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Pliocene shorelines and the epeirogenic motion of continental margins: a target dataset for dynamic topography models 上新世海岸线和大陆边缘的夷平运动:动态地形模型的目标数据集
IF 2.8 2区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2024-07-24 DOI: 10.5194/esurf-12-883-2024
A. Hollyday, M. Raymo, J. Austermann, Fred D Richards, M. 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 10 wave-cut 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 paleo-shoreline 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 that 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.
摘要上新世中期(3 Ma)的全球平均海平面由于全球冰盖覆盖面积的减少而明显高于现在,当时的二氧化碳和气温都高于现在的水平。然而,由于基于代用指标的海平面重建以及用于评估有限数据约束的固体地球动力学模型的高度不确定性,冰盖对上新世变暖的响应程度仍然是个问题。在这里,我们展示了一个全球数据集,其中包括 10 个由连续的上新世海平面振荡形成的波切痕,这些波切痕今天在海平面以上 6 至 109 米处被观测到。利用高分辨率数字高程模型和实地测绘相结合的方法,确定了这些地貌目前的海拔高度。利用 MATLAB 界面 TerraceM,我们对悬崖和平台表面进行了推断,以确定崖脚的海拔高度,在大多数情况下,崖脚被掩埋在数米高的滑石之下。我们根据冰川等静力调整校正了峭壁趾的海拔高度,发现仅凭这一过程无法解释全球各地观测到的上新世古海岸线海拔高度的差异。接下来,我们确定了与地幔动态地形相关的信号,方法是反演地幔现今的三维浮力结构,并使用对流代码 ASPECT 计算过去 3 Myr 的径向地表应力差异。我们将地震层析成像模型、地球动力学观测和岩石力学实验室实验所约束的各种现今地幔结构(浮力和粘度)包括在内。最后,我们根据动态地形变化预测与疤痕海拔高度的一致性,确定了首选的动态地形变化预测,并根据南非德霍普的一个疤痕海拔高度,利用最可靠的结果估算了上新世的全球平均海平面。这一推断(11.6 ± 5.2 米)是向下修正的,可能意味着冰原对温暖的上新世气候条件具有较强的抵抗力。不过,我们也得出结论,要根据本研究绘制的所有疤痕更可靠地推断上新世中期的全球平均海平面,还需要开发更有针对性的模型。
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引用次数: 0
Decadal-scale decay of landslide-derived fluvial suspended sediment after Typhoon Morakot 台风 "莫拉克 "过后源自山体滑坡的河道悬浮沉积物的十年尺度衰减
IF 2.8 2区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2024-07-17 DOI: 10.5194/esurf-12-863-2024
G. Ruetenik, K. Ferrier, O. Marc
Abstract. Landslides influence fluvial suspended sediment transport by changing sediment supply and grain size, which alter suspended sediment concentrations and fluxes for a period of time after landsliding. To investigate the duration and scale of altered suspended sediment transport due to landsliding, we analyzed suspended sediment concentration and water discharge measurements at 87 gauging stations across Taiwan over an 11-year period after Typhoon Morakot, which generated nearly 20 000 landslides in 2009. At each gauging station, we computed annual rating curves to quantify changes over time in the sensitivity of suspended sediment concentrations to water discharge. Among the 40 stations in basins that were impacted by landsliding, the discharge-normalized rating curve coefficient ã was higher than that before Morakot by a factor of 5.1±1.1 (mean ± standard error) in 2010, the first year after Morakot. The rating curve exponent b did not decrease at most stations until a year later (2011), when the average b value was lower than that before Morakot by 0.25±0.05. Across the compilation of gauging stations, post-Morakot changes in discharge-normalized sediment concentration (ã) were positively correlated with landslide intensity for 7 years after Morakot, while post-Morakot changes in the exponent of the discharge–concentration relationship (b) were negatively correlated with landslide intensity from 2011 to 2014. This reflects a tendency for larger changes in ã and b to occur in basins with more intense landsliding. At 26 of these 40 stations, elevated values of ã declined after the initial post-Morakot peak, consistent with a gradual return to pre-Morakot suspended sediment transport conditions. Exponential regressions to these ã values reveal a median characteristic decay time of 8.8 years (interquartile range: 5.7–14.8 years). Values of ã increased more and declined faster in basins with more intense landsliding, with a mean characteristic decay time of 6 years in the basins hit hardest by landsliding. Furthermore, changes in ã and b tended to be larger in basins with more intense landsliding. At stations that were not impacted or only minimally impacted by landsliding, neither ã nor b exhibited systematic responses to Morakot. To quantify the effect of landsliding on sediment discharge, we compared the measured sediment discharges after Morakot to the hypothetical sediment discharges that would have occurred if Morakot had induced no landslides, calculated by applying each station's pre-Morakot rating curve to its post-Morakot water discharge history. This analysis suggests that Morakot-induced landsliding increased sediment discharge by as much as > 10-fold in some basins in the 1–2 years after Morakot. Together, these results indicate that the influence of Morakot-induced landsliding on rating curves was large shortly after Morakot but diminished in less than a decade in most of the study rivers and will be imperceptible in an
