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Calanco (plural, calanchi) is a term widely used in the northern Apennines, Italy, to define a type of badland formed in clayey bedrock. However, no precise geomorphological definition of calanco has been established and a variety of map symbols are used to indicate the presence of calanco landforms. With the aim of developing an improved approach to identifying calanchi, a group of experienced surveyors identified 24 catchments with calanco characteristics among 67 catchments located between Bologna and Faenza in the northern Apennines. The morphology of each catchment was classified using traditional quantitative geomorphic approaches including fieldwork, map interpretation, hypsometric curve construction and computation of the annual sediment yield. Consideration of the parameters produced by these approaches indicated that none was capable of representing the presence of calanchi unequivocally and the basins were grouped into five classes on the basis of number and type of calanco criteria that they met. A characteristic of calanchi that is evident on topographic maps is crenulation of the contour lines and in this study a new topographic parameter was developed to represent the degree of contour crenulation. This parameter, LO/LF, is defined as the ratio of the actual length of a contour line (LO) to the length of the same line smoothed by an algorithm based on a moving average (LF). Calculated values of LO/LF ranged from 1·05 to 1·38. To test whether high values of the contour crenulation parameter were associated with calanchi, LO/LF values were added to other criteria for the five classes of catchment. Class 1 catchments, consisting of 14 of the 24 calanchi catchments identified in the field, displayed all of the criteria defining calanchi, and were characterized by the highest values of LO/LF (mean value 1·27 ± 0·15). It is proposed, therefore, that the contour crenulation ratio (LO/LF) may be useful in identifying the calanco landform. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
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Alan D. Howard 《地球表面变化过程与地形》1997,22(3):211-227
A drainage basin simulation model is used to interpret the morphometry and historical evolution of Mancos Shale badlands in Utah. High relief slopes in these badlands feature narrow divides and linear profiles due to threshold mass-wasting. Threshold slopes become longer in proportion to erosion rate, implying lower drainage density and higher relief. By contrast, in slowly eroding areas of low relief, both model results and observations indicate that drainage density increases with relief, suggesting control by critical shear stress. Field relationships and simulation modelling indicate that the badlands have resulted from rapid downcutting of the master drainage below an Early Wisconsin terrace to the present river level, followed by base level stability. As a result, Early Wisconsin alluvial surfaces on the shale have been dissected up to 62 m into steep badlands, and a Holocene alluvial surface is gradually replacing the badland slopes which are erocing by parallel retreat. © 1997 by John Wiley & Sons, Ltd. 相似文献
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Emilio Rodríguez-Caballero José Raúl Román Sonia Chamizo Beatriz Roncero Ramos Yolanda Cantón 《地球表面变化过程与地形》2019,44(14):2771-2779
Biological soil crust, or biocrust communities, are the dominating life form in many extreme habitats, such as arid and semiarid badlands, where water scarcity and highly erodible substrates limit vegetation cover. While climate, soil and biotic factors have been described as environmental filters influencing biocrust distribution in such biomes, little is known about the effect of terrain attributes on creating specific microhabitats that promote or restrict biocrust colonization. This study aimed to identify the main terrain attributes controlling biocrust distribution in the driest badland system in Europe, the Tabernas Badlands (SE Spain). To do this, we analysed the influence of different terrain attributes related to landscape stability and microclimate formation on the spatial distribution of lichen and cyanobacteria, using field measurements and topographical information from a LiDAR survey. Our results showed that the spatial distribution of cyanobacteria-dominated biocrusts, which are physiologically and morphologically adapted to extreme drought and high UVA radiation, was mostly associated with areas of high potential incoming solar radiation. The exception was bare south-aspect hillslopes with very high sediment transport potential, where bare physically crusted soils were the dominant ground cover. Lichen-dominated biocrusts, in contrast, colonized near the top of north-aspect hillslopes, characterized by low potential incoming solar radiation and potential evapotranspiration, and their cover decreased downstream, as conditions became good enough for vascular plants. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd. 相似文献
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Regolith surface characteristics and response were examined over a three‐year period in a badland area in a Mediterranean middle‐mountain zone near Vallcebre (Eastern Pyrenees). Preliminary work carried out in this area indicated clear seasonal patterns of regolith properties driven by frost heaving in winter and crusting and erosion in the rest of the year. Rainfall simulations were performed with a small portable nozzle simulator in order to study seasonal changes in runoff generation, erosion rates and raindrop effect on bulk density changes. The results showed large seasonal variations in runoff and erosion responses. In?ltration rates after runoff start were correlated with precipitation depth before runoff start; runoff generation was therefore related to regolith saturation only to a very limited extent. Erosion rates were more controlled by runoff rates than by the weakness of regolith against raindrop splash, and sediment grain size increased with concentration. The combined role of antecedent regolith moisture and bulk density explained most of the seasonal variability in in?ltration, bulk density changes during rainfall and erosion rates, but some seasonal differences in sediment detachability were not explained by these variables and may be attributed to changes in roughness. Overall, runoff and erosion responses were relatively stable during spring and autumn, whereas wide variations in in?ltration rates and sediment detachment occurred in winter and summer respectively. Experiments conducted in a single season would have produced poorly representative, if not erroneous, results. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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