Pyroklastisten

Pyroklastisten, known in English as pyroclasts, are solid fragments ejected during explosive volcanic activity. They range in size from fine ash particles a few micrometres across to volcanic bombs several metres in diameter. Pyroklasts form by rapid fragmentation of magma and surrounding rock as volatiles exsolve, causing explosive decompression and fracturing of the conduit and near-vent rocks. They can be magmatic, derived from magma, or phreatomagmatic, resulting from interaction with external water. Common examples include glassy ash shards, pumice, lapilli, and lithic clasts.

During eruptions, pyroclasts are transported by eruption columns, clouds, and gravity-driven currents. Airfall ash blankets areas downwind, while denser pyroclastic currents generate pyroclastic flows and surges that travel along the ground. Upon deposition, fine ash forms air-fall tephra beds, whereas larger fragments accumulate as lapilli beds or volcanic bombs and blocks. In high-temperature flows, some pyroclasts weld together to form ignimrites.

Classification is typically by size (ash < 2 mm, lapilli 2–64 mm, bombs/blocks > 64 mm) and by origin (magmatic or phreatomagmatic). The welding state at deposition (unwelded vs welded) and the mineralogical and chemical composition provide additional detail. Pyroklastisten are central to volcanic hazard assessment and stratigraphic reconstruction, documenting eruption style, magnitude, and dispersal. In geology, tephra layers enable tephrochronology and correlation between sites. Economically, some pyroclastic materials are mined as construction aggregates or industrial abrasives, and pumice and obsidian have notable value.