The thickness, volume and grainsize of tephra fall deposits

作者: David M. Pyle

DOI: 10.1007/BF01086757

关键词: TephraExtrapolationThinningGeologyPopulationIsopach mapMineralogyEruption columnGrain sizePyroclastic fall

摘要: An improved empirical method for the plotting of field data and calculation tephra fall volumes is presented. The widely used “area” plots ln(thickness) against ln(isopach area) are curved, implying an exponential thinning law. Use ln(thickness)−(area)1/2 diagrams confirm dependence many parameters (e.g. thickness, maximum median clast size) with distance from source, producing linear graphs allowing to be calculated without undue extrapolation data. agreement between theoretical models dispersion observation better than previously thought. Two new quantitative proposed which describe rates deposit (bt thickness half-distance) size (bc half-distance). Many deposits exhibit different grainsize rates, diminishing 1–3 times slower thickness. This implies that entrained population influences morphologic granulometric patterns resulting deposit, in addition effects column height wind-speed. characteristics a best described by reference half-distance ratio (bc/bt). A classification scheme may contoured terms height.

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