Researchers discover that colossal eruptions in the Yellowstone hotspot track were bigger than previously thought. Examination of individual eruption deposits was correlated with the use of a multi-technique approach, which includes whole-rock and mineral chemistries, radio-isotopic dates, and paleomagnetic data.
The Cassia Formation, estimated to be 1.95-kilometer-thick (1.2 miles), has 12 refined rhyolitic members. Each composition has a specific paleomagnetic, geochemical, geochronical, and mineralogic characteristics. The area recorded gigantic high-temperature Snake River explosive eruptions that range from 8 to 12 million years ago. These eruptions were able to weld rheomorphic ignimbrites and layers of ash fall.
Experts from the University of Leicester were able to deduce that the total number of eruptions that came from the Snake River Plain is about 50 percent less than what was previously believed. However, 12 of those eruptions were significantly bigger in volume.
One eruption, the Castleford Crossing, that occurred about 8 million years ago have an estimated volume of more than 1,900 cubic kilometers (456 cubic miles). Researchers stated that one volcanic sheet spans an area of more than 14,000 square kilometers (5,405 square miles) in southern Idaho and is more than 1.3-kilometer-thick (0.8 mile) in the caldera of the supervolcano.
Mike Branney, Tom Knott and Marc Reichow from the Department of Geology led the investigation of the gigantic eruptions in Yellowstone are positive that more discoveries will come in the future.
"The size and the magnitude of this newly defined eruption is as large, if not larger, than better known eruptions at Yellowstone, and it is just the first in an emerging record of newly discovered super-eruptions," said Knott.
This new finding suggests that the Yellowstone supervolcano may be just a part of a bigger and much more violent volcanic system. Evidence also points to intense hotspot magmatism as the cause of major crustal subsidence that formed the Snake River Basin.
The Yellowstone hotspot track is responsible for the volcanic activities in Idaho, Oregon, Nevada, and Wyoming. Its most recent super-eruption occurred about 640,000 years ago, made the Lava Creek Tuff and Yellowstone Caldera where it presently lies.
