Yellowstone not likely to see massive eruptions
About 16 million years ago, volcanoes erupted along what is today the OregonNevada border. Over the ensuing years volcanic activity migrated to the east, and today it produces the geysers and hot springs of Yellowstone National Park, located mainly in northwest corner of Wyoming.
Of course the volcanoes didn’t move. Instead, the North American continent moved west, at an average rate of about an inch a year, and subsequent volcanoes poked up through it, forming what is called the Yellowstone hotspot track.
Some of the eruptions were huge, covering thousands of square miles with ash and volcanic mudflows. Recent research has documented two of them in much greater detail.
Although their deposits were known previously, geologists thought their deposits were from multiple separate, smaller eruptions.
Now, based on trace element and mineral “fingerprinting,” plus moreprecise dating based on the magnetic directions “frozen” in the rocks, what were once thought to be a number of isolated eruptions are now known to have been parts of two big ones.
The older one, called the Mcmullen Creek eruption, occurred 8.99 million years ago.
Its deposits are unusual in containing no sanadine, a peculiar kind of hightemperature feldspar mineral common in most other volcanic deposits in the area.
Located mainly in southern Idaho, it erupted at least 370 cubic miles of rock. It covers over 4,000 square miles, a minimum estimate because parts of it are concealed under younger deposits.
The other, called the Grey’s Landing eruption, occurred 8.72 million years ago and covered major parts of southern Idaho and northern Nevada. It was even larger, with a minimum estimated volume of over 600 cubic miles of rock. It covers over 8,000 square miles, the largest eruption documented from the Yellowstone hotspot.
It was also the hottest, with emplacement temperatures estimated to have been 1,700 degrees Fahrenheit. It was so hot that fragments blown out melted together after settling, forming a rock type called a welded tuff.
Any organisms living in the area would have been incinerated.
Should we be worried about another such eruption?
The researchers suggest not. During its 16 million year history over 31 eruptions occurred along the Yellowstone hotspot track, including eleven socalled super-eruptions, those that ejected more than 100 cubic miles of rock. Since near the end of the Miocene Epoch, about 6 million years ago, their size, frequency, and temperature have all decreased, suggesting that the hotspot is waning, now averaging only about one eruption every 1.5 million years.
The Earth works on a different timescale than we do.
gnidovec.1@osu.edu