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Welded tuff identification and geology

A pyroclastic rock formed when hot volcanic ash, pumice, and glass fragments are deposited at such high temperatures often 500°C that the particles fuse and compact together before cooling. The welding process compresses and flattens pumice fragments into dark, lens-shaped fiamme, and the degree of welding increases toward the base and center of the deposit where temperatures were highest. Welded tuffs are also called ignimbrites. Field: volcanology. Example: The Bishop Tuff in eastern California is a massive welded tuff erupted from the Long Valley Caldera approximately 760,000 years ago, covering over 1,500 km² with deposits up to 200 m thick.. Related terms: Tuff, Ignimbrite, Pyroclastic flow, Fiamme.

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Sources, scope & corrections

These authoritative resources support category-level nomenclature, terminology, identification methods, and safety. When a specimen-specific safety warning appears, the public-health source listed here directly supports that precaution. They are not line-by-line citations for every other property on this entry, and natural specimens vary.

Editorial owner
GeoMiner
Last updated
2026-03-30T15:19:42.096023+00:00
Review status
Published; not independently peer-reviewed
  • USGS Thesaurus — U.S. Geological Survey. Controlled earth-science terminology used to describe USGS information resources.
  • Glossary of Geologic Terms — U.S. National Park Service. Geologic definitions prepared by the NPS Geologic Resources Inventory.

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Common questions

What does Welded tuff mean in geology?
A pyroclastic rock formed when hot volcanic ash, pumice, and glass fragments are deposited at such high temperatures often 500°C that the particles fuse and compact together before cooling. The welding process compresses and flattens pumice fragments into dark, lens-shaped fiamme, and the degree of welding increases toward the base and center of the deposit where temperatures were highest. Welded tuffs are also called ignimbrites.
What is an example of Welded tuff?
The Bishop Tuff in eastern California is a massive welded tuff erupted from the Long Valley Caldera approximately 760,000 years ago, covering over 1,500 km² with deposits up to 200 m thick.
Which earth-science field uses the term Welded tuff?
Welded tuff is used in volcanology.
Which terms are related to Welded tuff?
Related terms in this reference are Tuff, Ignimbrite, Pyroclastic flow, Fiamme.

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