Steep Hillslopes Research Articles

Old orogen – young topography: Evidence for relief rejuvenation in the Bohemian Massif

Abstract The Bohemian Massif is the relic of a major Paleozoic mountain range that is known to have exhumed and its surface levelled in the Permian, but its Neogene landscape evolution is largely unconstrained. The landscape is characterized by rolling hills and extended planation surfaces above an elevation of about 500 m. However, at lower elevations deeply incised gorges confined by steep hillslopes are abundant and contrast impressively with the low relief landscapes above. Rivers with a bimodal morphology (i.e. steep at lower elevations and gentle at higher elevations) drain either to the north into the Vltava (Moldau) River or to the south into the Danube River. Hence, a continental drainage divide runs through the Bohemian Massif. Here, we quantify spatial characteristics of the Bohemian Massif landforms by computing landscape metrics like steepness index or geophysical relief derived from digital elevation models. From this we infer temporal change of the landscape in the past and predict them for the future evolution of the region. We show that the landscape is characterized by out-of-equilibrium river profiles with knickpoints abundantly at elevations between 450 m and 550 m separating steep channel segments at lower elevations from less steep channels at higher elevations. Hypsometric maxima at or close above knickpoint elevations, along with high and low values in geophysical relief as indicator for the degree of fluvial landscape dissection downstream and upstream of major knickpoints, support the idea of landscape bimodality. Furthermore, we find a distinct drainage divide asymmetry, which causes the reorganization of the drainage network of the region. Across-divide gradients in channel steepness predict the northward migration of the Danube-Vltava drainage divide including growth and shrinkage of tributary catchments, thus controlling changes in the Central European drainage pattern. All aspects suggest that the region experienced relief rejuvenation during the last few million years. We suggest that this relief rejuvenation is related to the inversion of the Molasse basin with a long wavelength rock uplift pattern and low uplift rates. Vertical motion of crustal blocks at discrete faults may locally affect the uplift pattern. However, the contrasting bedrock properties between the sedimentary cover (Molasse sediments) and the crystalline basement (Bohemian Massif) cause substantial differences in erosion rate and are thus the superior control on the topographic variations of the entire region.

Spring shed development by employing traditional practices for spring revival and reducing women drudgery in Kumaun Himalayan Region

The Himalayan ecosystem is one of the most important and threatened life support systems on the earth. Ruthless exploitation of vegetal cover from steep hill slopes of Uttarakhand hills is adversely affecting the various natural resources. About 36% of springs have dried resulting into severe crisis of water for drinking as well as irrigation during the past 20 years. It is a dangerous sign that aquifers are depleting in a state where majority of the population in hills dependents on springs for drinking water. Women drudgery is high and bulk of their time is spent in collecting fodder, fuel-wood and water for which walking 4-6 Km/ day is common resulting in neglect of children and personal health. The present study was conducted at two villages (1646 -1715 m elevation) to evaluate the effect of various activities directed towards using a mix of traditional and scientific know how in reviving /improving the water discharge of springs, reducing women drudgery by planting fodder grasses in areas close to villages. The milk production increased by 0.8 to 1.2 liter/ cattle/household. Establishment of micro-reservoirs at each spring shed increased thedischarge of water during lean period.

Examining spatial variation in soil solutes and flowpaths in a semi-arid, montane catchment

