Yellowstone makes me happy…
Yellowstone also terrifies me…
To reach those animals, that Miocene killer ash travelled about a thousand miles from its eruption vent on the Snake River Plain. Ordinary volcanoes, even heavyweights like Tambora (Indonesia) and Vesuvius (Italy), historically have never shown that kind of power.
Another note: Farrell et al. reported in 2014 that what they call in this video the recently discovered second magma reservoir — sitting below this one — is more than twice as large as the upper chamber shown here. It’s not new, though; we just finally developed the “seismic CT” tools capable of imaging something that far (some fifteen miles) underground. Also, just a small part of it may be molten, while the upper chamber apparently is filled with “crystal mush,” per Hurwitz and Lowenstern; they find little to no melt in the crust and upper mantle directly under Yellowstone Caldera.
It’s a weird combination of emotions.
So let’s be objective: this is a natural world wonder and a US national park sitting atop a giant volcano that’s only sleeping, not extinct.
Now let’s try to wrap our minds around that.
The Yellowstone mantle plume
Remember our old friend from last week?
It’s only one of several models proposed to explain Yellowstone and other areas of unusual volcanism,
past and present, in the Pacific Northwest.
As a layperson, I chose it as an example because it’s a terrific graphic and the model itself does explain several features, not just Yellowstone. (Just remember that this is all cutting-edge research, not revealed truth: the real story behind Yellowstone, if ever discovered, might eventually prove to be different — edit: this, for instance.)
See last week’s post for details and references. Basically, as I understand Camp and Ross:
- About 17 million years ago, a plume of extra-hot material, rising from either Earth’s mantle or the semi-molten asthenosphere layer that crustal tectonic plates move through, hit the bottom of the planet’s outermost crust in the general region of McDermitt caldera, located on the Oregon/Nevada state line.
- Continental flood basalts erupted, first at Steens Mountain, Oregon, and then from fissures to the north, to form the huge Columbia River Basalt Group.
- There were big explosive eruptions, too, including but not limited to the roughly 1,000-cubic-kilometer McDermitt supereruption around 16.4 million years ago (Henry et al.); three 100 to 300-cubic-kilometer ash-flow eruptions a few million years later along the eastern part of the High Lava Plains (Ford et al.); and, relevant for us in this post, a series of caldera-forming eruptions through the North American tectonic plate that formed the Snake River Plain as that continent rolled over the plume and somehow, per Camp and Ross, decapitated it.
- The plume head moved west, according to Camp and Ross, forming the eruptive centers of the High Lava Plains along the way (6-million-year-old Glass Buttes being the last one), and now may be only partially molten, sitting about twenty miles underground east of the Cascades, north and South of the Plains. (Eagar et al.)
- The rest of the plume — its “tail” — is still in place and currently beneath Yellowstone.
Of course, this raises a lot of questions.
Perhaps the two that first come to us laypeople are:
- Why isn’t the plume constantly erupting, if it can blowtorch through North America?
- When is the next supereruption coming?
These topics are intertwined, but complex.
Supereruptions and volcano monitoring
We do live on the surface of a gigantic, ball-shaped chemistry/physics lab, after all. Down below our living zone, Earth operates on the periodic table of elements at temperatures and pressures beyond anything in our experience, over great stretches of geologic time.
So, answers to any questions about Yellowstone Volcano involve lots of nerd stuff. I’m not going to get into that here, though it might be a good topic for future posts.
The nerds come up with even more things — stuff that wouldn’t occur to most of us, like ‘where does all that material for a supereruption come from?’.
That’s a good one, if you think it over.
There’s only a finite amount of silica-like material in the Earth’s crust to be melted by the plume, and not much room there for magma to accumulate.
Nevertheless, the Yellowstone hotspot has managed to do it multiple times.
Such catastrophes don’t happen very often any more, fortunately. Yellowstone’s last “big one” was over half a million years ago. Even its much more frequent “normal” lava-flow eruptions haven’t occurred lately, not for about 70,000 years.
Nor does Yellowstone appear likely to go off again any time soon.
A blob of hot material can rise from the depths into a partly solidified magma chamber, remelting the old stuff, adding new stuff, and providing enough buoyancy to trigger an eruption of some sort, possibly even a supereruption. (Morgavi et al.)
