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オクモク山

Okmok

楯状火山 · United States · 1073m

The summit of 35-km-wide Okmok has two largely overlapping 10-km-wide calderas. Both calderas formed by voluminous eruptions of tephra and pyroclastic flows during the Holocene, one about 8,250 years ago and the other about 2,400 years ago. Numerous cones and lava domes formed on the caldera floor and flanks. Historical explosive eruptions and lava flows have originated from cones within the caldera.
The summit of 35-km-wide Okmok has two largely overlapping 10-km-wide calderas. Both calderas formed by voluminous eruptions of tephra and pyroclastic flows during the Holocene, one about 8,250 years ago and the other about 2,400 years ago. Numerous cones and lava domes formed on the caldera floor and flanks. Historical explosive eruptions and lava flows have originated from cones within the caldera. · 写真: Photo by John Reeder (Alaska Division of Geological & Geophysical Surveys). · Wikimedia Commons
タイプ
楯状火山
国
United States
地域
North America Volcanic Regions / Aleutian Ridge Volcanic Arc
標高
1073m
座標
53.430, -168.130
最終噴火
2008年
テクトニクス環境
Subduction zone / Intermediate crust (15-25 km)
火山地形
Shield
主要岩石
Basalt / Picro-Basalt
地質学的概要

The basaltic Okmok shield volcano forms the NE end of Umnak Island in the Aleutian Islands. The summit of the low, 35-km-wide volcano is cut by two overlapping 10-km-wide calderas formed during eruptions about 12,000 and 2,050 years ago when dacitic pyroclastic flows reached the coast. More than 60 tephra layers from Okmok have been found overlying the 12,000-year-old caldera-forming tephra layer. Numerous cones and lava domes are present on the flanks down to the coast, including the SE-flank Mount Tulik, which is almost 200 m higher than the caldera rim. Some of the post-caldera cones show evidence of wave-cut lake terraces; more recent cones were formed after the caldera lake, once 150 m deep, disappeared. Eruptions have been reported since 1805 from cinder cones within the caldera, where there are also hot springs and fumaroles.

Wikipedia の要約

英語版の要約

Mount Okmok is a volcano on eastern Umnak Island, in the central-eastern Aleutian Islands of Alaska. Part of the Aleutian Volcanic Arc, it was formed by the subduction of the oceanic Pacific Plate under the North American Plate. Okmok is a large shield volcano capped by a 10-kilometer (6.2 mi) wide caldera. The caldera contains numerous cinder cones, their lava flows, and a few lakes. Okmok erupts mainly basaltic lava, mostly from the cones within the caldera.

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噴火履歴

概要 (VEI時系列)
バーをクリックすると個別の噴火が表示されます
6310 BCE~6033 BCE · 1件 · 最大 VEI 4210 BCE~67 · 1件 · 最大 VEI 61731~2008 · 17件 · 最大 VEI 46310 BCE4369 BCE2151 BCE210 BCE1731

詳細タイムライン

  1. 2008年VEI 4観測記録
    2008-07-12 ~ 2008-08-19
    NE caldera floor
  2. 1997年VEI 3観測記録
    1997-02-11 ~ 1997-05-19
    SW part of caldera (Cone A)
  3. 1986年VEI 2観測記録
    1986-11-18 ~ 1988-02-26
    SW part of caldera (Cone A)
  4. 1983年VEI 2観測記録
    1983-07-08 ~ 1983-07-08
    SW part of caldera (Cone A)
  5. 1981年VEI 3観測記録
    1981-03-24 ~ 1981-03-24
    SW part of caldera (Cone A)
  6. 1960年VEI 3観測記録
    1960-10-15 ~ 1961-04-15
    SW part of caldera (Cone A)
  7. 1958年VEI 3観測記録
    1958-08-14 ~ 1958-08-25
    SW part of caldera (Cone A)
  8. 1945年VEI 2観測記録
    1945-06-04 ~ 1945-12
    SW part of caldera (Cone A)
  9. 1943年VEI 1観測記録
    1943-06 ~ 進行中
    SW part of caldera (Cone A)
  10. 1938年VEI ?観測記録
    1938 ~ 進行中
    SW part of caldera (Cone A)
  11. 1936年VEI ?地質学的推定
    1936 ~ 進行中
    SW part of caldera (Cone A)
  12. 1931年VEI 2観測記録
    1931-03-21 ~ 1931-05-13
    Cone A?
  13. 1899年VEI 3観測記録
    1899 ~ 進行中
    SW part of caldera (Cone A)
  14. 1878年VEI 2観測記録
    1878 ~ 進行中
    Cone A?
  15. 1824年VEI ?観測記録
    1824 ~ 1830
    Cone B?
  16. 1817年VEI 3観測記録
    1817-03-01 ~ 1820
    Cone E? or B?
  17. 1805年VEI ?観測記録
    1805 ~ 進行中
  18. 紀元前 100年 (±50年)VEI 6地質学的推定
    BCE 100 ~ 進行中
    Okmok II caldera
  19. 紀元前 6310年 (±500年)VEI 4地質学的推定
    BCE 6310 ~ 進行中

外部リンク

⚠ 参考情報です。緊急対応には使用しないでください。