Preliminary volcano-hazard assessment for the Katmai volcanic cluster, Alaska

The Katmai cluster is a 25-kilometer-long line of volcanoes along the Alaska Peninsula 450 kilometers southwest of Anchorage, including (from northeast to southwest) Snowy Mountain, Mount Griggs, Mount Katmai, Trident Volcano, Novarupta volcano, Mount Mageik, Mount Martin, and Alagogshak volcano. All but Alagogshak have erupted within the last 6,000 years, often explosively, to produce lava flows, domes, and widespread tephra (ash) deposits. No fewer than 15 eruptive episodes have originated from the Katmai cluster in postglacial time (within the last 10,000 years), each lasting days to tens of years and all of which could have produced ash clouds. Novarupta, a new vent in 1912, produced the world's largest eruption of the 20th century and sent ash around the globe. During that great eruption, nearby Mount Katmai collapsed, destroying its summit peaks and leaving behind a 2.5-kilometer-wide caldera, now filled with a 250-meter-deep lake. More recently, a new vent on Trident produced lava flows and ash plumes for at least 20 years, lasting from 1953 to 1974. Postglacial eruptions, vigorous fumaroles on Griggs, Trident, Mageik, and Martin, and continuing seismicity are good evidence of the potentially active state of the entire Katmai cluster. Any eruption of these volcanoes could affect air traffic, both overhead and on the ground, with severity of the ash-cloud hazard depending on the size of the eruption. An explosive eruption like that of Novarupta, 1912, could affect air traffic all over the North Pacific, Alaska, Canada, and the conterminous United States. Such an eruption might interrupt and inconvenience national and international commerce, perhaps for months, but Alaskan commerce would be temporarily devastated.