This takes time, though, and it triggers many changes in seismicity and other things that volcanologists can monitor.
Most of us think that experts try to predict such events.
Then we entertain ourselves by imagining the human dramas that unfold as Doomsday approaches:
Poor Fiona. The character with a cap, Rick, is the YVO scientist-in-charge; Matt’s job title is never given, but he functions in this fun 2004 BBC/Discovery Channel docudrama as the USGS on-scene rep.
Probably the most accurate part of this clip is geologists enjoying nature after work and shooting the breeze over some beer.
In real life, experts focus upon getting the most accurate picture of what is normal at a volcano.
So they can spot the first signs of changes due to a coming eruption early enough to warn everyone and get them as prepared as possible for it.
That’s why, for example, in the following video, the current real-life scientist-in-charge at Yellowstone is so proud of seismometers that can pick up quakes less than magnitude zero.
It doesn’t make intuitive sense, but you do need that kind of sensitivity when monitoring a sleeping giant.
They are going to know early on when Yellowstone finally does stir again. It will most likely be a lava-flow eruption, but given the amount of material involved, experts will probably also be able to spot a supereruption ahead of time, too. (Sorry, BBC/Discovery Channel!)
Believe it or not, the Yellowstone hotspot may actually be in a decline. (Knott)
All things do come to an end, even rising plumes of molten planetary material.
When (and if) that happens, and if humanity is still around, we won’t have to worry about supereruptions here any more.
But can removal of that extremely low probability hazard compensate us adequately for the loss of such continual wonder and beauty?
44.43° N, 110.67° W, Wyoming, USA. The GVP Volcano Number is 325010.
Per the Global Volcanism Program website:
- Within 5 km (3 miles): 0
- Within 10 km (6 miles): 0
- Within 30 km (19 miles): 234
- Within 100 km (62 miles): 20,692
- Eruption styles: Hydrothermal explosions (most common, per YVO), including at least eighteen big ones (those leaving a crater more than 330 feet in diameter) since the last ice age ended. (Christiansen et al.) There is also a large dome showing lots of hydrothermal activity on the floor of Yellowstone Lake; monitoring shows no changes there. (Farquhar)
Lava flows inside and just beyond the caldera rim are the next most common type of Yellowstone eruption and can be accompanied by explosive (but not supersized) activity. (Christiansen et al.; Hurwitz and Lowenstern)
The VEI 8 caldera-forming eruptions are rare (Christiansen et al.) but scary to think about.
Earth, like the fictional Hitchhiker’s Guide To The Galaxy, should come with the friendly label “Don’t Panic!”
Think of that very low likelihood, the present upper-chamber “crystal mush” and the mostly solid lower magma chamber, and — most of all — the fact that volcanologists are on this like white on rice, 24/7/365.
Getting back to some of Yellowstone’s much less scary and actually kind of fascinating qualities, it’s restless, like many other big calderas.
The caldera surface slowly, over years, rises and falls, without any eruption. This has been going on for at least 14,000 years and is probably due to some sort of underground fluid movement. Geoscientists are still studying the phenomenon. (Hurwitz and Lowenstern)
Speaking of underground fluids, geysers erupt here, thanks to a hydrothermal system of superheated water, mostly separate from regular groundwater flow, that’s located between Yellowstone’s upper magma chamber, three miles below our feet, and the ground surface where we stand and go, “Oooh! Aaaah!” (Farquhar; Hurwitz and Lowenstern)
Yellowstone makes me happy.
Old Faithful’s regularity is unusual.
Each of Yellowstone’s many geysers responds in a unique way to the ongoing forces that produce them. The geysers are also sensitive to earthquakes outside the caldera, sometimes even to distant but powerful temblors. (Hurwitz and Lowenstern)
- Biggest recorded event: For this caldera, that would be the Huckleberry Ridge eruption about two and a half million years ago, which buried the land under some 2,450 cubic kilometers of tephra.
But that’s not the hotspot’s personal best.
