Steady, balanced rates of uplift and erosion of the Santa Monica Mountains, California

Topographic change in regions of active deformation is a function of rates of uplift and denudation. The rate of topographic development and change of an actively uplifting mountain range, the Santa Monica Mountains, southern California, was assessed using landscape attributes of the present topography, uplift rates and denudation rates. Landscape features were characterized through analysis of a digital elevation model (DEM). Uplift rates at time scales ranging from 10⁴ to 10⁶ years were constrained with geological cross-sections and published estimates. Denudation rate was determined from sediment yield data from debris basins in southern California and from the relief of rivers set into geomorphic surfaces of known age. First-order morphology of the Santa Monica Mountains is set by large-scale along-strike variations in structural geometry. Drainage spacing, drainage geometry and to a lesser extent relief are controlled by bedrock strength. Dissection of the range flanks and position of the principal drainage divide are modulated by structural asymmetry and differences in structural relief across the range. Topographic and catchment-scale relief are ≈300–900 m. Mean denudation rate derived from the sediment yield data and river incision is 0.5±0.3 mm yr^?1. Uplift rate across the south flank of the range is ≈0.5±0.4 mm yr^?1 and across the north flank is 0.24±0.12 mm yr^?1. At least 1.6–2.7 Myr is required to create either the present topographic or the catchment-scale relief based on either the mean rates of denudation or uplift. Although the landscape has had sufficient time to achieve a steady-state form, comparison of the time-scale of uplift and denudation rate variation with probable landscape response times implies the present topography does not represent the steady-state form.     

Accordant summit heights, summit levels and the origin of the “upper denudation level” in the Serra do Mar (SE-Brazil, São Paulo): A study of hillslope forms and processes

In southern São Paulo the Serra do Mar is characterized by three distinct terrain types: 1) highly dissected areas with closely spaced ridges and accordant summit heights; 2) multiconvex hills; and 3) terrains with highly elevated watershed areas, irregular summit heights, and locally subdued relief. The development of this landscape is considered to be the result of the Cenozoic block-faulting and of the influences that are exerted by the differing lithological and structural setting of block-faulted compartments on weathering and erosion processes.In areas characterized by pronounced accordant summits the close coincidence between hillslope angle and the angle of limiting stability against landsliding points to a close adjustment of hillslope gradients and the mechanical properties of the regolith. The relative height of the hillslopes is functionally related to the spacing of the valleys and the gradient of the hillslopes. In areas with a regular spacing of v-shaped valleys and uniform rocks, this leads to the intersection of valley-side slopes in summits and ridges at a certain elevation. This elevation is determined by the length and steepness of the valley-side slopes. Therefore, the heights of the summits are geometrically constrained and are likely to indicate the upper limit of summit heights or an “upper denudation level” that is adjusted by hillslope processes to the incising streams. Accordant summit heights of this type are poor indicators of formerly more extensive denudation surfaces as it is also likely that they are a result of the long-term adjustment of hillslopes to river incision.The steep mountain flanks of block-faulted compartments on the other hand, comprise regolith-covered hillslopes that are closely adjusted to the maximum stable gradient as well as rock-slopes that are controlled by the rock-mass strength. Their summits are usually not accommodated into uniform summit levels. Highly elevated watershed areas exhibiting a subdued relief are detached from the base level response. On granitoid rocks these areas are often characterized by the rocky hills and domal rock outcrops. However, differences in the elevation of interfluves and summits between rocks of differing resistance and in the elevation of lithologically distinct individual fault-blocks imply that long-term weathering and erosion has transformed and lowered these landscapes. Therefore, these areas cannot be interpreted as a remnant of a pre-uplift topography and it appears to be unlikely that the height of the summits correlates with formerly more widespread planation surfaces in the far hinterland.The studies indicate that concepts such as the parallel retreat of hillslopes cannot account for the observed differences in the landscape. It is suggested that the Serra do Mar is consumed from the Atlantic and the inland side by spatially non-uniform developmental states. These states are determined by local differences in the coupling and distance to the regional base level and sea-level or are due to lithological and structural controls between and within the block-faulted compartments.     

