TEXTURAL STUDIES OF GRADING: VOLCANIC ASH FALLS

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SUMMARY

A theory of the lateral decrease of grain size and bed thickness with increasing distance of downwind transport is developed for ash falls. The theory is based on: the sediment load density of a turbulent slug of fluid, a turbulent diffusitivity coefficient, and the decay of turbulent velocity fluctuations. All three factors are founded on empirical observation and are generally accepted as having widespread applicability to turbulent sediment-fluid mixtures. The theory yields good qualitative agreement with observational data.

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