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Davidof Volcano

From Wikipedia, the free encyclopedia

Davidof Volcano is an inactive stratovolcano and caldera remnant in the Aleutian Islands of Alaska, USA, 1,237 miles (1,991 km) from Anchorage.[1] Located on the eponymous island, Davidof is part of the Rat Islands sub-chain. It is also part of the "Aleutian Krakatau", a group of four islands formed when a stratovolcano's caldera caved in during the late Cenozoic.

Accessibility

Since the island is uninhabited, very little transportation is available. Transport can be found in Adak, albeit that the town is 199 miles (320 km)[2] from the island.[2]

Geography and geology

Because of the inclusion of Alaska, the United States has the largest number of active volcanoes in the world, many of them geologically young.[3] In Alaska, at least 50 volcanoes, including those in the Aleutian archipelago, have erupted in historical time.[4] Alaska accounts for about 80% of the United States' volcanoes, excluding the seamounts in the area, about 8% of the world's volcanoes, and most of these are located among the Aleutian Islands.[4] The Aleutian Arc forms the northern boundary of the Pacific Ring of Fire,[4] where tectonic activity generates earthquakes and volcanic eruptions regularly.

The largest of four tiny islands in the "Aleutian Krakatau" caldera,[5] Davidof is a stratovolcano[5] and caldera remnant[1] of a larger stratovolcano, which presumably collapsed at the end of the Cenozoic period.[2] In all, the caldera extends for 262 feet (80 m) underwater.[5] Davidof Island's shape is abstract, with many inclining, steep features and several sea cliffs.[6] There are no visible water features.[6]

Davidof's exact composition is unknown, although studies conducted by W.H. Nelson of the United States Geological Survey (USGS) determined that the lava, at least, was layered over a base of red breccia. The lavas appeared to be differentiating, but stuck to gray color with either "glassy or fine-grained, compact or dikty-taxitic" composition.[7] Much like Segula Island, all of Davidof's lava and even pyroclastic deposits interact by overlapping with each other.[7] The uppermost layer of these deposits is formed by the pyroclastic flow deposits.[7] The lava is filled with phenocrysts like feldspar, olivine, and pyroxene, and these can be found easily about the lava areas.[7]

Eruptive history

Although no eruptions have been recorded at Davidof, there is evidence of activity at the volcano. Through aerial photography, lava flow deposits have been detected among the flanks of the island.[1] While the exact age of the deposits is still unknown, one source estimates that they are probably less than 10,000 years old.[8]

Wildlife

Despite its small size, Davidof is heavily vegetated,[1] with variations of moss, lichen, and heath.[9] Spread throughout the island are grass and sedges, which cover much of the lower surface.[9] Fungi, liverworts, horsetails, and ferns, can be found on the island, along with flowering plants, such as the narcissus anemone, lupines, and orchids. Seaweed is also common on the island's beaches.[9]

References

  1. ^ a b c d "Davidof description and statistics". Alaska Volcano Observatory. United States Geological Survey. Retrieved July 15, 2009.
  2. ^ a b c Wood and Kienle, page 20.
  3. ^ Ewert, John; Guffanti, Marianne; Cervelli, Peter; Quick, James (2006). "The National Volcano Early Warning System (NVEWS): U.S. Geological Survey Fact Sheet FS 2006-3142". United States Geological Survey. Retrieved July 9, 2009.
  4. ^ a b c "Alaska GeoSurvey News: NL 2008-1". 11 (1). Alaska Division of Geological & Geophysical Surveys. March 2008: 1–14. Retrieved July 9, 2009. Cite journal requires |journal= (help)
  5. ^ a b c "Davidof". Global Volcanism Program. Smithsonian Institution. Retrieved July 15, 2009.
  6. ^ a b Nelson, W. H., page 7.
  7. ^ a b c d Nelson, W. H., page 11.
  8. ^ 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". Open-File Report. ISSN 2331-1258.
  9. ^ a b c Nelson, W. H., page 8.

Bibliography

This page was last edited on 11 June 2018, at 03:54
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