No. 32: Mar-Apr 1984
Exploration and mapping of submarine canyons cut into the continental shelves of Alaska and Siberia emphasize once again the colossal scale of these crustal gashes:
"Erosion of some of the largest known submarine canyons has removed more than 20,000 km3 of former subduction margin between the Aleutian Islands and Cape Navarin, U.S.S.R. The canyons are incised as deeply as 2,400 m into Tertiary sedimentary and igneous rocks that make up the margin and attendant deep sedimentary basins along the outer Bering shelf. Cutting of the seven major canyons probably occurred during low stands of sea level when the Bering shelf was exposed to a depth of about -135 m, which allowed the ancestral Anadyr, Yukon, and Kuskokwim Rivers to carry large volumes of sediment to the outer shelf. Although their positions appear to be structurally influenced, the canyons apparently were cut by combinations of massive slumping and sliding of sediment deposited near the shelf edge and of scouring action of the resulting turbidity currents that carried debris to the abyssal sea floor, where deep-sea fans have formed."
(Carlson, Paul R., and Karl, Herman A.; "Ancient and Modern Processes in Gigantic Submarine Canyons, Bering Sea," Eos, 64:1052, 1983.)
Comment. The authors believe that submarine slumping and turbidity currents were sufficient to have eroded these huge canyons. Other geologists doubt this. The other possibility is that sea level was once a mile or more below present levels and that the canyons were cut by rushing water spilling over the continental shelves.
Reference. Grand Canyon anomalies (and there are several of them) are cataloged at ETV7 in our Catalog: Carolina Bays, Mima Mounds. Details here.