The volcano has been eroded by glaciers, which carved a large cirque into the northeastern flank of the mountain, forming its current crater.

Some Arctic–alpine plants can be found on the volcano, including mountain hemlock, ponderosa pine, bitterbrush, and Pacific silver fir.

[7] The Western Cascades consist of highly eroded layers of volcanic rock that drain into streams fed by runoff.

These streams supply the Willamette River basin, and during the winter season the flow is increased by rain and melting snow.

[14] Black Crater sits at the northern edge of the wilderness,[15] forming part of the Alpine Crest region.

This area incorporates the northeastern third of the Three Sisters Wilderness and includes most of its major mountains as well as its most popularly visited glaciers, lakes, and meadows.

The wet climate supports rapid regeneration of vegetation, but the soil infiltration capacity is not surpassed even after fires.

[6] On June 20, 2018, a debris flow coursed down the volcano, spurred on by runoff from a storm and secondary to the Milli Fire, which burned 24,000 acres (9,700 ha) of forest land one year prior.

[21] Black Crater forms part of a chain of Pleistocene, northward-trending volcanic activity characterized by scoria cones, lava flows, and agglutinates.

[11] It is part of a group of mafic shield volcanoes in central Oregon that also includes North Sister, Mount Washington, Broken Top,[10] and Black Butte.

[11] Later, additional cinder cones formed on the volcano, including one at the southern base known as Millican Crater,[11] which erupted basalt.

It erupted a lava flow with dimensions of 1.2 by 1.9 miles (2 by 3 km), which runs south and east and has been moderately eroded by glaciers.

[34] Lava deposits from Black Crater are slightly porphyritic; they consist of sparse plagioclase and clinopyroxene and contain 55 to 57 percent silica.

[30] A fault scarp runs along the northern side of the volcano[36] to the south, corresponding to an eruption at the Matthieu Lake fissure that occurred about 15,000 years ago, independent of Black Crater.

[37] The promontory Windy Point, which is made up of basaltic andesite lava and cinder, sits at the northwestern base of Black Crater.

[38] Belknap also erupted a heavy deposit of ash and scoria that covered the area between Black Crater and Dry Creek to the north.

[41] The settlers arrived with wagons and more than 60 oxen and 700 cattle.They moved into the forested region south of Black Crater, near what is now the city of Sisters.