Figure A1. Mount Baker Mount Baker forms a prominent landmark visible from much of southwestern British Columbia. The peak of the 3285 m high stratovolcano is often shrouded in clouds, but on a clear day, steam can be seen rising above Sherman Crater, which is just out of view to the right of the summit in this photograph. (Photograph by C.J. Hickson (Geological Survey of Canada)) larger image [JPEG, 21.0 kb, 400 X 264]

Mount Baker is a large, active, andesitic stratovolcano, rising to an elevation of 3285 m in the Cascade Range of northern Washington State (Figure A1). Its summit is approximately 100 km southeast of downtown Vancouver, British Columbia, 30 km south of the Canada-United States border, and 50 km due south of Chilliwack, British Columbia. It is visible on clear days from high points throughout this part of southwestern British Columbia.

Mount Baker is the largest volcanic complex in the northern part of the Cascade volcanic arc. Its volume is estimated at 72 km³ and it supports one of the largest geothermal fields in the Cascade Range. The geothermal field found near the summit in the 450 m wide Sherman Crater periodically produces clouds of steam from hot springs and fumaroles (Figure A2). On clear still days, the steam is prominently visible (Figure B).

Figure B. Mount Baker The steam plume of Mt. Baker on Sunday, February 11, 2001 from Vancouver B.C., which was featured widely in local news reports. The fumaroles of Sherman Crater, near the summit of Mt. Baker, produce steam constantly but it is only clearly visible on days when it is not obscured by clouds or disrupted by wind, such as this cold, clear, still winter day. The result is that people get the incorrect impression that Mt. Baker suddenly has pulses of activity. Mt. Baker is closely monitored by the U.S. Geological Survey and an emergency plan in the event of an eruption has recently been released. However Mt. Baker shows little seismic activity, for example on the day of this photograph there were no earthquakes, even exceedingly tiny ones, anywhere near it. An eruption of Mt. Baker would pose a significant threat to the Lower Mainland region due to ash fall and possibly from mudflows since one of Baker's drainages enters the Fraser River valley.

Figure A2. Sherman Crater, Mount Baker Snow shrouds the summit and much of the flanks of Mount Baker, but here, in the 450 m wide Sherman Crater, steam has melted through the ice, forming the 10 m wide hole along the west side of the crater. Steam also emanates from the steep back wall of the crater that leads to the summit. (Photograph by C.J. Hickson (Geological Survey of Canada)) larger image [JPEG, 26.6 kb, 400 X 260]

Remnants of two older volcanoes underlie the existing cone. The oldest is a caldera complex measuring 5 km by 8 km. This caldera, referred to as 'Kulshan caldera', is comparable in size to Crater Lake. Overlying it is an approximately 400,000-year-old dacitic to basaltic volcano, Black Buttes, that has been largely destroyed by erosion. The existing cone was formed before the last major glaciation in North America (25,000-10,000 years ago) and consists of interlayered, andesitic lava flows and breccia. Holocene activity (younger than 10,000 years old) at Mount Baker included pyroclastic flows, lava flows, and the eruption of tephra from Sherman Crater. Tephra, as well as at least one lava flow, was also expelled from a vent near the south base of the mountain at Schriebers Meadow. Increased hydrothermal activity, starting in March 1975 and tapering off in 1977, prompted a number of scientific studies to investigate the reason for the increased steam emissions. The United States Geological Survey is currently carrying out detailed geological investigations. The United States Geological Survey is currently carrying out detailed geological investigations, and after working with the Geological Survey of Canada and both U.S. and Canadian emergency management agencies, has released a Coordination Plan for Mt. Baker and Glacier Peak volcanoes.

Mount Baker's next major eruption is most likely to send a column of ash several kilometres into the atmosphere and erupt viscous lava flows. Neither of these events constitute a significant hazard. However, because the mountain is capped by an estimated 2 km³ of glacial ice and snow, even minor eruptions could generate significant mudflows and floods. Depending on which valley these floods descended, cities in the eastern Fraser River valley (such as low-lying parts of Abbotsford) could be flooded. In addition, because the volcano is almost directly under flight paths into and out of Vancouver, British Columbia, even minor eruptions of ash constitute a significant hazard to aviation in southwestern Canada.

Larger, more devastating eruptions are known from Mount Baker's past. If the style of future eruptions at Mount Baker were to change from the smaller eruptions that have occurred over the past few hundred years, any future eruption could have a far more significant impact on southwestern British Columbia. An emergency preparedness exercise in January 1997 tested the ability of government and inhabitants of the Fraser River valley to cope with a significant volcanic event resulting from an eruption of Mount Baker. The exercise, referred to as 'Thunderbird 3', was run by the British Columbia provincial government in collaboration with other levels of government. Emergency preparedness personnel in communities in the Fraser River valley were asked to cope with significant accumulations of ash and with flooding of many low-lying parts of the valley. Exercises such as Thunderbird 3 are crucial for developing volcanic-hazard safety awareness and action plans in communities likely to be affected by future volcanic eruptions.

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