Scientists have known for quite some time a series of volcanic eruptions generated by a super-volcano under Yellowstone left a trail of mega-eruptions across the Pacific Northwest, but new evidence discovered by an international team says instead of a number of eruptions, there were only 12 distinct eruptions, according to csmonitor.com.

Earlier theories suggested there were numerous, less intense eruptions, but Dr. Thomas Knott said in a press release, the size and magnitude of the newly defined eruption was as large as the better known eruptions at Yellowstone, if not larger.  Knott added it was just the first in an emerging record of newly discovered super-eruptions during a period of intense magmatic activity between 8 and 12 million years ago.

And the area below Yellowstone is still active.  A recent study found the super-volcano’s magma chamber is some 55 miles long and 18 miles wide, larger than scientists had previously believed.  That study, conducted in 2013, said should that super-volcano erupt, it may be 2,000 times as violent as the eruption of Mt. St. Helens.

The last eruption in Yellowstone occurred about 640,000 years ago, and that fact has some scientists worrying about a new eruption.  According to the BBC, “Three super-eruptions at Yellowstone appear to have occurred on a 600,000-700,000 year cycle starting 2.1 million years ago.  The most recent took place 640,000 years ago – suggesting Yellowstone is overdue for an eruption.”

The evidence uncovered by this new study suggests the super-volcano at Yellowstone could produce a catastrophic eruption on a much shorter cycle of about every 250,000 years.

Scientists used paleomagnetic data, radioisotope dating and rock and mineral characteristics to determine the locations and estimate the size of the ancient eruptions.  One of them, dubbed the Castleford Crossing eruptions, left behind a volcanic sheet the size of the state of Connecticut in southern Idaho.  The team located another 11 eruptions they say were similar in size to the super explosions at Yellowstone.

Dr. Knott commented, “While it is well-known that Yellowstone has erupted catastrophically in recent times, perhaps less widely appreciated is that these were just the latest in a protracted history of numerous catastrophic super-eruptions that have burned a track along the Snake River eastwards from Oregon to Yellowstone.”