中国主要流域盆地风化剥蚀率的控制因素

利用中国40余条主要河流及其支流的沉积物和溶解质载荷分别去表征流域盆地的物理剥蚀率和化学风化率。研究发现,中国流域盆地的总剥蚀率明显高于世界平均值,且具有南北低中间高的地理分布特点,黄河中游的皇甫川机械和总剥蚀率是世界上已知的最高值。根据流域盆地的机械剥蚀率、化学风化率和总剥蚀率及其影响因子之间的相关分析,得出中国流域盆地中的机械剥蚀率在总剥蚀率中占主导地位,机械剥蚀率和总剥蚀率主要由流域的干旱指数和相对高差来控制,不同流域之间总剥蚀率72%的差异是由于这两个参数所造成的。而化学风化率在总剥蚀率中总是处于次要地位,它主要受到流域年均降水量和气温的影响(39%),且不受机械剥蚀率的控制。流域盆地自身属性、径流量、最高海拔和森林覆盖率对流域岩石的风化剥蚀率影响不大。构造活动提高了流域的机械剥蚀率和化学风化率,且对机械剥蚀率的影响更强烈。与世界流域盆地相比,中国流域盆地受到流域干旱指数的影响更为显著。     

Landforms and landscape evolution in the Skardu,Shigar and Braldu Valleys,Central Karakoram

The Central Karakoram, which includes K2 in Pakistan, is one of the most rapidly rising areas on Earth and exhibits complex topography and extreme relief. Impressive valley fills and glacial landforms are present throughout the valleys. The dynamics of landscape evolution of the region are currently not well understood. Consequently, the landforms were mapped and assessed in the Skardu, Shigar, and Braldu valleys, to elucidate the spatio-temporal scale dependencies of surface processes active in the region. These valleys were examined using geomorphic field methods, remote sensing, geomorphometry, and terrestrial cosmogenic nuclides (TCNs) surface exposure dating. The glaciers in this region have oscillated considerably throughout the Late Quaternary, and four glacial stages have been recognized including at least six glacial advances. Surface processes readjusted after glacier retreat, and ubiquitous mass movements and catastrophic landsliding transported material from steep slopes to valley bottoms, while glaciofluvial meltwater and glacier outburst floods redistributed sediment down valley. Glacier geochronology and late Holocene ages of the outburst flood deposits indicate that landscape evolution has been dominated by glaciation and paraglaciation during the late Quaternary.     

Numerical modelling of landscape evolution on geological time-scales: a parameter analysis and comparison with the south-eastern highlands of Australia

Surface-process models (SPMs) have the potential to become an important tool in predicting sediment flux to basins, but currently suffer from a lack of quantitative understanding of their controlling parameters, as well as difficulties in identifying landscape properties that can be used to test model predictions. We attempt to constrain the parameter values that enter a SPM by comparing predictions of landscape form (as expressed by hypsometric and fractal measures) and process rates obtained for different parameter sets with observations from the south-eastern Australian highlands, a rifted margin mountain belt that has remained tectonically stable during Cenozoic times. We map the hypsometry and fractal characteristics of south-eastern Australia and find that the roughness amplitude (G) correlates well with local relief, whereas the hypsometric integral (H ) correlates slightly better with elevation than with relief. The fractal dimension (D) does not correlate with any other morphometric measure and varies randomly throughout the region. Variograms generally show three kinds of scaling behaviour of topography with increasing wavelength, with topography only being truly self-affine at wavelengths between ～1 and 10 km. From a review of the available data on long-term denudation rates in south-eastern Australia, we infer that these have been 1–10 m Myr^?1, and average escarpment retreat rates 0.2–1.0 km Myr^?1, throughout the Cenozoic. Model predictions, using a SPM that includes hillslope diffusion and long-range fluvial transport, suggest that landscape form evolves with time; after an initial phase where D, G and relief increase, all morphometric measures decrease with increasing denudation. The behaviour of GandH in the models is qualitatively compatible with the observations; D, however, varies predictably in the models, in contrast with its random behaviour in the real world. The observed present-day morphology of SE Australia does not impose quantitative constraints on parameter values. The fractal analyses do impose general conditions of relative parameter values that have to be met in order to create ‘realistic’ topographies. They also suggest that there is no theoretical basis for including hillslope diffusion in SPMs with a spatial resolution coarser than 1 km. A comparison of the observed denudation and retreat rates with model predictions places order-of-magnitude constraints on parameter values. Thus, data pertaining to landscape evolution are much more valuable than static present-day topography data for calibrating SPMs.     

