Tropical chemical weathering of hillslope deposits and bedrock source in the Aburrá Valley, northern Colombian Andes     

Edier Aristizbal  Barry Roser  Shuichiro Yokota 《Engineering Geology》2005,81(4):389-406

Tropical chemical weathering produces extensive lateritization and formation of deep weathering profiles. Both processes are fundamental to landscape evolution and slope instability. The Aburrá Valley of the northern Colombian Andes is characterized by tropical conditions. The valley slopes are mostly covered by hillslope deposits originating from four basement rock suites which comprise contrasting granitoid, volcanic–sedimentary, ophiolitic, and metamorphic sources, respectively. Tropical chemical weathering of the Aburrá hillslope deposits and their respective bedrock were examined using X-ray fluorescence and X-ray diffraction analysis, to document and quantify their chemical weathering profiles, compositions, and mineralogical properties. The Chemical Index of Alteration (CIA), loss on ignition (LOI), and the Mobiles index (Imob) were used to quantify the degree of weathering of hillslope deposits and bedrock source. Weathering trends were analyzed using A–CN–K and A–CNK–FM diagrams. The material mantling the slopes in the Aburrá Valley records an intense weathering history. Chemical weathering is characterized by increased development of clay minerals (kaolinite, halloysite) and iron and aluminum sesquioxides. Lateritization characterizes the final stage of the weathering profiles. Concentrations of CaO, Na₂O, K₂O decrease markedly in the weathering products compared to the fresh bedrock source, whereas concentrations of Al₂O₃, Fe₂O₃, and MgO increase significantly. CIA ratios of matrix slope deposits derived from all four sources near 100, whereas those of boulder slope deposits and saprolites are lower, but exceed source rock values. Different A–CN–K weathering paths are evident for each lithotype, validating the correlation established between the hillslope deposits and their various parents. Chemical weathering indices in some samples are strongly influenced by the presence of sesquioxides, as reflected by high LOI, anomalously low CIA, and varying enrichment trends on the A–CNK–FM diagrams. Consequently, different chemical indices based on different criteria need to be combined to obtain best results, as illustrated here by the combination of LOI, CIA, and Imob. The overall results suggest that tropical conditions have dominated for a long time in the northern Colombian Andes, leading to uniformly high weathering indices in matrix slope deposits irrespective of parent lithotype. Prolonged warm and humid conditions could thus be responsible for the weathering and remobilization of extensive old hillslope deposits during the Quaternary. However, in addition to the influence of climatic factors, tectonism has also undoubtedly influenced slope evolution in the Aburrá Valley.  相似文献   

Modeling degradation of terrace scarps in Grand Teton National Park, USA     

David B. Nash  James S. Beaujon 《Geomorphology》2006,75(3-4):400

The widely used linear diffusion model for hillslope evolution does not accurately predict the degradation of terrace scarps produced by the Late Pinedale West Spalding Bay Channelway (WSBC) near Jenny Lake in Grand Teton National Park, Wyoming USA. These scarps, cut into identical cohesionless quartzite gravel, were formed nearly simultaneously, during the brief period of time the WSBC was active. They are assumed to have had the same initial morphology as scarps currently forming along Snake River that are cut in the same material: a straight midsection sloping at 30° and a horizontal base and crest. The model best able to fit the observed morphology and the change in morphology with scarp height specifies the downslope debris flux is proportional to slope gradient raised to a power of 3.4.  相似文献   

Stone movement on hillslopes in the Mojave Desert,California: A 16-year record   总被引：1，自引：0，他引：1  

Athol D. Abrahams  Anthony J. Parsons  Ronald U. Cooke  Richard W. Reeves 《地球表面变化过程与地形》1984,9(4):365-370

Previous research has shown that either hydraulic action or creep may be the dominant process transporting coarse debris down hillslopes in the American Southwest. This study analyses the movement over 16 years of painted stones on two hillslopes in the central Mojave Desert to ascertain which of these two processes dominate in this region. The distance moved (M) is found to be directly related to length of overland flow (X) and hillslope gradient (S), and inversely related to particle size (D). The fact that M is more highly correlated with X than with S suggests that hydraulic action rather than creep is the dominant process. It is concluded that this is probably the case over most of the Mojave and Sonoran Deserts on slopes up to at least 24°, and that it is only at higher elevations where winters are more severe that creep may become dominant.  相似文献   

