This 6150 m high andesite-dacite composite volcano is an exceptionally well-exposed example of numerous similar volcanic constructs around the circum-Pacific "Ring of Fire." It is a large volcano, rising from a base at just over 3000 m. It consists of two essentially different units. At left, the reddish brown, snow-covered peak forms part of the "Old Cone," constructed mostly of basaltic andesite lavas, thin flows of which can be seen near the summit. At some unknown time, this cone failed, producing a massive débris avalanche deposit, not seen in the photo. Subsequently, a large dome of hornblende dacite lavas accumulated, forming the greyish massif on the right side. This dome became very steep, and many flow fronts of the lavas failed, yielding the visible scars, and forming an apron of hot avalanche debris, the upper parts of which are visible (pink toned) immediately below the lava scarps. Fumarolic activity continues to the present day on the summit of the dome. The foreground and middle distance is mantled with a plinian pumice fall deposit, creating a very smooth surface. (Fig. 12.4-12.6).

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