Individual ignimbrites may have volumes in excess of 1,000 cubic kilometers and travel for distances in excess of 100 km from their source. They form important parts of the landscape in many parts of the world, and are particularly well exposed over huge areas of the Central Andes. Two massive ignimbrites, each tens of meters thick, separated by a terrace, can be seen in this view of the canyon of the Rio Loa. As the photo suggests, they can be readily traced for tens of kilometers along the canyon. The pinkish weathering dacitic ignimbrites are an unwelded variety known by the Peruvian term sillar, the original pumices have undergone vapor phase alteration forming a light, strong homogenous rock much used for building stone. The lowermost unit is the 8.1 Ma old Sifon ignimbrite, which travelled at least 150 km from its source caldera, Pastos Grandes in Bolivia. (Chapter 10).

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