Convincing evidence for the important role of gas fluidization in the mobility of ignimbrites is provided by segregation structures which form as escaping gases cause clasts of different sizes and densities to jostle apart from one another, to provide direct routes for the gas through the body of the material. These lithic-filled pipes rise many meters through the 4.6 million year old Real Grande ignimbrite. The largest clasts within the pipes reach 20 cm in diameter, most of the finer material in the pipes has been blown away or elutriated. Landsat image of Cerro Galan volcano is shown in Slide 9--Part I. (Fig.10.8).

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