Origin and age of postglacial deposits and assessment of potential hazards from future eruptions of Mount Baker, Washington

Eruptions and other geologic processes at Mount Baker during the last 10,000 years have repeatedly affected adjacent areas, and especially the valleys that head at the volcano. Most mudflows from the volcano were caused by massive avalanches of volcanic rock that had been partly altered to clay by steam and other gases. Future mudflows like these could move down valleys for distances of tens of kilometres. Floods caused by rapid melting of snow and ice by lava flows or hot rock debris could affect valley floors far from the volcano, especially if they occurred at a time of high stream discharge due to other causes. Small amounts of tephra (airborne rock debris) have been erupted at least four times during the last 10,000 years. Eruptions like these in the future probably would not seriously endanger human life except within a distance of perhaps a few kilometres of the vent. Lava flows have been erupted at least twice during the last 10,000 years, but have moved down only two valleys. Future lava flows will not directly endanger people because movement typically is so slow that escape is possible. Eruptions which caused pyroclastic flows (flows of hot rock debris) evidently occurred during only one period, and the flows were restricted to only one valley. Pyroclastic flows seriously endanger human life in areas they affect. Such flows move at speeds of as much as 100 km/hr and can bury valley floors under tens of metres of hot rock debris to distances of as much as 15 km from the volcano.