Yellowstone: Geysers, Quakes and, Eventually, a Supereruption

Posted on September 2, 2023 by Brian H. Gill
Louis Prang's L. Prang and Co. lithograph (ca. 1875); from Thomas Moran's 'The Great Blue Spring of the Lower Geyser basin, Yellowstone National Park' (1874).
Litho. from Thomas Moran’s “The Great Blue Spring of the Lower Geyser basin, Yellowstone National Park”. (1874)

I started writing about Yellowstone, hazards, and science a few weeks ago.

Then life happened — there’s a link near the end of this post — something more timely came up, and now I’m back with a look at the area’s past, present and future.

Travelers’ Tales

Henry Wellge's map of Yellowstone National Park for the Northern Pacific Railway Company. (1904) David Rumsey Map Collection via Wikipedia, used w/o permission
Henry Wellge’s map of Yellowstone National Park for the Northern Pacific Railway Company. (1904)

The Yellowstone Plateau is one of North America’s beauty spots. A little over 3,400 square miles of it has been a National Park since 1872 and a World Heritage Site since 1978.

Folks have lived in the area for at least 11,000 years.

Folks who look a bit like me stumbled upon it about two centuries back. One of them, Jim Bridger, gave detailed reports of what he’d seen:

“…Bridger once described a petrified forest in Yellowstone that was home to ‘petrified birds that sang petrified songs’….

“…According to Bridger, there existed a lake of cool, trout-filled waters capped by a layer of hot water introduced from a nearby hot spring. When he needed a quick meal, Bridger would catch a trout and reel it in slowly, allowing time for it to cook as it passed through the overlying hot water….”
“Jim Bridger: Yellowstone’s Spinner of Tall Tales“, Yellowstone Volcano Observatory, U.S. Geological Survey (June 15, 2020)

Small wonder serious Euro-Americans didn’t follow up on Mr. Bridger’s reports.

At least one local’s description, passed along to the Lewis and Clark expedition, likely didn’t encourage a side-trip to find the Yellowstone River’s source.

“…There is only one hint of volcanic phenomena which Clark seems to have obtained from any source other than the presumed conversation with Colter, mentioned below. This was an Indian tale, received after Clark’s return, but before Colter’s return, to the effect that at the head of Tongue River, a branch of the Yellowstone, ‘there is frequently heard a loud noise like Thunder, which makes the earth Tremble, they state that they seldom go there because their children Cannot sleep—and Conceive it possessed of spirits, who were averse that men Should be near them.’…”
(“Colter’s Hell and Jackson’s Hole: The Fur Trappers’ Exploration of the Yellowstone and Grand Teton Park Region“, II. The Mystery of “La Roche Jaune” or Yellow Rock River, Merrill J. Mattes (1962, reprint 1970) via Gutenberg.org)[emphasis mine]

Can’t say I blame whoever told a foreigner about trembling earth, loud noises and reclusive spirits.

If I realized that outsiders were checking out my area, I might have encouraged them to stay away from a culturally-important place with natural wonders and good hunting.

Being strictly truthful, while giving an impression that the spot was geologically unstable and haunted to boot might seem like a good idea.1

Yellowstone: Hydrothermal and Other Hazards

National Park Service photo: geysers, from Thing to Do - Photography In Yellowstone. Used w/o permission.
Geysers in Yellowstone National Park.

About half of Earth’s active geysers are in Yellowstone National Park. They range from giants like Old Faithful and Steamboat Geyser, the world’s tallest (at the moment), to little one- and two-foot spurters.

ЮК's animated GIF, illustrating how a geyser works. (2009) via Wikimedia Commons, used w/o permission.A geyser is a manic-depressive hot spring.

Bipolar disorder is the current moniker for folks whose mood swings go from gloom to frenzy, and that’s another topic.

Anyway, hot springs happen when ground water goes through magma-heated rock on its way to an above-ground outlet.

We get geysers when heated ground water can’t flow out right away. Mainly because it cools off on its way to the surface.

Then we’ve got a (comparatively) cool plug of water keeping increasingly superheated water underground.

