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A Model of Subterranean Limestone Erosion in the British Isles Based on Hydrology

1971; Wiley; Issue: 54 Linguagem: Inglês

10.2307/621362

1475-5661

Malcolm Newson,

Groundwater and Isotope Geochemistry

The erosion of limestone by underground streams was studied using data obtained both in the field and the laboratory. A conceptual model, based on the Mendip Hills, Somerset, is quantified by study in the Burrington area. Measurements of the important variables were also made during field studies in South Wales, Sutherland in Scotland and County Clare in Ireland. The model incorporates the results of measuring abrasion and sediment movement in cave streams. Both quantitative and qualitative analyses were performed on sediment from sinking and resurging streams. Abrasion potential is realized only in floods. However, a comprehensive study of solution reveals it to be less effective in cave streams than has hitherto been suggested. Solution is most effective where chemically aggressive water flows under conditions suitable for the rapid or most complete reaction with limestone. A contrast is drawn between the flow in the percolation system and the flow of water which sinks in streams. The ratio between the two components was established by water tracing and stream gauging. It is an important control on the erosional regime and attempts are made to quantify the proportion attributable to solution in terms of this ratio, so as to explain both temporal and spatial variations in erosion. There is a need to collect more measurements of streamflow and direct erosion in karst areas in which water movements have been traced. EARLY work on limestone erosion was concerned mainly with the surface and with describing the distinct morphology of karst areas. J. Cvijic (I893) produced a cyclic model of solutional erosion and collapse. Process studies have since become more important, using simple methods of determining the concentration of dissolved limestone by chemical analysis of water samples from resurging streams (for example, D. I. Smith and D. G. Mead, 1962). J. Corbel (1959) and others have devised expressions for indirectly measuring regional rates of limestone solution from such analyses. Both at the descriptive and analytical levels there has been little work on elucidating. the role of processes other than chemical solution. Models of the development of karst landforms have therefore been based on those factors which affect the solution reaction, such as climate and lithology. I. Douglas (1968) has stressed hydrological factors and the work of A. F. Pitty (1966, 1968) shows how full analysis of the results of water sampling can be properly linked to climatic and hydrological data. Authors who have mentioned mechanical erosion in karst streams have left its role unsubstantiated. However, limestones have been proved, by mechanical tests for commercial users, to be among the weakest of rocks (D. W. Kessler and W. H. Sligh, I927; E. J. Lovegrove, 1929; J. E. Lamar, 1967). Work on sediments has been limited to historical interpretations apart from the theoretical exercises of E. L. and W. B. White (1967). Much of the neglect of processes such as abrasion has resulted from focusing attention on controversies surrounding the early stages of cave development, during which solution is