Kiss Your Ash Goodbye: The Yellowstone Supervolcano, Part II, A Vulcanology Primer – By Stephanie Osborn

Kiss Your Ash Goodbye: The Yellowstone Supervolcano, Part II, A Vulcanology Primer – By Stephanie Osborn

Excerpted from Kiss Your Ash Goodbye: The Yellowstone Supervolcano, © 2018
Images in this article are public domain unless otherwise noted.

How many supervolcanoes are there in North America?

There are ~170 active volcanos in the United States of America, most in Alaska and Hawaii, though there are quite a few along the West Coast states.

There are only an estimated 4-5 supervolcanoes in the USA. These include the Yellowstone Caldera (VEI:7-8), Mt. Mazama/Crater Lake (considered dormant) (VEI:7), Valles Caldera (VEI:7), Long Valley Caldera (VEI:7), La Garita Caldera (likely extinct) (VEI:8), with all except the last potentially capable of erupting. There were more, but they appear to be extinct. Extinct is relative, however; most show some degree of geothermal activity in the area.

Mt. Mazama/Crater Lake (VEI:7)

The central feature of Crater Lake National Park is Mount Mazama in southern Oregon. It is a composite volcano (a composite of alternating layers of ash/cinder and lava) in the Cascade Volcanic Range of the Pacific Northwest, which are fed by the subduction and subsequent melting of the Pacific Ocean floor tectonic plates.

Prior to the caldera-forming eruption, Mazama stood at least ~12,000ft (3,700m) in altitude. Post-eruption, it now has a maximum height of 8,934ft (2,723m) at Mount Scott (2mi/3km east of the caldera rim), which is a parasitic cone on the flank of the volcano. [Yes, that’s right, the caldera rim is some 800ft+ (240m+) lower.]

The caldera rim proper ranges from 7,000-8,000ft (2,100-2,400m) altitude, and is 5x6mi (8.0×9.7km) across. The bottom of Crater Lake goes 2,148ft (655m) down; it is the deepest lake in the U.S. The lake IS the caldera, so that’s at least how far it collapsed. Some say that the bottom is near the base of the mountain, others that it goes even deeper.


Crater Lake, the water-filled caldera of Mt. Mazama.


In relatively continuous eruption since 420,000 years ago, things changed around 30,000 years ago, when the chemistry of the melt feeding the magma chamber apparently began to change from a relatively basaltic, runny magma to a much more viscous, silica-rich melt. As this melt grew thicker, the eruptions became more violent.

The catastrophic eruption occurred 7,700 years ago, and was observed by the local Klamath indigenous people, who “recorded” it in myth. It “…started from a single vent on the northeast side of the volcano as a towering column of pumice and ash that reached some 30mi (50km) high. Winds carried the ash across much of the Pacific Northwest and parts of southern Canada…As the summit collapsed, circular cracks opened up around the peak. More magma erupted through these cracks to race down the slopes as pyroclastic flows. Deposits from these flows partially filled the valleys around Mount Mazama with up to 300ft (100m) of pumice and ash. As more magma erupted, the collapse progressed until the dust settled to reveal a caldera, 5mi (8km) in diameter and 1mi (1.6km) deep.” ~USGS website

Subsequent eruptions from vents inside the caldera created what became Wizard Island, as snow- and glacier-melt slowly filled the depression. Eventually eruption ceased, and the ruins of Mt. Mazama began to resemble the beautiful Crater Lake we know today.

Mt. Mazama is officially considered dormant by the U.S. Geological Society.


The Valles Caldera (VEI:7)

Sometimes called the Jimez Caldera, this supervolcano is located in northern New Mexico, 55mi (90km) north of Albuquerque. It is named for the numerous grassland valleys (Spanish: valles) contained within the circular caldera, which is about 13.7mi (22km) in diameter. It is similar to Yellowstone in that the caldera also contains hot springs, fumaroles (steam vents), gas vents, and volcanic domes, in addition to meadows and streams.


The Valles Caldera as viewed from the rim. Note the volcanic domes dotting the floor.

Credit: National Parks Service.

Geologically, it is one of the best-studied calderas in the U.S. There are at least two known calderas on this site, the Valles, and the older Toledo Caldera. The nearby and associated Cerros del Rio volcanic field is older still, indicating multiple supereruptions at this site. Overall, these and related nearby volcanic features are included within the Jemez Volcanic Field & Mountain Range, which stretches across three counties in New Mexico.

Several layers of silica-rich lava and tuff (welded ash) in the region are ample proof of the eruptions, the most recent of which was some 50-60 thousand years ago and resulted in the current Valles caldera. Previous eruptions date back at least 14 million years.

The cause of the vulcanism seems to be the intersection of the Rio Grande Rift (a continental rift zone, running N-S from central Colorado state, USA, to Chihuahua state, Mexico) and the Jemez Lineament (a series of faults running E-W 600mi (965km) from Arizona east possibly as far as western Oklahoma). The Valles Caldera does not, therefore, appear to be due to a solitary mantle hotspot as such, but to rifting occurring in the middle of the continental plate, though this rifting may be from convective uplift in the mantle.


The Long Valley Caldera (VEI:7)

The Long Valley Caldera is in central California along and slightly east of the westernmost Sierra Nevada Range. It and the adjacent Mammoth Mountain/Mono-Inyo complex are around 55mi (89km) northeast of Fresno, California.

long valley

Part of the Long Valley Caldera, looking east from the north rim.


