Yellowstone volcano geologists can trace all activity over the past 17 million years to a vast geographic feature dubbed the Snake River Plain. Stretching across most of Southern Idaho, the Snake River Plain violently formed when the North American plate passed over a scorching plume of magma in the Earth’s crust. This plume, which is believed to currently reside under Yellowstone National Park, pushed the land upwards and forced lava flows to the surface. Today, geologists refer to this region as the Yellowstone Plateau Volcanic Field (YPVF) – the youngest of many volcanic fields stretching from Northern Nevada to Southern Oregon.
The United States Geological Survey (USGS), which keeps a watchful eye on Yellowstone volcano, has dubbed this feature the Earth’s “largest volcanic structure”.
In the weekly edition of the Caldera Chronicles, USGS geologist Lisa Morgan explained how tectonic movements of the North American plate trigger a continuous cycle of evolution at the YPVF.
The geologist said: “The current YPVF has seen three cataclysmic caldera-forming eruptions, starting with the first at about 2.08 million years ago.
“That eruption produced multiple ash sheets originating from at least three separate volcanic vents located within the Huckleberry Ridge Caldera, a structure that is close to 100km across.
Yellowstone volcano: Powerful tectonic movements have created the Yellowstone landscape
“The second big eruption, the Henrys Fork Caldera, was considerably smaller, occurred about 1.3 million years ago, and was nested within the southwest portion of the older Huckleberry Ridge Caldera.”
Post-caldera lava flows represent some of the largest rhyolite flows on Earth
The last and most recent major eruption occurred about 631,000 years ago and formed the current shape of the Yellowstone caldera.
According to Dr Morgan, each of the three eruptions produced similar geological features across Yellowstone.
The Yellowstone caldera blast was characterised by a series of rhyolite lava and basalt flows, first starting about 1.2 million years ago.
The caldera eruption itself took place across two separate blasts, which happened only days or weeks apart.
Once the super-eruptions were over, the volcanic caldera collapsed in on itself and formed the park’s features as they are enjoyed by visitors today.
After that, the USGS has found evidence of volcanic eruptions right after the caldera formed and up until about 450,000 years ago.
Then, Yellowstone reared its ugly head once again about 250,000 years ago with a renewed period of volcanism.
The most recent lava flows at Yellowstone volcano occurred about 70,000 years ago.
Dr Morgan said: “The post-caldera lava flows represent some of the largest rhyolite flows on Earth, many in excess of several tens of cubic kilometres in volume, extending up to 30km from their source vents, and having thicknesses greater than 100m.”
Yellowstone’s ongoing stage of volcanism is characterised by frequent hydrothermal activity, which the USGS said started about 400,000 years ago.
Another factor in the constant evolution of the Yellowstone system is the effects of glaciation and the last ice age about 15,000 years ago.
But what does all of this mean for the future of volcanic activity at Yellowstone volcano?
As the landscape continues to shift and change with time, geologists believe caldera-forming eruptions will cease at some point in the future.
According to Dr Morgan, the North American plate will move over and away from the Yellowstone magma plume and Yellowstone will drop or subside “substantially”.
The geologist said: “Then, the cycle will begin once again. A new volcanic field complete with multiple, large nested calderas, lakes, geyser basins, and hydrothermal explosions, with accompanying tectonism, will form to the northeast of current-day Yellowstone.”
Is Yellowstone volcano overdue another major eruption?
Geologists studying volcanic activity at Yellowstone, past and present, do not believe the supervolcano is expecting another caldera-forming blast any time soon.
USGS geologist Michael Poland said: “We've heard many statements that Yellowstone is overdue – that it has a major eruption every 600,000 years on average, and since the last eruption was 631,000 years ago, well, you can see where this is going.
“Is this true? In a word, no. In two words, no way. In three words, not even close. Yellowstone doesn't work that way.”