Well, that sums up things nicely. Moving on to the Yellowstone Supervolcano…
What do you mean, “wait!”?
Okay, under its rugged exterior, the Pacific Northwest is a geological mess. (Xue and Allen) But this is being sorted out by some of the best minds on the planet.
It’s fascinating work for such specialists. More importantly to us laypeople, getting a better idea of what’s going on down there helps experts manage hazards in this region of many volcanic “Clark Kents” and that one “Superman” over in Wyoming, under the national park.
Folks living east of the Cascades are probably wondering about the “Plume Head Today” note on the graphic, too.
Relax. Science has your back.
An incredible amount of research is happening here, too. For example, to prepare for this post I could only select a few of the many highly cited papers out there. And more study results are published all the time.
Here’s another reassuring note. Experts agree that the plume of hot mantle material shown on that graphic (if it exists — nobody can go down twenty miles for a look at the bottom of our planet’s outer crust) hit North America about 17 million years ago.
In other words, the worst of that episode has been over for a long time.
But as we’re about to see, those mid-Miocene events were amazing. They built some of the most beautiful landscapes on Earth as well as, per Ford et al., one of the world’s biggest magmatic provinces since the nonavian dinosaurs went away, 66 million years ago.
Taking the long view, Yellowstone is just part of the Big Picture here, although a very important one given its size and ongoing active status.
And before visiting that supervolcano in next week’s post, we do need a little factual background information to clear away the fairy dust that tabloids keep throwing at it.
But it’s not easy to talk about that, since studies of the Pacific Northwest are a scientific work in progress, not to mention highly technical and occasionally contentious.
I really meant it when saying that the graphic above sums things up. The details of what the graphic is meant to illustrate are very difficult to describe in lay words.
I’m going to give it a try, though.
You might want to stop here and wait for next week’s post on the supervolcano itself, unless you have some time today and, like me, are curious about how Yellowstone and its related surroundings came to be.
After all, what we really need to know — volcano status, hazards, briefings and outreach, history, monitoring, multimedia, and related official links — is all there at the two USGS volcano observatories linked above.
The only thing to add here is that Newberry is not a supervolcano and is in no way connected to Yellowstone.
Yet geologic evidence suggests that the processes that formed Yellowstone and have led to Newberry are probably linked (Jordan) and can be traced back to the general area of little known, long extinct McDermitt Caldera (more on “thunder eggs” here), in northern Nevada/southeastern Oregon.
Nearby Steens Mountain in Oregon also played a major role in the events shown in that graphic.
The rest of this post is going a little outside the usual Sunday Morning Volcano approach. After first learning of an indirect link between Newberry and Yellowstone, I got curious, looked around, and found some interesting information in well-cited research papers about it (see the source list at end of post, as well as links in this text).
Be aware, though, that what I’ve written below is only based on those papers, not on the full spectrum of scientific interpretations on this region, some of which are quite different from the findings in my sources.
(Remember…scientific work in progress.)
So you’re not getting the whole picture here, plus it’s biased, since I only used what made sense to a layperson. I also have left out a lot of the technical stuff contained in those sources.
Still, in my opinion, there’s a lot to talk about.
When it comes to Yellowstone, most of the time we’re in the middle, with tabloids at one end screaming “It’s gonna blow!” (no, it’s not: Yellowstone is Code Green) and scientists at the other end saying “Get your information from official sources only” — definitely good advice! — and showing us simple models that, while helpful, clearly don’t explain the complexities we see.
Here’s a useful way to picture the general tectonic situation leading to so many “Clark Kents” in the Pacific Northwest. Our subduction zone is called Cascadia. Unfortunately, “Superman” and everything else in that graphic up at the top of the post is an exception to this rule. In oddball situations like that, an extra-hot part of what’s shown here as boiling soup rises straight up, smashing against the pot lid and interacting somehow with the normal convection cells and the cook’s spoon (the downgoing tectonic plate slab) in ways that aren’t clear yet but generate a lot of research papers.
So, once hazards have been addressed, we laypeople are sometimes left on our own in this amazing landscape, wondering how it formed.
For instance, in 2014 I moved to Oregon via cross-continental train from upstate New York (this brief life should be as adventuresome as possible, despite its often dreary realities).
When we got near the end of the journey, I had to get my camera out, amateur though I am. The landscape was like nothing that exists back East (or in most other parts of the world).
I knew intellectually that those were the Columbia River Flood Basalts, but the emotional impact of their enormous presence was overwhelming.
