Mount Baker - 140,000 years ago to present
Mount Baker visually dominates the volcanic field today, but rocks from earlier volcanoes make up most of its foundation. Eruptions that formed Mount Baker account for no more than 10% of the eruptive volume of the entire volcanic field.
Mount Baker itself edifice consists mostly of lava flows (as many as 200), and scattered evidence indicates that some of its products were broken up and carried away by glaciers. It is likely that eruptive activity began around 140 ka at Mount Baker, which was likely followed by a time gap until a major interval of cone growth started about 30-40 ka. Most of the upper cone is younger than approximately 20 ka, and its last period of major activity occurred at the close of the most recent glacial period, approximately 12 ka. Only a single eruption involving magma has been documented for the Holocene – an outburst of andesitic ash at approximately 6.7 ka.
There are two craters on Mount Baker. Carmelo Crater, at the summit, is 400 m (1300 ft) wide and breached to the north by the uppermost part of Roosevelt Glacier. At least 84 m (275 ft) fill this summit crater. Sherman Crater is on the southern slope of Mount Baker and is located 400 m (1300 ft) lower than, and 800 m (2600 ft) south of the summit. Most hydrothermal activity at Mount Baker is concentrated within Sherman Crater; although the smaller Dorr Fumarole Field exists about 2 km (1.2 mi) north of the summit. Numerous fumaroles on Sherman Crater's walls and floor, produces sulfur-rich vapor, which is always present, but during cold and windless days the plume often condense to form a dramatic steam plume above the volcano. No summit-erupted material drapes into Sherman Crater, indicating that the crater's formation occurred after the last summit activity.
The most recent lava flow eruptions at Mount Baker were a series about 12.7 ka that built a southeastern and northwestern fan of lava plus associated pyroclastic and debris flows. Since that time, only two eruptive episodes involving magma have occurred:1) The Schreibers Meadow cinder cone formed during a single eruption south of Mount Baker about 9.8 ka. This eruption produced basaltic to andesitic tephra and lava flows. The vent is marked by a 70-m-high spatter cone, and lava flowed down both Rock and Sulphur Creeks. The lava flow covers an area of about 24km2 and is the largest lava flow in the Cascade Range north of the Big Lava Bed basalt flow between Mount St. Helens and Mount Adams in southern Washington. The lava flowed on top of the scoria and ash from the cinder cone and, in turn, is overlain by the 9.6 ka Shreibers Meadow lahar.
(2) A sub-Plinian andesitic eruption from Sherman Crater occurred approximately 6.7 ka and distributed tephra up to 66 km (41 mi) from Mount Baker. The eruption was preceded by two debris avalanches, as the flanks of the volcano collapsed. One went west causing lahars to travel down the Middle Fork Nooksack River, while the other went east into Baker River valley where it dammed the river to form Baker Lake. The sub-Plinian eruption began as a large steam-driven, hydrothermal, explosion, which was directly followed by a regional tephra fall. To date, this is the only known eruption involving magma from Sherman Crater.
A steam-driven blast occurred from Sherman Crater in 1843, which produced a widely dispersed tephra fall that was composed of recycled crater rocks. This eruption was the start of a period of additional hydrothermal eruptions that lasted until the 1880s. This period also included numerous small to moderate flank collapses from the Sherman Crater area, including one within a year or two of 1843 that developed into a lahar that inundated the Baker River valley.
As with much of the post-glacial history at Mount Baker, recent history has included many debris avalanches that turn into lahars, as well as other events that produce smaller lahars. Such events are common and happen at Mount Baker, as at many other Cascade volcano, on a decade or so basis.