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. Large outcrops of the tuff are located in Inyo and Mono Counties, California, United States. Approximately 200 cubic kilometers of ash and tuff erupted outside the caldera.
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Bishop Tuff in the context of Pyroclastic rock
Pyroclastic rocks are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyroclasts. Pyroclastic rocks are a type of volcaniclastic deposit, which are deposits made predominantly of volcanic particles. Phreatic pyroclastic deposits are a variety of pyroclastic rock formed from volcanic steam explosions and are entirely composed of accidental clasts. Phreatomagmatic pyroclastic deposits are formed from explosive interaction of magma with groundwater. The word pyroclastic is derived from the Ancient Greek words πῦρ (pûr), meaning 'fire', and κλαστός (klastós), meaning 'broken'.
Unconsolidated accumulations of pyroclasts are described as tephra. Tephra may become lithified to a pyroclastic rock by cementation or chemical reactions as the result of the passage of hot gases (fumarolic alteration) or groundwater (e.g. hydrothermal alteration and diagenesis) and burial, or if it is emplaced at temperatures so hot that the soft glassy pyroclasts stick together at point contacts and deform. This process is called welding.
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