The caldera is ~20mi (32km) long, 10mi (16km) wide, and up to 3,000ft (910m) deep. It generated a massive supereruption some 760,000 years ago, producing the Bishop Tuff formation. The grand total of ejecta was some 150cu.mi (625km3), after which the surface sank nearly a mile (1.6km) into what had been the magma chamber.

The cause of the supereruption is unexplained; it is not fueled by a mantle hotspot, nor is it provided melt via subduction.

More, while it is adjacent to still-active Mammoth Mountain and the Mono-Inyo crater chain, and at least appears to be associated with them, the magma chemistries are very different, indicating they do not share a common melt system, and are NOT associated. This is an interesting puzzle.

“The caldera remains thermally active, with many hot springs and fumaroles, and has had significant deformation, seismicity, and other unrest in recent years.” ~USGS website

The activity is sufficient to run a geothermal power plant located there. But how much of this activity is due to the Mono/Mammoth complex and how much to the caldera source is not fully understood. Smaller eruptions have occurred around the caldera on a semi-regular long period, but the lava extruded has apparently been increasingly crystalline in nature, which may indicate that the magma source is cooling significantly.


La Garita/Creede Caldera (VEI:8)

The La Garita caldera-forming eruption is estimated as one of the largest eruptions on Earth. It lies in the midst of a huge region in the Rocky Mountains called the San Juan Volcanic Fields. The town of Creede sits on what would have been the north caldera rim, with Pueblo, Colorado 110-115mi (km) east-northeast; Colorado Springs ~120mi (193km) northeast; Denver ~150mi (240km) north-northeast.

This region became active some 35-40 million years ago, with an exceptional period of activity from 30-35 million years ago. At the tail end of this flurry of vulcanism, the La Garita supereruption took place, roughly 27 million years ago. It ejected some 1,200cu.mi. (5,000km3) of material, which became known as the Fish Canyon Tuff. This ash deposit covered an area of AT LEAST 11,000 sq.mi. (30,000km2) in a layer whose average depth was 328ft (100m). This tuff is surprisingly uniform chemically, indicating it was ejected all in a volume.

The resulting caldera was a monster 22mi (35km) wide, and anywhere from 47-62mi (75-100km) long. It is no longer recognizable as such to the untrained eye, however, as a single resurgent dome (Snowshoe Mountain) has filled it.


La Garita Caldera (red dotted outline), with resurgent dome (Snowshoe Mountain) inside it. Credit:


The energy of the eruption was some 5,000x the largest nuclear device ever detonated on Earth, the Tsar Bomba, a 50MT explosive. This places the La Garita supereruption at 250 GIGATONS of energy. The area devastated would have encompassed a substantial portion of what is modern-day Colorado, not counting ash fall.

Vulcanism in the San Juan Volcanic Field as a whole, including the La Garita supervolcano, apparently ended 2.5 million years ago. It is considered extinct.


What’s the strongest supervolcano ever known?

The biggest known eruption in geologic history IN THE USA — some say in the world — was the Fish Canyon eruption in the La Garita megacaldera.

The biggest known eruption in geologic history in the WORLD was the Guarapuava-Tamarana-Sarusas eruption in South America. The eruption occurred ~132 million years ago, produced an estimated 2,100 cu. mi. (8,600 km3) of ejecta, and was probably at least the equivalent of the La Garita eruption.


To obtain a copy of Kiss Your Ash Goodbye: The Yellowstone Supervolcano by Stephanie Osborn, go to: Kiss Your Ash Goodbye.

147 thoughts on “Kiss Your Ash Goodbye: The Yellowstone Supervolcano, Part II, A Vulcanology Primer – By Stephanie Osborn

              1. FYI, the geology in Australia is interesting. There ARE volcanic regions, a LOT of them, despite the continent being basically in the middle of the plate, and some of them may still be active. Most notable ones I came across that might still be active are mostly in South Australia state, though Mount Eccles in Victoria and a few sites in Queensland bear watching.

                Given all of the unusual minerals y’all have Down Under, from opals to gem corundum (sapphire & ruby) to garnets to uranium, lead, copper, silver, zinc and more, and structures like the Line of Lode in Broken Hill, I really want to dig more into the geology of the place.

                I’ve had a wish to visit down there one of these days, but never had the proverbial round tuit. Now, unfortunately, such geological perambulations (among other things) are probably not possible, thanks to my physical condition.

                1. Makes me wish I had a tanker full of Larry Niven’s Boosterspice. Then I could fix ya’all up in no time.

                2. Yeah, the gem sites tour is one of the things I hope to be able to do before I die; ditto the “walk along and find gold’.

                  I was actually surprised to find out that South Australia has earthquakes, because I had been vaguely aware that Australia sits pretty much nice and steady on the plate, as you mention. But Housemate says they have ’em, just not to the degree the Philippines or Japan would.

                  1. Well, the majority of the dormant/maybe-active volcanoes are in the southern parts, so I suppose it stands to reason. If you have volcanoes, you tend to have quakes in the region.

              2. IIRC, Australia also has some of the oldest continental crust and is one of the places that they look for the earliest evidence of life.

