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San Francisco volcanic field
The San Francisco volcanic field is an area of volcanoes in northern Arizona, north of Flagstaff, USA. The field covers 1,800 square miles (4,700 km²) of the southern boundary of the Colorado Plateau. The field contains 600 volcanoes ranging in age from nearly 6 million years old to less than 1,000 years (Miocene to Holocene), of which Sunset Crater is the youngest.〔Holm, R. F., and Moore, R. B., Holocene scoria cone and lava flows at Sunset Crater, northern Arizona, Geological Society of America Centennial Field Guide, 1987. pp. 393-7.〕 The highest peak in the field is Humphreys Peak, at Flagstaff's northern perimeter: the peak is Arizona's highest at 12,633 feet (3,851 m) and is a part of the San Francisco Peaks, an extinct stratovolcano complex.
==Description==
The volcanic field seems to have formed from a geological hotspot, a hot area in the mantle. As the North American plate moves over the spot, new volcanoes appear. Thus, the newest volcanoes are at the east side of the field. Most of the volcanoes are basalt cinder cones, but there are also large lava domes consisting of rhyolite and dacite.
Given that Sunset Crater is such a young volcanic feature of this area and that eruptions have occurred every several thousands of years in frequency, it is likely that there will be a future eruption in the San Francisco Volcanic field. However, it is impossible to predict when and exactly where a new eruption might occur. The United States Geological Survey does say that a future eruption would likely be in the eastern side of the volcanic field, where the most recent volcanic activity has occurred. Such an eruption is likely to be small and pose little hazard due to the remoteness of the area.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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