摘要山体滑坡通过改变泥沙供应和粒径来影响河流悬浮泥沙输移,从而改变山体滑坡后一段时间内的悬浮泥沙浓度和通量。2009 年台风 "莫拉克 "引发了近 20,000 起山体滑坡,为了研究山体滑坡导致悬浮泥沙输移改变的持续时间和规模,我们分析了台湾 87 个测站在台风过后 11 年间的悬浮泥沙浓度和排水量测量值。在每个测站,我们计算了年度等级曲线,以量化悬浮泥沙浓度对排水量的敏感性随时间的变化。在受山体滑坡影响的流域的 40 个测站中,2010 年(莫拉克山体滑坡发生后的第一年)的排水归一化评级曲线系数 ã 比莫拉克山体滑坡发生前高 5.1±1.1 倍(平均值 ± 标准误差)。直到一年后(2011 年),大多数测站的等级曲线指数 b 才下降,平均 b 值比莫拉克之前低 0.25±0.05。在所有测站中,莫拉克事件后 7 年内,莫拉克事件后排放归一化沉积物浓度(ã)的变化与滑坡强度呈正相关,而莫拉克事件后 2011 年至 2014 年期间,排放-浓度关系指数(b)的变化与滑坡强度呈负相关。这反映出在滑坡强度较大的流域,ã和b的变化往往较大。在这 40 个站点中的 26 个站点,ã的升高值在莫拉科特事件后的初始峰值之后有所下降,这与逐渐恢复到莫拉科特事件前的悬浮沉积物运移条件是一致的。对这些 ã 值的指数回归显示,特征衰减时间的中位数为 8.8 年(四分位间范围:5.7-14.8 年)。在山体滑坡更为严重的盆地,ã值增加得更多,衰减得更快,受山体滑坡影响最严重的盆地的平均特征衰减时间为 6 年。此外,在滑坡更为剧烈的流域,ã 和 b 的变化往往更大。在未受滑坡影响或仅受滑坡影响较小的站点,ã和b均未表现出对莫拉克的系统响应。为了量化滑坡对沉积物排放量的影响,我们将莫拉科特事件后测得的沉积物排放量与假设莫拉科特事件没有引起滑坡时的沉积物排放量进行了比较,计算方法是将每个站点莫拉科特事件前的水位变化曲线应用于其莫拉科特事件后的水位变化曲线。这一分析表明,在莫拉克事件发生后的 1-2 年中,莫拉克引发的山体滑坡使一些流域的沉积物排放量增加了 10 倍以上。这些结果表明,莫拉科特泥石流对等级曲线的影响在莫拉科特泥石流发生后不久就很大,但在大多数研究河流中,这种影响在不到 10 年的时间内就会减弱,在所有研究河流中,这种影响在几十年后就会消失。如果这些结果适用于其他地貌,则表明滑坡后沉积物迁移效率升高的时期应持续数年至数十年,即使滑坡沉积物持续数百年至数千年。
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引用次数: 0
Exotic tree plantations in the Chilean Coastal Range: balancing the effects of discrete disturbances, connectivity, and a persistent drought on catchment erosion 智利海岸山脉的外来植树造林:平衡离散干扰、连通性和持续干旱对集水区侵蚀的影响
IF 3.4 2区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2024-07-05 DOI: 10.5194/esurf-12-841-2024
Violeta Tolorza, Christian H. Mohr, Mauricio Zambrano-Bigiarini, Benjamín Sotomayor, Dagoberto Poblete-Caballero, Sebastien Carretier, Mauricio Galleguillos, Oscar Seguel
Abstract. The Chilean Coastal Range, located in the Mediterranean segment of Chile, is a soil-mantled landscape with the potential to store valuable freshwater supplies and support a biodiverse native forest. Nevertheless, human intervention has been increasing soil erosion for ∼ 200 years, culminating in the intense management of exotic tree plantations throughout the last ∼ 45 years. At the same time, this landscape has been severely affected by a prolonged megadrought. As a result, this combination of stressors complicates disentangling the effects of anthropogenic disturbances and hydroclimatic trends on sediment fluxes at the catchment scale. In this study, we calculate decennial catchment erosion rates from suspended-sediment loads and compare them with a millennial catchment denudation rate estimated from detrital 10Be. We then contrast both of these rates with the effects of discrete anthropogenic-disturbance events and hydroclimatic trends. Erosion and denudation rates are similar in magnitude on decennial and millennial timescales, i.e., 0.018 ± 0.005 and 0.024 ± 0.004 mm yr−1, respectively. Recent human-made disturbances include logging operations throughout all seasons and a dense network of forestry roads, thereby increasing structural sediment connectivity. Further disturbances include two widespread wildfires (2015 and 2017) and an earthquake with an Mw value of 8.8 in 2010. We observe decreased suspended-sediment loads during the wet seasons for the period 1986–2018, coinciding with declining streamflow, baseflow, and rainfall. The low millennial denudation rate aligns with a landscape dominated by slow diffusive soil creep. However, the low decennial erosion rate and the decrease in suspended sediment disagree with the expected effect of intense anthropogenic disturbances and increased structural (sediment) connectivity. Such a paradox suggests that suspended-sediment loads, and thus respective catchment erosion, are underestimated and that decennial sediment detachment and transport have been masked by decreasing rainfall and streamflow (i.e., weakened hydroclimatic drivers). Our findings indicate that human-made disturbances and hydrologic trends may result in opposite, partially offsetting effects on recent erosion, yet both contribute to landscape degradation.
