslope channels into rivers. Rapid and massive sediment supply to rivers by the debris flows has profoundly influenced the evolution of the alpine landscape. Nonetheless, there is a dearth of knowledge concerning the roles tectonic and climatic factors played in the intensified sediment erosion and transportation. In order to increase our awareness of the mass wasting processes and glacier changes, five debris flows that occurred at the Zelunglung catchment of the eastern syntaxis of the Himalayas since 1950 Assam earthquake are investigated in detail by field surveys and long-term remote sensing interpretation. Long-term seismic and meteorological data indicate that the four events of 1950–1984 were the legacies of the earthquake, and recent warming events drove the 2020 event. The transported sediment volume indexed with a non-vegetated area on the alluvial fan reduced by 91 % to a stable low level nearly 40 years after 1950. It is reasonable to hypothesize that tectonic and climatic factors alternately drive the sediment supplies caused by the debris flows. High concentrations of coarse grains, intense erosion, and extreme impact force of the 2020 debris flow raised concerns about the impacts of such excess sediment inputs on the downstream river evolution and infrastructure safety. In regard to the hydrometeorological conditions of the main river, the time to evacuate the transported coarse sediments is approximately two orders of magnitude of the recurrence period of periglacial debris flows.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"28 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140107501","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 : 2024-03-07DOI: 10.5194/esurf-12-433-2024
Chao Zhou, Xibin Tan, Yiduo Liu, Feng Shi
Abstract. The lateral movement of drainage divides is co-influenced by tectonics, lithology, and climate and therefore archives a wealth of geologic and climatic information. It also has wide-ranging implications for topography, the sedimentary record, and biological evolution and thus has drawn much attention in recent years. Several methods have been proposed to determine drainage divides' migration state (direction and rate), including geochronological approaches (e.g., 10Be) and topography-based approaches (e.g., χ plots or Gilbert metrics). A key object in these methods is the channel head, which separates the hillslope and channel. However, due to the limited resolution of topography data, the required channel-head parameters in the calculation often cannot be determined accurately, and empirical values are used in the calculation, which may induce uncertainties. Here, we propose two methods to calculate the migration rate of drainage divides based on the relatively accurate channel-head parameters derived from high-resolution topographic data. We then apply the methods to an active rift shoulder (Wutai Shan) in the Shanxi Rift and a tectonically stable area (Yingwang Shan) in the Loess Plateau, to illustrate how to calculate drainage-divide migration rates. Our results show that the Wutai Shan drainage divide is migrating northwestward at a rate between 0.21 and 0.27 mm yr−1, whereas the migration rates at the Yingwang Shan are approximately zero. This study indicates that the drainage-divide stability can be determined more accurately using high-resolution topographic data. Furthermore, this study takes the cross-divide differences in the uplift rate of channel heads into account in the measurement of drainage-divide migration rate for the first time.
{"title":"Quantifying the migration rate of drainage divides from high-resolution topographic data","authors":"Chao Zhou, Xibin Tan, Yiduo Liu, Feng Shi","doi":"10.5194/esurf-12-433-2024","DOIUrl":"https://doi.org/10.5194/esurf-12-433-2024","url":null,"abstract":"Abstract. The lateral movement of drainage divides is co-influenced by tectonics, lithology, and climate and therefore archives a wealth of geologic and climatic information. It also has wide-ranging implications for topography, the sedimentary record, and biological evolution and thus has drawn much attention in recent years. Several methods have been proposed to determine drainage divides' migration state (direction and rate), including geochronological approaches (e.g., 10Be) and topography-based approaches (e.g., χ plots or Gilbert metrics). A key object in these methods is the channel head, which separates the hillslope and channel. However, due to the limited resolution of topography data, the required channel-head parameters in the calculation often cannot be determined accurately, and empirical values are used in the calculation, which may induce uncertainties. Here, we propose two methods to calculate the migration rate of drainage divides based on the relatively accurate channel-head parameters derived from high-resolution topographic data. We then apply the methods to an active rift shoulder (Wutai Shan) in the Shanxi Rift and a tectonically stable area (Yingwang Shan) in the Loess Plateau, to illustrate how to calculate drainage-divide migration rates. Our results show that the Wutai Shan drainage divide is migrating northwestward at a rate between 0.21 and 0.27 mm yr−1, whereas the migration rates at the Yingwang Shan are approximately zero. This study indicates that the drainage-divide stability can be determined more accurately using high-resolution topographic data. Furthermore, this study takes the cross-divide differences in the uplift rate of channel heads into account in the measurement of drainage-divide migration rate for the first time.