          1. As much as I like watching her as an action movie heroine, I think she’d have severely impacted Stephanie’s bottom line. Of course if some TV producers (Natl Geo?) decided to do a presentation of her book and contracted Milla that way it would be off their nickel.

  1. I pointed one of my friends to this series of posts. She’s going to start teaching 5th Grade this year and they study geology a little in the science portion. Good job, Stephanie.

    1. Thank you most kindly. This is a fascinating subject for me; had I picked up a full degree in geology (which I seriously started to do, along with the other degrees), I’d have probably specialized in vulcanology and seismology. The fact that I already had all the pertinent physics courses by that point helped out a lot, and I think it set me a bit ahead of the rest of the class in that regard.

      Of course, I used my Optics studies when I took the racquetball course, too…

      Amazing, really, how you can use that stuff in so many different places.

        1. Which makes me wonder. Archaeologists are notoriously slow about writing up their digs as formal articles (which is why they often cite private correspondence with buddies in their footnotes).

          Are vulcanologists fast about writing articles, from a sense of urgency?

            1. It’s been my observation (from the outside) that in science if you publish fast, you repent for the rest of your life, and probably makes for a short career.

          1. Considering the description of the landscape on the ridge he was supposed to have been on, I suspect he was pretty much ripped into individual cells, vaporized, and blasted into the pyroclastic cloud/flow. I can’t imagine him being alive more than a second or two after it hit him. Mercifully fast. But I do wonder what was going through his mind as he watched it rushing at him.

              1. True.

                And yes, what I heard was different from what was put out in the media. The general public heard, “Vancouver! Vancouver! This is it! This is it!”

                In the presentation, I heard, “Vancouver! Vancouver! This is it! This is it! This is… it…” And the excitement drains away as he says that third “this,” and his voice breaks, then tapers off entirely, and it hit me that he had just realized he was about to die in that superheated maelstrom. And he knew, as did I, that there was nothing he could do to stop it. The blast/pyroclastic flow is estimated to have hit Mach, he was something under 4.5 miles away, directly in line with the blast, and from what the park ranger told me, it was MAYBE fifteen seconds between the end of his statement and the cessation of the carrier signal.

            1. Well, I think that’s mostly going a bit too far in terms of what happened to him.
              What I saw of the trees — and yes, there were tree remnants left — was on the order of sawdust and lots of splinters approximately one inch long. There were a couple stumps left near the ridgetop, twisted-off splintered things only about a foot tall for the most part; one near the top of the ridge might have been three feet.
              So kinda think about the equivalent damage to a human body, and that’s likely what happened to him.
              But yes, only a few seconds. And nothing of significance left for remains.

              The truth of the matter is, having been there and seen the devastation, and heard his voice in his last moments when he realized what was about to happen to him…I try not to think about the details of what DID happen to him.

  2. I wonder how these compare to the precursor of Krakatoa that went off some time around 1100 AD and has (if my memory is correct) a caldera about 10x larger than the Krakatoa caldera. I’m not sure it would have the same dynamics since it would have been a steam explosion like Krakatoa and generated a lot less in the line of eruption volume with a crap-load more in terms of explosive force.

    1. The 1883 eruption was a VEI 6, a bit shy of a true supervolcano eruption.

      There is no 1100AD event that I have been able to find. There is a reference to a possible caldera-forming eruption in 416AD, but this has no support in the geological evidence. There WAS one in 535AD, or thereabouts (it has been difficult to date), and this is apt to have produced some global weather effects for the next couple of years. The resulting caldera was, by the sound, at least as big as the current one, but still may not have reached VEI 7.

      1. That’s probably the one I’m thinking of – there are reports from the time period that this was when Java and Sumatra separated – I remember the weird stuff, not the dates.

        I wondered about the “proto-Krakatoa” because the estimated caldera is an order of magnitude bigger than the Krakatoa blast in 1883 (which in turn is an order of magnitude bigger than Anak Krakatoa today). Of course I’ve got zero idea how accurate that estimate is – but if it blew Java and Sumatra apart, it’s got to be pretty substantial.

        1. Yes, and I just went and studied the area on standard maps, and then switched to satellite viewing. Not only would that be one of the largest calderas in the world, I’m not really seeing any structures underwater to support that hypothesis. In fact, there’s a region in the Straits well west of Krakatau that is much deeper than the rest, and a central peak, which I might almost interpret as a separate caldera if the floor wasn’t so rough. It’s also bounded to the west by a ridge/escarpment. But I’m not seeing anything to make me think it’s a caldera.

      2. Yes, the mysterious 536 event. Some believe it to be the source of the “waste land” which figures in the Arthurian legend. It’s also around the same time that portions of the island of Sylla, off the coast of Cornwell, sunk and formed the Scillies, possibly giving rise to the legendary sunken land of Lyonesse.

        1. Yes, but given the distance — the Isles of Scilly are on the opposite side of the planet from Krakatoa — unlikely to be related. (The Mount’s Bay forest flooding occurred several millennia earlier.)

          1. Might be close enough for fictional work. The timing is . . . interesting.

            1. I don’t know of any realistic geological theory that would cause that degree of subsidence at that distance. Krakatoa is in the area of a mishmash of plate boundaries and itself sits on the Australian/Eurasian plate boundary. The British Isles are all well inland of the western edge of the Eurasian plate, which boundary is the Mid-Atlantic Ridge spreading zone. The subsidence is more apt to be as a result of activity on the Ridge than from Krakatau.

