Complex sentence: An ignimbrite is the deposit of a pyroclastic density current, or pyroclastic flow, a hot suspension of particles and gases that flows rapidly from a volcano, driven by a greater density than the surrounding atmosphere.
Split into simpler sentences: An ignimbrite is the deposit of a pyroclastic density current, or pyroclastic flow. It is a hot suspension of particles and gases flowing rapidly from a volcano driven by having a greater density than the surrounding atmosphere.