Biogeochemical properties of soils play a crucial role in soil and stream chemistry throughout a watershed. How water interacts with soils during subsurface flow can have impacts on water quality, thus, it is fundamental to understand where and how certain soil water chemical processes occur within a catchment. In this study, ~200 soil samples were evaluated throughout a small catchment in the Front Range of Colorado, USA to examine spatial and vertical patterns in major soil solutes among different landscape units: riparian areas, alluvial/colluvial fans, and steep hillslopes. Solutes were extracted from the soil samples in the laboratory and analyzed for major cation (Li, K, Mg, Br, and Ca) and anion (F, Cl, NO2, NO3, PO4, and SO4) concentrations using ion chromatography. Concentrations of most solutes were greater in near surface soils (10 cm) than in deeper soils (100 cm) across all landscape units, except for F which increased with depth, suggestive of surface accumulation processes such as dust deposition or enrichment due to biotic cycling. Potassium had the highest variation between depths, ranging from 1.04 mg/l (100 cm) to 3.13 mg/l (10 cm) sampled from riparian landscape units. Nearly every solute was found to be enriched in riparian areas where vegetation was visibly denser, with higher mean concentrations than the hillslopes and fans, except for NO3 which had higher concentrations in the fans. Br, NO2, and PO4 concentrations were often below the detectable limit, and Li and Na were not variable between depths or landscape units. Ratioed stream water concentrations (K:Na, Ca:Mg, and NO3:Cl) vs. discharge relationships compared to the soil solute ratios indicated a hydraulic disconnection between the shallow soils (<100 cm) and the stream. Based on the comparisons among depths and landscape units, our findings suggest that K, Ca, F, and NO3 solutes may serve as valuable tracers to identify subsurface flowpaths as they are distinct among landscape units and depth within this catchment. However, interflow and/or shallow groundwater flow likely have little direct connection to streamflow generation.

Effects of passive-storage conceptualization on modeling hydrological function and isotope dynamics in the flow system of a cockpit karst landscape

Abstract. Conceptualizing passive storage in coupled flow–isotope models can improve the simulation of mixing and attenuation effects on tracer transport in many natural systems, such as catchments or rivers. However, the effectiveness of incorporating different conceptualizations of passive storage in models of complex karst flow systems remains poorly understood. In this study, we developed a coupled flow–isotope model that conceptualizes both “fast-flow” and “slow-flow” processes in heterogeneous aquifers as well as hydrological connections between steep hillslopes and low-lying depression units in cockpit karst landscapes. The model tested contrasting configurations of passive storage in the fast- and slow-flow systems and was optimized using a multi-objective optimization algorithm based on detailed observational data of discharge and isotope dynamics in the Chenqi Catchment in southwestern China. Results show that one to three passive-storage zones distributed in hillslope fast-/slow-flow reservoirs and/or depression slow-flow reservoirs provided optimal model structures in the study catchment. This optimization can effectively improve the simulation accuracy for outlet discharge and isotope signatures. Additionally, the optimal tracer-aided model reflects dominant flow paths and connections of the hillslope and depression units, yielding reasonable source area apportionment for dominant hydrological components (e.g., more than ∼ 80 % of fast flow in the total discharge) and solute transport in the steep hillslope unit of karst flow systems. Our coupled flow–isotope model for karst systems provides a novel, flexible tool for more realistic catchment conceptualizations that can easily be transferred to other cockpit karst catchments.

Large Wood in Small Channels: A 20‐Year Study of Budgets and Piece Mobility in Two Redwood Streams

AbstractLarge wood (LW) influences geomorphic and ecological processes. However, most field data sets describing LW dynamics are conducted over the span of only a few years. We present a unique long‐term data set from northern California, USA of LW volumes, inputs, and transport in two small headwater streams, the North Fork (NF) and South Fork (SF) of Caspar Creek. We used data collected approximately every 2 years from 1998 to 2018 to assess how LW budgets change over time between catchments, what factors influence inputs from standing trees to the streams, and controls on LW piece mobility. We find that the SF, which experienced stream‐side logging and instream wood removal in the 1970s, continued to have lower LW volumes (range of 101–153 m3 km−1 over the 20‐year period) compared to the NF (range of 297–313 m3 km−1), which experienced logging in the 1980s but with buffer strips left near the channel. If current trends continue, it will likely take ∼100–200 years from the time of logging for the SF to reach NF instream wood volumes. We show that windstorms combined with precipitation events, very high winds, and hillslope steepness are strongly associated with LW piece inputs from standing trees. LW moves infrequently in the channel, with piece characteristics, the number of wood pieces per meter surrounding an LW piece, and discharge metrics influencing LW entrainment and displacement lengths. Our data set provides strong support to previously identified controls on LW dynamics in streams while also capturing variability over a 20‐year period.

