Katmai Volcano
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 deposits. No fewer than 15 eruptive episodes have originated from the Katmai cluster 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 e . . .
The ash, initially thrust upward as high as several kilometers by the power of the volcanic eruption, is carried upward higher still by convection of heated air, until the entrained particles and accompanying gas are captured by prevailing winds and carried away from the volcano as an ash cloud. The Alaska Volcano Observatory (AVO) operates a network of 19 seismometers to detect earthquakes around the Katmai cluster of volcanoes. In 1990, a five-station array of permanent benchmarks was installed around Novarupta. Many channels are already established for distributing this information: FAX, telephone, electronic mail, television, and radio. A graduated color code explains the degrees of concern regarding the likelihood and consequences of an eruption. Many large earthquakes occurred before and during the 1912 eruption, and the cluster of Katmai volcanoes remains seismically active. Such an eruption might interrupt and inconvenience national and international commerce, perhaps for months, but Alaskan commerce would be temporarily devastated. An explosive eruption like that of Novarupta, 1912, could affect air traffic all over the North Pacific, Alaska, Canada, and the conterminous United States. If an eruption were imminent, AVO would provide explanations of likely events and impacts. Volcanic earthquakes, caused by movement of magma or hydro-thermal fluids beneath an edifice, are used to monitor the activity level of volcanoes, because most eruptions are typically preceded for hours to months by increased seismicity. Sightings of new steaming ground, increased fumarolic activity, and possible ash plumes all prompt further investigation by AVO personnel. During heightened volcanic unrest and throughout and after any eruptive activity, AVO’s role is to provide information to appropriate authorities and the general public about the nature and status of the eruption. Whether large or small, explosive eruptions send fine ash particles upward. Over the last two decades, detailed studies of Novarupta deposits have contributed to a better understanding of how volcanoes work, the concurrent production of stratosphere-reaching ash plumes and valley-filling ash flows, the timing of caldera collapse relative to magma withdrawal, and how the pumice and ash were distributed so far from the source Heightened awareness of the dangerous mix of aircraft and volcanoes, and recognition of the abundance of both in this part of Alaska, has prompted various Government-sponsored comprehensive evaluations of the eruptive history of the whole Katmai volcanic cluster. The volcanoes near Novarupta form a 25-km-long line of contiguous stratovolcanoes on the drain-age divide of the Alaska Peninsula, 450 km southwest of Anchorage (population 260,283 ), 250 km southwest of Homer (population 4,000 ), 170 km west-northwest of Kodiak (population 6,334 ), and 100 km east-southeast of King Salmon (population 696 ).
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