CRATER  , the cavity at the mouth of a volcanic duct, usually

funnel-shaped or presenting the form of a bowl, whence the name, from the Gr . Kpari]p, a bowl . A volcanic hill may have a single crater at, or near, its summit, or it may have several minor craters on its flanks: the latter are sometimes called " adventitious craters " or " craterlets." Much of the loose ejected material, falling in the neighbourhood of the vent, rolls down the inner wall of the crater, and thus produces a stratification with an inward dip . The crater in an active volcano is kept open by intermittent explosions, but in a volcano which has become dormant or extinct the vent may become plugged, and the bowl-shaped cavity may subsequently be filled with water, forming a crater-lake, or as it is called in the Eifel a Maar . In some basaltic cones, like those of the Sandwich Islands, the crater may be a broad shallow pit, having almost perpendicular walls, with horizontal stratification . Such hollows are consequently called pit-craters . The name caldera (Sp. for cauldron) was suggested for such pits by Capt . C . E . Dutton, who regarded them as having been formed by subsidence of the walls . The term caldera is often applied to bowl-shaped craters in Spanish-speaking countries .