Flood patterns in a catchment with mixed bedrock geology and a hilly landscape: identification of flashy runoff contributions during storm events

Abstract. With flash flood events having been repeatedly observed in Central and Western Europe in recent years, there is a growing interest in how catchment physiographic properties and hydrological conditions are eventually controlling rapid and concentrated hydrological responses. Here we focus on a set of two nested catchments in Luxembourg (Europe) that have been exposed in 2016 and 2018 to flash flood events and study their seasonal runoff time transfer distributions. Both catchments are of similar size (∼ 30 km2) and have analogous hydrological distance distributions, but their geological bedrock and landscape features are notably different. The upper catchment (KOE) is dominated by a low land area (38 % of the catchment is located less than 30 m above the river network) consisting of variegated marly bedrock (middle Keuper Km3) and moderately steep Luxembourg sandstone outcrops (lower Liassic Li2). The lower catchment (HM) has its drainage network deeply cut into the Luxembourg sandstone, with half of it being covered by marly plateaus (Lower Liassic Li3, located between 80 and 100 m above the river network) featuring heavy clay soil. Based on data generated from a dedicated hydro-meteorological monitoring network, we calculated for 40 rainfall–runoff events observed between August 2019 and July 2021 the corresponding net rainfall transfer time distributions (TTDs) from the hillslopes to the catchment outlet. We then compared the TTD properties and related them to the catchment's hydrological state and rainfall properties. We observed a marked seasonality in TTDs for both catchments. The KOE catchment reacts fastest during the winter period (December–February), while its response time is most delayed and spread out during periods of catchment recharging (October–November) and drying (March–May). The HM catchment exhibits similar TTDs during the mid-October to mid-April period, but they diverge markedly during the remaining part of the year, with opposite variations. During the mid-April to mid-October period, the average response time increases progressively in the KOE catchment. This behavior is in stark contrast to the HM catchment, where response times are significantly shorter (peak discharge delay time decreases by −70 % ± 28 %) and more concentrated (runoff volume occurring in 1 h increases by +48 % ± 87 %) during the mid-April to mid-October, in comparison to the extended winter period. This opposite seasonality leads us to consider different control factors of the runoff transfer processes in relation with the topographic and geological layout of the catchment areas. In the KOE catchment, we found the TTD to be essentially driven by onset and cessation of hydrological connectivity on the flat marly terrain – the latter operating like a variable contributing area in terms of deep soil storage dynamics (except for one summer event). The HM section exhibits contrasted TTDs throughout the year, suggesting threshold-dependent hydrological processes. More specifically, particularly quick runoff transfers seem to dominate under dry conditions (mid-April to mid-October). Correlation analyses compared to the literature on runoff generation on the one hand and our descriptive knowledge of the catchments on the other hand suggest multiple causes for the triggering of these rapid flows. The fractured marly plateaus, but also the hydrophobic forest litter forming during dry conditions on steep slopes, stand as our main hypotheses in this respect. Moreover, the absence of a riparian zone, preventing any dampening of (observed) abrupt and massive flows during extreme precipitation events, also seems to be a key feature of the rapid runoff transfer. For improving our understanding and forecasting capabilities in Luxembourg (and more broadly in the nearby regions of Germany, Belgium, and France with similar physiographic and climate conditions), we recommend further studies focusing on catchments with fractured bedrock and limited riparian zones. Special attention may equally be given to the hypothesized responses of hydrophobic soil surfaces on steep hillslopes and marly soils to heavy precipitation events occurring after extended dry spells.

Erosion and runoff reduction potential of vetiver grass for hill slopes: A physical model study

