Crater

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. κρατήρ, 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. (See Volcano.)