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Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. [1] [2] Rock that contains greater than 75% ash is considered tuff, while rock containing 25% to 75% ash is described as tuffaceous (for example, tuffaceous sandstone). [3]
Ignimbrites are made of a very poorly sorted mixture of volcanic ash (or tuff when lithified) and pumice lapilli, commonly with scattered lithic fragments. The ash is composed of glass shards and crystal fragments. Ignimbrites may be loose and unconsolidated, or lithified (solidified) rock called lapilli tuff. Near the volcanic source ...
The Lava Creek Tuff is a voluminous sheet of ash-flow tuff located in Wyoming, Montana and Idaho, United States. It was created during the Lava Creek eruption around 630,000 years ago, which led to the formation of the Yellowstone Caldera. This eruption is considered the climactic event of Yellowstone's third volcanic cycle.
The Bishop Tuff is a welded tuff which formed 764,800 ± 600 years ago as a rhyolitic pyroclastic flow during the approximately six-day eruption that formed the Long Valley Caldera. [1] [2] [3] Large outcrops of the tuff are located in Inyo and Mono Counties, California, United States. Approximately 200 cubic kilometers of ash and tuff erupted ...
The illustration is fiamme in Archean Woman Lake rhyolitic tuff, Superior Province, Canada. Adopted and modified from photograph of Thurston (1980). [37] Felsic volcanic rocks also include felsic tuff that was formed when tephra was consolidated. [17] Tuff is composed of volcanic ash, glass shards and lithic fragments.
Rhyolitic ash-flow tuffs are among the most voluminous of continental igneous rock formations. Rhyolitic tuff has been used extensively for construction. Obsidian, which is rhyolitic volcanic glass, has been used for tools from prehistoric times to the present day because it can be shaped to an extremely sharp edge.
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The first three caldera-forming rhyolites – Blacktail Tuff, Walcott Tuff and Conant Creek Tuff – totaled at least 2250 km 3 of erupted magma. The final, extremely voluminous, caldera-forming eruption – the Kilgore Tuff – which erupted 1800 km 3 of ash, occurred 4.5 million years ago.