A volcanic agglomerate is a type of volcanic rock. During a volcanic eruption, the magma pierces through the overlying strata or older rocks, which breaks them into fragments of varying sizes. When the diameters of the rock fragments are is greater than 50 mm, the rock is called an agglomerate. A volcanic rock composed mainly of these aggregates is called a volcanic agglomerate, and these rocks are generally distributed around the crater. This is an important marker for determining the crater location.