Pyroclasts refers to ash, rock fragments and volcanic bombs ejected during volcanic eruption. When pyroclasts mix with super-heated gases ejected during volcanic eruption, this results in pyroclastic flow. Pyroclasts may then mix with water as it flows down the volcano. This gives rise to lahars which is a fast flowing mudflow created through the combination of pyroclasts(ash) and water. Thus, the combination of ash(pyroclasts) and water is called lahars.