Severe erosion is caused by intense rainfall in tropical regions. The erodible soil of steep hill slopes, accompanied by destruction of vegetation due to human interventions results in accelerated erosion. A sustainable and cost-effective solution such as vetiver grass (Chrysopogon zizanioides) is, thus, required to control the erosion process. In the current study, 6 small-scale glass models: 1 bare and 5 with vetiver grass, having a slope angle of 37° have been constructed. One year after planting, artificial rainfall of extremely high intensity was applied to all 6 small models and the role of vetiver canopy and roots in erosion and runoff control was observed. To see the effect of soil texture, one among these 5 models was made with silty sand and others contained sandy silt. The results demonstrated that, for sandy silt, the inclusion of vetiver reduced the soil loss by 94%–97%, and soil detachment rates were lowered by 95%. The average runoff also was reduced by 21%. The canopy cover showed a positive impact on reducing both quantities. An increase in average root diameter from 1.6 to 2.5 mm increases the soil loss due to its negative impact on added cohesion. The added cohesion showed a linearly negative correlation with soil loss. A composite system of vetiver and jute geotextile was most effective in erosion reduction among 4 vegetated models with sandy silt. Under same vetiver planting layout, the grass covered model of silty sand yielded 84% lower erosion and 62.5% lower runoff than the grass covered one with sandy silt. Thus, vetiver was more effective in erosion and runoff reduction for soil with a greater percentage of sand, and soil type dominated the erosion process.

Soil pedestal dating in the degraded Salitre River basin in the northeast of Bahia, Brazil

This study evaluated possible causes of degradation of a microbasin (16 ha) in an area of the Salitre River Basin undergoing desertification, in North-eastern Brazil. Interrill erosion in the microbasin was estimated based on measurements of topography, soil erodibility, rainfall erosivity and land use and occupation. The relief was surveyed by an unmanned aerial vehicle, equipped with precision optical meter. Based on the height, position and local erosion around 53 soil pedestals, the year of their origin was estimated, given that these microstructures resist erosion due to the presence of roots. The sediment yield in the microbasin is 71 Mg ha−1 per year. The dating indicates two main periods of pedestal generation: the first, during which 16% emerged, occurred in the 1960s, coinciding with the construction of an unpaved side road in the upper part of the microbasin. The second, in which 80% of the pedestals originated, dates from the 1990s, when there was intense cultivation of Agave sisalana in the region, even on the steep hillslopes. The dating also identified a significant reduction in pedestal formation during the 1980s, a period in which there was a drop in agricultural production of Agave sisalana in the region. Therefore, two development initiatives (the construction of the local road and the implantation of the Agave sisalana monoculture on the hillslopes) are the most likely factors that triggered the desertification in the area.

Coupled dynamics of aqueous biogeochemistry in contrasting floodplain environments: Implications for Critical Zone carbon sequestration along redox gradients

This study contributes to our evolving understanding of how coupled biogeochemical dynamics of Fe and Mn along the redox gradients affect C cycling and sequestration at Critical Zones. A 12-month monitoring of the in-situ soil pore-water biogeochemistry and redox gradients across the floodplain at the White Clay Creek Watershed in the Christina River Basin - Critical Zone Observatory was investigated. Topographically, eastern floodplain was narrow with a steep hillslope connected to the agricultural field while western floodplain was flat and wide. Soil profile consisted of post-colonial oxic deposits, pre-colonial anoxic buried wetland soils underlain by suboxic valley-bottom gravel. Contrasting soil pore-water chemistry including DOM quality, DOC, Fe and Mn, δ18O and δD profiles, and redox potentials were observed between the eastern and western floodplains due to seasonal fluctuations, divergent topographic and hydrologic settings. We observed diverse types of C pools across the floodplain from short (labile) to long term (recalcitrant) C forms: microbial origin DOM at eastern versus terrestrial or plant-derived DOM at western buried wetland soil pore-waters. Gravel was linked to the soluble microbial byproduct-like fractions indicating bioavailable DOM and microbial activity. Gravel beds may act as a natural filter (or C sink) of terrestrial DOM via adsorption and precipitation with Mn- and Fe (hydr)oxides, stimulating the long-term sequestration of sedimentary OC while retaining the microbially-derived DOM in the pore-water. In contrast, reductive dissolution of Mn- and Fe (hydr)oxides may result in re-mobilization of aromatic DOM and increase of DOC flux (C source) to the stream. Future studies are needed to improve our understanding of how in-situ redox gradients and/or microbial activity transform OC-mineral complexes and the coupled C dynamics at Critical Zones.