Relations between denudation,glaciation, and sediment deposition: implications from the Plio‐Pleistocene Central Alps

Despite abundant data on the early evolution of the Central Alps, the latest stage exhumation history, potentially related to relief formation, is still poorly constrained. We aim for a better understanding of the relation between glaciation, erosion and sediment deposition. Addressing both topics, we analysed late Pliocene to recent deposits from the Upper Rhine Graben and two modern river sands by apatite fission‐track and (U‐Th‐Sm)/He thermochronology. From the observed age patterns we extracted the sediment provenance and paleo‐erosion history of the Alpine‐derived detritus. Due to their pollen and fossil record, the Rhine Graben deposits also provide information on climatic evolution, so that the erosion history can be related to glacial evolution during the Plio‐Pleistocene. Our data show that Rhine Graben deposits were derived from Variscan basement, Hegau volcanics, Swiss Molasse Basin, and the Central Alps. The relations between glaciation, Alpine erosion, and thermochronological age signals in sedimentary rocks are more complex than assumed. The first Alpine glaciation during the early Pleistocene did not disturb the long‐term exhumational equilibrium of the Alps. Recent findings indicate that main Alpine glaciation occurred at ca. 1 Ma. If true, then main Alpine glaciation was coeval with an apparent decrease of hinterland erosion rates, contrary to the expected trend. We suggest that glaciers effectively sealed the landscape, thus reducing the surface exposed to erosion and shifting the area of main erosion north toward the Molasse basin, causing sediment recycling. At around 0.4 Ma, erosion rates increased again, which seems to be a delayed response to main glaciation. The present‐day erosion regime seems to be dominated by mass‐wasting processes. Generally, glacial erosion rates did not exceed the pre‐glacial long‐term erosion rates of the Central Alps.     

基于变点分析法提取地势起伏度——以青藏高原为例

以青藏高原区域大尺度SRTM3-DEM为数据源,运用GIS的窗口递增分析法依次计算2×2、3×3、4×4、5×5、…、32×32窗口下的地势起伏度,然后采用均值变点法科学的分析平均地势起伏度的最佳统计面积并进行分级分析,得出实验区最佳分析窗口面积为1.17 km2,地势起伏度可分出八级,其中小起伏山地分布最广。高原边缘的地势起伏度普遍较大主要是由于构造运动与河流朔源侵蚀作用强烈;而高原内部地势较为平缓,冰川、冻土作用下的侵蚀搬运可能对地势起伏的影响更大。     

Landscape evolution and glaciation of the Rwenzori Mountains, Uganda: Insights from numerical modeling

The Rwenzori Mountains are a high alpine mountain chain, about 40 × 80 km in size, just north of the equator in the western branch of the East African Rift System in Africa. The central part of the mountain chain is located in Uganda, and the highest peak, the Margherita Peak with 5119 m, lies on the border to the Democratic Republic of Congo. Topography is very pronounced, with steeply incised valleys and clear glacial landforms in the upper part of the mountain chain. The Rwenzori Mountains are an unusually high mountain chain located in the extensional setting of the East African Rift System, and the large elevation poses a challenging problem for geodynamists to explain.We have used the landscape evolution model ULTIMA THULE, which combines hillslope diffusion, fluvial erosion, and glacial abrasion and is driven by a climate driver, simulating the variations in temperature, precipitation, and relief over several glacial cycles. With a simulation time of 800 ka, we test the hypothesis of climate-tectonic interactions on the uplift of the Rwenzori Mountains.Our results show that a moderate cooling of around 6° causes widespread glaciation of the high mountain regions as observed during the peak glacial phases, and that morphological processes degrading the landscape allow for a tectonic uplift rate of around 0.5 mm a^− 1.     

