Predicting the Next Eruption at Yellowstone Volcano

The Yellowstone supervolcano has produced some of the largest eruptions known to man, thus there is understandably significant interest in monitoring its activity. But is it possible to predict when the volcano will next erupt?

Yellowstone National Park sits atop a giant supervolcano that is considered to be active, albeit currently dormant.

The most recent volcanic eruption at Yellowstone was a lava flow that occurred around 70,000 years ago, but scientists think it has the potential to erupt in the future, given that there is hot, fluid or semi-fluid material present beneath the ground (magma) as evidenced by the abundance of hydrothermal features and frequent seismic activity in the area.

Despite claims from some quarters, though, that an eruption is overdue, researchers have not detected any signs that one is imminent.

A supervolcano is a large volcano that has experienced at least one eruption of magnitude 8 or more—the highest value on the Volcanic Explosivity Index.

The Yellowstone supervolcano, located in northwestern Wyoming, has experienced three giant explosions in the past two million years or so, which were among the largest eruptions known to man. These eruptions occurred around 2.1 million years ago, 1.3 million years ago, and around 631,000 years ago, creating the caldera—massive craters that form when a volcano erupts and collapses—present today.

Since the giant explosion 631,000 years ago, there have been dozens of smaller eruptive events leading right up until the lava flow of 70,000 years ago.

While it is possible that another eruption will occur in the future given Yellowstone's history and the presence of magma, scientists simply do not know when such an event will happen again nor what it will look like. These eruptions do not happen at regular intervals making them difficult to predict, not to mention the fact that there is no direct way to see what is going on beneath a volcano.

Having said that, eruption forecasting has significantly improved in the past two decades or so, and there are now a number of signs scientists can look for that may be giveaways of an imminent eruption.

Researchers at the Yellowstone Volcano Observatory (YVO) are constantly monitoring the region for such signs using an array of technologies that provide real-time information.

These signs may include particularly strong earthquake swarms and rapid deformation of the ground, events that are often seen in the days and weeks before an actual eruption.

In the case of a large eruption, scientists expect that the period beforehand would be characterized by intense activity far exceeding normal background levels in various locations across the Yellowstone supervolcano. Signs of a catastrophic eruption may be detectable weeks, months or even years prior.

Due to the magma beneath the surface, the Yellowstone region experiences many small earthquakes, ground deformation and other geological activity on a regular basis. But as long as these processes do not stray too far outside normal levels they are not considered a sign that an eruption is imminent.

YVO scientists monitor seismic activity with a network of seismographs, and track ground deformation, or movement of the Earth's surface, using a combination of Global Positioning System and InSAR (Interferometric Synthetic Aperture Radar) satellite-based techniques. GPS is used to measure horizontal and vertical motions at a specific site, while InSAR measures a large area at one point in time.

This movement—in particular uplift, or elevation of the ground—can be a sign that magma is moving toward the surface but this is not necessarily an indicator of an imminent eruption. Many volcanoes—particularly calderas like Yellowstone—show signs of uplift and subsidence for many thousands of years without ever erupting.

In Yellowstone, ground uplift, for example, can be caused by other factors other than upward magma movements, like water or gas accumulation.

Scientists still monitor this kind of ground movement at Yellowstone though in order to gain a better understanding of what motion fits with normal long-term trends and what may be evidence of a potential upcoming eruption.

"The ground surface at Yellowstone is moving all the time, sometimes up and sometimes down, and it would not be cause for concern unless it was outside the normal patterns," Kari Cooper, a professor and chair of the University of California, Davis Department of Earth and Planetary Sciences, told the Associated Press.

The Yellowstone supervolcano sits above a hotspot—an area of anomalously high temperatures—in the Earth's mantle that causes melting of the material in the region. The resulting magma eventually feeds into a chamber just below Yellowstone.

Recently, a Facebook video claimed incorrectly that Yellowstone park had been closed down to rising volcanic uplift, indicating that this was a sign of an upcoming eruption. But not only was the park open, but the ground in Yellowstone has also actually been subsiding, or deflating, in recent years.

Michael Poland, scientist-in-charge at the YVO, told the AP "only if we saw a really dramatic uplift"—for example, the ground rising feet in weeks or months—"would it be something that we thought might be a hazardous change."

Despite the tools now available to scientists, one study published in the journal Nature Reviews Earth and Environment last year found that giant supervolcano eruptions are hard to predict because they are so diverse in the rapidity of onset, duration of eruption, and triggering mechanisms, among other factors.

These catastrophic "supereruptions" are the largest explosive volcanic eruptions on Earth, occurring roughly once every 100,000 years on average.

The paper found that they can start mildly over weeks to months before escalating, or going into vigorous activity immediately. Meanwhile, individual supereruptions can take place over periods of days to weeks, or be spread out over decades. There is also significant diversity in their triggering mechanisms.

While past giant eruptions help to define a supervolcano, they are not necessarily a good indicator of how a given volcano will behave in the future, the researchers said.

For example, if and when Yellowstone does erupt again, the most likely outcome would be a hydrothermal eruption, which is characterized by violent explosions that eject steam, water, mud, and rock.

Lava flows would be the most likely type of volcanic eruption. These could range in size dramatically, and may or may not include explosive phases. Meanwhile, the worst-case scenario would be a giant supereruption, although the risk of such an event occurring in any given century is tiny.

While extremely unlikely, such an event would be catastrophic, resulting in the ejection of vast amounts of ash and debris into the atmosphere that could have the potential to affect the global climate. Given the inherent uncertainties, however, it is even possible that Yellowstone will never see an eruption on such a scale again.

Other recent research has examined the processes taking place under the ground in the Yellowstone region, shedding light on the eruptive potential of the volcano.

One study published in the journal Science this year found that there was significantly more magma beneath the supervolcano than previously thought. In the paper, scientists analyzed seismic data to map the location and amount of melt—the liquid part of magma—under the caldera.

"An obvious but key requirement for an eruption is the presence of magma," Cooper wrote in a "Perspective" article about the Science study. "This magma also needs to be distributed so that it can mobilize and erupt as a coherent body. Therefore, a key issue for eruption hazard assessment is to ascertain how much magma is below the surface and where."

The authors of the Science article found that more melt was present than had previously been recognized and that it was located at shallow depths in the crust—in the depth range where previous eruptions were sourced. They also found that the magma reservoir below the caldera was approximately twice as large as previously thought.

But the scientists said the amount of melt is significantly lower than required for an eruption to occur in the near future.

"Continued monitoring of the subsurface should provide a clear picture if the situation begins to dramatically change," the researchers wrote in the paper.

Given that supervolcanoes often go through periods of unrest, including seismic activity, ground deformation, and gas emissions, the monitoring of these processes must contend with the challenge of differentiating "normal" unrest from signs that an eruption is imminent, the authors of the Nature study wrote.

Further research is needed to better understand the processes that cause these supervolcanoes to erupt in order to help predict such events.