摘要智利海岸山脉位于智利的地中海地区,是一片土壤覆盖的地貌,具有储存宝贵的淡水资源和支持生物多样性的本地森林的潜力。然而,在过去的 200 多年里,人类的干预加剧了土壤侵蚀,在过去的 45 年里,外来树木种植园的密集管理更是达到了顶峰。与此同时,这一地貌还受到了长期特大干旱的严重影响。因此,这些压力因素的结合使得在流域尺度上厘清人为干扰和水文气候趋势对沉积物通量的影响变得更加复杂。在这项研究中,我们根据悬浮物载荷计算出了十年一度的集水区侵蚀率,并将其与根据 10Be 碎片估算出的千年一度的集水区剥蚀率进行了比较。然后,我们将这两种速率与离散的人为干扰事件和水文气候趋势的影响进行对比。在十年和千年时间尺度上,侵蚀和剥蚀速率的大小相似,即分别为 0.018 ± 0.005 和 0.024 ± 0.004 毫米/年-1。近期的人为干扰包括四季伐木作业和密集的林道网络,从而增加了结构沉积物的连通性。其他干扰还包括两次大范围野火(2015 年和 2017 年)以及 2010 年发生的一次 Mw 值为 8.8 的地震。我们观察到,1986 年至 2018 年期间,雨季的悬浮泥沙负荷有所下降,这与溪流、基流和降雨量的下降相吻合。较低的千年侵蚀率与以缓慢扩散的土壤蠕动为主的地貌相吻合。然而,低十年侵蚀率和悬浮沉积物的减少与强烈人为干扰和结构(沉积物)连通性增加的预期效果不符。这种自相矛盾的现象表明,悬浮泥沙负荷以及相应的集水侵蚀作用被低估了,而且降雨量和溪流的减少(即水文气候驱动力减弱)掩盖了十年期泥沙剥离和迁移的作用。我们的研究结果表明,人为干扰和水文趋势可能会对近期侵蚀产生相反的、部分抵消的影响,但两者都会导致地貌退化。
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引用次数: 0
Role of the forcing sources in morphodynamic modelling of an embayed beach 淤积海滩形态动力学建模中强迫源的作用
IF 3.4 2区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2024-06-26 DOI: 10.5194/esurf-12-819-2024
Nil Carrion-Bertran, Albert Falqués, Francesca Ribas, Daniel Calvete, Rinse de Swart, Ruth Durán, Candela Marco-Peretó, Marta Marcos, Angel Amores, Tim Toomey, Àngels Fernández-Mora, Jorge Guillén
Abstract. The sensitivity of a 2DH coastal area (XBeach) and a reduced-complexity (Q2Dmorfo) morphodynamic model to using different forcing sources is studied. The models are tested by simulating the morphodynamic response of an embayed beach in the NW Mediterranean over a 6-month period. Wave and sea-level forcing from in situ data, propagated buoy measurements, and hindcasts, as well as combinations of these different data sources, are used, and the outputs are compared to in situ bathymetric measurements. Results show that when the two models are calibrated with in situ measurements, they accurately reproduce the morphodynamic evolution with a “good” Brier skill score (BSS). The calibration process reduces the errors by 65 %–85 % compared with the default setting. The wave data propagated from the buoy also produce reliable morphodynamic simulations but with a slight decrease in the BSS. Conversely, when the models are forced with hindcast wave data, the mismatch between the modelled and observed beach evolution increases. This is attributed to a large extent to biased mean directions in hindcast waves. Interestingly, in this small tide site, the accuracy of the simulations hardly depends on the sea-level data source, and using filtered or non-filtered tides also yields similar results. These results have implications for long-term morphodynamic studies, like those needed to validate models for climate change projections, emphasizing the need to use accurate forcing sources such as those obtained by propagating buoy data.