  3. Consider hubris of those who think that somehow man able to control the his environment — and shape a perfect world. There are forces at work that are far beyond our control.

    1. Forex: there was a eruption in iirc 2014 that was calculated to put more CO2 in the air than man did in five years.

        1. Well yes, but when people are arrogant enough to still think they can centrally plan economies, notwithstanding the historic proof to the contrary, it is any wonder that the same people think they can centrally plan climate as well. Of course both are simply pretexts for assertion of power over others (and it is always totalitarian power because “the crisis” must be averted).

          1. Some might argue that central planning has worked in Utopian fiction, so why not? It could be replied that there is a great deal of distopian fiction that indicates that consolidated power is a danger.

            1. The operative words being “utopian fiction”, as that all utopias ever are, and the efforts to achieve utopias inevitably ends with real, not fictional, dystopias.

            2. Utopia is boring. You might be warm and comfortably fed; but so a animals destined for slaughter.

        2. Have often pointed out the fact man’s contribution is less than the amount of variability in the earth’s over all. Though I did get some sod who claimed man’s CO2 is many times more effective than all the rest of the planets.
          Then again they claim 96 out of 10,233 is 97%.
          must be New Math

      1. I wonder how much CO2 has been put into the air by the Fires in California. They need to make a law against those fires.

  4. To our guest blogger, the Interstellar Woman of Mystery:

    Once again thank you for your contribution to our further education.  You have a clarity of thought and a felicitous ability with words that I greatly appreciate.

      1. Thank you, I do. I just finished reading Division One: Definition and Alignment this week and enjoyed it thoroughly. In it you managed what was probably the best handled synopsis of a story to date I have yet to come across.

              1. Based on some commentary off-blog, and because I haven’t been able to get Amazon or BN to list the series numbers consistently, I’m going to go ahead and throw this in here.

                Division One books in release:
                1) Alpha & Omega
                2) A Small Medium At Large
                3) A Very UnCONventional Christmas
                4) Tour de Force
                5) Trojan Horse
                6) Texas Rangers
                7) Definition & Alignment

                Coming soon:
                8) Phantoms (Oct 2018)
                9) Head Games (Jan 2019)
                10) Break, Break Houston (spring 2019)
                and I’m brainstorming more, plus looking at putting out The Division One Agents’ Handbook as an adjunct to the series.

                All are, or will be, available in print, Kindle, and Nook.

                  1. Aw, I liked the movies. Actually got a couple of the comics but was less enthused about those.

                    But no, this is my take on the same urban legend, and I make full use of all of the associated urban legends, so there are gonna be similarities just because we used the same research material.

                    Kinda like I LMBO when BBC Sherlock came up with the same full name for Holmes that I’d already used, because same research material.

                    I do have a lotta fun with it. I tell people that when I write it, my tongue is planted so deep in my cheek, it pokes out the side of my face.

                1. FYI. Picked up Nook version of: “Alpha & Omega” & just got “Kiss Your Ash Goodbye …” They are on my TBR list.

      1. Well that didn’t post in the order I thought it would. To be clear, I am seconding the praise to Stephanie, for the wonderful information.

  5. So we have the persistent mantle hot spots like the one currently under Hawaii, with its trail of ex-islands off across the Pacific in a generally west-north-west direction, and as I understand it the hotspot under Yellowstone has a traceable trail of prior vents and cones and flows and such off to the WSW, those trails being caused as plates move over the top of the persistent hotspots; then we have the vulcanism at the edge of plates, where we see Mts. Hood and St. Helen and Crater Lake and Shasta, caused by the action of the edges of the plates diving under and so on; and then we have the just-pops-up spots.

    Do the just-pops-up spots have any rhyme or reason, or are they “we don’t know” instances of vulcanism that fall outside of the known-causes categories?

    1. I think the theory s that the magma in the earth’s core has regular currents, and the hotspots are where they touch the mantle on their upward loop. But I’m not clear on this.

      1. The theory is relatively new to me personally, so I cannot claim to be expert on it, but it makes a good deal of sense to me. But yes, it is not universally accepted.

    2. One theory I’ve seen (Roadside Geology of Idaho, and other places) is that some in-plate hot-spots are the remains of meteor strikes that penetrated to the mantle, or that so weakened the continental crust that it allowed a mantle plume to break through. As you can imagine, a lot of people dispute that theory, or feel that while that explains [other hot spot], it does not apply to [their research hot spot]. IANAGeologist, nor do I play one on TV.

      1. I find it darkly amusing that almost invariably, especially in the history of geology, there is a thought that it MUST be ONLY one or the other, and again almost invariably it turns out to be BOTH. As in, these over here are from this, and dose over dere are from dat.

        1. I suppose it’s like the (pre-space capabilities) ideas at least some astronomers had that the lunar craters had to me mostly volcanic rather than impact.

          1. Well, it took scientists a surprisingly long time to recognize impact features for what they were. Barringer Crater (most commonly known as “Meteor Crater,” and sometimes “Canyon Diablo Crater” but the real name is Barringer, after the scientist who recognized it) was correctly identified by Daniel Barringer in the very early part of the 20th century, but this was not positively confirmed until Gene Shoemaker (yes, of Comet Shoemaker-Levy-9 fame) did so…in the 1960s. So within my lifetime.