Regional relief characteristics and denudation pattern of the western Southern Alps, New Zealand

The Southern Alps of New Zealand are the topographic expression of active oblique continental convergence of the Australian and Pacific plates. Despite inferred high rates of tectonic and climatic forcing, the pattern of differential uplift and erosion remains uncertain. We use a 25-m DEM to conduct a regional-scale relief analysis of a 250-km long strip of the western Southern Alps (WSA). We present a preliminary map of regional erosion and denudation by overlaying mean basin relief, a modelled stream-power erosion index, river incision rates, historic landslide denudation rates, and landslide density. The interplay between strong tectonic and climatic forcing has led to relief production that locally attains 2 km in major catchments, with mean values of 0.65–0.68 km. Interpolation between elevations of major catchment divides indicates potential removal of l0¹–10³ km³, or a mean basin relief of 0.51–0.85 km in the larger catchments. Local relief and inferred river incision rates into bedrock are highest about 50–67% of the distance between the Alpine fault and the main divide. The mean regional relief variability is ± 0.5 km.Local relief, valley cross-sectional area, and catchment width correlate moderately with catchment area, and also reach maximum values between the range front and the divide. Hypsometric integrals show scale dependence, and together with hypsometric curves, are insufficient to clearly differentiate between glacial and fluvial dominated basins. Mean slope angle in the WSA (ψ = 30°) is lower where major longitudinal valleys and extensive ice cover occur, and may be an insensitive measure of regional relief. Modal slope angle is strikingly uniform throughout the WSA (φ = 38–40°), and may record adjustment to runoff and landsliding. Both ψ and φ show non-linear relationships with elevation, which we attribute to dominant geomorphic process domains, such as fluvial processes in low-altitude valley trains, surface runoff and frequent landsliding on montane hillslopes, “relief dampening” by glaciers, and rock fall/avalanching on steep main-divide slopes.     

An early Holocene erosion phase on the loess tablelands in the southern Loess Plateau of China

A Holocene loess profile to the west of Xi'an China was studied multi-disciplinarily to investigate the relationships between soil erosion and monsoonal climatic change. The proxy data obtained from this aeolian loess and palaeosol sequence indicate large-scale variations of climate in the southern Loess Plateau since the last glaciation. A rainwash bed, indicative of a wetter climate, excessive runoff and erosion on the loess tablelands, was identified relating to the early Holocene before the onset of the “climatic optimum”. This is synchronous with the early Holocene physiographic erosional stage identified in the valleys in North China. It means that severe erosion took place when the region was undergoing climatic amelioration during the early Holocene. The evidence presented in this paper shows that the erosion occurred as a regional response to a monsoonal climatic shift in the southern Loess Plateau. During the last glaciation, prior to the erosion phase, the land surface on the tablelands had been largely stable except for the rapid accumulation of aeolian dust and the resultant increase in its elevation. Relatively slow dust accumulation and intensive bio-pedogenesis responding to the Holocene “climatic optimum” followed the erosion phase. The loess tablelands were most vulnerable to erosion during the large-scale monsoonal climatic shift from dry-cold glacial to humid-warm post-glacial conditions in the southern Loess Plateau.     

