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The elongated, 9 x 23 km island of Yunaska in the Islands of the Four Mountains group is comprised of two unnamed volcanic centers of greatly different morphology. The older, 950-m-high western center consists of the eroded remnants of four overlapping stratovolcanoes that form a linear, NNE-trending ridge. Cinder cones and fissure-fed lava flows extend from the western end of the complex. The younger, 550-m-high eastern complex consists of a shield volcano capped by two nested calderas. The 3.5-km-wide Coats caldera is located within an older 10 x 13 km caldera and contains cinder cones and a lava field. Two areas of particularly youthful lava flows extend down the flank through a gap in the SW caldera rim and blanket the upper northern flank of the caldera. Vents are found on the flanks of the caldera within a kilometer of its rim. A post-caldera cone is capped by a small summit crater. The eastern center is presumably the source of the island's historical eruptions, first recorded in 1817.
Summary of Holocene eruption dates and Volcanic Explosivity Indices (VEI).
|Start Date||Stop Date||Eruption Certainty||VEI||Evidence||Activity Area or Unit|
|1937 Nov 3||1937 Nov 4||Confirmed||3||Historical Observations|
|[ 1929 ]||[ Unknown ]||Uncertain|
|[ 1873 ]||[ Unknown ]||Uncertain||2|
|[ 1817 ]||[ Unknown ]||Uncertain|
This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.
|Feature Name||Feature Type||Elevation||Latitude||Longitude|
|The rim of the summit caldera of Yunaska volcano is seen from an older volcanic center on the western side of the island. The younger, 550-m-high eastern complex consists of a shield volcano capped by two nested calderas and is presumably the source of the island's historical eruptions, first recorded in 1817. A young lava flow at the far right descended through a notch in the caldera rim. In the background are the snow-capped peaks (left-to-right) of Carlisle, Cleveland, and Herbert volcanoes.
Photo by Jim Meyers, 1992 (University of Wyoming, courtesy of Alaska Volcano Observatory).
The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title.
Coats R R, 1950. Volcanic activity in the Aleutian Arc. U S Geol Surv Bull, 974-B: 35-47.
Henning R A, Rosenthal C H, Olds B, Reading E (eds), 1976. Alaska's volcanoes, northern link in the ring of fire. Alaska Geog, 4: 1-88.
IAVCEI, 1973-80. Post-Miocene Volcanoes of the World. IAVCEI Data Sheets, Rome: Internatl Assoc Volc Chemistry Earth's Interior..
Lamb D, Linneman S R, Myers J D, Nicolaysen K E, 1992. Caldera formation on Yunaska Island, central Aleutian arc (abs). Eos, Trans Amer Geophys Union, 73: 645.
Miller T P, McGimsey R G, Richter D H, Riehle J R, Nye C J, Yount M E, Dumoulin J A, 1998. Catalogue of the historically active volcanoes of Alaska. U S Geol Surv Open-File Rpt, 98-582: 1-104.
Motyka R J, Liss S A, Nye C J, Moorman M A, 1993. Geothermal resources of the Aleutian arc. Alaska Div Geol Geophys Surv, Prof Rpt, no 114, 17 p and 4 map sheets.
Myers J D, 1994. The Geology, Geochemistry and Petrology of the recent Magmatic Phase of the Central and Western Aleutian Arc. Unpublished manuscript, unpaginated.
Nicolaysen K E, Myers J D, Linneman S R, Lamb D, 1992. Geologic relations of the Yunaska volcanic complex, central Aleutian arc (abs). Eos, Trans Amer Geophys Union, 73: 645.
Smith R L, Shaw H R, Luedke R G, Russell S L, 1978. Comprehensive tables giving physical data and thermal energy estimates for young igneous systems of the United States. U S Geol Surv Open-File Rpt, 78-925: 1-25.
Wood C A, Kienle J (eds), 1990. Volcanoes of North America. Cambridge, England: Cambridge Univ Press, 354 p.