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Mount St. Helens

St. Helens

Stratovolcano · United States · 2549m

The 1980 eruption of Mount St. Helens dramatically altered the conical profile of the volcano. The eruption left a 2 x 3.5 km wide horseshoe-shaped crater, seen here from the NNE beyond Spirit Lake (center). The landslide of 18 May lowered the summit by 400 m and produced a highly mobile debris avalanche that swept into Spirit Lake and traveled down the North Fork Toutle River. The associated northward-directed lateral blast devastated about 600 km2.
The 1980 eruption of Mount St. Helens dramatically altered the conical profile of the volcano. The eruption left a 2 x 3.5 km wide horseshoe-shaped crater, seen here from the NNE beyond Spirit Lake (center). The landslide of 18 May lowered the summit by 400 m and produced a highly mobile debris avalanche that swept into Spirit Lake and traveled down the North Fork Toutle River. The associated northward-directed lateral blast devastated about 600 km2. · Photo: Photo by Lyn Topinka, 1981 (Cascades Volcano Observatory, U.S. Geological Survey). · Wikimedia Commons
Type
Stratovolcano
Country
United States
Region
North America Volcanic Regions / High Cascades Volcanic Arc
Elevation
2549m
Coordinates
46.200, -122.180
Last eruption
2008
Tectonic setting
Subduction zone / Continental crust (> 25 km)
Landform
Composite
Major rock type
Dacite
Geological summary

Prior to 1980, Mount St. Helens was a conical volcano sometimes known as the Fujisan of America. During the 1980 eruption the upper 400 m of the summit was removed by slope failure, leaving a 2 x 3.5 km breached crater now partially filled by a lava dome. There have been nine major eruptive periods beginning about 40-50,000 years ago, and it has been the most active volcano in the Cascade Range during the Holocene. Prior to 2,200 years ago, tephra, lava domes, and pyroclastic flows were erupted, forming the older edifice, but few lava flows extended beyond the base of the volcano. The modern edifice consists of basaltic as well as andesitic and dacitic products from summit and flank vents. Eruptions in the 19th century originated from the Goat Rocks area on the N flank, and were witnessed by early settlers.

From Wikipedia

Mount St. Helens is an active stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States. It lies 52 miles (83 km) northeast of Portland, Oregon, and 98 miles (158 km) south of Seattle. Mount St. Helens takes its English name from that of the British diplomat Alleyne FitzHerbert, 1st Baron St Helens, a friend of explorer George Vancouver who surveyed the area in the late 18th century. The volcano is part of the Cascade Volcanic Arc, a segment of the Pacific Ring of Fire.

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Eruption history

Summary (VEI over time)
Click a bar to see individual eruptions
2340 BCE~2143 BCE · 1 eruptions · max VEI 52143 BCE~1945 BCE · 1 eruptions · max VEI ?1945 BCE~1748 BCE · 2 eruptions · max VEI 61748 BCE~1550 BCE · 2 eruptions · max VEI ?1353 BCE~1155 BCE · 1 eruptions · max VEI ?1155 BCE~958 BCE · 2 eruptions · max VEI ?958 BCE~760 BCE · 2 eruptions · max VEI ?563 BCE~365 BCE · 1 eruptions · max VEI 5365 BCE~168 BCE · 3 eruptions · max VEI ?168 BCE~29 · 1 eruptions · max VEI ?29~227 · 2 eruptions · max VEI 0227~424 · 3 eruptions · max VEI 0622~819 · 1 eruptions · max VEI ?1412~1609 · 3 eruptions · max VEI 51609~1807 · 2 eruptions · max VEI 51807~2004 · 17 eruptions · max VEI 52340 BCE1353 BCE168 BCE8191807

