Following the eruption of the Tepic Pumice and the formation of an elongated caldera at the summit of San Juan volcano, a lava dome was constructed within the caldera. The dome forms the rounded forested area in front of the western caldera rim, which marks the horizon. The caldera is 4 km wide in the E-W direction of this photo and 1 km wide in a N-S direction. Andesitic lava flows (left center) erupted from the dome and flowed across the caldera floor to its eastern side.

Photo by Jim Luhr, 1979 (Smithsonian Institution).

This image is made available under the Public Domain Dedication CC0 license, but proper attribution is appreciated.

San Juan