The spatiotemporal dependencies of terrain indices with soil characteristics in a steep hillslope mountainous area

The spatiotemporal dependencies of terrain indices with soil characteristics in a steep hillslope mountainous area

Variable storage behavior controlled by rainfall intensity and profile structure upon saturation excess overland flow generation

The effects of rainfall intensity and terrain structure on hillslope storage behavior upon saturation excess overland flow (SOF) generation are not yet fully understood. Analytical solution techniques that provide direct insights into the hillslope storage behavior were adopted in this study. The Threshold of StOrage (TSO) at critical rainfall intensity N0 (the minimum rainfall intensity to generate SOF) and the storage upon SOF generation (SO) at rainfall intensity N (>N0) were derived using analytical solutions of the kinematic wave equation over unit-width shallow sloping aquifers. The derived analytical solutions match the results of the numerical models of the Boussinesq equation for 25 idealized hillslopes under various rainfall intensities. It was found that as N = N0, TSO is determined by hillslope structures, i.e., TSO on the convex hillslopes is always greater than that on concave hillslopes with the same gradient, and TSO on convex and concave hillslopes gradually approaches as the gradient increases. As N > N0, hillslope storage dynamics is characterised by variable storage behavior as rainfall intensity increasing, i.e., SO increases with N. An inflection point of rainfall intensity N1, below which the curvature of the bedrock profile has a limited effect on SO, was found. Although N1 was greater on steeper hillslope, the corresponding values of SO1 on hillslopes under different gradients are close, which means that the effects of rainfall intensity and profile structure on SO is balanced at N = N1. This study helps to deepen our understanding of the quantitative role of rainfall intensity and profile structure in the process of runoff generation, and has the potential to improve the free storage capacity parameter in conceptual models.

Capturing the complexity of soil evolution: Heterogeneities in rock cover and chemical weathering in Montana's Rocky Mountains

We investigate the relationship between chemical weathering, persistence of soil cover, and topography in two neighboring mountain ranges in the northern Rockies of western Montana, USA. We augment existing tools for measuring chemical weathering with adjustments for both local and landscape-scale contributions from unweathered rock fragments, boulders, and bedrock exposure. Adjusted weathering intensities recognize that quantifying weathering in mountainous systems should account for rock exposure, rather than focusing solely on fine-grained soil mantles. Our study systems' distinct morphologies are shaped by their unique climate histories. The previously glaciated Bitterroot Mountains consist of steep hillslopes with abundant rock cover, while the neighboring unglaciated Sapphire Mountains display convex, soil-mantled hillslopes. Over 380 soil thickness measurements, 118 analyses of soil and rock geochemistry, and digital terrain analysis reveal that patchy soils in the bedrock-rich system are roughly half as thick as those in the continuously-soil-mantled landscape, and ~45% less weathered, despite wetter conditions that would be expected to enhance weathering. These disparities increase when accounting for coarse rock fragments in soils and bedrock cover across the study catchments. The near continuously soil-mantled Sapphire system experiences ~1.5 times greater weathering intensity at a catchment scale compared to the bedrock-rich Bitterroot system. Rock exposure across the mountainous study system increases with increasing slope gradient. However, we find no clear threshold at which soils decrease in abundance or weathering intensity, and soils are surprisingly resilient even at the steepest hillslopes (comprising ~60% of the landscape area at slopes >30°). Our new data quantify soil abundance and chemical weathering intensity at both local and landscape scales. This work highlights how measurements of soil and rock cover need to be incorporated into studies quantifying chemical weathering, as traditional approaches may significantly overestimate and mischaracterize weathering regimes in mountain environments.

Rainfall Triggering of Post-Fire Debris Flows over a 28-Year Period near El Portal, California, USA