      2. I think that any impact large enough to “create” a hotspot would leave a gigantic crater itself, as well as ejecta from the impact.

        1. Actually, probably the other way around. Rather than a giant crater, it would be apt to raise a mountain, because it would punch through the crust and leave a hole straight through to the melty bits.

          Which is why, when the iridium layer was discovered at the KT boundary, Iceland was a prime candidate for the impact. (An impact along a plate boundary like that would be almost sure to punch through.)

            1. *snork*

              No, because the actual impact site was the Chixulub crater on/off the Yucatan coast. (And evidently it was indeed a coastline at the time of the impact, because there are megatsunami debris remnants found well inland on modern North America.)

              1. could still be her fault.
                maybe the rock intended to silence her slingshot around the sun and went back in time . . .
                Why you looking at me like that?

                for the record, I don’t mind her singing
                just thought I’d pick on her

    3. Well, when you get down to it, there are no “just pops up” volcanoes. There are subduction zone volcanoes (the vast majority), there are spreading-rift volcanoes (think Iceland, the #2 cause), and there are mantle plume hotspots.

      1. Also delamination, where the lower crust peels away and sinks, exposing the mid/upper crust to hot rock from the mantle/asthenosphere. This doesn’t fit neatly into a plate tectonic model, and could mimic hotspot activity. All of this makes it difficult to identify with certainty. The volcanic zones just east of the Sierra Nevada might be an example of this. Imaging suggests that there is a “drip” of (relatively) cold material in the upper mantle beneath the Sierras, and hotter material (possibly) flowing in from somewhere beneath the Basin and Range province.

        1. Well, there is also the Yellowstone plume which runs through a whole big mess out there, AND the passage of the Farallon Plate after it was almost completely subducted, so it really is a very complicated region.

          1. Nature is messy.

            A subducting plate can tear, opening a window through which hot material can rise. Depending on where the rip occurs it is possible to get a surge of eruptions far inland from the coastal volcanic chain. Something like this happened in the Rocky Mountain region about 30-50 million years ago. The Challis eruptions (Montana) and the San Juan volcanics (which include the La Garita eruption) may have been produced in this manner. Even if you remove all the extension which occurred in the Basin and Range afterward the Rockies were still very far from the coast.
            There may also be “hotspots” which have shallow sources and those which originate deeper. has links to a number of papers which examine/offer alternatives to the deep mantle plume hypothesis. Some “hotspots” might have originated as areas of unusually fertile (for magma production) upper mantle. Once something triggers the first eruptions the process can continue until that region of the mantle is depleted.

            I realize that these complications aren’t necessary in an introductory book. One needs to get the overall picture before tackling the exceptions.

            1. Actually I DO discuss the relatively recent theory that it originated from the Farallon Plate subduction, but in the ebook, not in the guest blogs, if memory serves. It was a longish discussion and in the end I don’t find that a viable theory, moreso as they’ve FOUND the mantle plume, and I didn’t want to confuse readers here by trying to compress the discussion.

    4. I think they may still be researching some of the fundamental fluid mechanics that could be involved.

    5. I’m more interested in the Farallon plate being way the heck over on the eastern side of the continent. Seems to me that the Yellowstone hotspot plume should have acted like a welding torch and sliced the plate in half as it passed through the plume. But it’s hard to see if that happened or not from the graphics on the site.

      1. If a Yellowstone plume was active for that long (before the North America Plate overran it) it would have been producing a chain of islands in the Farallon Plate (or possibly the Kula plate), like the Hawaiian Islands and Emperor Seamounts. Those islands would either subduct with the plate or be scraped off at the subduction zone. The thickened oceanic crust might also resist subduction, at least for a while, initiating a period of “flat subduction”. In this scenario the oceanic crust underthrusts the continent, sometimes for hundreds of miles, instead of diving down immediately. This is happening now beneath sections of the Andes Mountains, and incoming seamounts on the Nazca Plate are involved.

        1. I’m not an expert. But given that there is a defined start to the caldera track, and said start is on the North American plate, I don’t see how the hotspot could have produced islands in the Farallon plate.

          1. My intent was not to agree that the Yellowstone hotspot is far older than the Columbia Basalts. I just wanted to point out that such a hotspot would produce a string of volcanic islands and not cut the plate in half. At least that is not what happens to an oceanic plate. I then began to ramble a bit.

            Yellowstone displays essentially all of the expected traits of a “classic” hotspot, according to theory. The timing of initiation, when the large plume head impinges the lower crust and causes widespread volcanic activity, agrees with not only the basalt province north of the hotspot track but also the Northern Nevada Rift south of it. The trend of the dikes to the north and the NNV rift to the south pretty much point at the first caldera in the Yellowstone chain. If Yellowstone didn’t begin at that time and place then the coincidences are just staggering.

      2. Yes, and while I don’t particularly hold by the notion that the Farallon Plate CAUSED the Yellowstone hotspot, because truly honkin’ bigass plume found, it had to have interacted some kinda way, because the bits of plate in the PacNW’s Cascadia Subduction Zone (Juan de Fuca and Gorda) are actually the last bitsy-bits of the Farallon, along with the larger Nazca and Cocos Plates, and the tiny Rivera Plate (a breakoff of the Cocos), which are west of South and Central America, respectively. So in effect, it’s still subducting.

