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Online Library

Mount St. Helens - Summary of Volcanic History

The following summary table is provided as a courtesy by the U.S. Geological Survey, Cascades Volcano Observatory, Vancouver, Washington. We duplicated the table here to assist teachers, educators and students in developing their educational programs as part of the Mount St. Helens National Volcanic Monument Teacher's Corner.

If you use any of the material on this page, please credit the U.S. Geological Survey, Cascades Volcano Observatory, Vancouver, Washington. We thank them for their support of the Teacher's Corner.


Mount St. Helens -
Summary of Volcanic History

-- Excerpt modified from: Doukas, 1990, U.S.Geological Survey Bulletin 18591 unless subscripted otherwise.
(Eruptive stages and periods are separated by dormant intervals for which no unequivocal volcanic products have been recognized. Years before 1980 are based on tree-ring dates (Yamaguchi, 1983), Carbon14 ages, and (or) historical records. A.D. dates during the Goat Rocks and Kalama eruptive periods from Yamaguchi (1983, 1985). All tephras consist of multiple layers not subdivided further here; only the thickest layers of W, B, and Y tephras are distinguished. After Crandell and others (1981), Mullineaux and Crandell (1981), and Crandell (1988))1

Eruptive stages and periods

Eruptive products

Spirit Lake
Eruptive Stage
Modern eruptive period Began 1980
  • Avalanche
  • Lateral blast
  • Blast deposita
  • Lahars
  • Pyroclastic flows
  • Tephra
  • Domes (dacitic)
Goat Rocks eruptive period 150-100 years B.P.
  • Dome (dacitic)
  • Lava flows (andesitic)
  • 19th Century Lithic Ash - 1842(?)2
A.D. 1800
  • T tephra (dacitic)
Kalama eruptive period 500-338 years B.P.
  • Pyroclastic flows (dacitic, andesitic)
A.D. 1647?
  • Summit dome (dacitic)
  • Lahars from summit
  • Lava flows (andesitic)
  • X tephra (andesitic)
A.D. 1482
  • We tephra
A.D. 1480
  • Wn tephra
Sugar Bowl eruptive period 1,200 years B.P.
  • Dome (dacitic) -- Northeast flank of volcano
  • Pyroclastic flows (dacitic)
  • Deposits of lateral blast (dacitic)
  • D tephra2
Castle Creek eruptive period

(first appearance of mafic magma at the surface, which initiated the modern Mount St. Helens)2

2,500-1,600 years B.P.
  • Bu tephra (basaltic)
  • Bi tephra (dacitic)
  • Bo tephra (andesitic)
  • Bh tephra (andesitic)
  • Lava flows (basaltic)
  • Pyroclastic flows (dacitic, andesitic)
Pine Creek eruptive period 3,000-2,500 years B.P.
  • P tephra (dacitic)
  • Pyroclastic flows (dacitic)
  • Domes (dacitic)
  • Lahars
Smith Creek eruptive period 4,000-2,200 years B.P.
  • Ye tephra (dacitic)
  • Pyroclastic flows (dacitic)
  • Yn tephra (dacitic)
A dormant period of more than 6,000 years2 (10,500 - 4,000 years ago)
Swift Creek eruptive stage 13,700-9,200 years B.P.1
(between about 13,000 and 10,500 years ago)2
  • J tephra (dacitic)
  • Pyroclastic flows (dacitic)
  • Lahars
  • Domes (dacitic)
  • S tephra (dacitic)
Mostly dormant interval of about 5,000 years2
Fraser Glaciation - ended approximately 13,000 years B.P.
Cougar eruptive stage 20,400-19,200 years B.P.1
(began about 20,500 years ago, lasted only 2,000-3,000 years)2
  • K tephra (dacitic)
  • Pyroclastic flows (dacitic)
  • Domes (dacitic)
  • Avalanche
  • Lava flows (andesitic)
  • M tephra (dacitic)
Mostly dormant interval of about 15,000 years2
Ape Canyon eruptive stage approximately 40,000?-25,000 years B.P.
  • C tephra (dacitic)
  • Pyroclastic flows (dacitic)
  • Lahars
a The term "blast deposit" is here used to designate a deposit resulting from any process initiated by the lateral explosion. Precise transport and deposition mechanisms are controversial (Walker and McBroome, 1983; Hoblitt and Miller, 1984; Waitt, 1984a; Walker and Morgan, 1984)

1 -- Michael P. Doukas, 1990, Road Guide to Volcanic Deposits of Mount St. Helens and Vicinity, Washington: U.S.Geological Survey Bulletin 1859, 53p.

2 -- Donal R. Mullineaux, 1996, Pre-1980 Tephra-Fall Deposits Erupted From Mount St. Helens, Washington: USGS Professional Paper 1563.

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