Yellowstone supervolcano: ‘Anomaly’ could explain volcanic activity

Yellowstone supervolcano: Expert on ‘danger’ of Caldera in 2015

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Yellowstone National Park sits above an enormous volcanic hotspot responsible for large-scale volcanism in the states of Idaho, Montana, Nevada, Oregon and Wyoming. A hotspot is an area of the Earth’s crust where hot plumes rise from the mantle below and cause volcanic activity at the surface. The Yellowstone hotspot has produced three supereruptions in total — 2.1 million, 1.3 million, and approximately 640,000 years ago, each forming their own caldera.

Its formation has been the subject of intense debate for decades, with scientists facing difficulties studying what lies in the deeper mantle as mantle plumes can easily evade detection since they are generally quite slender.

However, a breakthrough study in 2018 analysed the seismic waves beneath the surface at Yellowstone, and detected an “anomaly”.

Using a dense network of seismometers, researchers Peter Nelson and Stephen Grand from the University of Texas analysed the seismic waves detected by 71 earthquakes across the US to gain a greater understanding of the material in the mantle.

Seismic waves travel faster through cold rock than hot rock, and so something extremely hot, such as a mantle plume, would slow the waves.

Mr Nelson and Mr Grand’s research found a “single narrow, cylindrically shaped slow anomaly, approximately 350 kilometres in diameter that we interpret as a whole-mantle plume”.

Their research, published in Nature, said the “anomaly” is the “deep origin for the Yellowstone hotspot”.

They added that the evidence for the existence of these thin mantle plumes is “currently beyond the resolution of global tomography models”.

The plume, Mr Nelson and Mr Grand said, is “rooted at the core-mantle boundary near the Mexico/California border” and runs northeast beneath the western US to Yellowstone as it gradually rises through the mantle.

The research continued: “We conclude that a plume rising from the CMB is the ultimate heat source driving Yellowstone volcanism.”

According to the study, the volcanic plume, around 600 to 800 ºC warmer than surrounding areas, is responsible for the volcanism witnessed in Yellowstone.

Global topography, they said, would not detect such a plume, and they may also exist elsewhere too.

Barbara Romanowicz, a planetary seismologist at the University of California, told Earth Magazine in 2018: “Yellowstone presents a unique opportunity to image a plume under a continent.

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“There’s probably a plume under Hawaii, and another under Iceland, but we don’t have the seismic coverage [from seafloor instruments] to image those.”

Similar plumes may also exist beneath Africa and Antarctica, but seismic detection technology is not yet adequate enough to register them.

Given that most hotspots also lie beneath the ocean floor, it is unlikely that there will be a sufficient seismometer network to establish a satisfactory picture of what lies beneath.

Mr Nelson and Mr Grand’s breakthrough discovery came as volcanologists speculated that it may never erupt on an enormous scale again.

According to the United States Geological Survey (USGS), volcanoes do not follow “predictable schedules”, despite claims Yellowstone is “overdue” for an eruption.

The USGS website says: “Most volcanic systems that have a supereruption do not have them multiple times.

“When supereruptions do occur more than once in a volcanic system, they are not evenly spaced in time.

“Although another catastrophic eruption at Yellowstone is possible, scientists are not convinced that one will ever happen.

“The rhyolite magma chamber beneath Yellowstone is only 5-15% molten (the rest is solidified but still hot), so it is unclear if there is even enough magma beneath the caldera to feed an eruption.

“If Yellowstone does erupt again, it need not be a large eruption.

“The most recent volcanic eruption at Yellowstone was a lava flow that occurred 70,000 years ago.

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