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"84 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140057275","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 : 2024-03-04DOI: 10.5194/egusphere-2023-3006
Wolfgang Aumer, Ingo Hartmeyer, Carolyn-Monika Görres, Daniel Uteau, Stephan Peth
Abstract. The active layer thickness (ALT) refers to the seasonal thaw depth of a permafrost body and is an essential parameter for natural hazard analysis, construction, land-use planning and the estimation of greenhouse gas emissions in periglacial regions. The aim of this study is to model the annual maximum thaw depth for determining ALT based on temperature data measured in four shallow boreholes (SBs, 0.1 m deep) in the summit region of the Kitzsteinhorn (Hohe Tauern Range, Austria, Europe). We set up our heat flow model with temperature data (2016–21) from a 30 m deep borehole (DB) drilled into bedrock at the Kitzsteinhorn north-face. For modeling purposes, we assume 1D conductive heat flow and present an analytical solution of the heat transport equation through sinusoidal temperature waves resulting from seasonal temperature oscillations (damping depth method). The model approach is considered successful: In the validation period (2019–21), modeled and measured ALT differed by only 0.1±0.1 m. We then applied the DB-calibrated model to four SBs and found that the modeled seasonal ALT maximum ranged between 2.5 m (SB 2) and 10.6 m (SB 1) in the observation period (2013–2021). Due to small differences in altitude (~ 200 m) within the study area, slope aspect had the strongest impact on ALT. To project future ALT deepening due to global warming, we integrated IPCC climate scenarios SSP1-2.6 and SSP5-8.5 into our model. By mid-century (~ 2050), ALT is expected to increase by 48 % at SB 2 and by 62 % at DB under scenario SSP1-2.6 (56 % and 128 % under scenario SSP5-8.5), while permafrost will no longer be present at SB 1, SB 3 and SB 4. By the end of the century (~ 2100), permafrost will only remain under scenario SSP1-2.6 with an ALT increase of 51 % at SB 2 and of 69 % at DB.
摘要活动层厚度（ALT）指的是冻土体的季节性解冻深度，是冻土地区自然灾害分析、建筑、土地利用规划和温室气体排放估算的重要参数。本研究的目的是根据基茨施泰因峰（欧洲奥地利豪赫陶恩山脉）山顶地区四个浅钻孔（SB，0.1 米深）测得的温度数据，建立年度最大解冻深度模型，以确定 ALT。我们利用在基茨坦峰北面钻入基岩的 30 米深钻孔（DB）的温度数据（2016-21 年）建立了热流模型。出于建模目的，我们假设存在一维传导热流，并通过季节性温度振荡产生的正弦温度波（阻尼深度法）给出了热量传输方程的解析解。该模型方法被认为是成功的：在验证期（2019-21 年），模型和测量的 ALT 仅相差 0.1±0.1 米。然后，我们将 DB 校准模型应用于四个 SB，发现在观测期（2013-2021 年），模型的季节 ALT 最大值介于 2.5 米（SB 2）和 10.6 米（SB 1）之间。由于研究区域内海拔高度差异较小（约 200 米），坡度对 ALT 的影响最大。为了预测全球变暖导致的未来 ALT 加深，我们将 IPCC 气候情景 SSP1-2.6 和 SSP5-8.5 纳入了模型。到本世纪中期（约 2050 年），在 SSP1-2.6 情景下，SB 2 的 ALT 预计将增加 48%，DB 的 ALT 预计将增加 62%（在 SSP5-8.5 情景下分别增加 56% 和 128%），而 SB 1、SB 3 和 SB 4 将不再存在永久冻土。到本世纪末（约 2100 年），只有在 SSP1-2.6 情景下，SB 2 的 ALT 将增加 51%，DB 的 ALT 将增加 69%，永久冻土才会继续存在。
{"title":"Modelling active layer thickness in mountain permafrost based on an analytical solution of the heat transport equation, Kitzsteinhorn, Hohe Tauern Range, Austria","authors":"Wolfgang Aumer, Ingo Hartmeyer, Carolyn-Monika Görres, Daniel Uteau, Stephan Peth","doi":"10.5194/egusphere-2023-3006","DOIUrl":"https://doi.org/10.5194/egusphere-2023-3006","url":null,"abstract":"<strong>Abstract.</strong> The active layer thickness (ALT) refers to the seasonal thaw depth of a permafrost body and is an essential parameter for natural hazard analysis, construction, land-use planning and the estimation of greenhouse gas emissions in periglacial regions. The aim of this study is to model the annual maximum thaw depth for determining ALT based on temperature data measured in four shallow boreholes (SBs, 0.1 m deep) in the summit region of the Kitzsteinhorn (Hohe Tauern Range, Austria, Europe). We set up our heat flow model with temperature data (2016–21) from a 30 m deep borehole (DB) drilled into bedrock at the Kitzsteinhorn north-face. For modeling purposes, we assume 1D conductive heat flow and present an analytical solution of the heat transport equation through sinusoidal temperature waves resulting from seasonal temperature oscillations (damping depth method). The model approach is considered successful: In the validation period (2019–21), modeled and measured ALT differed by only 0.1±0.1 m. We then applied the DB-calibrated model to four SBs and found that the modeled seasonal ALT maximum ranged between 2.5 m (SB 2) and 10.6 m (SB 1) in the observation period (2013–2021). Due to small differences in altitude (~ 200 m) within the study area, slope aspect had the strongest impact on ALT. To project future ALT deepening due to global warming, we integrated IPCC climate scenarios SSP1-2.6 and SSP5-8.5 into our model. By mid-century (~ 2050), ALT is expected to increase by 48 % at SB 2 and by 62 % at DB under scenario SSP1-2.6 (56 % and 128 % under scenario SSP5-8.5), while permafrost will no longer be present at SB 1, SB 3 and SB 4. By the end of the century (~ 2100), permafrost will only remain under scenario SSP1-2.6 with an ALT increase of 51 % at SB 2 and of 69 % at DB.