[Illustration: Steam plume rises from lava dome atop Augustine Volcano on April 30, 1986. (_Photograph by M.E. Yount._)] Augustine Volcano. One of the most active volcanoes in Cook Inlet is Augustine, whose symmetrical cone rises 1,254 meters above the sea. Since Captain James Cook discovered and named it in 1778, Augustine has erupted in 1812, 1883, 1935, 1963-64, 1976, and 1986. Curiously, the quiet intervals between these eruptions apparently have shortened from 70 to 10 years. Augustine’s 1986 eruption was similar to the pattern of events observed in 1976. After eight months of earthquake activity beneath the volcano, a violent explosion began on March 26. Billowing ash plumes rose more than 10 kilometers above the vent, pyroclastic flows sped down the volcano’s flanks into the sea, and ash spread throughout Cook Inlet. A second stage began April 23, when lava began erupting near the volcano’s summit and added about 25 meters to the top of the existing lava dome. Small pyroclastic flows accompanied growth of the dome. Scientists were worried that this eruption might trigger a giant landslide from Augustine’s steep upper cone, which could enter the sea to create a _tsunami_ (powerful seismic sea wave). At least 12 landslides are known to have occurred at Augustine. The most recent slide took place at the onset of the 1883 eruption when a part of the volcano’s summit collapsed into the sea. Within one hour, a tsunami as high as 9 meters crashed ashore on the coast of the Kenai Peninsula 80 kilometers away. No one was killed and property damage was only minor because the tsunami hit at low tide. Subsequent eruptions have rebuilt a steep cone of overlapping lava domes similar to the cone that existed just before the 1883 landslide. [Illustration: Pyroclastic flow descending the upper flanks of Augustine Volcano. (_Photograph by M.E. Yount._)] Novarupta, Katmai National Monument. The largest eruption in the world this century occurred in 1912 at Novarupta on the Alaska Peninsula. An estimated 15 cubic kilometers of magma was explosively erupted during 60 hours beginning on June 6—about 30 times the volume erupted by Mount St. Helens in 1980! The expulsion of such a large volume of magma excavated a funnel-shaped vent 2 kilometers wide and triggered the collapse of Mount Katmai volcano 10 kilometers away to form a summit caldera 600 meters deep and about 3 kilometers across. Extrusion of the lava dome, called Novarupta, near the center of the 1912 vent marked the end of the eruption.