It’s not easy to accurately measure the volume of earlier eruptions from old calderas, as the plume tail tracked through the Snake River Plain (Watts et al.), but last year scientists reported their discovery of an even bigger blast — Grey’s Landing — that happened almost nine million years ago and had a volume of more than 2,800 cubic kilometers. (Knott)
Back then, Knott writes, supereruptions apparently happened every 500,000 years or so.
Today, he notes, it’s more like every 1.5 million years.
Yes, there was some talk, twenty years ago, about the eruption interval being 600,000 years and Yellowstone being “due.”
More information is available now, and that figure isn’t used much these days.
Of course, for all we know, 1.5 million years isn’t correct, either.
But whatever the actual number may be, it looks like:
1. Yellowstone is not “due” or “overdue.” This volcano is sound asleep today.
2. The hotspot may be waning, as Knott suggests.
- Most recent eruption: The last big hydrothermal explosion happened around 1350 BC, forming what’s now Indian Pond.
The last lava flows occurred between 170,000 and about 70,000 years ago, in the Central Plateau area. There was some explosive activity, too, including the formation of Yellowstone Lake’s West Thumb, which is actually a caldera. (Hurwitz and Lowenstern)
The last supereruption was the Lava Creek Tuff: roughly 1,000 cubic kilometers of tephra. This left us with today’s 28 x 53-mile-wide caldera. (Global Volcanism Program)
- Past history: See the above video with Dr. Poland, YVO Scientist in Charge.
Yellowstone Volcano Observatory. (Click the menu triple-bar icon at the top of the screen and then the “+” by “Yellowstone” to access information pages.)
Here are some National Park Service webcams.
The University of Utah runs a seismic network here and has live seismograms online (stations at Yellowstone are clustered in northwestern Wyoming on that map). Learn how to read the tracings here, and don’t worry if the seismogram looks intense — it’s winter, and these instruments do pick up wind and other nonseismic signals. I think the experts sometimes use computer programs to filter out as much of that “noise” as possible; they’re also highly skilled at what they do.
Edited February 1, 2021.
Featured image: Lane V. Erickson/Shutterstock
Christiansen, R. L.; Lowenstern, J. B.; Smith, R. B.; Heasler, H.; and others. 2007. Preliminary assessment of volcanic and hydrothermal hazards in Yellowstone National Park and vicinity. U. S. Geological Survey.
Farquhar, B. 2020. Yellowstone Lake — where fire meets ice. https://www.yellowstonepark.com/things-to-do/fire-meets-ice Last accessed January 29, 2020.
Farrell, J.; Smith, R. B.; Husen, S.; and Diehl, T. 2014. Tomography from 26 years of seismicity revealing that the spatial extent of the Yellowstone crustal magma reservoir extends well beyond the Yellowstone caldera. Geophysical Research Letters, 41(9): 3068-3073. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2014GL059588
Hurwitz, S., and Lowenstern, J. B. 2014. Dynamics of the Yellowstone hydrothermal system. Reviews of Geophysics, 52(3): 375-411.
Knott, T. 2020. Discovery of ancient supereruptions suggests the Yellowstone hotspot may be waning. https://www.usgs.gov/center-news/discovery-ancient-super-eruptions-suggests-yellowstone-hotspot-may-be-waning?qt-news_science_products=4#qt-news_science_products Last accessed January 29, 2021.
Mastin, L. G.; Van Eaton, A. R.; and Lowenstern, J. B. 2014. Modeling ash fall distribution from a Yellowstone supereruption. Geochemistry, Geophysics, Geosystems, 15(8), 3459-3475.
Morgavi, D.; Arienzo, I.; Montagna, C.; Perugini, D.; and Dingwell, D. B. 2017. Magma mixing: history and dynamics of an eruption trigger. Volcanic Unrest: 123. https://library.oapen.org/bitstream/handle/20.500.12657/23133/1007021.pdf?sequence=1#page=129
Watts, K. E.; Bindeman, I. N.; and Schmitt, A. K. 2011. Large-volume rhyolite genesis in caldera complexes of the Snake River Plain: insights from the Kilgore Tuff of the Heise Volcanic Field, Idaho, with comparison to Yellowstone and Bruneau–Jarbidge rhyolites. Journal of Petrology, 52(5): 857-890.