You can hear some of the other passengers sounding surprised in the background. A bit later, I was too full of the sights to film our passage through the Gorge (behind us, in the video above). Everybody in the observation car quieted down and just stared out the window until we were almost to Portland.
Someone said, “It looks like another planet” and they were right.
Here’s a video, from the other side, two years later, taken from a motor vehicle, that captures a little of the Gorge’s visual wonder. Just a little.
That land is all basalt “Hawaiian-style” lava flows, piled one on top of the other — part of some 200,000 cubic kilometers of the stuff that poured out of the ground in a very short span of geological time. (Camp and Ross)
There is a reason why they call such formations flood basalts.
My wonder would only have been increased by knowing that those flows outside my train window could be linked to “explosive” Yellowstone, as we’ll see below.
Location aside, the two eruption styles just don’t seem to go together.
And I hadn’t even heard of Oregon’s Steens Mountain and the High Lava Plains yet, let alone little known, long dead McDermitt Caldera, not far from Steens and on the Oregon-Nevada state line.
McDermitt Caldera has an appropriate though coincidental keyhole shape, since it is considered a key to understanding the whole picture.
I want to share with you some of what I understand from reading about Yellowstone’s real setting and its connections with other parts of the region.
There’s no narrative or meaning here, just some “Wow!” moments.
But by the end, hopefully, you will get the general gist of the graphic at the top of this post. That’s perhaps the biggest “Wow!” of all.
There will be lots of images…
Amateur geologizing with Google Earth
Remember the graphic?
It’s just one of many models proposed to explain the Yellowstone hotspot as well as some unusual volcanism in eastern Oregon, southern Washington State and Idaho, northern Nevada, and maybe part of California, too (we’re not going to get into that today).
They label Yellowstone as “Plume Tail,” and there is its famous “Hotspot Track” along the Snake River Plain. The whole thing started in the middle Miocene epoch, about 17 million years ago.
I outlined that general track in orange on a satellite view:
What most of us don’t realize is that there’s also what some geoscientists call the “Newberry track,” since it stops at Newberry Volcano. As a topographic feature, it’s known as the High Lava Plains.
I outlined it in yellow on this view:
It’s peculiar for a couple of reasons.
- The average elevation is about a mile above sea level, for no apparent reason: there’s no mountain building going on and active volcanism is limited to Newberry Volcano, at the northwest end of the Plains. Most plains are much lower than this.
- The lava consists of flat beds of rhyolite pyroclastic flows, with rhyolite lava domes and ridges sometimes rising a few hundred feet. Basalt flows are there, too, especially around Newberry, but it’s the rhyolite that puzzles volcanologists.
That lava consistently gets younger as you move west. The oldest lava found so far — more than ten million years old — comes from Duck Creek Butte on the eastern end. The youngest is at Newberry — the Big Obsidian Flow, just 1,300 years old. (Brogan et al.)
Oh, wow! Hotspot track, like Yellowstone’s, right?
Well, probably not. The chemistry of Newberry’s lava is isotopically similar to the Cascade subduction-zone volcanoes (Jordan et al.), and the track of the Plains doesn’t match the direction of North American plate motion. (Ford et al.; Jordan)
That’s why some geoscientists, like Ford et al., are trying to leave Newberry out of it and call this the “High Lava Plains trend,” instead.
Many explanations of the High Lava Plains are out there, but none of them satisfy everyone.
One point that many experts seem to agree on is that both tracks overlap at one point:
And guess what? McDermitt Caldera is in the overlapping part, with Steens Mountain nearby (that dark shape to the northwest just outside the red line).
All of this goes back to roughly the same time, too, about 17 million years ago (though the High Lava Plains are a little younger than that).
Well, I’m just going to cut to the chase here — you’re terrific for hanging in here with me this far!
One last look at the graphic, this time with the explanation given in that study.
As I understand what Camp and Ross wrote, a plume of extra-hot material did impact on North America in the general area of McDermitt Caldera roughly 17 million years ago.
There does seem to be consensus on this, though experts disagree on the plume’s origin, either deep in the mantle or at a more shallow level associated with processes going on at the Cascadia subduction zone.
Either way, here’s the very general picture of what happens when a plume hits the overlying crust:
Everybody uses Hawaiian Islands for hotspot examples, quite rightly. I chose this video not only because he mentions Yellowstone but also because he doesn’t take sides in the plume-origin debate.
