. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. 368 MENARD AND I>ADD [chap. 15 the temperature duriiiii the year falls below about 18 C for ap])reciable intervals (Wells. 1957). The importance of temperature in large part explains the absence of reefs around islands such as Ascension and St. Helena in the eastern Atlantic and the (Jalapagos Islands in the eastern Pacific. In the eastern parts of both oceans the u])welling of cold waters prevents reef development. Many oceanic islands, for example Eua in the Tonga Group (Hoffmeister, 1{)32) and Oahu in Hawaii, are par
. The Earth beneath the sea : History. Ocean bottom; Marine geophysics. 368 MENARD AND I>ADD [chap. 15 the temperature duriiiii the year falls below about 18 C for ap])reciable intervals (Wells. 1957). The importance of temperature in large part explains the absence of reefs around islands such as Ascension and St. Helena in the eastern Atlantic and the (Jalapagos Islands in the eastern Pacific. In the eastern parts of both oceans the u])welling of cold waters prevents reef development. Many oceanic islands, for example Eua in the Tonga Group (Hoffmeister, 1{)32) and Oahu in Hawaii, are partly or completely encircled hy fringing reefs. Fig. 1. Seamovints, low islands and submarine banks, volcanic islands and active volcanoes in the Pacific Basin. Broken line marks the structural boundary of the basin on the southwest (andesite line). —platforms that may extend outward from the shore for distances of .several hundred feet. Islands such as Ongea and many others in Fiji are protected by barrier reefs, structures comparable in size and constitution to fringing reefs but separated from the shore by a lagoon that may be several miles in width (Ladd and Hoffmeister, 1945). On some islands, such as Lakemba, Fiji, both fringing and barrier reefs are developed. Some reef-encircled islands are com- posed entirely of volcanic rock, others entirely of limestone; on some islands both types of rock are exposed, the limestones resting unconformably on the volcanic Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Hill, M. N. (Maurice Neville), 1919-. New York : Interscience Pub.
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