        What I find especially interesting is that so much of the Farallon Plate appears to have managed to survive the subduction process to actually enter the mantle and be detected. Based on studies I’ve seen of the western side of the Pacific Ring of Fire (e.g. the Japan Trench; the Japanese have studied this A LOT, for obvious reasons) HAS NOT, to my knowledge, given evidence of surviving the subduction. I’ll admit to not having checked up on it in a while, but the last I knew, they were able to trace the Pacific plate down past the trench and under the Eurasian plate, to the point where the Pacific plate essentially dissipated.

        So I have some digging to do, just in order to satisfy my own curiosity. I may look into that as soon as I finish the manuscript for Head Games and get it to the betas and the editor.

  6. Ah, Jemez Lineament, the bane of OttoCorrupt when I was typing my dissertation (the name of the author of the primary paper is long and Slavic.)

    Valle Grande just opened (as in last four years) for public access. The history of human use in the caldera is complicated, messy, and still touchy. If you want to see how later humans made use of some of the tuff et al, Frijoles Canyon/ Bandolier National Monument is a great place to visit. Just remember the altitude, please (7,000′ and more above sea level.)

    1. I have not been to altitude in a while, but heretofore I have found that I tend to operate reasonably well in the 5-7k feet range, though I have to slow down a bit, or suck air rather hard, at least at the upper end of that range. It’s up around 9-10k that I start to experience problems unless I am in great shape. I used to go to CoSpr on business fairly regularly, and learned how to train to counter that issue. But of course that was before the knees went, and the Giant Mutant Cyst from Hell totally hosed everything.

      FWIW I never had any problems IN CoSpr; it was rare that I could even tell I was at a higher than usual altitude. But I had a friend who lived up in the Front Range and I would often stay there, and that was at about 9000′, 9500′ altitude, which did tend to cause me problems.

      I do remember learning to shower, and then go crawl in the bed under blankets, to counter the chill from the rapid evaporation of water off my skin…

      1. I find that I can tell when I hit 8K but don’t mind higher. It’s just that I can *tell*. But we live at 7000-ish.

        If anyone comes down here to visit volcano stuff, don’t skip Tent Rocks.

        1. I live at 3600′, and do OK at 7-9K the first day if I don’t push it. After that I’m good to 12K, just a touch short of breath. I’m sure that is altitude, not age or rotundity. Yeah. Altitude.

          1. LOL no. I hit around that many words yesterday.
            Occasionally the plot bunny bites — usually right at the end of the novel — and I start slamming in the words. I think my record was in the vicinity of 15K in one day. As Travis likes to say, I had to let the smoke out of my computer the next day, and I wasn’t good for anything for almost a week.

    2. At some point — I wanted to do it during research for the book, but didn’t get around to it — I want to see if the Jimez Lineament has any relationship at all to the Southern Oklahoma Aulacogen, or if they are unrelated rift systems.

    3. Speaking of tuff, the other night while watching a documentary, I discovered another ancient people who made significant use of tuff — the Rapa Nui. It turns out that the moai on Easter Island were carved from tuff, because it is a relatively soft stone and easy to work.

  7. Crater Lake was also one of the first commonly available high-resolution DEMs (digital elevation models)

    Off to find more SIGGRAPH stuff to report.

    1. I have been to Crater Lake, though it was only a few years after the knees went, so I didn’t try to hike down to the edge of the lake (though I badly wanted to do so). I did bring along a collapsible (and therefore packable) hiking pole to ensure stability, and explored the place fairly thoroughly otherwise. It is impressive. As long ago as it was, the pumice desert surrounding the peak is still largely devoid of life, other than the odd scrubby tree. And there were chunks of pumice bigger than my head that you could lift with one hand.

      1. It is a great walk down the one trail to lake in the Crater.

        Hard on knees going down.

        Trail is hard & wide. Lots of switch backs.

        Hard on lungs back up.

        “Oh. /gasp/ Look /gasp/ at /gasp/ scenery /gasp/ must /gasp/ take /gasp/ picture /gasp/”

        Been down/up* many times. Although is was much later before I realized why mom wouldn’t go down every time, just waited for us kids at the top for when us kids ran ahead of dad on the way back.

        * When I learned Newton was not 100% forth coming in gravity. You know:

        Newton: “What goes up must come down.”

        He left out: “What goes down must come up, because no one else is hiking your A$$ out of here.”

        1. It was hiking up and down a mountainside in the Front Range that first showed up my bad knees. My friend was building a house near the top, and she kept horses, and the barn was gonna be AT the top (why not the house, I do not know; I’d have swapped ’em), and the horses were there, along with the hay, but the barn was not yet built. Snow coming, hey Steph, come help me throw tarps over the stacks of bales. Sure, says I, and we took an ATV up to the house site, then walked the rest of the way. The next day, left knee is nearly the size of a basketball, and I can barely get my jeans on it — probably could not have before the advent of lycra in ladies’ jeans. About a month or so later, as left knee is starting to go down, right knee decides to join the act.

          Oh well.

  8. This series is making me curious about the geology of the Tucson area; supposedly the Tucson Mountains were split off from the Santa Catalinas by an eruption which occurred 65 mya, according to the marker at the vista loop on Gate Pass.

    However it seems that not a lot of books have been written about the geology of Southern Arizona. I check Amazon for these after Part I posted.