ABSTRACT Wildfires frequently affect the steep hillslopes near El Portal, California (United States), a small community established during the California Gold Rush in the mid-1800s. In addition to the historical significance of El Portal, State Route 140 (SR 140) is a major transportation and economic corridor connecting the San Joaquin Valley to Yosemite National Park (YNP). In 2019, an estimated 4.5 million tourists visited and accessed YNP via SR 140. In the years after wildfires, the burned watersheds produced debris flows during intense rainfall, impacting the El Portal community and motorists traveling on SR 140 and local roads. The steepness of the hillslopes and confinement of the valley limit options for mitigating debris-flow risk. As such, emergency managers are left with evacuation orders or temporary road closures as the best options for risk reduction. The effectiveness of these options is highly dependent on establishing an accurate local rainfall intensity-duration threshold that officials can use to guide emergency response actions and timing. We present an overview of the rainfall conditions that initiated 12 post-fire debris-flow events near El Portal from 1991 to 2018 and objectively define rainfall intensity-duration thresholds from triggering rainfall rates. Our results highlight the modest rainfall rates that triggered debris flows in these steep watersheds, while radar data from more recent events (2012–2018) portray the spatial variability of intense rainfall in the area. Additional rainfall monitoring is needed to provide a robust rainfall threshold that will effectively mitigate risk for residents and motorists while minimizing the impact of road closures and evacuations.

德令哈地区柏树山不同生境气候对祁连圆柏径向生长的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 德令哈地区柏树山不同生境气候对祁连圆柏径向生长的影响 DOI: 10.5846/stxb202108022102 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41771051，41630750） Impacts of climate on the radial growth of Sabina przewalskii in different habitats in Baishu Mountain, Delingha region, China Author: Affiliation: Fund Project: National Natural Science Foundation of China (41771051, 41630750) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为探究德令哈地区柏树山不同生境气候对祁连圆柏（Sabina przewalskii）径向生长的影响，在该区域设置3个采样点（S1：地势较低的陡坡地，S2：坡度缓和的凹形坡地，S3：地势较高的陡坡地），运用树木年轮学方法收集了58棵祁连圆柏共113根样芯。通过建立3个样点的祁连圆柏差值年表，分析在半干旱区不同生境内祁连圆柏径向生长对气候响应的特征以及气候因子对祁连圆柏径向生长的贡献。结果表明：不同生境的祁连圆柏径向生长对降水的响应基本一致，对温度的响应则存在显著差异，其中当年5月的降水对不同生境祁连圆柏径向生长的贡献作用最大（P<0.01），当年6月的降水次之（P<0.05）。温度对S1和S3祁连圆柏径向生长的贡献均不显著（P>0.05）。当年9月的平均最高温对S2祁连圆柏径向生长有显著的贡献作用（P<0.05），低温对其的贡献并不显著（P>0.05）。研究结果论证了受地形差异的影响，不同生境下的气候对树木径向生长的影响具有多样性。因此，在研究树木生长与气候的关系时，应综合考虑不同生境的特点，以选取适宜的生境进行科学研究。 Abstract:We set up three sampling sites (S1:steep hillslope with lower terrain, S2:hollow hillslope with gentle slope, S3:steep hillslope with higher terrain) and collected a total of 113 cores from 58 Sabina przewalskii using dendrochronological methods in Baishu Mountain of the Delingha region to investigate the impacts of climate on the radial growth of S. przewalskii in different habitats. By establishing the residual chronologies of S. przewalskii at the three sampling sites, we analyzed the response characteristics of the radial growth of S. przewalskii to climate and the contribution of the climate factors to the radial growth of S. przewalskii in different habitats in the semi-arid area. Results revealed that the radial growth of S. przewalskii in different habitats had basically same response to precipitation, but the response to temperature was of significant difference. The precipitation in May of the current year contributed the most to the radial growth of S. przewalskii in different habitats (P<0.01), followed by the precipitation in June of the current year (P<0.05). The contribution of temperature to the radial growth of S. przewalskii at S1 and S3 was not significant (P>0.05). The mean maximum temperature in September of the current year had a significant contribution to the radial growth of S. przewalskii at S2 (P<0.05), while the contribution of low temperature to it was not significant (P>0.05). The results demonstrated that the effects of climate in different habitats on the radial growth of trees were diversified under the influence of the difference in topography. Therefore, the characteristics of different habitats should be considered comprehensively before studying the relationship between tree growth and climate to select suitable habitats for scientific research. 参考文献 相似文献 引证文献

Mapping Natural Exposures of Siliceous Marls and Cherts as Potential Zones of Raw Material Acquisition. The Case of the Eastern Polish Carpathian Foothills and the Rzeszów Settlement Region (SE Poland) in the Neolithic and Bronze Age. Preliminary Results