Detailed timeline

  1. 2004VEI 2Observed
    2004-10-01 – 2008-01-27
    South of 1980-1986 lava dome
  2. 1990VEI 3Observed
    1990-11-05 – 1991-02-14
    North side of lava dome
  3. 1989VEI 2Observed
    1989-12-07 – 1990-01-06
    North side of lava dome
  4. 1980VEI 5Observed
    1980-03-27 – 1986-10-28
    Summit and north flank
  5. 1921VEI ?Geological estimate
    1921-03-18 – Ongoing
  6. 1903VEI ?Geological estimate
    1903-09-15 – Ongoing
  7. 1898VEI ?Geological estimate
    1898-04-05 – Ongoing
  8. 1857VEI 2Observed
    1857-04 – Ongoing
  9. 1854VEI 2Observed
    1854-02 – 1854-04
    North flank
  10. 1853VEI 2Observed
    1853-03-15 – 1853-08
    North flank
  11. 1850VEI 2Observed
    1850-03 – 1850-05
    North flank
  12. 1849VEI 2Geological estimate
    1849 – Ongoing
    North flank
  13. 1848VEI 2Observed
    1848-04-01 – Ongoing
  14. 1847VEI 2Observed
    1847-03-26 – 1847-03-30
    North flank (Goat Rocks)
  15. 1842VEI 3Observed
    1842-11-22 – 1845-09-18
    North flank (Goat Rocks)
  16. 1835VEI 2Observed
    1835-03 – Ongoing
    North flank (Goat Rocks area)
  17. 1831VEI 3Observed
    1831-08 – Ongoing
    North Flank (Goat Rocks area)
  18. 1800VEI 5Geological estimate
    1800-01-15 – Ongoing
    N flank--Goat Rocks area
  19. 1610 (±40 yrs)VEI ?Geological estimate
    1610 – Ongoing
    Pre-1980 summit dome
  20. 1525 (±25 yrs)VEI ?Geological estimate
    1525 – Ongoing
  21. 1482VEI 5Geological estimate
    1482-01-15 – Ongoing
  22. 1480VEI 5Geological estimate
    1480-01-15 – Ongoing
  23. 780 (±300 yrs)VEI ?Geological estimate
    780 – Ongoing
    NE flank (Sugar Bowl)
  24. 420VEI ?Geological estimate
    420 – Ongoing
  25. 270VEI ?Geological estimate
    270 – Ongoing
  26. 230VEI 0Geological estimate
    230 – Ongoing
  27. 190VEI ?Geological estimate
    190 – Ongoing
    Lower E flank (East Dome)
  28. 100VEI 0Geological estimate
    100 – Ongoing
    SW flank (Cave basalts)
  29. 100 BCEVEI ?Geological estimate
    BCE 100 – Ongoing
  30. 220 BCEVEI ?Geological estimate
    BCE 220 – Ongoing
    NNE flank (Dogs Head)
  31. 250 BCEVEI ?Geological estimate
    BCE 250 – Ongoing
  32. 280 BCEVEI ?Geological estimate
    BCE 280 – Ongoing
  33. 530 BCEVEI 5Geological estimate
    BCE 530 – Ongoing
  34. 800 BCEVEI ?Geological estimate
    BCE 800 – Ongoing
  35. 830 BCE (±75 yrs)VEI ?Geological estimate
    BCE 830 – Ongoing
  36. 1010 BCEVEI ?Geological estimate
    BCE 1010 – Ongoing
  37. 1100 BCEVEI ?Geological estimate
    BCE 1100 – Ongoing
  38. 1180 BCEVEI ?Geological estimate
    BCE 1180 – Ongoing
  39. 1610 BCEVEI ?Geological estimate
    BCE 1610 – Ongoing
  40. 1680 BCEVEI ?Geological estimate
    BCE 1680 – Ongoing
  41. 1770 BCE (±100 yrs)VEI 5Geological estimate
    BCE 1770 – Ongoing
  42. 1860 BCEVEI 6Geological estimate
    BCE 1860 – Ongoing
  43. 2100 BCE (±300 yrs)VEI ?Geological estimate
    BCE 2100 – Ongoing
  44. 2340 BCEVEI 5Geological estimate
    BCE 2340 – Ongoing

External links

⚠ For reference only. Not for emergency response.