SCIENTISTS have discovered a hidden lid that keeps the vast reservoir of magma beneath the Yellowstone supervolcano at bay.
For years scientists have suspected that a mysterious chamber beneath the northeastern part of the Yellowstone caldera may hold molten rock.
3
3
How deep the reservoir lies, or just how much magma it holds is still up for debate.
But scientists say they have found a hidden magma cap atop this reservoir that helps stop the supervolcano from erupting.
There have long been questions over when Yellowstone’s expansive volcanic system could see an eruption.
Historically Yellowstone has erupted every about 600,000 years or so, but it has been stagnant for 630,000 years – meaning it is 30,000 years overdue.
But this cap – which stretches between 3.5 and 4 km (2.2 and 2.5 miles) below the Earth’s surface – allows the volcano to ‘breathe’, according to scientists.
They say new models show the cap to be regularly releasing small belches of gas that keep internal pressures stable and hold off an eruption.
Based on the timing of previous explosions, scientists at the United States Geological Survey predict the risk of a Yellowstone super-eruption is about 0.00014% each year.
If enough air was restricted in the supervolcano’s ‘throat’, scientists believe a catastrophic explosion could follow.
“For decades, we’ve known there’s magma beneath Yellowstone, but the exact depth and structure of its upper boundary has been a big question,” Earth scientist Brandon Schmandt from Rice University explained.
“What we’ve found is that this reservoir hasn’t shut down – it’s been sitting there for a couple million years, but it’s still dynamic.“
Using a new technique developed by Schmandt’s co-lead author Chenglong Duan, scientists sent vibrations into the ground to create a model of layers in Earth’s crust.
Duan says the technique has provided the “first super clear images of the top of the magma reservoir beneath Yellowstone caldera.”
The vibrations – seismic waves – flowed through the rock but began moving slowly, suggesting they were penetrating a muddy mixture of supercritical fluid and magma.
This was located between 3km and 8km deep.
“Seeing such a strong reflector at that depth was a surprise,” added Schmandt.
“It tells us that something physically distinct is happening there — likely a buildup of partially molten rock interspersed with gas bubbles.”
But atop this reservoir is a “sharply defined top” – the cap.
It is considered a ‘self-sealed’ lid because it is only slightly porous – meaning it can let out trace amounts of gases to release any pressure build up.
Beneath the lid there appears to be supercritical water, which is heated and pressurised to a point where the line between liquid and gas blur.
This process could result in an eruption, if not for the gradual cooling and crystallisation of the sludgy material in the upper crust which creates a minimally leaky magma cap.
It looks like the system is venting gas – which is good news.
“Although we detected a volatile-rich layer, its bubble and melt contents are below the levels typically associated with imminent eruption,” Schmandt said.
“Instead, it looks like the system is efficiently venting gas through cracks and channels between mineral crystals, which makes sense to me given Yellowstone’s abundant hydrothermal features emitting magmatic gases.”
3
