A cinder cone is a steep conical hill of loose pyroclastic fragments, such as volcanic clinkers, volcanic ash, or scoria that has been built around a volcanic vent. The pyroclastic fragments are formed by explosive eruptions or lava fountains from a single, typically cylindrical, vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as either cinders, clinkers, or scoria around the vent to form a cone that often is symmetrical; with slopes between 30 and 40°; and a nearly circular ground plan. Most cinder cones have a bowl-shaped crater at the summit.
Cross-section diagram of a cinder cone or scoria cone
Cinders at a cinder cone in San Bernardino Valley, Arizona
SP Crater, an extinct cinder cone in Arizona
Sunset Crater, a young monogenetic cinder cone in Arizona that began forming around the year 1075 CE
Scoria is a pyroclastic, highly vesicular, dark-colored volcanic rock formed by ejection from a volcano as a molten blob and cooled in the air to form discrete grains called clasts. It is typically dark in color, and basaltic or andesitic in composition. Scoria has relatively low density, as it is riddled with macroscopic ellipsoidal vesicles, but in contrast to pumice, scoria always has a specific gravity greater than 1 and sinks in water.
Scoria
Pine trees growing on the slope of Cinder Cone, a volcanic cone of scoria in Lassen Volcanic National Park, California
Tuff moai with red scoria pukao on its head.