摘要研究了二维沿岸地区(XBeach)和简化(Q2Dmorfo)形态动力学模式对不同强迫源的敏感性。通过模拟地中海西北部一个内陷海滩 6 个月的形态动力响应,对模型进行了测试。使用了来自原位数据、传播浮标测量数据、后报数据以及这些不同数据源组合的波浪和海平面作用力,并将输出结果与原位测深数据进行了比较。结果表明,当这两个模型与现场测量数据进行校准时,它们都能准确地再现形态动力学的演变过程,且布赖尔技能评分(BSS)为 "良好"。与默认设置相比,校准过程减少了 65%-85% 的误差。浮标传播的波浪数据也能产生可靠的形态动力模拟,但 BSS 略有下降。相反,当模型使用后报波浪数据时,模型与观测到的海滩演变之间的不匹配增加。这在很大程度上归因于后报波浪的平均方向有偏差。有趣的是,在这个小潮位点,模拟的准确性几乎不取决于海平面数据源,使用过滤或非过滤潮汐也能得到相似的结果。这些结果对长期形态动力学研究(如验证气候变化预测模型所需的研究)具有重要意义,强调了使用精确的强迫源(如通过传播浮标数据获得的强迫源)的必要性。
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引用次数: 0
Equilibrium distance from long-range dune interactions 远距离沙丘相互作用的平衡距离
IF 3.4 2区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2024-06-20 DOI: 10.5194/egusphere-2024-1634
Jean Vérité, Clément Narteau, Olivier Rozier, Jeanne Alkalla, Laurie Barrier, Sylvain Courrech du Pont
Abstract. Flow perturbations induced by dune topography affect sediment transport locally, but can also be felt over long distances altering the dynamics of isolated neighbouring dunes downstream. In order to work under optimal conditions that eliminate transverse flow components, collisions and mass exchange between dunes, we study here these long-range interactions using a 2D numerical model where two equal-sized dunes lying on a non-erodible bed are exposed to a symmetric reversing flow. Depending on the initial spacing, dunes either attract or repel each other, to eventually converge towards a steady-state spacing. This equilibrium distance decreases with flow strength and increases with period of flow reorientation and dune size. It is mainly controlled by the reversing dune shape and the structure of the turbulent wake it generates, which continuously modulates the mean shear stress on the downstream dune. Under multi-directional wind regimes, these long-range flow perturbations offer an alternative mechanism for wavelength selection in dune fields with non-erodible interdune areas. Within these dune fields, estimates of mean shear stress could be used to assess the relative migration rate and the state of attraction/repulsion between neighbouring dunes.
摘要沙丘地形引起的水流扰动会影响局部的沉积物迁移,但也会在长距离上影响下游相邻孤立沙丘的动态变化。为了在消除沙丘间横向流动成分、碰撞和质量交换的最佳条件下工作,我们在此使用二维数值模型研究了这些长程相互作用。根据初始间距的不同,沙丘要么相互吸引,要么相互排斥,最终趋于稳定的间距。这种平衡距离随水流强度的增加而减小,随水流重新定向的周期和沙丘大小的增加而增大。它主要受反向沙丘形状及其产生的湍流尾流结构的控制,湍流尾流不断调节下游沙丘上的平均切应力。在多向风机制下,这些长程流动扰动为具有不可侵蚀沙丘间区域的沙丘场提供了另一种波长选择机制。在这些沙丘区域内,平均剪应力的估计值可用于评估相邻沙丘之间的相对迁移率和吸引/排斥状态。
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引用次数: 0
An empirically-derived hydraulic head model controlling water storage and outflow over a decade in degraded permafrost rock slopes (Zugspitze, D/A) 根据经验得出的水头模型,控制退化永冻土岩坡(祖格斯皮采,D/A)十年间的蓄水和排水量
IF 3.4 2区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2024-06-19 DOI: 10.5194/egusphere-2024-1512
Riccardo Scandroglio, Samuel Weber, Till Rehm, Michael Krautblatter
Abstract. While recent permafrost degradation in Alpine peri- and paraglacial slopes has been documented in several studies, only restricted information is available on the respective hydrology. Water boosts permafrost degradation by advective heat transport and destabilizes periglacial mountain slopes. Even if multiple recent rock slope failures indicate the presence of water, only a few studies provide evidence of water availability and related hydrostatic pressures at bigger depths, showing a significant research gap. This study combines a unique decennial data set of meteorological data, snowmelt modeling, and discharge measurements from two rock fractures in a tunnel located ≈ 55 m under the permafrost-affected N-S facing Zugspitze Ridge (2815–2962 m asl). To decipher the hydrological properties of fractures, we analyze inputs, i.e., snowmelt and rainfall, and outputs, i.e., discharge from fractures, baseflow, and no-flow events, detecting flow anomalies. For summer precipitation events, we developed i) a uniform recession curve, ii) an empirical water storage model, and iii) an approximate hydraulic water pressure model according to Darcy’s falling-head law. Extreme events with up to 800 l/d and 58 l/h are likely to fully saturate the observed fractures with corresponding hydraulic heads of up to 40 ± 10 m and to increase fracture interconnectivity. The average daily