Spatial variation of erosion in a small,glaciated basin in the Teton Range,Wyoming, based on detrital apatite (U‐Th)/He thermochronology

Evolution of mountain landscapes is controlled by dynamic interactions between erosional processes that vary in efficiency over altitudinal domains. Evaluation of spatial and temporal variations of individual erosion processes can augment our understanding of factors controlling relief and geomorphic development of alpine settings. This study tests the application of detrital apatite (U‐Th)/He thermochronology (AHe) to evaluate variable erosion in small, geologically complex catchments. Detrital grains from glacial and fluvial sediment in a single basin were dated and compared with a bedrock derived age‐elevation relationship to estimate spatial variation in erosion over different climate conditions in the Teton Range, Wyoming. Controls and pitfalls related to apatite quality and yield were fully evaluated to assess this technique. Probability density functions comparing detrital age distributions identify variations in erosional patterns between glacial and fluvial systems and provide insight into how glacial, fluvial, and hillslope processes interact. Similar age distributions representing erosion patterns during glacial and interglacial times suggest the basin may be approaching steady‐state. This also implies that glaciers are limited and no longer act as buzzsaws or produce relief. However, subtle differences in erosional efficiency do exist. The high frequency of apatite cooling ages from high altitudes represents either rapid denudation of peaks and ridges by mass wasting or an artifact of sample quality. A gap in detrital ages near the mean age, or mid‐altitude, indicates the fluvial system is presently transport limited by overwhelming talus deposits. This study confirms that sediment sources can be traced in small basins with detrital AHe dating. It also demonstrates that careful consideration of mineral yield and quality is required, and uniform erosion assumptions needed to extract basin thermal history from detrital ages are not always valid.     

Quaternary hydrological development in the Morecambe Bay karst,northwest England

The distribution of active and abandoned caves in the Morecambe Bay karst is indicative of at least two phases of subsurface drainage development, separated by an episode of valley incision, landscape dissection and surface lowering. It is suggested that the phase of erosion was associated with glaciation by ice from the adjoining Cumbrian massif, and that the earlier phase of drainage development was of at least last interglacial age. This view is supported by the evidence of the age and mode of deposition of the sedimentary infill in the caves, and by estimates of cave palacocatchment area. The caves of the earlier phase of drainage development were formed in valleys that were already deeply incised. It would therefore appear that the last glaciation only succeeded in slightly modifying an existing topography, a view at odds with conventional ideas of landscape development in Cumbria as a whole.     

Influence of orographic precipitation on the topographic and erosional evolution of mountain ranges

The influence of climate on mountain denudation has been the topic of an intense debate for two decades. This debate partly arises from the covariation of rainfall and topography during the growth of mountain ranges, both of which influence denudation. However, the denudational response of this co-evolution is poorly understood. Here, we use a landscape evolution model where the rainfall evolves according to a prescribed rainfall–elevation relationship. This relationship is a bell curve defined by a rainfall base level, a rainfall maximum and a width around the rainfall peak elevation. This is a first-order model that fits a large range of orographic rainfall data at the ca. 1-km spatial scale. We carried out simulations of an uplifting block with an alluvial apron, starting from an initially horizontal surface, and testing different rainfall–elevation relationships. We find that the denudation history is different from that with constant rainfall models. The results essentially depend on the ratio between the final steady-state summit elevation H_ss and the prescribed rainfall peak elevation H_p. This ratio is hard to predict because it depends on the transient coupling of rainfall and elevation. We identified three types of results according to H_ss/H_p. If H_ss/H_p > 4 (Type I), the denudation rates peak when the summits reach values close to H_p. If H_ss/H_p > 1.5 and < 4 (Type II), the denudation is strongly accelerated when the elevation of the summits approaches H_p, and then the denudation increases slowly towards the uplift rate. If H_ss/H_p < 1.5 (Type III), the denudation evolution is similar to situations with constant and homogeneous rainfall. In the Type I and II experiments, the mountain top is subjected to aridification once the summits have passed through H_p. To adapt to this reduced rainfall, the slopes increase. This can lead to a paradoxical situation where the mountain relief increases faster, whereas the denudation increases more slowly. The development of orographic precipitation may thus favour the stability of the mean denudation rate in a rising mountain. Despite the model limitations, including a constant rainfall–elevation relationship, our study suggests that the “classical” exponential increase in the denudation rate predicted by constant rainfall models is not the common case. Instead, the common case involves pulses and acceleration of the denudation even in the absence of uplift or global climate variations.     

