The National Geographic Magazine (vegyes számok) (5 db) [antikvár]

VOL. XCIV, NO. 3 WASHINGTON September,1948 TME NATBOMAl ÎQ)TU T. 1948, BY NATIONAL GEOGRAPHIC SOCIETY. WASHINGTON, 0. C. COPYRIGHT SECURED Exploring the Mid-Atlantic Ridge By Maurice Ewing Professor of Geology, Columbia University Leader, National Geographic Society-Woods Hole Oceanographic Institution-Columbia University Expeditions to the Mid-Atlantic Ridge Photographs from the Staff of Woods Hole Oceanographic Institution 'w: i-E'RE over the Ridge!" All hands were tense as the word spread through the little research vessel Atlantis, for it meant we had reached our goal. A mile or so beneath our keel stretched the gloom-shrouded peaks, valleys, and ridges of the longest mountain system on earth—the mysterious Mid-Atlantic Ridge, which we had come to explore. From 300 to 600 miles wide, this mighty submarine mountain range extends nearly 10,000 miles from Iceland almost to the Antarctic Circle. It separates the Atlantic Ocean into eastern and western basins roughly three miles deep (pages 280, 281, and 283). The range is probably continuous except for a narrow break at the Equator called the Romanche Trench. From its base on the ocean iioor, at a depth of about three miles, the Ridge rears its rugged crest to an average height of 10,000 feet, or a mile below the surface. A few of its peaks actually emerge as the islands of the Azores, St. Paul Rocks (Rochedos Sao Paulo), Ascension, Tristan da Cunha, Gough, and Bouvet.* Ever since its discovery 75 years ago, this ocean-covered mountain range of continental size has stirred the imagination of men in many lands. Romanticists inevitably connect the Ridge with the legend of the lost Atlantis, the mythical Atlantic continent which Plato related sank beneath the waves "in a single day and one fatal night." Though our ship was named Atlantis, we had no illusions of solving that age-old mystery story. In an expedition sponsored jointly by the National Geographic Society, the Woods Hole (Massachusetts) Oceanographic Institution, and Columbia University, we hoped to pierce the veil of hundreds of fathoms of water with our deep-sea camera, probe this dark undersea world with new instruments, map its hidden geography, and bring up rocks and sediments eloquent of its structure and age. Ridge a Center of Earthquakes Almost the only earthquakes in the Atlantic Ocean occur along the entire length of the Ridge. The crust of the earth is being deformed and broken on this line of submarine mountains, while the rest of the ocean basin remains undisturbed. This is perhaps the most definite information we have about the Ridge. It comes from observations made on land thousands of miles away by the world-wide system of seismograph stations, developed during the last 40 years, which continually records and locates all the major earthquakes of the world. Except for the soundings which have outlined its extent, the Ridge itself is unexplored territory in comparison with mountains on the continents, as is most of the ocean floor. * See "Our Global Ocean—Last and Vast Frontier," by F. Barrows Colton, National Geographic Magazine, January, 1945. S SI