Sooner or later, there’s enough pressure to push the superheated water out. The pressure release lets the superheated water flash into steam.

That’s when a fountain of steam, water droplets, minerals, and anything else that has accumulated, shoots up in a, well, a geyser. The underground reservoir re-fills and the cycle starts again.

Some geysers, like Old Faithful and Grand Geyser, are predictable; but not very.

Old Faithful, for example, spouted every 66 and a half minutes in 1939. That’s 66 and a half minutes on average. Actual intervals were anywhere between 60 and 110 minutes.

These days, Old Faithful’s eruptions come every 92 minutes. Again, on average; with intervals ranging from 35 to 120 minutes.

There’s math describing relationships between how long an eruption lasts and how long it’ll be before the next one.2 But that’s not what I’m talking about this week.

Explosions and Boardwalks

USGS map, adapted from Morgan et al., 2022: 'Color-shaded bathymetric map of Yellowstone Lake showing locations of sediment cores and major tectonic features (faults, fractures, lineaments, caldera margins) and hydrothermal areas (vents, domes, hydrother­mal explosion craters).' Used w/o permission.
Yellowstone Lake, showing depth and tectonic features, including Elliott’s Crater.

Every now and then, the outlet for a hot spring or a geyser gets plugged or throttled down, or underground pressures rises, or both. Like so much else in this world, it’s complicated.

Sometimes underground pressure gets too high, and whatever’s holding it back breaks.

That happened to Porkchop Geyser.

Up until 1984, it was a porkchop-shaped heated pool about 10 feet across that occasionally erupted — every few years or so. The eruptions weren’t spectacular, a few yards high, emptying the pool, which refilled.

In march of 1985, it started spouting continuously. Sometimes the escaping steam and water roared so loud, folks could hear it more than a mile away.

Four years later, at 2:40 p.m. local time, September 5, 1989, eight visitors were watching Porkchop Geyser from a boardwalk. Porkchop’s plume shot up 65 to 100 feet. Then the geyser exploded.

Rocks more than a yard across were uprooted. Smaller debris landed up to 200 feet from the vent. Porkchop’s pool became a crater about 30 feet across.

None of the eight visitors were hurt. Startled, I’d imagine, but not hurt. That’s why boardwalks for visitors are so far from geysers.

Small hydrothermal explosions like Porkchop’s happen a few times per century.

Large hydrothermal explosions in Yellowstone happen on average every 700 years, leaving craters upwards of 100 meters, 328 feet, across.

Then there’s Elliott’s Crater, under Yellowstone Lake: named after Henry Wood Elliott, artist, who was with the Hayden Geological Survey of 1871.

About 8,000 years back, at least three “pulses” left a crater upwards of 900 yards across. Since then, much smaller explosions left craters inside Elliott’s Crater; and the area’s still hydrothermally active.3

Earthquake Lake and a 1959 Landslide

USGS photo: aerial view of Quake Lake, Montana, formed when a landslide flooded Hebgen Dam. via Wikipedia, used w/o permission.
Quake Lake, Montana, formed after the 1959 earthquake.
Google Maps satellite view: Earthquake Lake and Hebgen Dam, Montana.
Quake Lake, Montana, formed after the 1959 earthquake.

Hydrothermal features like geysers and hot springs, and geothermal activity in general, happen when hot material from deep inside Earth has been pushed near the surface.

Moving masses of magma make for earthquakes. Or earthquakes make for moving masses of magma. Either way, where we’ve got geysers and hot springs, we’ve got tourist attractions: and earthquakes.

And earthquakes plus tourists make for headlines. Which brings me to the 1959 Hebgen Lake earthquake.

The it-could-be-worse news is that only about two dozen folks died when part of a mountain slid onto Rock Creek campground and the Madison River, downstream of the Hebgen Dam. I’ve seen fatality estimates ranging from 19 to 28: possibly because some folks who were missing turned out to be dead.

Repairing Hebgen Dam took a few weeks. That was a concern. But it wasn’t the only one.

The landslide had also blocked the Madison River. Which is why the U.S. Army Corps of Engineers scrambled to dig a stable outlet for the rapidly-filling Earthquake/Quake Lake.