Erosions on the southern Tibetan Plateau: Evidence from in-situ cosmogenic nuclides 10Be and 26Al in fluvial sediments

Investigating topographic and climatic controls on erosion at variable spatial and temporal scales is essential to our understanding of the topographic evolution of the orogen.In this work,we quantified millennial-scale erosion rates deduced from cosmogenic 10Be and 26Al concentrations in 15 fluvial sediments from the mainstream and major tributaries of the Yarlung Zangbo River draining the southern Tibetan Plateau (TP).The measured ratios of 26Al/10Be range from 6.33 ± 0.29 to 8.96 ± 0.37,suggesting steady-state erosion processes.The resulted erosion rates vary from 20.60 ± 1.79 to 154.00 ± 13.60 m Myr-1,being spatially low in the upstream areas of the Gyaca knickpoint and high in the downstream areas.By examining the relationships between the erosion rate and topographic or climatic indices,we found that both topography and climate play significant roles in the erosion process for basins in the upstream areas of the Gyaca knickpoint.However,topography dominantly controls the erosion processes in the downstream areas of the Gyaca knickpoint,whereas variations in precipitation have only a second-order control.The marginal Himalayas and the Yarlung Zangbo River Basin (YZRB) yielded significantly higher erosion rates than the central plateau,which indicated that the landscape of the central plateau surface is remarkably stable and is being intensively consumed at its boundaries through river headward erosion.In addition,our 10Be erosion rates are comparable to present-day hydrologic erosion rates in most cases,suggesting either weak human activities or long-term steady-state erosion in this area.     

A model for post‐orogenic development of a mountain range and its foreland

Decaying mountain ranges often show a surprisingly dynamic pattern of landscape evolution. Although one might expect a simple, monotonic decline in relief over time, evidence from several inactive mountain ranges shows alternating sequences of deposition and erosion in the associated basins, suggesting variations in relief and exhumation rate in the ranges themselves. Examples include the Southern Rocky Mountains, the Pyrenees, the European Alps and the Atlas Mountains. In this paper, we explore the possible origins of post‐orogenic landscape dynamics using a simple mathematical model of a mountain range and an adjacent foreland basin. The analysis highlights the importance of mass balance. In particular, a switch from basin exhumation to renewed sedimentation requires either an increase in sediment influx from the range or a decrease in sediment outflux beyond the basin margin. Although it is widely understood that post‐orogenic changes in erosion and sediment flux can have multiple causes (including climate change, regional tectonic uplift or tilting, or exhumation of variable lithologies), an important implication of our analysis is that the impact of such changes must differ in sign or magnitude between the range and the basin to be recorded. This requirement places an important constraint on viable explanations for alternating sequences of deposition and erosion in a decaying mountain‐basin pair.     

Human-driven topographic effects on the distribution of forest in a flat,lowland agricul-tural region简

Complex topography buffers forests against deforestation in mountainous regions. However, it is unknown if terrain also shapes forest distribution in lowlands where human impacts are likely to be less constrained by terrain. In such regions, if important at all, to- pographic effects will depend on cultural-historical factors and thus be human-driven （an- thropogenic） rather than natural, except in regions where the general climate or extreme soils limit the occurrence of forests. We used spatial regression modeling to assess the extent to which topographic factors explain forest distribution （presence-absence at a 48x48 m resolu- tion） in a lowland agricultural region （Denmark, 43,075 km2） at regional and landscape scales （whole study area and 10x10 km grid cells, respectively）, how landscape-scale for- est-topography relationships vary geographically, and which potential drivers （topographic heterogeneity, forest cover, clay content, coastal/inland location） determine this geographic heterogeneity. Given a moist temperate climate and non-extreme soils all landscapes in Denmark would naturally be largely forest covered, and any topographic relationships will be totally or primarily human-driven. At regional scale, topographic predictors explained only 5% of the distribution of forest. In contrast, the explanatory power of topography varied from 0%-61% at landscape scale, with clear geographic patterning. Explanatory power of topog- raphy at landscape scale was moderately dependent on the potential drivers, with topog- raphic control being strongest in areas with high topographic heterogeneity and little forest cover. However, these conditioning effects were themselves geographically variable. Our findings show that topography by shaping human land-use can affect forest distribution even in flat, lowland regions, but especially via localized, geographically variable effects.     

