In addition to the great ridges and volcanic chains, the oceans conceal another form of underseamountains: the strange guyot, or flat-topped seamount. No marine geologist even suspected theexistence of these isolated mountains until they were discovered by geologist Harry H. Hess in 1946.www.DeThiThuDaiHoc.comFB.com/ThiThuDaiHocHe was serving at the time as a naval officer on a ship equipped with a fathometer. Hess named thesetruncated peaks for the nineteenth-century Swiss-born geologist Arnold Guyot, who had served onthe faculty of Princeton University for thirty years. Since then, hundreds of guyots have beendiscovered in every ocean but the Arctic. Like offshore canyons, guyots present a challenge tooceanographic theory. They are believed to be extinct volcanoes. Their flat tops indicate that theyonce stood above or just below the surface, where the action of waves leveled off their peaks. Yettoday, by definition, their summits are at least 600 feet below the surface, and some are as deep as8,200 feet. Most lie between 3,200 feet and 6,500 feet. Their tops are not really flat but slope upwardto a low pinnacle at the center. Dredging from the tops of guyots has recovered basalt and coralrubble, and that would be expected from the eroded tops of what were once islands. Some of thismaterial is over 80 million years old. Geologists think the drowning of guyots involved two processes:Trọng lượng tuyệt vời của dãy núi lửa chán nản đáy biển bên dưới họ, và mức độ của cácbiển tăng một số lần, đặc biệt là khi kỷ băng hà cuối cùng kết thúc, khoảng 8.000 đến 11,000 năm trước
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