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Sedimentation Not surprisingly, larger particles fall earlier than small particles. Carey and Sparks (1986) do a very good job of quantifying this observation. Their work allows column heights to be reconstructed from lithic isopleth maps -- maps showing contours of maximum particle size. Lithic particles are used because settling or fall velocity depends greatly on particle density, and lithic partilces are nearly always ~2.5 g/cm^3, whereas pumices can range in density from <0.7 to 2.5 g/cm^3 to Additionally, their work allows for a reconstruction of wind speed during deposition. In order to determine how high the column went, compare the area for a particular isopleth (a contour of particle size) with the figure below.
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The effects of wind on ispleth distributions can be profound TO the left is an isopleth map of the Main stage of the Ksudach KS1 eruption. a column 30-35 km high produced these deposits. Contours are in cm. In the figures below, Carey and Sparks (1986) model the effects a 10, 20, and 30 m/s wind from the left on a plume with a buoyant height, Hb, of 30 km. |