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A cave or cavern is a hollow place in the ground,〔Whitney, W. D. (1889). "Cave, n.1." def. 1. ''The Century dictionary: An encyclopedic lexicon of the English language'' (Vol. 1, p. 871). New York: The Century Co.〕〔"Cave" ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) © Oxford University Press 2009〕 especially a natural underground space large enough for a human to enter. Caves form naturally by the weathering of rock and often extend deep underground. The word ''cave'' can also refer to much smaller openings such as sea caves, rock shelters, and grottos. Speleology is the science of exploration and study of all aspects of caves and the cave environment. Visiting or exploring caves for recreation may be called ''caving'', ''potholing'', or ''spelunking''. ==Types and formation== The formation and development of caves is known as ''speleogenesis''. Caves are formed by various geologic processes and can be variable sizes. These may involve a combination of chemical processes, erosion from water, tectonic forces, microorganisms, pressure, and atmospheric influences. It is estimated that the maximum depth of a cave cannot be more than due to the pressure of overlying rocks.〔authors И. Кудрявцева, Д. Люри. name Geography. publishing house Аванта+. year 1994. volume 3. page 472. ISBN 5-86529-015-0〕 For karst caves the maximum depth is determined on the basis of the lower limit of karst forming processes, coinciding with the base of the soluble carbonate rocks.〔(Комиссия спелеологии и карстоведения. Д. А. Тимофеев, В. Н. Дублянский, Т. З. Кикнадзе. Терминология карста. Базис карстования ) D.A. Timofeev, V.N. Dublyansky, T.Z. Kiknadze, 1991, ''Karst Terminology,'' The Commission Speleology and Karst, Moscow Center of the Russian Geographical Society〕 Most caves are formed in limestone by dissolution.〔(【引用サイトリンク】publisher=Nova (TV series) )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「cave」の詳細全文を読む スポンサード リンク
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