      1. The writer keeps talking (in both the news article and the blog post) about the Santa Catalina Mountains being to the east of Tucson. It just bugs me, the Catalinas are on the north side of the Tucson basin, the Rincon Mountain are the eastern side.

        Other than that it was an interesting over view of what we don’t know. Like the fact my office seems to anchor an end of a fault I didn’t know existed.

          1. Given the author’s rather loose description, I’d guess the start of the fault is closer to the junction of Gates Pass and Kinney Roads than actually within Old Tucson’s boundaries.

            Kinda want to go out with a camera and see if I can document any physical surface signs.

            The Tucson Mountain Chaos seems to also cover the lower end of caldera sizes.

            And given Tucson in general, that part of the local geology is named “Chaos” seems all to apropos.

              1. Driving into work this morning, because the fast route for me is through Gates Pass, I was aware, on an emotional level, of the caldera for the first time.

                I’ve been driving this route for five years (as of the 29th of this month), so sometimes even a kitsune can be dense.

                1. Well, you do have to know what you’re looking at in order to recognize a thing, generally.
                  I hadn’t realized that Cripple Creek, CO was in an ancient volcanic crater until someone told me, and then I stood on the rim and looked out over the town and went, “Duh!”
                  The caldera is really obvious on a satellite view.

                  FYI, where is Gates Pass in relation to the caldera? It’s not showing up on my maps, and I’ve not yet been to the area…

                  1. Gates Pass starts (from the Tucson side) as a canyon that empties east into the Tucson Valley, when you hit the top and start descending as you go west it drops you in the southeastern part of the caldera. The western part of the road going through the pass is steep, narrow and windy.

                    One of the things that makes it hard to notice is that it doesn’t have a wall encompassing the whole caldera, the western edge is delineated by the fault line the writer of the news article talks about.

                    Or I could have misunderstood the article and be completely off base.

                    1. It’s a lot steeper than the satellite image makes it look. From the loop at the top of the pass to the kinda switchback at the Yertman Trailhead is around a 400 foot drop, with another 200 foot drop between the trailhead and Old Tucson.

                      The top of the pass is about 3200′ and Old Tucson’s sitting around 2600′.

  9. I am bemused by the total acceptance of plate tectonics in this age, when the first book I read about the history of the Earth as a planet subscribed to the ‘shrinking apple’ model of mountain formation.

    That was THE EARTH FOR SAM by William Maxwell Reed, published in 1929. A little dated when it was read to me by my Parents, but well written enough that it is still selling today.

    Plate tectonics was generally accepted when evidence of seafloor spreading emerged in the late 1950’s. But it was proposed decades earlier.

    Makes me wonder what theories are even now working their way to acceptance.

    1. Geology went through a period of huge debate for a couple of centuries, and only really resolved itself in the mid-20th. The two sides were known as uniformitarianism and catastrophism. Proponents of the former held that all geological processes were gradual and steady; proponents of the latter held that geological change was percussive, sudden and violent.

      We now know that reality is a combination of the two. Certain processes, such as erosion, generally tend to be steady and gradual processes, punctuated by the catastrophic processes, such as floods, quakes, and volcanic eruptions.

      1. And then there are the myriad people who want the slow, steady processes like erosion to be stopped for their convenience, and frame it as an issue of Environmentalism.

        Het, nitwit! You built a vacation home on a barrier island. It’s eroding. That’s what barrier islands DO. It’s always pretty to build a home near a large body of water, but one of the costs is the, sooner or later, that body of water IS going to come for a visit. Cope. The Environment (and the geology) or any art of the Earth is ALWAYS changing.

        I recall the hoorah over the famines in the areas of Africa just south of the Sahara. And I recall reading an interview with an expert on the geography of the area who said, in effect, the Sahara expands and contract on a fairly regular cycle (I think he said 200 years each way, but it’s been a while). The last time it expanded all the people affected picked up and moved elsewhere. This time there are international borders in the way. It isn’t Global Warming. It’s just what the Sahara does.

        1. Pretty much, yeah.

          And I remember eliciting a $#!^storm on social media just because one year at the holiday season, I pointed out this one song with the lyrics, “…and there ain’t no snow in Africa at Christmastime” was kind of stupid, because the northern regions were equatorial, and the southern regions were in the Southern Hemisphere where it is SUMMER at Christmastime, so of COURSE there’s no snow in Africa then…

          So…yeah. I dunno. Go figure.

                    1. Oh, well, along the northern coast, along the Mediterranean, sometimes, sure. (And on top of some of the highest peaks, like Kilimanjaro, Kenya, or Stanley. Because altitude.) That’s the only part that’s northern hemi outside the tropics, and even that is considered subtropical. Where I am in north Alabama is also subtropical, about on a latitude with Tunisia, and while we get snow, it isn’t often, and very rarely before January — we don’t get snow for Christmas here much, either. I think we had an ice storm for Chistmas one year, and that’s the only frozen precip for Christmas I can remember here, in over 3 decades of living here.

                      (Note that the southern tip of Africa is also considered subtropical and thus capable of the occasional snowfall, but again, southern hemi. They’d be getting whatever they got in July and August.)

