Mount Baker - Early HistoryU.S. Geological Survey (USGS) research in the last decade shows Mount Baker to be the youngest of several volcanic centers in the area and one of the youngest volcanoes in the Cascade Range. Volcanic activity in the Mount Baker area began more than one million years ago, but many of the earliest lava and tephra deposits have been removed by glacial erosion. The pale-colored rocks northeast of the modern volcano mark the site of ancient Kulshan Caldera that collapsed after an enormous ash eruption one million years ago. Subsequently, eruptions in the Mount Baker area have produced cones and lava flows of andesite, the rock that makes up much of other Cascade Range volcanoes like Mounts Rainier, Adams, and Hood. From about 900,000 years ago to the present, numerous andesitic volcanic centers in the area have come and gone, eroded by glaciers. The largest is the Black Buttes edifice, active between 400,000 and 300,000 years ago and formerly bigger than today's Mount Baker.Today's Mount BakerModern Mount Baker formed during and since the last ice age, which ended about 15,000 years ago. Lava flows from the summit vent erupted between 30,000 and 10,000 years ago and, during the final stages of edifice construction, blocky pyroclastic flows poured down most of the volcano's drainages. An eruption 6,600 years ago produced a blanket of ash that extended more than 20 miles to the northeast. This eruption probably occurred from the presently ice-filled summit crater. Subsequently, sulfurous gases have found two pathways to the surface -- Dorr Fumaroles, northeast of the summit, and Sherman Crater, south of the summit. Both these area are sites of pervasive bedrock alteration, converting lavas to weak, white-to-yellow material rich in clays, silica, and sulfur-bearing minerals. At Sherman Crater, collapses of this weakened rock created lahars in 1843 and as recently as the 1970's.Flank Collapses, Lahars, and Tephra Eruptions, about 6,600 Years AgoA series of discrete events culminated with the largest tephra-producing eruption in post-glacial time at Mount Baker. First, the largest collapse in the history of the volcano occurred from the Roman Wall and transformed into a lahar that was over 300 feet deep in the upper reaches of the Middle Fork of the Nooksack River. It was at least 25 feet deep 30 miles downstream from the volcano and probably reached Bellingham Bay. Next, a huge hydrovolcanic explosion occurred near the site of the present day Sherman Crater, triggering a second collapse of the flank just east of the Roman Wall. That collapse also became a lahar that mainly followed the course of the first one for at least 20 miles, but also spilled into tributaries of the Baker River. Finally, an eruption cloud deposited several inches of ash as far as 20 miles downwind to the northeast.Sherman Crater Forms in 1843The present shape of Sherman Crater originated with a large hydrovolcanic explosion. In 1843, explorers reported a widespread layer of newly fallen rock fragments "like a snowfall" and the forest "on fire for miles around." Rivers south of the volcano were clogged with ash, and Native Americans reported that many salmon were killed. A short time later, two collapses of the east side of Sherman Crater produced two lahars, the first and larger of which flowed into the natural Baker Lake, rising its level at least 10 feet. The location of the 19th-century lake is now covered by waters of the modern dam-impounded Baker Lake. Similar but lower level hydrovolcanic activity at Sherman Crater continued intermittently for several decades afterwards.Flank Collapse and Lahar in 1891In 1891, about 20 million cubic yards of rock fell from the scar shown in the photo on the front page (web note: see Report) producing a lahar that traveled more than 6 miles and covered 1 square mile.Sherman Crater Heats Up in 1975, Triggering ConcernBeginning in March 1975, the rate of gas and steam emission from Sherman Crater increased significantly. Heat flow increased more than tenfold. The activity gradually declined over the next 2 years but stabilized at a higher level than before 1975. Several small lahars formed from material ejected onto the surrounding glaciers. Acidic water was discharged into Baker Lake for many months. |
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