The Yellowstone supervolcano produced a huge eruption around 613,000 years ago, when it ejected 240 cubic miles of material. That's more than double the volume of Lake Erie, and 2,500 times bigger than the 1980 eruption of Mount St. Helens.
And since then, the volcano has produced many more smaller eruptions of rhyolite (igneous, volcanic rock) lava flows.
Scientists with the U.S. Geological Survey's volcano observatories are now working to better understand these smaller events in order to understand the hazards posed by the magmatic system at Yellowstone.
Yellowstone has produced at least 28 rhyolite eruptions over the last 610,000 years, a statement from California Volcano Observatory said. These were not small eruptions, producing lava flows ranging from 0.1 to 17 cubic miles—in comparison, Mount St. Helen's produced 0.06 cubic miles of material.
What scientists are hoping to work out is whether these lava flows were produced slowly over time, or whether it came from short, clustered eruptions. "If eruptions are clustered in time then the occurrence of one eruption may indicate that the next eruption may follow closely," the statement said.
Researchers used a dating technique based on the decay of the radioactive potassium-40 to radioactive argon-40, which can tell them when the rock crystalized, allowing them to work out time of origin.
By analyzing the volcanic rocks at Yellowstone, researchers discovered that rhyolite lava flows were "highly clustered in time," with eruptions taking place in episodes. In one phase of activity there were seven eruptions over a period of around 1,000 years. The team now hopes to further refine these episodes—including the timing and length—and build this into volcanic hazard assessments for Yellowstone.
Monitoring volcanoes across the U.S. is a priority for the USGS, and the agency is currently in the process of establishing a National Volcano Early Warning System. The system will help scientists better monitor all dangerous volcanoes in the U.S. by modernizing and expanding its networks using broadband seismometers, real-time continuous GPS receivers and volcanic gas sensors, among other technologies. New networks are also being introduced to "under-monitored" volcanoes like Mount Baker in Washington.
"Improvements to volcano monitoring networks allow the USGS to detect volcanic unrest at the earliest possible stage," Tom Murray, the USGS Volcano Science Center director, said in a statement. "This provides more time to issue forecasts and warnings of hazardous volcanic activity and gives at-risk communities more time to prepare."