Grand Prismatic Spring
Credit: Wikipedia photo by James St. John, CC BY 2.0.

Grand Prismatic Spring is world famous, and one of many incredible things to see in Yellowstone National Park. Like everything there, its existence is temporary and will cease the next time the supervolcano erupts. This is the third-largest hot spring in the world, and it is continuously about 160 degrees (70 C) all the time.[1]

Do you know what's fueling all the hot springs and pretty geysers?

The volcano that sits underneath Yellowstone Lake, and the geyser basins of Yellowstone National Park is in fact one of three true supervolcanoes on our planet.  The others are Toba in Indonesia, and Taupo in New Zealand.[2]

Supervolcanoes are defined by the size of their eruptions, with a supervolcanic eruption involving a minimum of 1,000 cubic kilometers of material being erupted. This hasn’t happened since Taupo in New Zealand did it about 26,500 years ago.[2]

In modern times we haven’t seen anything like it.  The largest eruption in the past 10,000 years was Mount Tambora in Indonesia in 1815, which erupted about 160 cubic km of material.[3]  Mount St. Helens in the USA in 1980 erupted one cubic km.[4]  Mount Pinatubo in the Philippines in 1991 was the second-largest eruption of the 20th century, and it erupted 10 cubic km.[5]

In fact, only a large asteroid impact could be a worse natural disaster.[6] Even Mount Tambora altered Earth’s climate enough that crops failed around the Northern Hemisphere, livestock died en masse, famines ensued, and overall hundreds of thousands of people died from the effects.[7]

The last time Yellowstone had a supervolcanic eruption was 640,000 years ago.  Although that may seem like a long time, it also did it 2.1 million years ago.  It had a very large – although not fully supervolcanic size – eruption 1.3 million years ago as well.  And it has had many smaller eruptions, most recently spilling some lava between 3,200 and 3,500 years ago.[8]

Steamboat Geyser
Credit: Wikipedia photo by Hsing-Mei Wu, CC BY-SA 3.0.

Steamboat geyser within Yellowstone Caldera has larger eruptions than any other, although its eruptions are unpredictable and occur with years in between each one.[9]

What exactly is a supervolcano?

None of the supervolcanoes have been studied more extensively than Yellowstone. Supervolcanoes are entirely different things from regular volcanoes, and operate in a completely different manner.[10]

For more basic information on the types of volcanoes and other basic information and terms related to volcanology, which is the science of volcanoes, see my article here on InfoBarrel, Types of Volcanoes and Volcanology Terms.

Yellowstone Cross-section
Credit: Public domain image courtesy of NPS.

Diagram showing the basic construction of the Yellowstone Supervolcano.

Yellowstone's three major past eruptions

Three major eruptions have occurred here, two of which were supervolcanic. The eruptions ejected 2,500 cubic km of material (2.1 million years ago), 280 cubic km of material (1.3 million years ago), and 1,000 cubic km of material (640,000 years ago).[8] The big question is when the next one will occur.

In one million years from now, the volcano will be located under Southwestern Montana. It used to be located under Idaho, and is the reason the Craters of the Moon Volcano exists in Idaho. The hotspot actually doesn’t move, it’s the North American tectonic plate that moves over it over time.[11][8]

The magma chamber underneath Yellowstone Caldera is enormous. In 2013 it was estimated to have a volume of 960 cubic miles (4,000 cubic km), which is 2.5 times larger than previous estimates - but this is also much more accurate than previous estimates.[12]

The magma chamber continues to slowly fill, and frequently produces small earthquakes, and sometimes larger ones.[8] The ground is slowly rising, and some years it has risen three inches (7.6 cm).[13]

The two past supervolcanic eruptions covered large portions of what is now the USA in ash, and also parts of what is now Southern Canada and Northern Mexico. Even the smaller eruption of 1.3 million years ago covered most of what is now Wyoming, Colorado, Kansas, and Nebraska with ash.[8]

Lava Creek Eruption
Credit: Public domain image.

Map showing the extent of ash from Yellowstone's most recent supervolcanic eruption, called the Lava Creek Eruption, which occurred about 640,000 years ago.

What if Yellowstone erupted?

The good news is that geologists who have extensively studied the Yellowstone Supervolcano recently concluded that a fully supervolcanic eruption is probably one million years away. The bad news is that they concluded their report by stating that they could be wrong, and anything can happen in geology.[11]

I’ve read numerous news articles about Yellowstone, and it seems that whenever there’s an earthquake people begin to worry that the supervolcano might erupt. An earthquake at the Yellowstone Caldera does indicate that magma is moving and an eruption is getting closer, but does not necessarily mean that an eruption is about to occur.

The other two supervolcanoes on our planet are located on islands, which would somewhat lessen the effects of a large eruption on humans. Lots of ash would fall into the oceans, for example. Yellowstone however is located within a continent in a heavily populated country. Ash could fall down on tens of millions of people, and anyone within 100 miles (60 km) or so would be unlikely to survive because ash could be more than ten feet (three meters) thick.[8]

If an eruption were to happen in the USA as it is now, it would easily be the largest natural disaster to ever affect humans, the economic damage would be in the trillions of dollars, and there would be major disruptions to life as we know it. Water would be polluted over a wide area, air would be unbreathable over a wide area until ash settled, crops would be destroyed, and food shortages would be guaranteed to cause many lives to be lost.[14]

A severe volcanic winter, probably lasting decades or more, would be guaranteed. In the short term there would be millions of lives lost, and there would be major chaos for those who survived the eruption and its immediate aftermath.[14]

Let this potential scenario inspire you to be prepared, because it’s unknown when a large disaster could strike, which could actually be any of a large number of things. Supervolcanoes are just one possibility.