Continental Margin

The most distinctive features of the continental slopes are the submarine canyons. These are V-shaped features, often with tributaries, similar to canyons found on dry land. The deepest of the submarine canyons easily rivals similar landforms on the continents. The Monterrey Canyon off the coast of northern California, for example, drops from a water depth of 354 ft (108 m) below sea level near the coastline to 6,672 ft (2,034 m) below sea level. That vertical drop is half again as great as the depth of the Grand Canyon.

There seems little doubt that the submarine canyons, like their continental cousins, have been formed by erosion. But, for many years, oceanographers were puzzled as to the eroding force that might be responsible for formation of the submarine canyons. Today, scientists agree that canyons are produced by the flow of underwater rivers that travel across the continental slopes (and sometimes the continental shelf) carrying with them sediments that originated on the continents. These rivers are known as turbidity currents.

Evidence for the turbidity current theory of canyon formation was obtained in 1929 when an earthquake struck the Grand Banks region of the Atlantic Ocean off Newfoundland. An enormous turbidity current was set in motion that traveled at a speed ranging from 25 to 60 mph (40 to 100 km per hour), breaking a sequence of transatlantic telegraph cables along the way. The pattern of cable destruction was what made it possible, in fact, for scientists to track so precisely the movement of the giant turbidity current.