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Little Sitkin Island description and information




Official Name: Little Sitkin Island
Type:Stratovolcano within nested calderas
Most Recent Activity:1900
Seismically Monitored: Yes
Color Code:GREEN
Alert Level:NORMAL
Elevation: 3898 ft (1188 m)
Latitude: 51.9531° N
Longitude:178.5356° E
Quadrangle:Rat Islands
CAVW Number:311050
Pronunciation: Sound file
Associated Features:Caldera One
Caldera Two
Nearby towns:Shemya Station 194 mi (312 km) NW
Adak 206 mi (332 km) SE
Attu Station 233 mi (375 km) NW
Atka 309 mi (497 km) NE
Anchorage 1343 mi (2161 km) NE
From Miller and others (1998) [1]: "The active stratovolcano on Little Sitkin Island occurs within the eroded remnants of a nested double caldera of probable late Pleistocene age. The older caldera (Caldera One) is about 4.8 km in diameter and is centered slightly northeast of the island's midpoint. The caldera formed at the site of a large stratovolcano, the remnants of which are the oldest rocks exposed on the island (unit Qtw [2]).

"A second stratovolcano was constructed almost entirely of lava flows (unit Qd) within Caldera One and attained a height of about 900 m. A cataclysmic eruption, possibly in early post-glacial time, resulted in the formation of a second, smaller caldera (Caldera Two) that partially destroyed this cone. Caldera Two is elliptical in outline and measures 2.7 by 4 km; the inferred eastern and southern margins are coincident with those of Caldera One. Field relations suggest that the northern boundary of Caldera Two is a hinge along which a large block, comprising most of the Caldera One stratovolcano, was tilted southward during the caldera eruption. The highest peak on the island is on the post-caldera remnant of the second cone.

"A deposit of partly welded tuff up to 100 m thick (unit Qp) extends from the remnant cone northwest across the Caldera Two boundary fault, to slightly beyond the inferred location of the Caldera One boundary fault. The deposit is thought to have been emplaced by one of more pyroclastic flows, possibly associated with formation of Caldera Two [2].

"Post-Caldera Two deposits are mainly lava flows (units Qls, Qlp, and Qlw). Two relatively recent aa flows have well developed levees; one originated from the breached central crater of Little Sitkin volcano, and the other from a fissure along the western trace of the Caldera One boundary fault [2]."

Catalog of the historically active volcanoes of Alaska, 1998
citation imageMiller, T. P., McGimsey, R. G., Richter, D. H., Riehle, J. R., Nye, C. J., Yount, M. E., and Dumoulin, J. A., 1998, Catalog of the historically active volcanoes of Alaska: U.S. Geological Survey Open-File Report 98-0582, 104 p.
Download PDF title page PDF : 52
Download PDF intro and TOC PDF : 268 KB
Download PDF eastern part - Wrangell to Ukinrek Maars PDF : 972 KB
Download PDF central part - Chiginagak to Cleveland PDF : 2,463 KB
Download PDF western part - Carlisle to Kiska PDF : 956 KB
Download PDF references PDF : 43 KB

Geology of Little Sitkin Island, Alaska, 1959
citation imageSnyder, G. L., 1959, Geology of Little Sitkin Island, Alaska: in Investigations of Alaskan volcanoes, U.S. Geological Survey Bulletin 1028-H, p. 169-210, 1 plate, scale 1:20,000.
Download PDF full-text PDF : 2 MB
Download PDF plate 23 PDF : 7 MB

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