discharge during snowmelt, 10 l/h, can lead to hydraulic heads up to 27 ± 6 m. Water dynamics suggest hydraulic conductivities in the range of 10−4 m/s, with variations according to the fracture’s saturation. E.g., no-flow and baseflow events indicate unsaturated and partially saturated conditions. Here, we show an empirical fluid flow approximation model of hydrostatic pressure regimes in high-alpine deep-bedrock fractures. Pressures from water accumulation in bedrock reach levels that can weaken or even destabilize rock slopes. This process can easily outpace thermal conductive warming of active layers in the foreseeable future, provide positive feedback on water infiltration, and is crucial for the stability of the rapidly warming alpine permafrost environments.
摘要虽然多项研究记录了阿尔卑斯山围冰期和副冰期山坡最近出现的永久冻土退化现象,但有关其水文情况的资料却十分有限。水通过平流传热促进永久冻土退化,并破坏冰川山坡的稳定性。即使最近发生的多起岩石斜坡崩塌表明了水的存在,但只有少数研究提供了在更大深度上水的可用性和相关静水压力的证据,这显示了巨大的研究差距。这项研究结合了一个独特的十年期数据集,包括气象数据、融雪模型以及从位于受永久冻土影响的南北向祖格峰山脊(海拔 2815-2962 米)下 55 米处的一条隧道中的两条岩石裂缝测量到的排水量。为了破解断裂的水文特性,我们分析了输入(即融雪和降雨)和输出(即断裂排水、基流和无流事件),检测流量异常。对于夏季降水事件,我们开发了 i) 均匀衰退曲线;ii) 经验储水模型;iii) 根据达西水头下降定律建立的近似水压模型。高达 800 升/天和 58 升/小时的极端事件可能会使观测到的断裂完全饱和,相应的水头高达 40 ± 10 米,并增加断裂的互联性。融雪期间的日平均排水量(10 升/小时)可导致高达 27 ± 6 米的水头。水动力学表明,水导率在 10-4 米/秒的范围内,随裂缝饱和度的变化而变化。例如,无水流和基流事件表明了非饱和和部分饱和的条件。在此,我们展示了高山深层岩石断裂中静水压力机制的经验流体流近似模型。基岩中积水产生的压力可达到削弱甚至破坏岩坡稳定的程度。在可预见的未来,这一过程很容易超过活动层的导热升温,对水的渗透提供正反馈,对迅速变暖的高山永冻土环境的稳定性至关重要。
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引用次数: 0
Geomorphic imprint of high mountain floods: Insight from the 2022 hydrological extreme across the Upper Indus terrain in NW Himalayas 高山洪水的地貌印记:喜马拉雅山西北部上印度河地形 2022 年水文极值的启示
IF 3.4 2区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2024-06-18 DOI: 10.5194/egusphere-2024-1618
Abhishek Kashyap, Kristen Cook, Mukunda Dev Behera
Abstract. The interaction of tectonics, surface processes, and climate extremes impacts how the landscape responds to extreme hydrological events. An anomalous precipitation event in 2022 occurred during the monsoon season along the lower reaches of the Upper Indus River, resulting in short-lived high-magnitude flooding and socioeconomic disruption downstream. To understand the spatial relationship between the geomorphic response and climatic controls of this flood event, as well as their primary triggers, we performed a landscape analysis using topographic metrics and quantified the causal association between hydro-climatic variables. Temperature anomalies in upstream glaciated sub-catchments had a considerable impact on snow cover distribution, based on our observations. As snow cover changed, glacial melt runoff rose, contributing to increased fluvial stream power after traversing higher-order reaches. The higher-order reaches of the Upper Indus River received an anomalously high amount of precipitation, which, when combined with substantial glacial and melt discharge, contributed to an extreme flood across the high-relief steep gradient channels. The flood-affected regions had a high mean basin ksn and SL-index, including numerous spikes in their magnitudes along their channel profiles downstream. To determine how the lower reaches of the Upper Indus River responded to this flood event, we employed the Enhanced Vegetation Index (EVI) and Normalized Difference Water Index (NDWI) as change indicator metrics. We observed an inverse causal influence of NDWI on EVI and a statistically significant relationship between anomalous stream power and relative EVI, suggesting that downstream channel morphology changed rapidly during this episodic event and highlighting EVI as a useful indicator of geomorphic change. We suggest that this extreme flood event is a result of the interaction of anomalous glacial melt and anomalous precipitation over a high-relief landscape, with a certain causal connection with anomalous temperature over the event duration. The synoptic observations suggest that this meteorological condition involves the interaction of the Indian Summer Monsoon (ISM) and Western Disturbance (WD) moisture fluxes. However, the geomorphic consequences of such anomalous monsoon periods, as well as their influence on long-term landscape change, are still unclear.
