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Crater refers to an annular pit formed on the ground by volcanic ejecta around its spout. Usually funnel-shaped or bowl-shaped, it is generally located at the top of the volcanic cone (a crater without a cone is located on the ground and is called a negative crater). The depth of craters varies, generally only two or three hundred meters, and the diameter is generally less than one kilometer; The bottom diameter is very short, usually only a little larger than the volcano tube below.