The Neolithic and Bronze Age communities that settled the eastern Carpathian Forelands and Carpathian Foothills used a variety of local and non-local siliceous raw materials. Raw materials identified in the archaeological record differ in quality and usefulness for making tools. Obsidian, Jurassic flint from the Cracow-Częstochowa Upland, chocolate flint, or Świeciechów and Volhynian flints represent the best quality. On the other hand, some local raw materials were also in use, most popular among them being siliceous marls and cherts. Sources of siliceous marls and cherts are known from many locations in the Dynów, Strzyżów and Przemyśl foothills. Moreover, systematic field surveys in this area have provided new information on the availability of cherts and siliceous marls at many new locations in the region. They appear in the primary autochthonous, secondary autochthonous, and more rarely in sub-autochthonous or residual, sources. Exposures on steep hill slopes and dissected river valleys provide easy access to the best quality raw materials in the primary autochthonous sources. Raw materials from secondary autochthonous sources in the riverbeds were also available, but they were of lesser quality than those from the exposures. The aim of this paper is to present natural exposures of siliceous marls and cherts and discuss them as a potential source of raw materials for the Neolithic and Bronze Age communities inhabiting loess areas of the eastern Carpathian foreland (Rzeszów Settlement Region).

Improving Hillslope Link Model Performance from Non-Linear Representation of Natural and Artificially Drained Subsurface Flows

This study evaluates the potential for a newly proposed non-linear subsurface flux equation to improve the performance of the hydrological Hillslope Link Model (HLM). The equation contains parameters that are functionally related to the hillslope steepness and the presence of tile drainage. As a result, the equation provides better representation of hydrograph recession curves, hydrograph timing, and total runoff volume. The authors explore the new parameterization’s potential by comparing a set of diagnostic and prognostic setups in HLM. In the diagnostic approach, they configure 12 different scenarios with spatially uniform parameters over the state of Iowa. In the prognostic case, they use information from topographical maps and known locations of tile drainage to distribute parameter values. To assess performance improvements, they compare simulation results to streamflow observations during a 17-year period (2002–2018) at 140 U.S. Geological Survey (USGS) gauging stations. The operational setup of the HLM model used at the Iowa Flood Center (IFC) serves as a benchmark to quantify the overall improvement of the model. In particular, the new equation provides better representation of recession curves and the total streamflow volumes. However, when comparing the diagnostic and prognostic setups, the authors found discrepancies in the spatial distribution of hillslope scale parameters. The results suggest that more work is required when using maps of physical attributes to parameterize hydrological models. The findings also demonstrate that the diagnostic approach is a useful strategy to evaluate models and assess changes in their formulations.

The world's second-largest, recorded landslide event: Lessons learnt from the landslides triggered during and after the 2018 Mw 7.5 Papua New Guinea earthquake

Events characterized by widespread landslides provide rare but valuable opportunities to investigate the spatial and size distributions of landslides in relation to seismic, climatic, geological and morphological factors. This study presents a unique event inventory for the co-seismic landslides induced by the February 25, 2018 Mw 7.5 Papua New Guinea earthquake. The mainshock rupture was dominated by reverse fault motion, and this was also the case for the aftershocks. The latter also triggered widespread landslides in combination with rainfall during the period between February 26 and March 19. We mapped approximately 11,600 landslides of which, more than 10,000 were triggered by the mainshock, with a total failed planimetric area of about 145 km2. Such a large area makes this inventory the world's second-largest recorded landslide event after the 2008 Mw 7.9 Wenchuan earthquake, where the motion changed from predominantly thrust to strike-slip. Large landslides are abundant throughout the study area located within the remote Papua New Guinea Highlands. Specifically, more than half of the landslide population is larger than 50,000 m2 and overall, post-seismic landslides are even larger than their co-seismic counterparts. To understand the factors controlling the distribution of landslides' occurrence and size, we combine descriptive statistics as well as more rigorous bivariate and multivariate analyses. We statistically show that the 15-day antecedent precipitation plays a role in explaining the spatial distribution of co-seismic landslides. Also, we examine four strong aftershocks (Mw ≥ 6.0) within 9 days after the mainshock and statistically demonstrate that the cumulative effect of aftershocks is the main factor disturbing steep hillslopes and causing the initiation of very large landslides, up to ~5 km2. Overall, the dataset and the findings presented in this paper represent a step towards a holistic understanding of the seismic landslide hazard assessment of the entire Papua New Guinea mainland.