Our plume head may have been 250 miles wide at that point. (Henry et al.)
The flood basalts then started at Steens Mountain (there seems to be consensus on this, too) and became the Columbia River Basalt Group as vents migrated northward (I think they moved because of the underlying crustal geology)
Meanwhile, North America kept lumbering on to the southwest and over the next 2 million years, somehow “decapitated” the plume (Camp and Ross don’t go into details here).
The plume tail kept rising, and since it was still extra-hot and stationary, it burned through the crust, forming the Yellowstone Hotspot Track. What we call the Yellowstone Volcano is where the plume tail intersects the crust today.
The plume head, after its “decapitation” 15 million years ago, flowed in a general westward direction (why? check out Camp and Ross). The volume of this extra material, as well as its buoyancy, raised a mile-high “lithospheric swell.”
Some of the material leaked out, erupting as the High Lava Plains. The volume of erupted material, as well as its explosivity, I think, decreased over time, with 6-million-year-old Glass Buttes being the last big dome complex, according to Ford et al.
Nowadays, there still may be some partly molten material down below the crust east of the Cascades and north and south of the High Lava Plains (Eagar et al.), what I think Camp and Ross call “Plume Head Today” on their graphic.
However, since it hasn’t already erupted through the Plains during the last 12-15 million years, seems to me that it could just stay down there and freeze into place as a pluton or batholith.
I’m going to leave a big question mark over Newberry and the westernmost extension of the High Lava Plains. They’re still working it out. Too, that’s close to the Cascades — a complex area, at least to this layperson.
Again, this whole hypothesis is just one view among the many ways that volcanologists see the Pacific Northwest’s history.
Well, now we’re finally ready to see what new and exciting things this ancient “plume tail” or whatever it might be is doing these days…
Besides playing with the neighbors.
Brogan, P.; Peterson, N.; and MacLeod, N. n.d. High Lava Plains. (No other information available.) https://people.wou.edu/~taylors/gs407rivers/High_Lava_Plains.pdf
Camp, V. E., and Ross, M. E. 2004. Mantle dynamics and genesis of mafic magmatism in the intermontane Pacific Northwest. Journal of Geophysical Research: Solid Earth, 109(B8).
Eagar, K. C.; Fouch, M. J.; James, D. E.; Carlson, R. W. 2011. Crustal structure beneath the High Lava Plains of eastern Oregon and surrounding regions from receiver function analysis. Journal of Geophysical Research: Solid Earth, 116(B2).
Faccenna, C.; Becker, T. W.; Lallemand, S.; Lagabrielle, Y.; and others. 2010. Subduction-triggered magmatic pulses: A new class of plumes?. Earth and Planetary Science Letters, 299(1-2): 54-68.
Ford, M. T.; Grunder, A. L.; and Duncan, R. A. 2013. Bimodal volcanism of the High Lava Plains and Northwestern Basin and Range of Oregon: Distribution and tectonic implications of age‐progressive rhyolites. Geochemistry, Geophysics, Geosystems, 14(8): 2836-2857.
Henry, C. D.; Castor, S. B.; Starkel, W. A.; Ellis, B. S.; and others. 2017. Geology and evolution of the McDermitt caldera, northern Nevada and southeastern Oregon, western USA. Geosphere, 13(4): 1066-1112.
Humphreys, E. D.; Dueker, K. G.; Schutt, D. L.; and Smith, R. B. 2000. Beneath Yellowstone: Evaluating plume and nonplume models using teleseismic images of the upper mantle. GSA Today, 10(12): 1-7.
Jordan, B. T. 2006. The Oregon High Lava Plains: Proof against a plume origin for Yellowstone? http://www.mantleplumes.org/HighLavaPlains.html
Jordan, B. T.; Grunder, A. L.; Duncan, R. A.; and Deino, A. L. 2004. Geochronology of age‐progressive volcanism of the Oregon High Lava Plains: Implications for the plume interpretation of Yellowstone. Journal of Geophysical Research: Solid Earth, 109(B10).
Long, M. D.; Till, C. B.; Druken, K. A.; Carlson, R. W.; and others. 2012. Mantle dynamics beneath the Pacific Northwest and the generation of voluminous back‐arc volcanism. Geochemistry, Geophysics, Geosystems, 13(8).
Xue, M., and Allen, R. M. 2010. Mantle structure beneath the western United States and its implications for convection processes. Journal of Geophysical Research: Solid Earth, 115(B7).