Scientists reveal why the mighty Yellowstone isn't ready to blow

There's not even a hint of a looming eruption at Yellowstone.

But you might wonder why, considering its violent past: Yellowstone has hosted "supereruptions" — the most explosive type of volcanic blast that would be regionally devastating, and blanket a large swathe of the U.S. in ash. These blasts were much larger than any in recorded history. (The last eruption, though not "super," happened some 70,000 years ago and poured lava over the present-day national park.)

New research reveals why the famously steamy park, hosting over 500 hot geysers, shows no signs of blowing its top. These days, the reservoirs of magma (molten rock) that feed Yellowstone hold pretty low concentrations of this magma. They simply don't contain enough volcanic fuel to drive the heat and pressure that would stoke an eruption.

"We can definitely say that these areas could not source an eruption in the present day," Ninfa Bennington, a U.S. Geological Survey research geophysicist who led the study recently published in Nature, told Mashable.

There are different reservoirs, or pods, of magma below the Yellowstone Caldera, which is the sprawling basin formed during an immense eruption and dramatic collapse some 631,000 years ago. You can think of each reservoir like a sponge, filled with pores. There's some magma in these pores spaces, but it's not nearly saturated.

One future day, these sponges may fill up with magma and reach a critical percentage — wherein immense pressure builds beneath the ground and spawns an eruption. Today, however, there is no explosive threat.

"We're so far off from that right now," Bennington said.

Modeled ashfall from a Yellowstone supereruption. Credit: USGS / Mastin et al.

The most destructive type of eruptions at Yellowstone, which form great depressions called calderas, are by far the rarest. Credit: USGS

To grasp what's transpiring in these critical reservoirs of magma today, the geologists used a technique called magnetotellurics. In contrast to radar or sonar, the scientists don't create or beam signals to discern what lies beyond or below. Instead, these surveys capitalize on the currents naturally created by Earth's electromagnetic field. And magma, due to its composition, is really good at conducting electricity, allowing insight into its presence deep beneath Earth's surface.

The surveys, beyond revealing Yellowstone's inability to host an eruption today, showed that the most primitive magma flowing up from Earth's mantle to Yellowstone connects directly to a reservoir in the northeast region of the Yellowstone Caldera. This suggests this northeast region would become the future center of volcanic activity in Yellowstone.

But there's no evidence of those reservoirs filling up. "It could be a long, long time," Bennington said.

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If magma does once again snake its way from deep inside Earth and saturate these shallower reservoirs, an eruption wouldn't be a surprise. We'd have many decades, if not centuries, of warning. The moving magma would trigger swarms of potent earthquakes, and the ground would majorly deform.

"These parameters are well monitored, so there will be ample warning of any potential future eruption," the U.S. Geological Survey says.

Today, Yellowstone remains a place of low volcanic risk. Sure, there are sometimes small explosions stoked by hot water and steam. But it's mostly thermal pools and awesome geysers, reminding us of what could potentially awake, one distant day.