贵州省乌江流域人口分布与地形的关系

研究流域人口分布与地形的关系,有助于了解地理环境对人口分布的影响。以贵州省乌江流域为研究区,基于DEM数据和人口数据,提取海拔、坡度、起伏度等地形因子,研究人口分布与地形因子的关系。研究结论：① 人口数量在海拔800~1400 m的地区超过60%,人口密度在1000~1200 m的地区最高。② 人口数量与人口密度随着坡度上升总体呈下降趋势。③ 人口密度在起伏度小于50 m的地区超过1000人/km ²,人口密度随着起伏度上升总体呈下降趋势。     

Landslide susceptibility mapping using GIS and the weight-of-evidence model

The weights-of-evidence model (a Bayesian probability model) was applied to the task of evaluating landslide susceptibility using GIS. Using landslide location and a spatial database containing information such as topography, soil, forest, geology, land cover and lineament, the weights-of-evidence model was applied to calculate each relevant factor's rating for the Boun area in Korea, which had suffered substantial landslide damage following heavy rain in 1998. In the topographic database, the factors were slope, aspect and curvature; in the soil database, they were soil texture, soil material, soil drainage, soil effective thickness and topographic type; in the forest map, they were forest type, timber diameter, timber age and forest density; lithology was derived from the geological database; land-use information came from Landsat TM satellite imagery; and lineament data from IRS satellite imagery. Tests of conditional independence were performed for the selection of factors, allowing 43 combinations of factors to be analysed. For the analysis of mapping landslide susceptibility, the contrast values, W ⁺ and W ^-, of each factor's rating were overlaid spatially. The results of the analysis were validated using the previous landslide locations. The combination of slope, curvature, topography, timber diameter, geology and lineament showed the best results. The results can be used for hazard prevention and land-use planning.     

我国地形小气候研究概况与展望

我国山地和丘陵的面积约占土地总面积的70%.因此,研究地形小气候对于了解山区气候资源,合理开发山区经济,发展农业生产具有重要意义.地形小气候与山地气候不同,前者是指相对高差在几米到几百米,水平距离在10米到10公里范围内的小的起伏地形对气候的影响,其特征主要表现在个别气象要素的数值和个别的天气现象上,且局限在近地面的空气层中.     

Reconstructing ancient topography through erosion modelling

One of the main aims of geomorphology is to understand how geomorphic processes change topography over long time scales. Over the last decades several landscape evolution models have been developed in order to study this question. However, evaluation of such models has often been very limited due to the lack of necessary field data. In this study we present a topography based hillslope erosion and deposition model that is based on the WATEM/SEDEM model structure and works on a millennial time scale. Soil erosion, transport and deposition are calculated using slope and unit contributing area. The topography is iteratively rejuvenated by taking into account modelled erosion and deposition rates, thereby simulating topographic development backwards in time. A first attempt has been made to spatially evaluate the model, using detailed estimates for historical soil erosion and sediment deposition volumes, obtained from an augering campaign in a small catchment in the Belgian Loess Belt. The results show that the model can simulate realistic soil redistribution patterns. However, further research is necessary in order to deal with artificial flaws that cause routing problems and significantly influence results. Common problems and issues related to this type of backward modelling are also discussed.