Mount Baker (elevation ) is an active glaciated andesitic stratovolcano in the Cascade Volcanic Arc and the Cascades of Washington State in the United States about due east of the city of Bellingham, Whatcom County, making it the northernmost volcano in the Cascades. Additionally, it is the fourth highest mountain in Washington State and the sixth highest in the Cascade Range. Located in the Mount Baker Wilderness, it is also easily visible from much of Greater Victoria, Greater Vancouver and the Fraser Valley just across the Canadian border to the north. It is also visible from the communities of Mission and Abbotsford, both about east of Vancouver, as well as from some locations in Everett and even Seattle to the southwest. Local Native Americans call the mountain "Koma Kulshan," meaning Great White Watcher. However, the explorer George Vancouver named the mountain for 3rd Lieutenant Joseph Baker of HMS Discovery, who saw it on April 30, 1792.
After Mount Rainier, Baker is the most heavily glaciated of the Cascade volcanoes: the volume of snow and ice on Mount Baker (0.43 cubic miles, 1.8 cubic kilometers) is greater than that of all the other Cascades volcanoes (except Rainier) combined. It is also one of the snowiest places in the world; in 1999, Mount Baker Ski Area, located on a subsidiary peak, set the world record for snowfall in a single season—1,140 inches (95 feet or 2,896 cm).
The British explorer George Vancouver left England a year later in 1791. His mission was to survey the northwest coast of America. Vancouver and his crew reached the Pacific Northwest coast in 1792. While anchored in Dungeness Bay on the south shore of the Strait of Juan de Fuca, third lieutenant Joseph Baker made an observation of Mount Baker which Vancouver recorded in his journal:
About this time a very high conspicuous craggy mountain ... presented itself, towering above the clouds: as low down as they allowed it to be visible it was covered with snow; and south of it, was a long ridge of very rugged snowy mountains, much less elevated, which seemed to stretch to a considerable distance ... the high distant land formed, as already observed, like detached islands, amongst which the lofty mountain, discovered in the afternoon by the third lieutenant, and in compliment to him called by me Mount Baker, rose a very conspicuous object ... apparently at a very remote distance.
Six years later the official narrative of this voyage was published, including the first printed reference to the mountain.
By the mid-1850s, Mount Baker had become a well-known feature on the horizon to the various explorers and fur traders traveling in the Puget Sound region. Isaac I. Stevens, the first governor of Washington Territory, wrote about Mount Baker in 1853:
Mount Baker ... is one of the loftiest and most conspicuous peaks of the northern Cascade range; it is nearly as high as Mount Rainier, and like that mountain, its snow-covered pyramid has the form of a sugar-loaf. It is visible from all the water and islands ... [in Puget Sound] and from the whole southeastern part of the Gulf of Georgia, and likewise from the eastern division of the Strait of Juan de Fuca. It is for this region a natural and important landmark.
For his second attempt later that same year Coleman recruited Edward Eldridge, John Bennett and John Tennant. After approaching via the North Fork of the Nooksack River, the party navigated what is now known as Coleman Glacier and ascended to within several hundred feet of the summit before turning back in the face of an "overhanging cornice of ice" and threatening weather.
Coleman returned to the mountain two years later. At 4:00 p.m. on August 17, 1868, Coleman, Eldridge, Tennant and two new companions (David Ogilvy and Thomas Stratton) gained the summit.
The present-day cone of Mount Baker is relatively young, perhaps less than 30,000 years old, but it sits atop a similar older volcanic cone called Black Buttes Volcano which was active between 500,000 and 300,000 years ago. Much of Mount Baker's earlier geological record was eroded away during the last ice age (which culminated 15,000–20,000 years ago), by thick ice sheets that filled the valleys and covered much of the region. In the last 14,000 years, the area around the mountain has been largely ice free, but the mountain itself remains heavily mantled with snow and ice.
Isolated ridges of lava and hydrothermally altered rock, especially in the area of Sherman Crater, are exposed between glaciers on the upper flanks of the volcano: the lower flanks are steep and heavily vegetated. The volcano rests on a foundation of non-volcanic rocks in a region that is largely non-volcanic in origin.
Deposits which record the last 14,000 years at Mount Baker indicate that Mount Baker has not had highly explosive eruptions like those of other volcanoes in the Cascade Volcanic Arc, such as Mount St. Helens, Mount Meager or Glacier Peak, nor has it erupted frequently. During this period only four episodes of magmatic eruptive activity can be definitively recognized. Magmatic eruptions have produced tephra, pyroclastic flows, and lava flows from summit vents and from the Schriebers Meadow cinder cone. However, the most destructive and most frequent events at Mount Baker have been lahars or debris flows and debris avalanches, many, if not most, of which were not related to magmatic activity but may have been induced by steam emissions, earthquakes, heavy rainfall, or in some other way.
Research in the 1990s 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 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.
Modern 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 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 are sites of 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 1970s.
6,600 years ago, a 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 deep in the upper reaches of the Middle Fork of the Nooksack River. It was at least deep 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 , but also spilled into tributaries of the Baker River. Finally, an eruption cloud deposited several inches of ash as far as downwind to the northeast.
Historical activity at Mount Baker includes several explosions during the mid-19th century, which were witnessed from the Bellingham area, and numerous small-volume debris avalanches since the late 1950s. A possible eruption was seen in June of 1792 during the Spanish expedition of Dionisio Alcalá Galiano and Cayetano Valdés. Their report read, in part:
During the night [while anchored in Bellingham Bay] we constantly saw light to the south and east of the mountain of Carmelo [Baker] and even at times some bursts of flame, signs which left no doubt that there are volcanoes with strong eruptions in those mountains.
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 . 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.
In 1891, about of rock fell producing a lahar that traveled more than and covered .
In early March, 1975, a sudden and dramatic increase in fumarolic activity and snow melt in the Sherman Crater area caused concern that an eruption might be imminent. Heat flow increased more than tenfold. Additional monitoring equipment was installed and several geophysical surveys were conducted to try to detect the movement of magma. The increased thermal activity 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. However, few anomalies other than the increased heat flow were recorded during the geophysical surveys, nor were any other precursory activities observed to indicate that magma was moving up into the volcano. Several small lahars formed from material ejected onto the surrounding glaciers and acidic water was discharged into Baker Lake for many months.
The activity gradually declined over the next two years but stabilized at a higher level than before 1975. The increased level of fumarolic activity has continued at Mount Baker from 1975 to the present, but there are no other changes that suggest that magma movement is involved.
There are 10 main glaciers on the mountain. The Coleman Glacier is the largest with a surface area of 5.2 km². The other large glaciers, with areas greater than 2.5 km², are Roosevelt Glacier, Mazama Glacier, Park Glacier, Boulder Glacier, Easton Glacier and Deming Glacier. All retreated during the first half of the century, advanced from 1950–1975 and have been retreating increasingly rapidly since 1980.
Mount Baker is drained on the north by streams flowing into the North Fork Nooksack River, on the west by the Middle Fork Nooksack River, and on the southeast and east by tributaries of the Baker River.