摘要构造、地表过程和极端气候的相互作用影响着地貌对极端水文事件的响应。2022 年,印度河上游下游在季风季节发生了一次异常降水事件,造成了短时间的大洪水和下游社会经济混乱。为了了解这次洪水事件的地貌反应和气候控制之间的空间关系及其主要触发因素,我们利用地形指标进行了景观分析,并量化了水文气候变量之间的因果关系。根据我们的观察,上游冰川子流域的温度异常对积雪覆盖分布有相当大的影响。随着积雪覆盖率的变化,冰川融化的径流量也随之增加,从而使流经高阶河段的河水流量增加。上印度河高阶河段的降水量异常高,再加上大量的冰川融水径流,导致高河谷陡坡河道发生特大洪水。洪水影响区域的平均流域 ksn 和 SL 指数较高,包括沿河道剖面向下游的许多峰值。为了确定印度河上游下游对此次洪水事件的反应,我们采用了增强植被指数(EVI)和归一化差异水指数(NDWI)作为变化指标。我们观察到 NDWI 对 EVI 的反向因果影响,以及异常溪流功率与相对 EVI 之间在统计学上的显著关系,这表明在这次偶发事件中,下游河道形态发生了快速变化,突出表明 EVI 是地貌变化的有用指标。我们认为,这次特大洪水事件是高地形上异常冰川融化和异常降水相互作用的结果,与事件持续期间的异常气温有一定的因果关系。同步观测结果表明,这种气象条件涉及印度夏季季风(ISM)和西部扰动(WD)水汽通量的相互作用。然而,这种异常季风期的地貌后果及其对长期地貌变化的影响仍不清楚。
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引用次数: 0
A machine learning approach to the geomorphometric detection of ribbed moraines in Norway 挪威肋状冰碛地貌检测的机器学习方法
IF 3.4 2区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2024-06-10 DOI: 10.5194/esurf-12-801-2024
Thomas J. Barnes, T. V. Schuler, S. Filhol, K. S. Lilleøren
Abstract. Machine learning is a powerful yet underutilised tool in geomorphology, commonly used for image-based pattern recognition. Analysing new high-resolution (1–10 m) elevation datasets, we investigate its usefulness for detecting discrete geomorphological features. This study develops a machine-learning-based method for identifying ribbed moraines in digital elevation data and progresses to test its performance versus time-consuming, manual methods. Ribbed moraines share geomorphometric characteristics with other glacial landforms, hence representing a valuable test of our new methodology in terms of differentiating between similar features, and for detecting landforms with similar characteristics. Furthermore, mapping ribbed moraines may provide valuable indications of their origin, a topic of debate within glacial geomorphology. To automatically detect ribbed moraines, we extract simple morphometrics from high-resolution digital elevation model data and mask regions where ribbed moraines are unlikely to form. We then test several machine learning algorithms before examining the best performer (K-means clustering) for three study areas of 15 km2 in Norway. Our results demonstrate a balanced accuracy of 65 %–75 % when validating versus ground-truthing. The performance depends on the availability of high-resolution elevation data in Norway that are needed to resolve the spatial scale of the target (10–100 m). We find the method effective at detecting both fields of ribbed moraines, as well as individual ribbed moraines. We propose pathways for the future implementation of this method on a large scale and for increasing the detail of information gained about detected landforms. In conclusion, we demonstrate K-means clustering as a promising method for detecting ribbed moraines, with great potential to reduce the time needed to produce landform maps.