Lateral moisture flow beneath a sandy hillslope without an apparent impeding layer     

James T. McCord  Daniel B. Stephens 《水文研究》1987,1(3):225-238

Part of a small drainage basin on the Sevilleta National Wildlife Refuge (about 25 km north of Socorro, NM) was intensively instrumented with soil monitoring equipment to estimate natural ground-water recharge. Soil-moisture data were analysed with special attention to characterizing the influence of topography on the direction of vadose water flow paths in fine to medium aeolian sand. Moisture content data were obtained by the neutron scattering technique, and hydraulic head data were obtained using tensiometers. In addition, tracer experiments were conducted on a sandy hillslope to delineate the flow paths of vadose water. The results indicate that there is a strong lateral component to unsaturated flow on a hillslope, even in the absence of apparent sublayers of much lower permeability. Darcian calculations estimate the long-term, steady, deep flux beneath a concave location to be about 4 per cent of an assumed mean annual precipitation of 20 cm. The deep soil water flux downward varied by several orders of magnitude during the 17 month period of record.  相似文献   

Seasonal soil water dynamics in the jarrah forest,Western Australia. II: Results from a site with fine-textured soil profiles     

J. K. Ruprecht  N. J. Schofield 《水文研究》1990,4(3):259-267

Seasonal soil water dynamics were measured at a fine-textured, upslope site within the jarrah forest of southwest Western Australia and compared to the results from a coarse-textured hillslope transect. Gravity drainage dominated during winter and early spring. This reversed in early summer and an upward potential gradient was observed to 7 m depth. A shallow ephemeral saturation zone was observed above a clay pan at 1.5 m depth. This saturation zone persisted through late winter and early spring, contrasting with the short-lived saturation in the duricrust on the hillslope transect. The annual maximum to minimum unsaturated soil water storage was about 530 mm, 50 mm greater than the hillslope transect and higher than most values reported elsewhere in Australia. Significant soil water content changes following winter rain were generally restricted to 6 m but at one site occurred to 9 m. These depths were significantly less than the coarser-textured hillslope transect. Soil water drying rates averaged 5 mm day^?1 during extended dry periods compared to 3.5 mm day^?1 on the hillslope transect. The drying rate occurred uniformly through the profile until late summer when a significant decrease in the upper 3 m was observed.  相似文献   

Seasonal soil water dynamics in the jarrah forest,Western Australia. I: Results from a hillslope transect with coarse-textured soil profiles     

J. K. Ruprecht  N. J. Schofield 《水文研究》1990,4(3):241-258

Seasonal soil water dynamics were measured on a hillslope transect in the jarrah forest of southwest Western Australia over the period 1984-86 using mercury manometer tensiometers, gypsum blocks, and a neutron moisture meter. The soil water potential gradients indicated downward vertical drainage flux through winter and spring. There was generally a change to an upwards flux in early summer which was sustained through to autumn. A shallow ephemeral saturation zone was identified in and above a duricrust layer, lasting up to three days after heavy, late winter rainfall. The annual maximum to minimum unsaturated soil water storage on the hillslope was approximately 400 mm to 6 m depth and 480 mm to 15 m depth. This did not change significantly in years of substantially different winter rainfall. The magnitude of seasonal soil water storage was similar to other forested areas with deep soil profiles. The depth of observable infiltration was dependent on annual rainfall. This was consistent with the observation that groundwater levels responded to rainfall over the whole hillslope in wet years but only responded on the lower slopes in dry years. The average summer drying rate of the soil profile to 6 m depth of 3.5 mm day^?1 was within the range of values reported for forests elsewhere. In late summer, following an extended drought period, the drying rate decreased downslope but increased midslope.  相似文献   

