pyroclastisch

Pyroclastic (German: pyroklastisch) is a term used in geology to describe volcanic ejecta produced by explosive fragmentation of magma. The term derives from Greek pyro 'fire' and klastos 'broken'. Pyroclastic materials, or pyroclasts, include particles that are ejected during eruptions and subsequently transported by wind or by density currents along the ground.

Pyroclasts vary widely in size and form. They include ash (<2 mm), lapilli (2–64 mm), and bombs and blocks (>64 mm). They can be glassy or crystalline, and may be vesicular or solid. Common pyroclastic products are volcanic ash, pumice (a highly vesicular, light rock formed from frothy lava), and scoria.

Pyroclastic rocks are consolidated deposits formed from pyroclastic materials. Tuff is volcanic ash cemented into rock; ignimbrite is deposited by pyroclastic density currents and often shows a massive, welded texture if hot enough. Pyroclastic breccia contains coarser fragments derived from fragmentation of preexisting rocks or from lava fragments. Deposits are generated by different processes: explosive ashfall leaves airborne layers, while pyroclastic density currents produce chaotic, hot flows that surmount obstacles and can travel long distances.

Studying pyroclastic materials helps reconstruct eruption histories and regional tectonics, and informs hazards assessment for volcanic regions. The German term pyroklastisch is used similarly to refer to processes and materials of this nature in German-language volcanology.