Belknap Crater

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Belknap Crater

Belknap shield volcano with lava flows in foreground
Elevation 6,876 feet (2,096 metres)
Location Oregon, USA
Range Cascades
Coordinates 44°17′05.80″N, 121°50′32.04″W
Topo map USGS Mount Washington 44121-C7
Type Shield volcano
Easiest route hike

Belknap Crater and its distal lava tongues cover 98 square kilometres of the crest of the central High Cascades in Oregon, USA. Prior to 2,900 years before present, the first eruptive phase distributed basaltic cinders and ash over a broad area to the northeast and southeast, while basaltic lavas moved 10 km eastward from a growing shield. A second phase, 2,883 years before present (carbon-14), produced an adventive shield of basaltic andesite on the east flank, known as Little Belknap. The third phase was responsible for the bulk of the modern Belknap volcano. It was constructed by effusion of basaltic andesite lavas from the central vent (Belknap Crater), 1,495 years before present (carbon-14), and from a vent 2 km to the south (South Belknap cone), 1,775 years before present (carbon-14). The final eruptions from the northeast base of Belknap Crater sent lavas 15 km westward into the valley of the McKenzie River.

Belknap volcano is a well preserved Holocene example of the type of volcanic process responsible for construction of the Pleistocene High Cascade platform. Eruption of mafic lava and ash from a single vent area produced a broad shield with a core of cinders. Belknap is intermediate in scale between diminutive cinder cones with small lava flows such as Twin Craters or Yapoah Cone (south of Belknap) and larger composite cones on a shield base which may reach elevations of 2,500 metres, such as Mt. Washington or Three Fingered Jack (north of Belknap).

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