"Perched water tables are very common, and we certainly see that here," Phillip Pearthree of the Arizona Geological Survey said. Because the river and water table are at different levels, the cave dates are in no way related to the formation of the canyon, he added. Karlstrom's team also believes that hot, buoyant mantle material is flowing out from beneath the thick crust of the Colorado Plateau and pushing up underneath the canyon. Over the past six million years, this uplift has been most pronounced in the east, accounting for 1,300 feet (400 meters) of its 5,200-foot (1,600-meter) depth near the famous South Rim. The uplift becomes less dramatic heading west, where the canyon is cut by a series of major faults. "Everyone talks about canyons being passively incised by a river," Karlstrom said. "But no, it's actively uplifting. It's like cutting a layer cake with a knife. The cake is cutting the knife, but there's also a component of the cake coming up through the knife." Related Links: |
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