Final answer:
A small volcano with a conical pile of pyroclastic debris at an angle of repose is known as a cinder cone volcano, composed of volcanic ash and larger volcanic fragments.
Step-by-step explanation:
A relatively small volcano composed of a conical pile of pyroclastic debris, which rests on its slopes at an angle of repose, is a cinder cone volcano. These volcanoes are characterized by the accumulation of volcanic ash, fragments of rock, minerals, and volcanic glass that are created during volcanic eruptions. Usually, these particles are smaller than 2 mm in diameter, but a cinder cone can also include larger fragments, known as agglomerates, which have been ejected out of a volcanic vent. The steep slope angle of a cinder cone is due to the angle of repose, which is the steepest angle at which loose material can rest on a slope without sliding down.