in addition to the great ridges and volcanicchains, the oceans conceal another form ofundersea mountains: the strange guyot, or flat-topped seamount. No marine geologist even suspected the existence of these isolated mountains until they were discovered by geologist Harry H. Hess in1946. He was serving at the time as naval officer on a ship equipped with a fathometer. Hess named thesetruncated peaks for the nineteenth-centurySwiss-born geologist Arnold Guyot, who had served on the faculty of Princeton University for thirty years.Since then, hundreds of guyots have been discovered in every ocean but the Arctic. Like offshore canyons, guyots present a challenge to oceanographic theory.They are believed to be extinct volcanoes.Theirflat tops indicate that they once stood aboveor just below the surface, where the action of waves leveled off their peaks. Yet today, bydefinition, their summits are at least 600 feet below the surface, and some are as deep as 8,200 feet. Most lie between 3,200 feet and 6,500 feet. Their tops are not really flat but slope upward to a low pinnacle at the center.Dredging from the tops of guyots has recovered basalt and coral rubble, and thatwould be expected from the eroded tops of what were once islands. Some of this material is over 80 million years old. Geologists think the drowning of the guyots involved two processes: The great weight of the volcanicnúi chán nản đáy biển bên dướihọ, và mức độ của biển tăng một sốlần, đặc biệt là khi kỷ băng hà cuối cùng kết thúc, khoảng 8.000 để 11.000 năm trước.
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