A two dimensional model for the dispersal of volcanic ash, modified from that of Suzuki (1983), is applied to the 16 September 1986 eruption of Lascar, in northern Chile. The result is an isopach map predicting ground concentrations of ash. The map shows two local maxima along distinct dispersal axes and predicts that the deposit was detached from the source. Predict concentrations are in agreement with a single reported thickness measurement. ¿ American Geophysical Union 1991