12 June 1987
Vol 236, Issue 4807

About The Cover

Mount St. Augustine volcano, Alaska, in pyroclastic flow eruption, 29 August 1986. View is toward the volcano (hidden in clouds) from Burr Point, 6 kilometers from the summit. A pyroclastic flow at the 350-meter level on the northern flank of the volcano is moving toward the camera at a speed of about 30 meters per second. The flow is a dry density current of dust, gas, and volcanic rock debris that probably originated by sudden vesiculation of molten andesite near the base of an emerging lava spine on the summit dome (about 1200-meter level). The ridge in the foreground is part of an 1883 debris avalanche that produced a tsunami in lower Cook Inlet. See page 1442. [J&uumlaut;rgen Kienle, Geophysical Institute, University of Alaska—Fairbanks, Fairbanks, AK 99775-0800]