stratovolcano

stratovolcanoStratovolcanoes, also called composite or cone volcanoes, are known for their stature as mountains and for their variety of utterance. Venting at times pyroclastic—“fire-broken”—particulates, as Mount St. Helens did in 1980, and at other times exuding lava, a stratovolcano develops a layered composition as it grows (hence the name). The steeply bedded ash and cinders of its pyroclastic explosions tend to give it a conical form, while its gentler expressions of lava provide structural stability. All the major Pacific Rim volcanoes are stratovolcanoes. By present measurements, it takes anywhere from roughly twenty thousand (St. Helens) to more than half a million years (Hood and Rainier) to build a stratovolcano of respectable size. Some erupt so exuberantly that they self-destruct. Mount Mazama, a twelve-thousand-foot peak in the southern Oregon Cascades composed of several overlapping volcanoes, emptied its magma chamber and blew off its upper four thousand feet— twelve cubic miles of rock—in a single day some 6,800 years ago, collapsing into a caldera we call Crater Lake.

John Daniel