Everything you need to know about Yellowstone’s supervolcano


Geysers. Hot springs. Wildlife. A few words probably come to mind when you think about Yellowstone National Park. But there’s one word that might come as a surprise: supervolcano. Because, if you didn’t know it already, the land that makes up Yellowstone National Park is actually one of the world’s largest active (yes, we said active) volcanoes.
A supervolcano describes any volcano that spews 240 cubic miles of magma or more, and three of Yellowstone’s eruptions have met this mark. Don’t worry, they happened a long time ago on a human scale. Though on a geological scale, not so long ago at all.
To be clear, just because it’s a supervolcano doesn’t mean it’s the deadliest. Volcanoes that erupt more frequently or powerfully are far more dangerous to humans. There are at least 12 supervolcanoes worldwide, and so far they haven’t managed to wipe out the human race. So we’re probably doing just fine.
But still, if you’re visiting Yellowstone National Park, it’s a lot more mesmerizing when you know exactly what’s beneath your feet.
Yellowstone’s Volcanic Past

The first time Yellowstone went “boom” was around 2.1 million years ago—although the eruption seemed to occur over several decades rather than one single, massive lava outpouring. The ash from those eruptions reached from Canada to Texas and “likely caused a notable decrease in temperatures around the globe,” according to the U.S. Geological Survey (USGS). These are King Kong-sized eruptions compared to anything in recorded history. If you're worried about barbecued ancestors, rest assured that there's no evidence early humans were in North America at that time.
More recent eruptions were smaller but still big. When a volcano erupts and collapses, you get what’s called a caldera—think of the classic open mouth at the top of a conical volcano like Mount St. Helens. An eruption 640,000 years ago created Yellowstone’s present-day caldera, which reaches from Artist Point in the north to just south of Lewis Lake, as far west as the Bechler River and encompassing half of Yellowstone Lake to the east. It’s 30 miles by 45 miles wide. When you drive the park roads from West Yellowstone to Mammoth Hot Springs, or from the Grand Canyon of Yellowstone to Yellowstone Lake, you’re quite literally driving through the mouth of a volcano.
In case you’re concerned your National Park vacation may turn into a dystopian action movie, like the ‘90s flick Dante’s Peak, worry not: Scientists say Yellowstone isn’t on track to blow in any of our lifetimes. If volcanoes were set by a calendar, Yellowstone wouldn’t be due for an eruption for another 100,000 years. And geologists aren’t sure that Yellowstone will ever erupt again. The magma below the park is only 5-15 percent molten these days, meaning most of it is solid below ground instead of swishing around, which may not be enough to cause an eruption.
Plus, if it did erupt, it wouldn’t necessarily be a big one. The most recent volcanic activity was a relatively relaxed lava flow 70,000 years ago.
Where You Can See Evidence of Yellowstone’s Volcanic Activity


If you want to see evidence of Yellowstone’s volcano activity, the good news is that, like Dolby, it’s all around you. Here are a few spots that illustrate the park’s volcanic activity, both past and present.
Glimpse the caldera at Washburn Hot Springs overlook
While the caldera encompasses much of the park, it can be hard to get a sense of where its edges are. The best place to see its rim is at Washburn Hot Springs overlook. There’s a sign here explaining which parts of the vista are the caldera. Hint: It probably won’t look like you expect—less bubbly magma hellscape and more like a very big forested depression in the ground. You’ll have to use your imagination to picture what it looked like way back when.
Learn about turning lava into early human tools at Obsidian Cliff
When magma contains lots of silica and manages to cool without creating crystals, it forms a kind of black glass: obsidian. Obsidian has been used by humans for thousands of years because it can be shaped into extremely thin edges, making it a useful sharp tool. Think arrowheads and blades. Yellowstone had an entire, 98-foot thick wall of obsidian known as the Obsidian Cliff. Obsidian from this area was being used by humans more than 11,000 years ago and remnants of those tools have been found from western Canada to Ohio.
Picture Obsidian Cliff both as a major source of early human technology as well as a 10-story tall wall of magma.
Get geyser-wild at Norris Geyser Basin
Geysers require three things: heat, water, and an underground natural “plumbing” system, according to the National Park Service. Yellowstone has these in spades.Underground magma provides the heat. Rain and snow provide water. And a bunch of fissures and cracks make up the “plumbing.” So it’s no wonder the park has more than 500 geysers and more than 10,000 hydrothermal features.
You’ll probably see plenty as you drive through the park, but one stands out: Norris Geyser Basin. It’s the hottest and oldest geyser system in the area—nature’s proof that you can be both old and smokin’ hot. Scientists sometimes drill in the area to figure out exactly how steamy it gets. Their highest recorded number? 459 degrees Fahrenheit. Almost all of the thermal features at Norris are above boiling point. (When the park tells you not to step in the water, believe them!)
Another fun fact: in addition to being hot, some of the geysers in Norris are as acidic as vinegar, according to the NPS. That’s pretty rare for geysers.
The established boardwalk can take you through and around the features in under three miles. Be sure to watch your step.
Find four types of hydrothermal features at Fountain Paint Pot


There are five types of hydrothermal features found at Yellowstone: geysers, hot springs, mud pots, fumaroles, and travertine terraces. You can find four of them at Fountain Paint Pot. Here’s what you should know about each.
Hot Springs: Of all the hydrothermal features in Yellowstone, hot springs are the most common, according to the NPS. They’re basically nature’s Jacuzzi, except only suitable if you’re an organism that can survive super-hot temperatures. (And no, being from Arizona doesn’t count.) In fact, those heat-tolerant microorganisms are what give the park’s hot springs their rainbow of colors.
How does a hot spring work? Basically, rainwater seeps into the ground, which gets heated up by underground magma. Because there are all kinds of cracks and fissures in the ground, that hot water rises back to the surface, and you get your Jacuzzi-jet action.
Geysers: Geysers are just like hot springs, except their underground plumbing is a little bit blocked, causing them to build up pressure that needs to periodically be released.
Mudpots: The NPS says to think of mudpots as a “natural double boiler.” An impermeable depression in the ground collects water—it’s often a layer of clay—while H2O below the surface fires up and releases as steam, heating up the collected surface water. Oh, and they typically smell like rotten eggs, because there’s usually hydrogen sulfide gas hanging about. On the plus side, iron oxides can also tint these areas pink, beige, and gray, hence the affectionate name “paint pot.”
Fumaroles: Fumarole is just a fancy word for steam vent. When a hydrothermal system has very little water, it boils away before it gets above ground, reaching the surface as steam and other gases. Some even whistle and hiss like a stovetop kettle.
(The only feature you won’t find at Fountain Paint Pot is travertine terraces. Travertine terraces are hot springs that travel through limestone and deposit calcium, which creates travertine terraces—the most classic of which is Mammoth Hot Springs.)
More like this: