One of the best known examples of a coulée, and the largest of its type in the world, is the Chao dacite (Figure M4, a&b), occupying the saddle between Paniri and Léon volcanoes (Guest & Sanchez, 1969; de Silva et al., 1988). 39Ar-40Ar ages indicate it is less than 100,000 years old (Drake et al., unpub. data, 1989). It is a 14.5 km long coulée, with flow fronts 350-400 m high and has a total erupted volume of ~26 km3. A characteristic feature of this body are the prominent 30 m high flow ridges or ogives on its surface, resulting from folding during emplacement of surface layers with different mechanical properties due to differential cooling of the lava. Eruption of the huge coulée appears to have occurred in two main stages; 1) explosive eruption of a small volume of dacitic ignimbrites (<1 km3) followed by passive effusion of the main mass of lava (Chao I and II) which constitutes 22 km3; and 2) explosive eruption of small rhyolitic airfall and formation of a dense pumice cone followed by passive effusion of Chao III (~3 km3). The lava is high-K, very porphyritic, and thought to have erupted over a period of 100-150 years (de Silva et al., 1994).
de Silva, S.L., Self, S., Francis, P.W., Drake, R.E., and Carlos Ramirez, R., 1994. Effusive silicic volcanism in the Central Andes: The Chao dacite and other young lavas of the Altiplano-Puna Volcanic Complex. Journal of Geophysical Research, 99:17,805-17,825.
de Silva , S.L., Self, S., and Francis, P.W., 1988. The Chao dacite revisited (abstract). Eos Trans. AGU, 69:1487-1488.
Guest, J.E., and Sanchez, J.. 1969. A large dacitic lava flow in Northern Chile. Bull. Volcanol., 33:778-790.