A debris cone is commonly made when rock from a high-up narrow slit or gorge falls into a ﬂat-ﬂoored valley. Here the soil and loose materials are deposited, leaving a mound of conical shape. While an alluvial fan is formed when ﬂowing water rushes rock and soil down a slope, debris cones come from a dry process known as “mass wasting”—that is, gravity pulling loose materials downslope. Such mounds can reach sizes large enough to obstruct river channels. Similar deposits can also be found lying on boulders moved by a landslide, or on a glacier, where a cone-shaped mound of ice or snow may be covered with a veneer of debris thick enough to prevent the underlying ice from melting. A debris cone is also called a dirt cone or cone of detritus.