Bruneau-Jarbidge supervolcano
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The Bruneau-Jarbidge supervolcano, located in present-day southwest Idaho, erupted in the Miocene between ten and twelve million years ago, spreading a thick blanket of ash in the Bruneau-Jarbidge event. Animals in the prime of life were suffocated and preserved in ashfall where they stood, or where they collected at a water hole, such as at Ashfall Fossil Beds.
The existence of the event was discovered by Prof. Mike Voorhees, a paleontologist at the University of Nebraska State Museum, in 1971, at a lagerstätte in Orchard, Nebraska, the Ashfall Fossil Beds; there, two hundred fossilized rhinoceros remained at a single site, together with the prehistoric skeletons of camels and lizards, horses and turtles, a death assemblage preserved in two meters of volcanic ash.
By its uniquely characteristic chemical "fingerprint" and the distinctive size and shape of its crystals and glass shards, the supoervolcano stood out among dozens of prominent ashfall horizons laid down in the Cretaceous and Tertiary of central North America. The event responsible for this fall of volcanic ash was identified at Bruneau-Jarbidge, 1600 kilomenters west, in Idaho, a site represented today by a caldera. Prevailing westerlies deposited distal ashfall over a vast area of the Great Plains.
[edit] References
- BBC: "Supervolcanoes" Program transcript, 3 February 2000
- W. I. Rose, C. M. Riley, and S. Dartevelle, "Sizes and Shapes of 10-Ma Distal Fall Pyroclasts in the Ogallala Group, Nebraska" (pdf file) Includes bibliography.
- Izett, G. A. 1981. "Volcanic ash beds: recorders of Upper Cenozoic silicic pyroclastic volcanism in the western United States." "Journ. Geophysical Res. 86:10, 200–10, 222.
