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Internal Tides and the Continental Slope

Curious waves coursing beneath the surface of the sea may shape the margins of the world's landmasses

David Cacchione, Lincoln Pratson

Figure 4. Tides arise in large part . . .Click to Enlarge Image

Offshore from the world's landmasses, the shallows of the continental shelf give way rather abruptly to the ocean's abyssal depths along a feature called the continental slope, which generally ramps downward with only a few degrees of dip. This is a puzzle, because marine muds can support inclines of 15 degrees or more, and the sediments being shed from the continents and washed over the edge of the continental shelves onto these slopes should, in principle, steepen them over time. One reason that these slopes remain shallow may be because they are constantly bombarded by the semi-diurnal internal tides-great waves of energy that course through the body of the ocean twice a day. When the slope of the bottom reaches a few degrees, these waves become sufficiently strong to prevent the deposition of suspended sediment and may even erode the seabed.

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