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A floating island is a mass of floating aquatic plants, mud, and peat ranging in thickness from a few inches to several feet. Floating islands are a common natural phenomenon that are found in many parts of the world. They exist less commonly as a man-made phenomenon. Floating islands are generally found on marshlands, lakes, and similar wetland locations, and can be many hectares in size. == Natural occurrences == Sometimes referred to as ''tussocks'', ''floatons'', or ''suds'', natural floating islands are composed of vegetation growing on a buoyant mat of plant roots or other organic detritus. Some cenotes in northern Mexico have natural floating islands. They typically occur when growths of cattails, bulrush, sedge, and reeds extend outward from the shoreline of a wetland area. As the water gets deeper the roots no longer reach the bottom, so they use the oxygen in their root mass for buoyancy, and the surrounding vegetation for support to retain their top-side-up orientation. The area beneath these floating mats is exceptionally rich in aquatic lifeforms. Eventually, storm events tear whole sections free from the shore, and the islands thus formed migrate around a lake with changing winds, eventually either reattaching to a new area of the shore, or breaking up in heavy weather. In the Brazilian Amazon floating island form in lakes on the floodplanes of white-water rivers.〔 They are known as Matupá and range in size from a few square meters to a few hectares. In the traditional belief system of the indigenous population the Matupá are known as the house of the Giant Anaconda.〔 Natural floating islands may have been the source of many "disappearing island" legends, such as those surrounding Avalon. Explosive volcanic eruptions may create pumice rafts, which can float on the ocean for months or even years before becoming fully saturated and sinking. Over time, larger rafts can have grasses and palm trees growing on them . 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「floating island」の詳細全文を読む スポンサード リンク
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