DESCRIPTION:
Mount Baker Thermal Activity 1975 - 1976

Eyewitness reports of small ashy plumes and active steam vents on Mount Baker dating as far back as the mid-1800's were clear evidence that the ice-covered volcano had one of the most active geothermal systems among Cascade volcanoes. When new fumaroles and unusually dark vapor plumes appeared abruptly in March 1975, however, people in the Northwest became concerned about an impeding eruption and possible avalanches and lahars from Sherman Crater, a vent just south of Mount Baker's summit. Despite a tenfold increase in the release of heat by the volcano during the next 12 months, which resulted in extensive changes to the ice cover in Sherman Crater and produced minor releases of ash, no eruption occurred. The thermal activity was not accompanied by earthquakes, which generally precede most eruptions, and since 1976, the volcano has not showed additional signs of activity.

The increased thermal activity between 1975 and 1976 prompted public officials and Puget Power to temporarily close public access to the popular Baker Lake recreation area and to lower the reservoir's water level by 10 meters. Significant avalanches of debris from the Sherman Crater area could have swept directly into the reservoir, triggering a disastrous wave that would have caused loss of life and damage to the reservoir.

... a major episode of steam activity persisted at Sherman Crater from March 1975 to early 1976. A large jet shot pressurized steam to 760 meters, new fumaroles were active, crevasses developed in the ice concentric to the crater walls, a 70-meter-wide plug of ice collapsed to form a warm water lake, and minor amounts of non-juvenile tephra were spread around the crater area.

From the time when Lassen Peak quieted until March 1980 -- (Mount St. Helens activity) -- , the only other known increase in activity at a Cascade volcano occurred at Mount Baker, when a sudden increase in emanations of heat, steam, and other gases from a previously steaming old crater began on March 10, 1975. Although new fumaroles were formed and minor amounts of "volcanic dust" and sulfur were emitted, "the greatest undesirable natural results" that were observed at Mount Baker were "an increase in local atmospheric pollution and a decrease in the quality of some local water resources" (Bortleson and others, 1977, p.B1). Since 1976, however, even those effects have subsided to levels only slightly higher than those that prevailed before 1975.

Mount Baker Volcano
-- Geographic Setting, Geologic and Eruptive History -- includes Sherman Crater, Dorr Fumarole Fields, Mount Baker's Eruptive History, etc.

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