Mount Baker is the northernmost and most isolated of the Cascade volcanoes in the USA. The andesitic cone rises nearly 2 kilometers above the older metamorphic and sedimentary rocks at its base and it is almost completely covered by glaciers -- hence its original Nooksack Indian name "White Steep Mountain".
After Mount Ranier, it is the most heavily glaciated of the Cascade volcanoes: the volume of snow and ice on Mount Baker (about 1.8 cubic kilometers; 0.43 cubic miles) is greater than that of all the other Cascades volcanoes (except Rainier) combined.
Mount Baker's summit crater is covered by snow and ice, and little is known of its nature or age. A prominent crater partly filled with ice, known as Sherman Crater, is 350 meters lower than, and about 800 meters south of, the summit. Its east rim, above the head of Boulder Glacier, is breached by a notch about 150 meters deep. Another low point, about 100 meters deep, is on the southwest rim above Deming Glacier.
The present day cone is relatively young, perhaps less than 30,000 years old, but it sits atop a similar older volcanic cone called Black Buttes volcano that was active between 500,000 and 300,000 years ago. Much of Mount Baker's earlier geologic 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.
Mount Baker is an active volcano. There are various accounts of activity at Mount Baker in the mid-1800's. An 1843 eruption resulted in a major fish kill in the Baker River, a large forest fire, and a dusting of volcanic ash over the adjacent countryside. Further eruptions occurred in the 1850's and the first expedition to Sherman Crater in 1868 reported active fumarole fields. Steam activity continued at Sherman Crater and at the Dorr fumarole field on Baker's north flank until the 1940's and 1950's, by which time steaming was uncommon. After resumption of mild activity in the 1960's, a major episode of steam activity persisted at Sherman Crater from March 1975 to early 1976. A large jet shot pressurized steam to 760 meters, new fumaroles were active, crevasses developed in the ice concentric to the crater walls, a 70-meter-wide plug of ice collapsed to form a warm water lake, and minor amounts of non-juvenile tephra were spread around the crater area.
Mount Baker's most recent activity, in the mid-1800's, was at a time when permanent populations around its base were few and infrastructures, such as roads, powerlines and other structures, were virtually non-existent. Although most of the area adjacent to Mount Baker is still largely unpopulated (much of the mountain is in the Mt.Baker-Snoqualmie National Forest), population patterns and infrastructure are much different than 150 years ago, and each year greater and greater numbers of people live and play in areas that could be affected by future volcanic activity.