Орегон штатындағы Белькнэп кратері

Shield volcano in the U. S. state of Oregon

Belknap Crater is a shield volcano in the Cascade Range in the U. S. state of Oregon. Located in Linn County, it is associated with lava fields and numerous subfeatures including the Little Belknap and South Belknap volcanic cones. It lies north of McKenzie Pass and forms part of the Mount Washington Wilderness. Belknap is not forested and most of its lava flows are not vegetated, though there is some wildlife in the area around the volcano, as well as a number of tree molds formed by its eruptive activity. Belknap was named for J. H. Belknap, whose father R. S. Belknap developed Belknap Springs. Early routes through the area extended near Belknap and its lava fields, and in the early 20th century, herds of sheep were moved to the two steptoes that lie among the Little Belknap lava flows to graze. The Oregon Skyline Trail, which runs to the west of Belknap's lava flows, follows paths used by Native American populations, who harvested huckleberries in the area. Today, there are a number of trails that run near Belknap, including ones that extend to Little Belknap and Belknap Crater. Belknap can be seen by tourists at the Dee Wright Observatory, which was built in part with lava blocks from Belknap Crater. A precise determination for Belknap's age has not been made, as its early history remains obscure. Belknap has likely been built up by eruptive activity over a long period of time. Belknap Crater has had four Holocene eruptive periods confirmed by geological evidence. In total, the Belknap shield and its multiple vents were formed in less than 1,500 years, its last eruptive episode finishing about 1,500 years ago. Belknap formed on the lower slopes of Mount Washington, a highly eroded volcano, and is one of the larger mafic (rich in magnesium and iron) volcanoes in the Sisters Reach. Belknap consists of a shield volcano and pyroclastic cone and consists of basaltic and basaltic andesite lava with sub alkaline composition, and it is characteristic of High Cascade volcanism. Well preserved, its core is made of cinder materials; its eruptive deposits have well preserved pressure ridges (tumuli) and levees. There are a number of subfeatures including the Inaccessible Cones, Little Belknap, South Belknap, and Twin Craters, as well as the Belknap hot springs. Postglacial, mafic eruptions are more common in the Sisters Reach — which includes Belknap — than anywhere in the Cascade volcanic arc. However, the Volcano Hazards Program of the United States Geological Survey considers it unlikely that Belknap will erupt again soon.

Belknap Crater lies to the north of the Three Sisters, in the U. S. state of Oregon. Located within Linn County, L. A. McArthur and L. L. McArthur (1984) described Belknap as "one of the important features of the Cascade Range." It lies to the north of McKenzie Pass and can be seen from McKenzie Highway. Hildreth (2007) lists Belknap Crater's summit elevation at McArthur and McArthur (1984) list its elevation at 6877 feet (2096 m), while according to the U. S. National Geodetic Survey, Belknap reaches an elevation of 6876 feet (2096 m), and has a "bald" appearance. Belknap itself is not forested and its lava flows are generally not vegetated, though there were trees growing on its lava flow deposits in the 1960s according to Taylor (1965). He observed only sparse growth of trees on lava flows from Little Belknap in a report published in the 1980s, noting that soil from Belknap was about 3 feet (1 m) thick and made up of lapilli and volcanic ash, which came mostly from Belknap Crater. Along the trail to Little Belknap Crater, there is a tree island with lodgepole pine, mountain hemlock, and true fir. There are also ground squirrels running around on lava flows from Belknap. Along the Oregon Skyline Trail, which passes west of Belknap, there are black tailed and mule deer as well as lakes stocked with Eastern brook trout

Along the western flows produced by Belknap, there are several dozen tree molds, which range from in diameter and in depth. Some fell into the lava, forming hemi cylinder shaped trenches up to 35 feet (11 m) in length. Taylor (1965) identified a system of radial roots that were charred from the lava under soil at one of the molds. The material underwent radiocarbon dating to determine an age of 360 ± 160 years A. D.