Time passed.

When my parents and I visited the Yellowstone area, we saw where the landslide had left a gap in the Madison River valley’s side. The U.S. Forest Service’s Earthquake Lake Visitor Center opened in 1967. I’m pretty sure that’s after our trip.

It’s funny. For someone with a degree in history, my memory for dates is shaky at best. Except for things like “in fourteen hundred and ninety-two, Columbus sailed the ocean blue”, and that’s yet another topic.

The 1959 landslide wasn’t, by far, the biggest in that area.

About 47,500,000 million years back, give or take, a whacking great chunk of limestone and dolomite went sliding across what we call the Bighorn Basin.4 And that’s yet again another topic.

Looking Ahead

USGS graphic: illustrating frequency of representing frequency of tectonic and geothermal events in Yellowstone area.
Small hydrothermal explosions to caldera-forming eruptions: figuring the odds. (USGS)

If more caldera-forming eruptions started in Yellowstone, that would push even election-years headlines and op-eds off the front page. Well, off the front page’s banner at any rate.

The last I checked, the U.S. Geological Survey says there’s “no evidence that another such cataclysmic eruption will occur at Yellowstone in the foreseeable future.”

I think they’re right. I also think they mean “foreseeable future” as in “the next few decades or maybe centuries”.

Films like “2012” notwithstanding, geologists have been learning quite a bit about how volcanoes, supervolcanoes and tectonics in general work. They’re also keeping close tabs on what’s happening on and under Yellowstone.

I don’t doubt that we have a very great deal left to learn. But I’m pretty sure that “they” don’t really know a supervolcano is about to cancel the next Super Bowl, and are selling tickets to an unsuspecting public.

Although that might make a good story. And I’m drifting off-topic again.

Now, about the Yellowstone Caldera. The last big eruption there happened about 631,000 years back. Before that there were two: about 1,300,000 years and 2,080,000 years back.

There may be another one coming, but there’s also a good chance that the Yellowstone hotspot is running out of steam. Magma, actual.

Taking the three known supereruptions and doing some simple math could tell me that we’re overdue for something that’ll put a crimp in presidential politics. But as the USGS points out, supervolcanoes don’t run on a timetable.5

That hasn’t stopped filmmakers from making screen spectacles.

Supereruptions: and a Film Clip

If, and it’s a big if, another supereruption is imminent — it wouldn’t be good for real estate prices in the American West, Midwest or South. At all.

But I strongly suspect that quite a few folks here would survive.

And, barring daft decisions, we might even keep our political units in operation. And that is still another topic or two.

My suspicions aren’t blind optimism. We’ve been through this before.

New Zealand’s Taupō Volcano blew about 25,500 to 25,700 years back. As far as I could tell after a quick check, it’s the most recent supereruption on Earth.

Some 69,000 to 77,000 years ago, a supereruption left Sumatra with Lake Toba. It had a measurable effect on Earth’s climate. Direct and indirect effects of the eruption probably killed a great many folks living in that part of the world. But many of us survived.6

I was going to talk about Yellowstone events, past, present and future; the Toba catastrophe theory; and why I take ‘science news’ with a pallet or two of salt.

But now it’s Friday afternoon. It’s been one of those weeks, and I got distracted.

So what’s (probably) ahead for the Yellowstone hotspot, and a little of my speculation, will wait until another time.

Bottom line?

Movies are movies, science is science.

Entertainment can be fine. But decisions? They’re better if there’s science in the mix. Or at least common sense.

I haven’t talked about geology nearly as much as I though I had:

1 Science, history and tall tales:

2 Hot water, mostly:

3 History and geology — or — jumping into a hot spring may be hazardous to your health:

4 Somewhat recent earthquakes:

5 Science, mostly:

6 Geography and supereruptions:

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About Brian H. Gill

I was born in 1951. I'm a husband, father and grandfather. One of the kids graduated from college in December, 2008, and is helping her husband run businesses and raise my granddaughter; another is a cartoonist and artist; #3 daughter is a writer; my son is developing a digital game with #3 and #1 daughters. I'm also a writer and artist.
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