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  Archipelago

  An archipelago ( /ɑrkɨˈpɛləɡoʊ/ ark-i-PEL-ə-goh), sometimes called an island group, is a chain or cluster of islands. The word archipelago is derived from the Greek ἄρχι- – arkhi- ("chief") and πέλαγος – pélagos ("sea") through the Italian arcipelago. In Italian, possibly following a tradition of...
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  Cave

  A cave or cavern is a natural underground space large enough for a human to enter. The term applies to natural cavities some part of which is in total darkness. The word cave also refers to smaller spaces like rock shelters, sea caves, and grottos. Speleology is the science of exploration and study...
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  Impact crater

  In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body. In most common usage, the term is used for the approximately circular depression in the surface of a planet, moon or other...
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  Caldera

  A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption. They are sometimes confused with volcanic craters. The word comes from Spanish caldera, and this from Latin CALDARIA, meaning "cooking pot." In some texts the English term cauldron is...
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  Dune

  In physical geography, a dune is a hill of sand built either by wind or water flow. Dunes occur in different forms and sizes, formed by interaction with the flow of air or water. Most kinds of dunes are longer on the windward side where the sand is pushed up the dune and have a shorter "slip face"...
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  Desert

  A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Most deserts have an average annual precipitation of less than 400 millimetres (16 in). A common definition distinguishes between true deserts, which receive...
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  Glacier

  A glacier (UK  /ˈɡlæsiə/ GLASS-ee-ər or US /ˈɡleɪʃər/ GLAY-shər) is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation (melting and sublimation) over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier...
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  Island

  An island  /ˈaɪlənd/ or isle /ˈaɪl/ is any piece of sub-continental land that is surrounded by water. Very small islands such as emergent land features on atolls can be called islets, cays or keys. An island in a river or an island in a lake may be called an eyot /ˈaɪ.ət/ (also ait /ˈeɪt/), or holm...
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  Lake

  A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land apart from a river, stream, or other form of moving water that serves to feed or drain the lake. Lakes are inland and not part of the ocean and therefore are distinct from...
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  Loch

  Loch ( /ˈlɒx/ or /ˈlɒk/) is the Irish and Scottish Gaelic (cognate with the now obsolete Welsh word for lake, llwch) word for a lake or a sea inlet. It has been anglicised as lough, although this is pronounced the same way as loch. Some lochs could also be called a firth, fjord, estuary, strait or...