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Belknap Crater and its distal lava tongues cover 98 square kilometers of the crest of the central High Cascades in Oregon, USA. Prior to 2,900 years before present, the first eruptive phase distributed basaltBasalt is an extrusive igneous rock, sometimes porphyritic, and is often both fine-grained and dense. Basalt in the tops of subaerial lava flows and cinders will often be highly vesiculated, imparting a lightweight "frothy" texture to the rock. The term bic cinders and ash over a broad area to the northeast and southeast, while basaltic lavas moved 10 kilometers eastward from a growing shield. A second phase, 2,883 years before present (carbon-14), produced an adventive shield of basaltic andesiteAndesite is an igneous, volcanic ( extrusive) rock, of intermediate composition, with aphanitic to porphyritic texture. Mineral assembly is usually quartz and plagioclase. Biotite, hornblende and pyroxene are common accessory minerals. Alkali feldspar is 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 kilometers 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 kilometers westward into the valley of the McKenzie River.

Belknap volcano is a well preserved HoloceneThe Holocene Epoch is a geologic period that extends from the present back about 10,000 radiocarbon years. The beginning of the Holocene was punctuated by the Younger Dryas cold period, the final part of Pleistocene epoch. The end of the Younger Dryas has example of the type of volcanic process responsible for construction of the PleistoceneThe Pleistocene epoch is part of the geologic timescale, usually dated as 1. 6 million to 10,000 years before present, with the end date expressed in radiocarbon years. It covers most of the latest period of repeated glaciation, up to and including the Yo High Cascade platform. Eruption of maficMafic is a term used in geology for silicate minerals, magmas, volcanic, and intrusive igneous rocks that have relatively high concentrations of the heavier elements. The term is a combination of " magnesium" and ferric the Latin word for iron(III), but m 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 coneVolcanic cones are among the simplest volcano formations. They are built by fragments (called ejecta thrown up (ejected) from a volcanic vent, piling up around the vent in the shape of a cone with a central crater. Volcanic cones are of different types, ds 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 meters, such as Mt. WashingtonMount Washington is a shield volcano in the Cascade Range of Oregon. The mountain dates to the late Pleistocene. However, it does have a line of basaltic andesite spatter cones on its northeast flank which are approximately 1,330 years old according to ca or Three Fingered Jack (north of Belknap).

Belknap Crater and its distal lava tongues cover 98 square kilometers 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 kilometers 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 kilometers 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 kilometers 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 meters, such as Mt. Washington or Three Fingered Jack (north of Belknap).