Black Butte (Oregon)

Black Butte is an extinct stratovolcano in the U.S. state of Oregon. Located in Jefferson County, it is part of Deschutes National Forest. Black Butte forms part of the Cascade volcanic arc. The butte lies just south of the Metolius Springs, which merge to form the headwaters of the Metolius River. The Metolius River's basin sustains a wide array of plant life, large and small mammals, and more than 80 bird species.

Black Butte last erupted during the Pleistocene; geologists have estimated its age at 0.4, 0.5, and 1.43 ± 0.33 million years ago. The duration of the eruptions that built the volcano remains unclear, though the activity likely coincided with large-scale block faulting in the vicinity of the Metolius Springs. Black Butte has a prominent volcanic cone and is made up of mafic (rich in magnesium and iron) basaltic andesite lava. Despite having a well-preserved, symmetrical shape and an unexposed pyroclastic core, the butte has undergone moderate erosion, with shallow ravine on its sides, and rocks with weathering rinds. A number of cinder cones and a volcanic field also lie nearby the butte.

There was a fire lookout ground house on the butte, which was burned down by the United States Forest Service in 2016. A white cupola structure sits on the top of the butte as well as a more modern fire lookout tower. The resort community Black Butte Ranch lies nearby and offers recreational activities like horseback riding, biking, hiking, canoeing, kayaking, and paddleboarding; during the winter, activities include Nordic skiing and snowshoeing.

Geography

Black Butte lies about to the southeast of Mount Jefferson and about northwest of the junction of U.S. Route 126 and U.S. Route 20, at the eastern edge of the city of Sisters. The butte is part of Jefferson County in the U.S. state of Oregon. Other volcanoes such as Three Fingered Jack and Mount Washington lie about to the west.

According to the U.S. National Geodetic Survey and scientists from the United States Geological Survey, Black Butte has an elevation of ; the Geographic Names Information System database lists its elevation as , while ''Oregon Geographic Names'' lists its elevation at . The butte has proximal and draping reliefs of and , which are the "difference between summit elevation and that of highest exposure of older rocks overlain by the edifice" and the "difference between summit elevation and that of lowest distal lavas of the edifice (not including distal pyroclastic or debris flows)," respectively. According to E. M. Taylor, Black Butte has a diameter of .

The U.S. National Geodetic Survey report describes Black Butte as a "very prominent" mountain; it is an imposing feature and landmark in the Deschutes Valley because of its dark color and symmetry. Part of the Cascade volcanic arc in the northwestern United States, it lies within a rain shadow about to the east of the major mountain range. In the High Cascades, the equilibrium line altitudes for valley glaciers follow a gradient of about , which is significantly steeper than the gradient for the Western Cascades. Moving east, precipitation decreases across the Cascade arc; the gradient is even steeper east of the major crest at Black Butte, where the gradient is more than . W. E. Scott argues that the volcano displays no evidence of glaciation.

Black Butte lies just south of the Metolius Springs, which lie in the southwestern corner of Jefferson County. Accessible by roads branching off U.S. Route 20, the springs are located about northwest of the cities of Bend and Redmond. Black Butte rises above the surrounding Metolius Valley, which has a width of about and an elevation above sea level of . At the volcano's northern base lie two openings spaced about apart, which give rise to the Metolius Springs. Bubbling out at a temperature of , the springs merge to form the headwaters of the Metolius River, generating a total flow of over the course of each year. The river runs for to the north and east before reaching the Deschutes River, picking up along the way from other springs and tributaries along the eastern Cascade Range. As glaciers advanced and retreated and snow fields formed over time, they caused erosion, which was carried by streams associated with the Metolius River to spread across the river valley's floor.

The last of these glaciers existed until about 10,000 years ago, with their end points marked hummocks of debris. The glaciers formed glacial troughs, deposited moraines, and moved sand and gravel along with volcanic ash and cinders to cover the Metolius Valley floor. Black Butte lies about east–southeast of Suttle Lake, which occupies one of the local glacial troughs.

