Supervolcanoes

Few things are certain in life, but lots of things are certain in geology. We know that earthquakes will shake, tsunamis will crash, and volcanos will erupt. The question is not if, but when, which makes predictions and warnings crucial. Most of these disasters are regional concerns (although sometimes these regions can be quite large), but some can have global effect: supervolcanos. So, we should all be relieved that scientists have published a new paper showing that we should expect plenty of early warning when the next supervolcano eruption comes around.

Supervolcanos are just what they sound like: really big volcanos. Unlike the smaller volcanoes we usually picture, though, these tend not to look like mountains, but like enormous sunken bowls within the landscape, called calderas. These calderas can be enormous. For example, the caldera at Yellowstone is 75km (44mi) long, and within it are forests, mountains and valleys. As a visitor hiking and driving around I struggled to see the caldera from the ground—it takes a map to really grasp that it exists.

These calderas are formed after eruptions, when the ground sinks down onto the emptied magma chamber. Supervolcanoes, and their calderas, are scattered around the world, from the United States to Indonesia and South America to New Zealand. Eruptions have devastating local effects, but can affect the entire planet as well, changing the atmosphere and the weather. Particularly large eruptions have been suggested as factors in multiple mass extinctions, including Cretaceous/Paleogene event 65 million years ago that led to the extinction of dinosaurs and the rise of mammals.

Massive eruptions have shaped life on earth more recently as well. Our species, Homo sapiens, was almost driven to extinction in an event that some researchers think was caused by the eruption of the Mount Toba supervolcano 76,000 years ago.

Having warning of the next one might allow humans time to prepare, and early enough warning might give us a chance to avert disaster altogether. Methods of preventing a massive eruption have been proposed (although obviously not tested so far). So, a new paper examining the triggers and warnings for supervolcano eruptions in Geophysical Research Letters by Haley Cabaniss and Eric Grosfils from the University of Illinois at Urbana-Champaign and Patricia Gregg from Pomona College should be a welcome result.

They examined the geological factors leading to supervolcano eruptions by modeling the Taupo Caldera in New Zealand. Supervolcanoes tend to occur in areas where the Earth is stress, such as places where different tectonic plates intersect. Their model found that certain types of stress were more likely to trigger eruptions than others. Places where the Earth’s plates were being stretched apart were more unstable than places where they were being compressed together, and therefore more likely to have eruptions, but other factors, like the amount of magma entering chambers beneath the caldera, were also significant factors.

The model also allowed them to test what the lead up to a massive eruption would look like, and, thankfully for life on earth, they found that there would be ample warning. A caldera preparing to erupt should rise very significantly in the centuries, and maybe millennia, before an eruption of supervolcanic scale. The landscape would rise by tens to hundreds of meters, something easy to measure and interpret.

The more we learn about volcanic eruptions, the more it becomes clear that volcanoes are very considerate natural disasters. Unlike earthquakes, there’s typically warning that an eruption is coming and indications of what that eruption will be like. This gives humans the chance to prepare for the disaster, and the more we learn about volcanoes the better those predictions become.

How worried should we be about the Yellowstone Supervolcano?

News stories about increased earthquakes, geyser activity, or rising magma levels at the Yellowstone Caldera, or Yellowstone Supervolcano, appear in the press multiple times per year. This trend can lead to fears that a massive eruption must be imminent, but these fears are misplaced.

These changes can be indicators of approaching eruptions, but not all eruptions are created equal. The massive eruptions with global effects described in documentaries about supervolcanos very rare and would be preceded by much more dramatic changes. Most eruptions at Yellowstone would have only local effects, and even those might not be as frightening as we fear.

The most common type of eruption at Yellowstone isn’t even technically volcanic, because there’s more than just magma underneath the ground there. Reservoirs of water lie below the surface, feeding the famous geysers in the national park. The most likely eruption there would involve this water instead of lava, creating dramatic but merely geothermal eruptions. However, although water may be less dangerous, these eruptions can still create local dangerous, blasting huge craters and moving large amounts of rock, but don’t presage a more hazardous volcanic eruption.

Even the volcanic eruptions are mostly local though. There might be local lava flows and other hazards, but these would be more like the eruptions in recent history at Mt. St. Helens in the US in 1980 or Mount Pinatubo in 1991. While these would be serious hazards to people in and around Yellowstone, they would not be the epoch-defining disaster a supervolcanic eruption. Either way, we should know in advance what kind of hazard to expect, given the types and amounts of changed activity in the area, and therefore be prepared for whatever Yellostone throws our way.

Sarah Leach is studying for an MSc in Science Communication at Imperial College London

Banner Image: Pahoeoe fountain, Wikimedia Commons