Geology topics
Publications and source records attributed to T. P. Miller.
Alaska has over 40 historically active volcanoes and normally averages one eruption a year. Alaskan volcanoes were unusually active in 1986. Augustine, Pavlof, and Akutan volcaneos all erupted vigorously; at one time in April, all three were erupting.
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Ash flows around Aniakchak and Fisher calderas in the Aleutian volcanic arc show evidence of having flowed over formidable topographic barriers at distances of tens of kilometres from their source. Ash flows swept down glaciated valleys on the south side of Aniakchak caldera, crossed a broad lowland with an altitude of less than 35 m, and continued on through passes as much as 260 m high in the Aleutian Range into the Pacific Ocean, a distance of some 50 km. North of Fisher caldera, ash flows flowed over a ridge barrier of 500 m and into the Bering Sea. Knowledge that ash flows have this mobility may help in understanding the distribution of other ash flows and in the discovery of their sources. © 1977 Geological Society of America.
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Recently discovered deposits of obsidian in the Koyukuk valley may be the long-sought-for source of obsidian found in archeological sites in northwestern Alaska. Obsidian from these deposits compares favorably in physical characteristics and sodium-manganese ratio with the archeological obsidian, and there is evidence that the deposits have been "mined" in the past.
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