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The actual investigation of submarine canyons as field work was begun about 50 years ago. A large amount of factual information has accumulated as result of operations of deep diving vehicles, first in the Pacific Coast canyons and more recently in the remarkable dives of the Woods Hole minisubmarine Alvin into East Coast canyons. Taking the results of these recent dives and combining them with earlier investigations, including much work done by the French in the Mediterranean as well as our extensive studies off California and Baja California, we can now say with some confidence that these amazing deep excavations into the sea floor off so many coastal areas can be explained.
New methods such as side scanning have also given us a greater understanding of the exact character of submarine canyons, particularly in the Bay of Biscay. The development of multichannel sonar has greatly increased our knowledge of the nature of continental margins and hence their history. This has given us more insight into the history of canyon development, particularly off the east Coast where drilling for oil and gas has become so important.
In the past we have seen a great variety of hypotheses for explaining submarine canyons. Unfortunately almost all of these have been based on information from a small selection of the canyons, usually from one area. From the new information, it is evident that canyons are of composite origin and that many of the hypotheses suggested in the past were partly correct but did not appreciate that coordination of other processes was required. Thus there is growing evidence that, in the history of many canyons, there was a period in which subaerial erosion was an important precursor, but that present features are predominantly the result of marine erosion. Those advocating turbidity currents as the unique cause of canyons failed to appreciate that debris flows down the incipient valleys, as ell as other types of landslides, could be an almost equally important factor in marine erosion. The great effect of biologic activity on the rock walls of incipient canyons has been almost completely neglected in explanations, and various types of currents such as those of the tides have been left largely out of the picture. Perhaps the most important feature absent in these various hypotheses has been the realization that canyons may well be the result of a long period of formation, much longer than the short episodes of Pleistocene glacial sea-level lowering features which commonly cut into hard crystalline rock. New information is showing that the canyons may date back to at least the Cretaceous.
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