New mapping of the magma lying beneath the iconic national park sheds light on where volcanic activity is shifting, and the likelihood of a full-scale eruption.
With its famous hot springs and gushing geysers, Yellowstone is one the most iconic national parks in the country and astonishes millions of visitors every year.
Those awe-inspiring sights are thanks to the magma buried miles beneath the surface, part of one of the world's largest active volcanic systems. How exactly the magma is stored there -- and therefore, how it would erupt -- has been a mystery.
Now, scientists have used advanced techniques to find the answers to some of these questions. A volcanic eruption is unlikely to occur at Yellowstone National Park because of the magma formations underneath, according to research published in the journal Nature on Wednesday, and the concentration of volcanic activity will be shifting northeast.
"Nowhere in Yellowstone do we have regions that are capable of eruption," said lead author Ninfa Bennington, a research geophysicist at the Hawaiian Volcano Observatory. "It has a lot of magma, but the magma is not connected enough."
Because there's so much magma, Bennington said, the region will stay volcanically active. But that magma is stored in segregated reservoirs, so it is not concentrated enough to lead to a volcanic eruption, at least within our lifetimes, she added.
Two types of magma exist under the park. One is basaltic magma, which triggers most volcanic activity on Earth. It erupts more easily because it has a lower resistance to flow, but underneath Yellowstone, it's dense and buried deep in the Earth's crust. So it's unlikely to erupt.
Rhyolitic magma, on the other hand, is much thicker and more resistant to flow. Underneath Yellowstone, basaltic magma heats the surrounding rock to help create this kind of magma in the Earth's upper crust.
But this formation is also unlikely to cause a volcanic eruption in the park because a lot of pressure needs to build up to erupt rhyolitic magma. The sort of massive upheaval required to cause such an eruption is very different from the day-to-day activity that delights tourists. If the rhyolite does erupt, Bennington said, it could lead to very explosive eruptions with lots of ash.
Recent volcanic eruptions in Hawaii, including one on the Big Island in late December, have primarily been caused by basaltic magma. But it was a rhyolite eruption that created the Yellowstone Caldera.
The rhyolitic magma that erupted explosively at Yellowstone in the past had the same consistency as asphalt, said Michael Manga, professor of earth and planetary science at the University of California at Berkeley who was not involved with the study.
In the past 2.1 million years, Yellowstone has had three major eruptions, the most powerful ones in the world's recorded history and producing enough ash and lava to fill the Grand Canyon. But the last eruption was a small one nearly 70,000 years ago, and the last major one was hundreds of thousands of years before that.
"By no means is Yellowstone 'due for an eruption,' " said Erik Klemetti Gonzalez, an associate professor of earth and planetary sciences at Denison University who was not involved with the study. "There will be eruptions, but it will probably be thousands of years before we can expect an eruption."
The study's finding that volcanic activity is shifting is what scientists would expect, Klemetti Gonzalez said, as the North American plate continues inching to the west-southwest over the volcanic hot spot of underneath. However, Bennington said, it's unlikely to affect visitors' experience in our lifetimes.
Reaching definitive conclusions about Yellowstone is challenging, Manga said, because there aren't frequent volcanic eruptions there, like in Hawaii or Iceland.
Much of the scientific literature surrounding volcanoes uses seismic data -- using seismic waves to map geologic structures -- to measure the magma under the surface. Waves move more slowly through molten rock than solid rock, but they could also be affected by factors like pressure and temperature.
This study used the less common method of magnetotellurics, a geophysical technique that uses the Earth's electromagnetic field to image what lays beneath the surface. It's most sensitive to magma, Bennington said, so the brightest anomalies will show magma formations. With this mapping method, scientists can track the basaltic magma, which is the power source fueling volcanic activity in Yellowstone.
"They put together a really compelling story about what's happening underground and the relationship between the past and future volcanic activity," Manga said.