Science: Rivers Under the Sea

Columbia University’s research ship Vema steamed back into New York Harbor last week with new information about the “rivers” that flow on the bottom of the ocean. About 600 miles east of Philadelphia, where the Atlantic is 17,000 ft. deep, the Vema’s sensitive sounding apparatus found a steep-walled canyon two or three miles wide and about 180 ft. deep. The scientists followed it for 100 miles and they have reason to believe that it may run for 500 miles across the bottom of the ocean (see map).

This discovery was no surprise to Bruce C. Heezen of Lament Geological Observatory, the Vema’s scientific skipper. Two years ago, the Vema found another canyon south of Greenland, which it traced north and south for 1,200 miles on the bottom of the Atlantic. Heezen believes that there must be many such gorges and that they are the channels of mud rivers that formed the level plain on the ocean floor.

The bottoms of the deep oceans were once believed to be smooth, but modern sounding gear has found all sorts of irregularities. Certain great areas, however, are almost as level as the water surface above them, and the origin of these smooth “abyssal plains” is something of a mystery. Many theories about them have been proposed, including the easy explanation that the plains are smooth because nothing ever happened to make them otherwise.

Heezen believes that they are the flood plains and deltas of “turbidity currents”: rivers of mud, heavier than clear water, that coursed intermittently down the slopes of the continents and deposited their sediment far out on the bottom of the ocean. Most of the sediment, he thinks, was carried down in remote geological ages. The turbidity currents probably started near land. They cut deep gorges (e.g., the famous Hudson Canyon) in the continental slopes and dumped their silt and sand in deep basins in the irregular ocean bottom. When the nearest basin was full, the mud-river ran across it just as a river would do on dry land, and started to fill the next basin. The canyon just found east of Philadelphia is probably cut in the sediment of a filled-up basin.

To prove this theory the Columbia scientists took cores of the material that forms the abyssal plains. They found what they hoped to find. On top is a thin layer of “lutite,” very fine silt deposited from still water. Below it is the coarse sand that was carried over the sea bottom for hundreds of miles by mighty under-ocean rivers.