摘要机器学习是地貌学中一种功能强大但利用率不高的工具,通常用于基于图像的模式识别。通过分析新的高分辨率(1-10 米)高程数据集,我们研究了机器学习在检测离散地貌特征方面的实用性。本研究开发了一种基于机器学习的方法,用于识别数字高程数据中的肋状冰碛,并对其性能与耗时的人工方法进行了对比测试。肋冰碛与其他冰川地貌具有共同的地貌特征,因此是对我们的新方法在区分类似特征和检测具有类似特征的地貌方面的一次宝贵测试。此外,绘制带肋冰碛图还能为冰川地貌学中争论不休的冰川起源提供有价值的信息。为了自动检测带肋冰碛,我们从高分辨率数字高程模型数据中提取了简单的形态计量数据,并屏蔽了不可能形成带肋冰碛的区域。然后,我们对几种机器学习算法进行了测试,最后对挪威三个面积为 15 平方公里的研究区域进行了性能最佳的聚类(K-means 聚类)测试。我们的结果表明,在验证与地面实况对比时,准确率在 65%-75% 之间。其性能取决于挪威高分辨率高程数据的可用性,而高分辨率高程数据是解析目标空间尺度(10-100 米)所必需的。我们发现,该方法既能有效地检测到带肋冰碛区,也能有效地检测到单个带肋冰碛区。我们提出了未来大规模实施该方法的途径,以及增加所探测到地貌的详细信息的途径。总之,我们证明了 K 均值聚类是一种很有前途的检测带肋冰碛的方法,在缩短制作地貌图所需的时间方面具有很大的潜力。
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引用次数: 0
Geomorphic indicators of continental-scale landscape transience in the Hengduan Mountains, SE Tibet, China 中国西藏东南部横断山脉大陆尺度景观瞬变的地貌指标
IF 3.4 2区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2024-05-22 DOI: 10.5194/esurf-12-783-2024
Katrina Gelwick, Sean D. Willett, Rong Yang
Abstract. Landscapes are sculpted by a complex response of surface processes to external forcings, such as climate and tectonics. Several major river captures have been documented in the Hengduan Mountains, leading to the hypothesis that the region experiences exceptionally high rates of drainage reorganization driven by horizontal shortening and propagating uplift. Here we determine the prevalence, intensity, and spatial patterns of ongoing drainage reorganization in the Hengduan Mountains and evaluate the relative timescales of this transience by comparing drainage divide asymmetry for four geomorphic metrics that operate at different spatial and temporal scales. Specifically, we calculate the migration direction and the divide asymmetry index (DAI) for drainage divides using catchment-restricted topographic relief (CRR), hillslope gradient (HSG), normalized channel steepness (ksn), and normalized channel distance (χ). ksn and χ are both precipitation-corrected to account for the strong precipitation gradient across the region. The different spatial scales of these geomorphic metrics allow us to establish the relative timescales of observed landscape transience in the Hengduan Mountains, where local-scale metrics measure short-term change and integral quantities measure long-term disequilibrium. We find a high incidence of strongly asymmetric divides in all metrics across the Hengduan Mountain region. Although the magnitude of asymmetry varies significantly between metrics, possibly due to a combination of metric-specific thresholds and varying proxy relationships with erosion rate, a majority of divides agree on divide migration direction. Agreement in divide migration direction indicates an actively responding landscape when asymmetry is high and a state of quasi-equilibrium when asymmetry is low. Disagreements between the integral quantity, χ, and the other geomorphic metrics can be explained by different timescales of the underlying geomorphic processes, with χ reflecting a long-term response and CRR, HSG, and ksn capturing short-term perturbations to catchment structure. These perturbations include various transient mechanisms, such as differential tectonic uplift or erodibility, glacial alteration, and river captures. Our work confirms the high incidence of drainage reorganization across the Hengduan Mountains and highlights both transient and stable areas in the landscape with high resolution. We also offer valuable insights into the application of geomorphic metrics that can be generalized and applied to the study of landscape transience and drainage divide asymmetry in other settings.