The Lasting Signatures of Past Landslides on Soil Stripping From Landscapes

AbstractRainfall‐induced shallow landslides scar the Earth surface and deliver sediment pulses into fluvial systems and thus play an important role in landscape evolution. Previous landslide legacy affects local soil depths and soil regeneration rates thus modifying future landslide susceptibility and sediment dynamics. Here, we couple an advanced hydromechanical landslide model with a soil depth regeneration model and quantify landslide legacy effects by placing landslide dynamics in a perspective of landscape soil depth evolution. Results show increased landslide susceptibility near recently failed regions due to alteration of hydrological processes in a thinner soil mantle that imposes constraints on released soil volumes. Landslide recurrence in failed regions levels off when soil depths are gradually restored to steady state pre‐failure values. Cumulative effects of past landslides divert future landslide activity from steep hillslopes to alluvial channels and valley margins thus affecting sediment dynamics and yields. Consideration of landslide legacy improves landslide prediction and quantification of landslide erosion and fluvial sediment yield rates.

Formation of low-gradient bedrock chutes by dry rockfall on planetary surfaces

AbstractChannel-like forms are ubiquitous on steep hillslopes on Earth, Mars, and other planetary bodies. On Earth and Mars, these landforms are commonly attributed to water activity, especially for slopes below the angle of repose (∼30°) where dry granular flows are considered ineffective. While the angle of repose characterizes loose sediment stability, it is unclear whether dry rockfall can traverse and erode channels in bedrock or cemented substrates. We used a large-scale experiment to show that bedrock chutes can form spontaneously at low gradients from dry rockfall. Our results, combined with observations of rocky outcrops and boulders on Mars, indicate that rockfall can be an important bedrock degradation process that can produce low-gradient channels in the absence of water.

Low hydrological connectivity after summer drought inhibits DOC export in a forested headwater catchment

Abstract. Understanding the controls on event-driven dissolved organic carbon (DOC) export is crucial as DOC is an important link between the terrestrial and the aquatic carbon cycles. We hypothesized that topography is a key driver of DOC export in headwater catchments because it influences hydrological connectivity, which can inhibit or facilitate DOC mobilization. To test this hypothesis, we studied the mechanisms controlling DOC mobilization and export in the Große Ohe catchment, a forested headwater in a mid-elevation mountainous region in southeastern Germany. Discharge and stream DOC concentrations were measured at an interval of 15 min using in situ UV-Vis (ultraviolet–visible) spectrometry from June 2018 until October 2020 at two topographically contrasting subcatchments of the same stream. At the upper location (888 m above sea level, a.s.l.), the stream drains steep hillslopes, whereas, at the lower location (771 m a.s.l.), it drains a larger area, including a flat and wide riparian zone. We focus on four events with contrasting antecedent wetness conditions and event size. During the events, in-stream DOC concentrations increased up to 19 mg L−1 in comparison to 2–3 mg L−1 during baseflow. The concentration–discharge relationships exhibited pronounced but almost exclusively counterclockwise hysteresis loops which were generally wider in the lower catchment than in the upper catchment due to a delayed DOC mobilization in the flat riparian zone. The riparian zone released considerable amounts of DOC, which led to a DOC load up to 7.4 kg h−1. The DOC load increased with the total catchment wetness. We found a disproportionally high contribution to the total DOC export of the upper catchment during events following a long dry period. We attribute this to the low hydrological connectivity in the lower catchment during drought, which inhibited DOC mobilization, especially at the beginning of the events. Our data show that not only event size but also antecedent wetness conditions strongly influence the hydrological connectivity during events, leading to a varying contribution to DOC export of subcatchments, depending on topography. As the frequency of prolonged drought periods is predicted to increase, the relative contribution of different subcatchments to DOC export may change in the future when hydrological connectivity will be reduced more often.