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The Eruptive History of Mount St. Helens

by Donal R. Mullineaux and Dwight R. Crandell


The Goat Rocks eruptive period began about A.D. 1800 with the explosive eruption of the dacitic pumice of layer T. This pumice was carried northeast-ward across Washington to northern Idaho (Okazaki and others, 1972, p. 81) and apparently was the only eruptive product of that time. Many minor explosive eruptions of the Goat Rocks period were observed by explorers, traders, and settlers from the 1830's to the mid-1850's. The Floating Island Lava Flow (andesite) was erupted before 1838 (Lawrence, 1941, p. 59) and evidently was followed by extrusion of the Goat Rocks dacite dome on the north flank of the volcano (Hoblitt and others, 1980, p. 558).

The last eruption of the Goat Rocks eruptive period was in 1857, when "volumes of dense smoke and fire" were noted (Frank Balch, quoted in Majors, 1980, p. 36). A recent study of old records has suggested that minor eruptions of Mount St. Helens also occurred in 1898, 1903, and 1921 (Majors, 1989, p. 36-41). The published descriptions of these events suggest that they were small-scale steam explosions, and none produced deposits that were recognized in our studies.

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