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Maximum Pumice and Lithic Isopleth Maps
for the Rio Blanco Tephra Deposit
Maximum pumice and lithic clast diameters and tephra thickness were measured at 47 outcrops (average of 3 largest pumice and lithic fragments). Invariably, the maximum pumice and lithic clasts at each outcrop occur in either the middle or upper coarse horizons, presumably when episodes of vent-widening and maximum eruption intensity occurred. The diagrams above show the size of both lithic and pumice fragments decreasing exponentially away from the vent, with lithic fragment size decreasing more rapidly than pumice fragment size. The dispersal axis of the lithic fragments is skewed slightly SW from that of the pumices, showing that the westerly wind component had a greater effect on the pumices, which were less dense and traveled farther from source.
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