Eruptions from Black Butte buried the ancestral Metolius River and left boulders of lava in the area, and Black Butte's formation dammed drainages for the Metolius, dividing the Metolius Valley into the northern segment where the river now runs and a southern portion that includes Black Butte Swamp, Glaze Meadow, and Indian Ford Creek. Black Butte Swamp and Glaze Meadow were likely formerly shallow lakes, though they now serve as sumps for streams and drainages from the Cascades, which are located to the southwest. Black Butte Swamp is a particularly important sump for extensive drainage from the southwest, its basin water lapping against Black Butte's southern base. Because it is elevated about above the Metolius Springs, the swamp acts as a hydraulic head for the spring water keeping the flow of the springs constant, and ensuring that there is a net influx of water into the swamp. Any excess water exits through Indian Ford Creek to flow east then south past the city of Sisters. In modern times, the Metolius Valley consists of glacial outwash, lava strata, and stream sediment, which together act as a sponge for snow and rain water percolating into the river basin.

Ecology

Black Butte lies east of the major crest of the Cascades, which is more arid compared to the Western Cascades. Two forest populations at Black Butte were analyzed in a 1975 study conducted by D. B. Zobel of Oregon State University. These forest areas included ponderosa pine and tree species intermediate to grand and white firs. The study found that trees at Black Butte did not experience significant moisture stress and that photosynthesis rates during dry summer seasons were more reduced at tree sites in the Western Cascades compared to at Black Butte. Black Butte was found to have a shorter growing season and less favorable winter temperatures for photosynthesis at its forest sites than study areas in the Western Cascade Province. Along the trail that runs up Black Butte, the forest is diverse, with yellow-bellied ponderosa pines, mixed conifers, and subalpine vegetation.

Black Butte is part of the Deschutes National Forest, which covers close to in central Oregon. It is also part of the Metolius Black Butte Scenic area within the Metolius Conservation Area, which encompasses about and includes suitable habitat for northern goshawks. The Metolius River passes through old-growth forests of ponderosa pine, as well as forests of Douglas fir and western larch. Every May native plants and wildflowers appear, including early blue violets, larkspur, serviceberry, Sitka valerian, and western buttercups. During the summer season, river trails more prominently display plant species like arrowleaf balsamroot, American brooklime, bigleaf lupine, Douglas's spirea, Indian paintbrush, and monkeyflower plants. On islands in the river, wildflowers occasionally grow after their seeds bloom after falling into the water and accumulating over time. The area is noted for a rare species of Penstemon known as ''Penstemon peckii'', a wildflower that appears in 7 different colors, which is endemic to the Sisters area. Other plants within the Metolius Preserve include incense cedar trees, nutka rose, ocean spray, snowberry, and vine maple trees.

More than 80 species of bird inhabit the Metolius Preserve area such as the white-headed woodpecker. The area supports large mammals like American black bears, badgers, bobcats, beavers, deer, cougars, elk, and otters, as well as smaller mammals like northern flying squirrels, shrews, and voles.

Geology

In the Oregon segment of the Cascade Volcanoes that runs for south of Mount Hood, there are at least 1,054 Quaternary volcanoes, which form a volcanic belt in width. This volcanic belt extends up to to the north of the border with California, where Quaternary volcanic activity is interrupted by a gap up to the Quaternary volcanoes near Mount Shasta. The Quaternary volcanoes within the Oregon Cascades are extremely dense, concentrated within an area of about . Rocks within the Metolius Springs area form part of the High Cascades province and include both volcanic and glaciofluvial deposits.

Black Butte marks the edge of the Sisters fault zone, which includes about 50 known faults that extend southeast through the cities of Sisters and Bend. In total, the Sisters fault zone runs for in length, with its width varying between . Black Butte itself sits on a small fault that straddles the graben, and its lava deposits have been displaced slightly by a fault on the northwestern side of the volcano. To the north lies the Green Ridge fault scarp, which trends to north and rises about above the Metolius Valley. The fault's steep escarpment contains exposed, alternating layers of basaltic andesite, breccia, and agglomerate from shield volcanoes, which mark the oldest rocks in the area. They are of Pliocene, pumice, and tuffaceous sandstone layers.

Most of the volcanoes in the Oregon Cascades are either scoria cones, small shield volcanoes, or lava fields, though the segment contains a number of basaltic andesite stratovolcanoes such as Mount McLoughlin. Black Butte is one such stratovolcano (also known as a composite volcano), with a mafic (rich in magnesium and iron) composition. It is an extinct volcano.

Also composed of basaltic andesite, the cone rises over the surrounding plateau. Black Butte is a striking feature just north of US Highway 20, which descends from the east flank of the Cascades. It is nearly symmetrical with a youthful profile, though it is actually older than any other visible High Cascades volcano. Black Butte is well-preserved due to a lack of glaciation east of the major Cascade arc. Black Butte has undergone mild erosion, with shallow ravine

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