Multivariate analysis of soil moisture history for a hillslope     

Sanghyun Kim   《Journal of Hydrology》2009,374(3-4):318-328

In this study, the spatial distribution of measured soil moisture was analyzed on the platform of multivariate modeling. Soil moisture time series for two seasons were selected and used for analysis to reveal similarities and differences in soil moisture responses for a few rainfall events. The development of a soil moisture transport process that considers the representative element volume and uncertainty of soil media provides the hydrological basis for time series modeling. The systematic procedure of Box–Jenkins with noise modeling was used to delineate the final models for all monitoring points. The physical basis of mass balance and the continuity in inflow contribution, as well as statistical criteria, were used in the model selection procedure. Heuristic approaches provide the spatial distribution of selected models along the transect of a hillside. Comparative analysis for two different depths and seasons provide an understanding of the variation in soil moisture transfer processes at the hillslope scale. Differences in soil moisture models for both depths and seasons are associated with eco-hydrological processes. The relationships between distributed topographic features and modeling results were explored to configure dominant hydrological processes for each season.  相似文献   

An integral-balance nonlinear model to simulate changes in soil moisture,groundwater and surface runoff dynamics at the hillslope scale     

《Advances in water resources》2014

We present a system of ordinary differential equations (ODEs) capable of reproducing simultaneously the aggregated behavior of changes in water storage in the hillslope surface, the unsaturated and the saturated soil layers and the channel that drains the hillslope. The system of equations can be viewed as a two-state integral-balance model for soil moisture and groundwater dynamics. Development of the model was motivated by the need for landscape representation through hillslopes and channels organized following stream drainage network topology. Such a representation, with the basic discretization unit of a hillslope, allows ODEs-based simulation of the water transport in a basin. This, in turn, admits the use of highly efficient numerical solvers that enable space–time scaling studies. The goal of this paper is to investigate whether a nonlinear ODE system can effectively replicate observations of water storage in the unsaturated and saturated layers of the soil. Our first finding is that a previously proposed ODE hillslope model, based on readily available data, is capable of reproducing streamflow fluctuations but fails to reproduce the interactions between the surface and subsurface components at the hillslope scale. However, the more complex ODE model that we present in this paper achieves this goal. In our model, fluxes in the soil are described using a Taylor expansion of the underlying storage flux relationship. We tested the model using data collected in the Shale Hills watershed, a 7.9-ha forested site in central Pennsylvania, during an artificial drainage experiment in August 1974 where soil moisture in the unsaturated zone, groundwater dynamics and surface runoff were monitored. The ODE model can be used as an alternative to spatially explicit hillslope models, based on systems of partial differential equations, which require more computational power to resolve fluxes at the hillslope scale. Therefore, it is appropriate to be coupled to runoff routing models to investigate the effect of runoff and its uncertainty propagation across scales. However, this improved performance comes at the expense of introducing two additional parameters that have no obvious physical interpretation. We discuss the implications of this for hydrologic studies across scales.  相似文献   

Distribution of caesium-137 in soils across a hillslope hollow     

C. D. Morris  R. J. Loughran 《水文研究》1994,8(6):531-541

The distribution of soil ¹³⁷Cs in relation to selected soil and landform properties was studied across a 16 ha hillslope hollow in the Hunter valley, New South Wales, Australia. The hillslope was used as grazing for cattle. Caesium-137 was not significantly related to the amount of sand, silt, or clay, the bulk density, the organic matter content, the slope angle or the relative distance downslope. However, ¹³⁷Cs was significantly related to the thickness of the soil A horizon. Spatial variations in ¹³⁷Cs were compared with topographic units and a six-element hillslope model, but there was little correspondence. It was thought that the effects of microtopography could have masked potential interrelationships between ¹³⁷Cs and broader scale landform parameters.  相似文献   

丹霞地貌的坡地形态演化——以浙江新昌丹霞地貌为例   总被引：3，自引：2，他引：1  

高善坤  竺国强  董传万  余仲辉 《热带地理》2004,24(2):131-135

在对新昌丹霞地貌进行调查、研究并对国内外的坡地研究回顾的基础上,对丹霞地貌的坡地形态、组成和演化方式及成因进行分析.丹霞地貌坡地在形态和演化方式上的特点比较符合King的坡地理论,在形态组成上可以分为凸形面、自由面、搬运坡和凹形面4部分,在演化上以平行后退和坡地替代两种方式为主.丹霞坡地的类型根据发育阶段可分为幼年期陡壁形态、中年期King型完整King模式形态及老年期丘陵坡地形态.丹霞坡地地貌演化的过程是自由面逐渐后退、缩小的过程,丹霞坡地在坡地退行速度上远小于其他现代坡地.  相似文献