Postglacial, mafic eruptions are more common in the Sisters Reach — which includes Belknap — than anywhere in the Cascade volcanic arc. A lava flow lies next to South Cinder Peak, the Nash Crater–Lost Lake cone cluster, Sand Mountain Volcanic Field, Inaccessible Cone chain, Blue Lake Crater, and a number of monogenetic scoria cones and chains. The McKenzie and Santiam Pass area saw more than a dozen distinct mafic eruptions between 4,500 and 1,100 years ago according to radiocarbon dating, which corresponded to a pulse of mafic eruptions in the late Holocene epoch. Other nearby mafic eruptive units occur at Sims Butte, Cayuse Crater, LeConte Crater, Mount Bachelor, the Egan Cone cluster, and the Katsuk Talapus chain, which likely were all emplaced between 18,000 and 8,000 years ago. At the south of Sisters Reach, there is a postglacial, basalt lava flow that lies on the eastern flank of Sitkum Butte (a cone that is older than this lava flow). The recent eruptive activity at Belknap Crater means that it is one of the youngest mafic volcanoes in the Oregon Cascades. There are about 6,500 people living within of Belknap Crater, with a population of about 362,000 within However, most eruption hazards from basaltic volcanoes are generally restricted to within of the vent, with some exceptions. According to the Volcano Hazards Program of the United States Geological Survey's Cascades Volcano Observatory, the threat potential from Belknap is "Low/Very Low". It does not seem likely that Belknap Crater will erupt again, though eruptions with similar characteristics to its past eruptions might occur in the surrounding area, disrupting transportation on major highways in the vicinity including U. S. Route 20, Oregon Route 22, and Oregon Route 242. The eruption of tephra could pose a threat to surrounding communities, particularly within central Oregon to the east. High volume lahars (mudflows or debris flows composed of a mix of pyroclastic material, rocky debris, and water) would travel far to the west. Moreover, low volume lahars from eruptions would likely enter the McKenzie River valley, which is broad and fairly gently sloped, where they might move downstream through flood plains or small channels. Near Belknap Springs and McKenzie Bridge, deposits from the eruption could also block off water upstream, leading to downstream lahars and floods.

Belknap was named for J. H. Belknap, who lived along the McKenzie River and was the son of R. S. Belknap, responsible for developing Belknap Springs. J. H. Belknap had an interest in the toll road constructed over McKenzie Pass during the early 1870s. The Belknap family came to the state of Oregon in 1847 with the Orem family, followed by G. Belknap and J. Belknap in 1848. The Belknap Springs in Lane County were found by R. S. Belknap in November 1869 and developed them, and he became the postmaster for the Salt Springs post office, which was established in October 1874. The name for the Salt Springs office changed to Belknaps Springs in June 1875, then Belknap Springs in 1891. During the days of the American pioneer, the Santiam and McKenzie passes were the two major routes through the Deschutes Forest area, eventually transforming into highways for Oregon's interior. The Willamette Pass to the south was used as a route by travelers as early as 1853, noting its difficult as the "route was far from a road." Still, the road was heavily used in spite of its poor conditions, later becoming the Willamette Pass Highway, better known as Oregon Route 58. In 1862, the Scott brothers and colleagues formed the McKenzie Fork Wagon Road Company to create a better road passing over lava fields in the area, then later the McKenzie River Wagon Road Company, which had as its objective a road that crossed the Cascade Range near the Three Sisters volcano complex at the Deschutes River. A third group followed that aimed to forge a road across the Deschutes north of the Sisters. The original route pursued by the Scott brothers reached the Belknap hot springs. In the early 20th century, herds of sheep were moved to the two steptoes that lie among the Little Belknap lava flows to graze. The Oregon Skyline Trail, which runs to the west of Belknap's lava flows, follows paths used by Native American populations, who harvested huckleberries in the area.

The Dee Wright Observatory was built with lava blocks from the lava fields produced by Belknap, Yapoah cinder cone, and other volcanoes. It offers views of local volcanoes; Belknap lies to the north. Both Belknap Crater and Little Belknap Crater can be reached from spurs of the Pacific Crest Trail. The round trip from intersection of the Pacific Crest Trail and Oregon Route 242 to Little Belknap Crater is about 5.6 mile (9 km) and ranges in elevation from , with an easy to moderate difficulty level. The round trip to Belknap Crater is about 6.8 mile (11 km) from the trailhead and is more difficult owing to the steep climb to the summit on fine cinders. The trail offers views of nearby Mount Washington, Black Crater, and the Three Sisters, as well as lava features. Trees and other forms of wildlife are rare along the trail. There is also a trail that extends to Belknap Crater, which runs about 6.8 mile (11 km) round trip, with an intermediate difficulty level. It can also be skied. The Oregon Skyline Trail, part of which runs for 38 mile (61 km) through the Deschutes National Forest, passes westward of the Belknap lava fields. It has been recognized as a major scenic route since 1920.