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"11 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140025493","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 : 2024-02-27DOI: 10.5194/egusphere-2024-524
Justin A. Nghiem, Gen K. Li, Joshua P. Harringmeyer, Gerard Salter, Cédric G. Fichot, Luca Cortese, Michael P. Lamb
Abstract. Flocculation controls mud sedimentation and organic carbon burial rates by increasing mud settling velocity. Floc settling velocity can be predicted using a semi-empirical model that depends on turbulence, sediment concentration, and geochemical variables or an explicit Stokes law-type model that depends on floc diameter, permeability, and fractal properties. However, validation of the semi-empirical and explicit models with direct field measurements is lacking. We employed a camera, in situ particle sizing, and analysis of grain size-specific suspended sediment concentration profiles to measure flocs in the freshwater channels and wetlands of Wax Lake Delta, Louisiana. Sediment finer than ~20 to 50 μm flocculates with median floc diameter of 30 to 90 μm, bulk solid fraction of 0.05 to 0.3, and floc settling velocity of ~0.1 to 1 mm s-1, with little variation along depth. These values are consistent with the semi-empirical model, which indicates that turbulence limits variation in floc settling velocity on flood-to-seasonal time scales. In the explicit model, the effective primary particle diameter, commonly assumed to be the median primary particle diameter, differs by a factor of ~2 to 6 smaller than the median and can be better described using a simple fractal theory. Flow through the floc increases settling velocity by a factor of ~2 and can be explained by parameterizing flocs as effectively permeable clusters of primary particles. Our results provide the first full field validation of effective primary particle diameter and floc permeability theories, which improve floc settling velocity predictions of the explicit model.
{"title":"Validating floc settling velocity models in rivers and freshwater wetlands","authors":"Justin A. Nghiem, Gen K. Li, Joshua P. Harringmeyer, Gerard Salter, Cédric G. Fichot, Luca Cortese, Michael P. Lamb","doi":"10.5194/egusphere-2024-524","DOIUrl":"https://doi.org/10.5194/egusphere-2024-524","url":null,"abstract":"<strong>Abstract.</strong> Flocculation controls mud sedimentation and organic carbon burial rates by increasing mud settling velocity. Floc settling velocity can be predicted using a semi-empirical model that depends on turbulence, sediment concentration, and geochemical variables or an explicit Stokes law-type model that depends on floc diameter, permeability, and fractal properties. However, validation of the semi-empirical and explicit models with direct field measurements is lacking. We employed a camera, in situ particle sizing, and analysis of grain size-specific suspended sediment concentration profiles to measure flocs in the freshwater channels and wetlands of Wax Lake Delta, Louisiana. Sediment finer than ~20 to 50 μm flocculates with median floc diameter of 30 to 90 μm, bulk solid fraction of 0.05 to 0.3, and floc settling velocity of ~0.1 to 1 mm s<sup>-1</sup>, with little variation along depth. These values are consistent with the semi-empirical model, which indicates that turbulence limits variation in floc settling velocity on flood-to-seasonal time scales. In the explicit model, the effective primary particle diameter, commonly assumed to be the median primary particle diameter, differs by a factor of ~2 to 6 smaller than the median and can be better described using a simple fractal theory. Flow through the floc increases settling velocity by a factor of ~2 and can be explained by parameterizing flocs as effectively permeable clusters of primary particles. Our results provide the first full field validation of effective primary particle diameter and floc permeability theories, which improve floc settling velocity predictions of the explicit model.","PeriodicalId":48749,"journal":{"name":"Earth Surface Dynamics","volume":"11 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139978765","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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