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Lionel Wilson (Department of Environmental Sciences, University of Lancaster, England) has brought physics to volcanology and transformed a largely descriptive and petrolqgical science by development of a quantitative and predictive understanding of eruption dynamics. Lionels involvement in volcanology started in 1971 when he helped George Walker determine the rates of fall of pyroclasts. This fairly simple problem led to questions of settling of ash particles onto the earth, and Lionel embarked on a series of papers that progressively traced volcanic debris back to its source crater. He described the physical processes affecting pyroclasts in strombolian and plinian eruptions, and with Steve Sparks and others modeled the formation (1976) and emplacement (1978) of ignimbrites by gravitational collapse of an eruption column. In a paper important to understanding the dispersal of tephra, Lionel and others demonstrated that eruption cloud heights are proportional to the fourth root of the mass eruption rate of magma (1978), leading ultimately to the inversion of the problem to deduce cloud height and associated eruption characteristics from mapped tephra distributions. The correctness and utility of Lionel's theoretical descriptions of explosive activity were demonstrated by a series of papers applying the models to actual eruptions at Fuego, Guatemala (1980), Ngauruhoe, New Zealand (1979), La Soufriere, St. Vincent (1982), and St. Helens, Washington (1982), as well as to tephra deposits at Askja, Iceland (1981), Toluca, Mexico (1977), and Thera, Greece (1978).