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Uinkaret volcanic field
The Uinkaret volcanic field is an area of monogenetic volcanoes in northwestern Arizona, United States, located on the north rim of the Grand Canyon.〔
Lava flows from the Uinkaret volcanic field that have cascaded down into the Grand Canyon, damming the Colorado River, have been used to date the canyon's carving. One of these cascades is today's Lava Falls. Lava Falls Rapid, below Lava Falls on the Colorado River, is "at all water levels, the most severe rapid in Grand Canyon." 〔(New Debris Flow at Lava Falls ), at Grand Canyon River Guides. Accessed 5/26/09.〕
The Colorado River was dammed by lava flows multiple times from 725,000 to 100,000 years ago.〔''Karlstrom, K., Crow, R., Peters, L., McIntosh, W., Raucci, J., Crossey, L., and Umhoefer, P., 2007, 40Ar/39Ar and field studies of Quaternary basalts in Grand Canyon and model for carving Grand Canyon: Quantifying the interaction of river incision and normal faulting across the western edge of the Colorado Plateau: GSA Bulletin, v. 119, no. 11/12, p. 1283-1312.〕 While some believe that these lava dams were stable, lasting up to 20,000 years and forming large reservoirs,〔Hamblin, W.K., 1994, Late Cenozoic lava dams in the western Grand Canyon: Geological Society of America Memoir 183, 139 p.〕 others think they failed quickly and catastrophically as massive floods.〔Fenton, C.R., Poreda, R.J., Nash, B.P., Webb, R.H., and Cerling, T.E., 2004, Geochemical discrimination of five Pleistocene lava-dam outburst-flood deposits, western Grand Canyon, Arizona: The Journal of Geology, v. 112, p. 91–110, .〕 Lava flows traveled downriver 76 miles (121 km) from river mile 178 to 254.
One lava flow, from Little Springs, south of Pliocene Mount Trumbull, has a cosmogenic helium age of 1300 +/- 500 years BP. Pottery shards dated to between A.D. 1050 and 1200 were found within the lava flow, produced around the same time as the Sunset Crater eruption in the San Francisco volcanic field on the South Rim.〔
==Notable Vents==
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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