ABSTRACT

In May, 1957, a brief survey of the Congo Submarine Canyon was conducted from the Research Vessel VEMA. The canyon was found on the continental slope near the seaward limit of earlier surveys and traced to the west for 150 miles. Where the survey was discontinued, in depths of 2,200 fathoms, the leveed canyon was still a prominent feature. At the 550-fathom contour the canyon is about 5 miles wide at its rim and 500 fathoms deep. The canyon is V-shaped and echoes from the thalweg are usually recorded after the echoes from the steep walls. The outer parts of the canyon, in depths exceeding about 1,800 fathoms, are bounded by huge natural levees. In 1963 a 30-mile-long section of the canyon was surveyed 150 miles west of the 1957 study.

Four biological trawls and ten sediment cores were collected from the canyon region. One trawl in 2,140 fathoms contained abundant tree leaves and a rich fauna. The canyon cores contain silt, sand, and organic debris.

The canyon was discovered in 1886 by a cable route survey. Between 1887 and 1937 the Luanda-Saō Thomé cable broke 30 times in the canyon. Breaks occurred most frequently during months of maximum river discharge and consequently at the times of greatest bed-load discharge. Cable breaks were limited to periods of years when the river channel was undergoing major changes in position and depth. The cable breaks which occurred up to 120 miles seaward of the river mouth are attributed to turbidity currents generated at the river mouth at times of maximum bed-load transport. These turbidity currents flowed down the continental slope, eroding the deep slope canyon and building the natural levees of the continental rise, and eventually spread out on the Angola Abyssal Plain. In contrast to other great rivers, the Congo is not building a subaerial delta; virtually its entire bed load is being carried by turbidity currents via the Congo Submarine Canyon to the great Congo Cone on the floor of the Angola Basin.

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