摘要。地表过程对气候和构造等外部作用力的复杂反应塑造了地貌。横断山脉的几条主要河流被记录在案,这导致了一种假设,即横断山脉地区在水平缩短和隆升传播的驱动下经历了极高的排水重组率。在此,我们确定了横断山脉正在进行的排水重组的普遍性、强度和空间模式,并通过比较在不同时空尺度上运行的四种地貌指标的排水分异不对称性,评估了这种瞬变的相对时间尺度。具体而言,我们利用流域限制地形起伏(CRR)、山坡坡度(HSG)、归一化河道陡度(ksn)和归一化河道距离(χ)计算了排水分界线的迁移方向和分界线不对称指数(DAI)。这些地貌指标的不同空间尺度使我们能够确定在横断山脉观测到的地貌瞬变的相对时间尺度,其中局部尺度指标测量短期变化,整体量测量长期失衡。我们发现,横断山脉地区的所有指标都存在强烈的不对称分异。虽然不同指标之间的不对称程度差异很大,这可能是由于特定指标的阈值以及与侵蚀率之间不同的替代关系共同造成的,但大多数分界线在分界线迁移方向上是一致的。当不对称程度较高时,鸿沟迁移方向的一致表明地貌正在积极做出反应;当不对称程度较低时,地貌处于准平衡状态。积分量 χ 与其他地貌指标之间的分歧可以用基本地貌过程的不同时间尺度来解释,χ 反映的是长期响应,而 CRR、HSG 和 ksn 反映的是对流域结构的短期扰动。这些扰动包括各种瞬时机制,如不同的构造隆起或侵蚀、冰川变化和河流俘获。我们的工作证实了横断山脉排水系统重组的高发生率,并以高分辨率突出显示了地貌中的瞬变区域和稳定区域。我们还为地貌指标的应用提供了宝贵的见解,这些见解可以推广应用于其他环境下的地貌瞬变和排水分异不对称研究。
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引用次数: 0
Evaluating the accuracy of binary classifiers for geomorphic applications 评估二元分类器在地貌应用中的准确性
IF 3.4 2区 地球科学 Q1 Earth and Planetary Sciences Pub Date : 2024-05-17 DOI: 10.5194/esurf-12-765-2024
M. Rossi
Abstract. Increased access to high-resolution topography has revolutionized our ability to map out fine-scale topographic features at watershed to landscape scales. As our “vision” of the land surface has improved, so has the need for more robust quantification of the accuracy of the geomorphic maps we derive from these data. One broad class of mapping challenges is that of binary classification whereby remote sensing data are used to identify the presence or absence of a given feature. Fortunately, there is a large suite of metrics developed in the data sciences well suited to quantifying the pixel-level accuracy of binary classifiers. This analysis focuses on how these metrics perform when there is a need to quantify how the number and extent of landforms are expected to vary as a function of the environmental forcing (e.g., due to climate, ecology, material property, erosion rate). Results from a suite of synthetic surfaces show how the most widely used pixel-level accuracy metric, the F1 score, is particularly poorly suited to quantifying accuracy for this kind of application. Well-known biases to imbalanced data are exacerbated by methodological strategies that calibrate and validate classifiers across settings where feature abundances vary. The Matthews correlation coefficient largely removes this bias over a wide range of feature abundances such that the sensitivity of accuracy scores to geomorphic setting instead embeds information about the size and shape of features and the type of error. If error is random, the Matthews correlation coefficient is insensitive to feature size and shape, though preferential modification of the dominant class can limit the domain over which scores can be compared. If the error is systematic (e.g., due to co-registration error between remote sensing datasets), this metric shows strong sensitivity to feature size and shape such that smaller features with more complex boundaries induce more classification error. Future studies should build on this analysis by interrogating how pixel-level accuracy metrics respond to different kinds of feature distributions indicative of different types of surface processes.
摘要随着高分辨率地形图获取能力的提高,我们绘制从流域到景观尺度的精细地形图的能力发生了革命性的变化。随着我们对地表 "视野 "的改善,我们也需要对根据这些数据绘制的地貌图的准确性进行更有力的量化。二元分类是制图挑战中的一大类别,通过二元分类,我们可以利用遥感数据识别特定地物的存在与否。幸运的是,数据科学领域已经开发出一整套指标,非常适合量化二元分类器的像素级精度。本分析的重点是,当需要量化地貌的数量和范围如何随环境因素(如气候、生态、材料属性、侵蚀率等)而变化时,这些指标的表现如何。一套合成地表的研究结果表明,最广泛使用的像素级精度指标 F1 分数尤其不适合量化此类应用的精度。众所周知,在特征丰度不同的环境中校准和验证分类器的方法策略会加剧不平衡数据的偏差。马修斯相关系数在很大程度上消除了广泛特征丰度范围内的这种偏差,因此准确度分数对地貌环境的敏感性反而包含了有关特征大小和形状以及误差类型的信息。如果误差是随机的,则马修斯相关系数对地物的大小和形状不敏感,但对优势类的优先修改会限制可比较分数的范围。如果误差是系统性的(例如,由于遥感数据集之间的共同注册误差),该指标就会对特征大小和形状表现出很强的敏感性,例如,边界更复杂的较小特征会引起更大的分类误差。未来的研究应在这一分析的基础上,探讨像素级精度指标如何对不同类型的地表过程特征分布做出响应。
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Earth Surface Dynamics
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