Tuesday, March 29, 2016

Scientists: Idaho volcanic explosion rivaled Yellowstone

[Post Register] Before the hotspot that created Yellowstone National Park’s incredible geysers, fumaroles and mud pots arrived in what is now northwestern Wyoming, it made a rowdy passage through southern Idaho.
Recent research has looked at that ancient geological history in greater detail and identified 12 major eruptions in southern Idaho, one of which was a super eruption similar in scale to Yellowstone’s most recent caldera-forming explosion about 640,000 years ago.
“Initially, people thought there were a lot more eruptions that were smaller,” said David Finn, a graduate student at the University of California Santa Cruz who took part in the study. “We’ve shown there were fewer and they were bigger — some of the largest in North America.”
The research is outlined in a recently published paper in the Geological Society of America Bulletin, of which Finn was a co-author. The lead author was Thomas Knott of the University of Leicester.
Over the course of its 17-million-year lifespan, the Yellowstone hotspot has migrated across the Snake River Plain in southern Idaho and northern Nevada to its present location.
“The Great Basin, formed 20 to 30 million years ago, was in existence before Yellowstone was formed and it was already fractured,” explained Bob Smith, a University of Utah scientist who has studied the geodynamics of Yellowstone for 60 years.
About 20 million years ago the Great Basin began stretching to what is now twice its original width, Smith said, fracturing the Earth’s crust and upper mantle in the region. Those fractures and thinning of the lithosphere made it easier for the Yellowstone magma plume to push to the surface and create a series of about 150 volcanic eruptions.
“What we showed were the volcanic eruptions were most intense in early years, then got smaller as they came across the Snake River Plain,” Smith said of some of his earlier research. Read More