OCEAXOGRAPHIC IXFORAL\TIOX FOR SUBMARIXE CABLES 1065 



A mid-ocean canyon three miles wide with precipitous walls which 

 drop fifty fathoms to the canyon floor runs down the length of the 

 Labrador and Newfoundland Basins as shown on Fig. 8. Profiles across 

 this canyon are shown in Fig. 9. Other mid-ocean canyons have recently 

 been discovered in the equatorial Atlantic as well as in the basin south 

 of Nova Scotia. Studies of sediments obtained in these canyons suggest 

 that they were cut by turbidity currents. 



2.4.3 Mid-Atlantic Ridge 



The principal topographic feature of the Atlantic is the Mid-Atlantic 

 Ridge which runs the entire length of the Atlantic and continues into 

 the Indian and Arctic Oceans. The ridge is about 1,200 miles wide and 

 can be thought of as a broad swell or arch with ^'aried and generally 

 extremely irregular topography. Along the axis of the ridge is a narrow 

 crest about 60 miles wide with a characteristic median depression which 

 cleaves the crest zone. Depths in the median depression exceed the 

 maximum depths of the adjacent flanks of the ridge out to 100 miles 

 or more. In some cases they reach depths equal to those of the abyssal 

 plains. The tops of the highest peaks of the ridge, excluding those which 

 emerge as islands, lie at about 800 fathoms while the median rift falls to 

 depths of about 2,000 fathoms and locally to depths as great as 2,800 

 fathoms. 



Near the outer margins of the ridge there is a discontinuous line of 

 sea mounts which rise as isolated peaks. The major part of the ridge 

 lies at depths intermediate between the abyssal plains and the central 

 highlands, with extensive areas of flat intermountain basins, particularly 

 in the area just south of the Azores. The earthquake epicenter belt 

 accurately follows the median rift throughout the length of the ridge. 



Other areas of the Atlantic which have topograph}^ similar to the 

 Mid-Atlantic Ridge include an oval area trending northeast-southwest 

 from Bermuda with a long axis of about 800 miles and a short axis of 

 about 500 miles. The area is characterized, in part, by low irregular 

 relief, but with a number of large sea mounts. 



III. XATURE OF THE SEA BOTTOM 



3.1 Methods of Investigation 



There are four principal methods of investigating the nature of the 

 bottom : 



(a) Visual in.spections and photographs. 



(b) Physical sampling. 