                      I guess I just find it darkly amusing; many of the African cultures are not Christian and do not therefore celebrate Christmas (note I did not say all, but many — the Christian enclave is in the south and west, and as of 2002 comprised ~40% of the total population; ~38% in 2016 — can’t find it for 1984, the year of Band-Aid, but what numbers I’m finding indicate probably <40%), therefore the song is written with a Western cultural bias. More, since the continent is either (as aforementioned) essentially tropical/equatorial (except for the extreme north/south bits) or Southern Hemisphere, the song is written with a Northern Hemisphere bias, which when combined with the Western culture bias means a distinctly European/North American bias.

                      Which means the songwriters (both white, both male, both European) applied their personal bias to an entire continent. Woke much?

                      I applaud their desire to help people in the midst of a famine, mind. I just find the dichotomy between rhetoric and method…interesting. Especially when I was attacked for pointing it out.

                    2. All the snow I dealt with in the south was mostly well after Christmas as well. When I lived in the New Orleans area, Houma and the locality (Dulac, Chauvan, etc) got a “snow storm” of about an inch . . . on April 1st (this would be the 90’s). The year my folks stayed in Corpus, TX for the winter it snowed there too, iirc not long after New Years. Few years ago when I was still in DFW, Burleson did get a dusting on Christmas day. Just this past winter Brownsville got snow, and we had shipments held up due to snow in northern Mexico.

                      All that music junk really was a posturing by those gits anyhow.
                      I read somewhere Bob Geldof was bemoaning the fact the hated GWB was the one president who did the best job dealing with the carp that is Africa. Better by far than 0bama did.

                    1. Well, I’d just finished mine. It’s quiet at night — no phones ringing, nobody knocking on the door, no lawnmowers, weedeaters, leafblowers, big ol’ trucks rumbling by. I can concentrate.

  10. I have some doubts our opposition even knows what a “powder keg” is.

    Silencing the Opposition Is Like Tamping Down a Powder Keg
    By Sarah Hoyt
    I’ve hesitated a long time in writing this post, partly because of the injunction to “never disturb the enemy when he’s making a mistake.”

    That still operates, but honestly, we’re at a transition point in history — also known as the “leading to” circumstances before the map gets all arrowy and full of red and explosions — when there is a high probability of confrontation and violence. Or not. We might actually slide under this and end the civil cold war as we ended the international Cold War, without a major conflagration despite several minor ones.

    Note that I’m not sure that was the right way to end the international Cold War. It allowed the communists to rinse, deny the USSR, and come back again for a repeat of their craptastic act. But on the other hand, I’m not absolutely sure what would have survived the more … “expected” end to the Cold War, nor what would have emerged after. There was a non-trivial chance we’d found ourselves in the world of Robert A. Heinlein’s Farnham’s Freehold.

    In the similar predicament we face, where something will happen in the civil cold war and bring it to an end, I don’t know precisely what form a violent confrontation would take. But I know if it does happen, it won’t proceed as anyone — on the Right or the Left — expects. And I know what emerges afterward, both for us and for the world, would probably be very different from a constitutional republic, and therefore inevitably worse.

    So in an attempt to make everyone understand the “leading to” circumstances before we see the arrows and the explosions, let me say the Left thinks it’s mustered some kind of giant coup by getting Alex Jones of Infowars banned.

    They did. I’ve never seen a neater case of shooting oneself through the foot while scaring people who don’t respond well to being scared. …

    1. Some of us have studied the Nazis from a preventive perspective. That includes such things as “First they came for…”. A truly broad deep study of such phenomena also means such things as “How we burned in the camps…”. Which is Soviet Gulags, not Nazi death camps, but still quite informative.

  11. When I was younger, there was a spate of books where the Valley of the Protagonist was completely surrounded by the Mountains of Scary Magic. The resemblance to a caldera was not lost on me.

    This got me to wondering: what would a setting be like if the inhabitants KNEW that the entire Land of Plot would eventually go boom on a scale of a few centuries? How different would the reaction be if the inhabitants were able to live that long (i.e. some kinds of elves)?

    1. It’s an interesting concept.
      I must admit to spending considerable time at various points, analyzing the geology of Tolkien’s Middle Earth, with especial emphasis on trying to figure out Mordor…

    2. I was once working on a story set somewhere inside an ancient caldera, on the slope of an ancient volcano. The protagonist was predicting boom within the decade, but was largely disbelieved in spite of subterranean grumblings and rumblings. He collected a band of believers, and moved them out of the caldera…just in time.

      1. Back many many years ago (I think I was still in undergrad school) I encountered an historical fiction novel that was set on what evidently turned out to be Santorini, pre-eruption. The whole novel was about various people in Minoan Akrotiri, with the bull cult and everything, and the climax of the novel was the eruption, and the attempt of the protagonist to get clear before the whole thing went. It made for an interesting plot. I’m not sure how realistic it was, because I’m not that sure of the timeline of that eruption — how long between the start of the eruption and the time the whole thing went blooie — whether there was actually time for the climactic events of the novel to take place, or not. But I liked the story.

        1. …I also don’t know how much of the cultural reconstruction is accurate given what’s been unearthed, but it would have been reasonably accurate to what was known at that time, I think.

    3. IIRC Gondolin matches the description of a caldera with a central lava dome. Of course it could also have been an impact crater with a central peak

      1. It could be read either way, since the central hill is steep and in the exact center. Of course, Tolkien’s explanation for orogeny is ‘a demigod did it’, so we can read too much into it.

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