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

*For those putting his up at home, this took installing a different browser and pasting as text (after already copying and pasting as plain text on a text editor) under the html tab.  I hope this is not the new normal, but if it is, at least I know how to do it. – SAH*

Kiss Your Ash Goodbye: The Yellowstone Supervolcano, Part IV, 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.

Geological History — Known Yellowstone Eruptions
There have been 3 known “Yellowstone” eruptions with detectable welded-ash (which forms a rock called “tuff”) strata, all of which occurred in approximately the same location:
1) Island Park/Huckleberry Ridge
2) Henry’s Fork/Mesa Falls
3) Yellowstone/Lava Creek


A map depicting the ash bed strata for all three major Yellowstone supereruptions, along with the Long Valley eruption’s Bishop ash bed, and the Mt. St. Helens ash fall, for comparison.
Credit: USGS.

The Island Park/Huckleberry Ridge Eruption
The Huckleberry Ridge Eruption is the oldest eruption at the current location, some 2.1 million years ago. The caldera formed by this eruption is known as the Island Park Caldera; the stratum of tuff (also “tufa”; a kind of rock composed of welded ash — upon landing, the ash was still hot enough to be partly molten, and the particles literally stuck together, or “welded,” into a single rock layer; it is often porous, fine-grained, but may contain larger, pebble-like particles, especially close to the eruptive source) is the Huckleberry Ridge Tuff.

Etruscan paving stones composed of tuff from the Italian peninsula.
Credit: Patafisik,, public domain.

One of the world’s largest calderas, the Island Park Caldera is at a minimum 50x40mi (80x65km) up to possibly as large as 60x37mi (95x60km) and possibly up to ~0.6mi (1km) deep. This would have been bigger than the state of Rhode Island. The eruption was 2,500x greater than Mt. St. Helens.


Exposed Huckleberry Ridge tuff strata (there were several ashfalls in quick succession here) along the Gardner River near Osprey Falls, above Mammoth Hot Springs in WY.
Note vehicles for scale.

The Henry’s Fork/Mesa Falls Eruption
The Mesa Falls eruption occurred 1.3 million years ago and produced the Henry’s Fork caldera along with the Mesa Falls Tuff. The Henry’s Fork megacaldera is approximately 18x23mi (11x14km) in dimension, though some argue for a rounder shape, anywhere from 10-20mi (16-32km) in diameter.
This was “only” a VEI 7 eruption, but partly due to its density, and partly its overall size, it is considered a supervolcano eruption.

Mesa falls

Exposed Mesa Falls tuff at south rim of the Island Park Caldera/Henry’s Fork Caldera overlap; near Ashton, ID. Note vehicle for scale.

The Yellowstone/Lava Creek Eruption
This eruption is the most recent supereruption, and the only one dubbed “Yellowstone”; it occurred “only” ~630,000-640,000 years ago and produced the current Yellowstone caldera, creating the Lava Creek Tuff formation. The current caldera measures 53x28mi (85x45km). The current caldera rim ranges from some 100ft (30m) tall up to nearly a third of a mile (500m) high. This was without doubt a VEI 8 eruption.


Tuff Cliff in Yellowstone National Park, showing an exposed section of the Lava Creek tuff.

NOTE: It is essential to realize that the maps depict THE EXTENT OF THE TUFF STRATUM FOR EACH ERUPTION, and do NOT indicate the full extent of the ASH FALL. As aforementioned, tuff is formed when the falling ash is still hot enough to be partly molten, so the particles stick together when they contact. Ash can and does fall far beyond the extent of the formation of tuff — the ash plume from a Yellowstone super-eruption would be caught up in the jet streams and swept worldwide.

Other Yellowstone Activity
So. Three honkin’ big eruptions from the Yellowstone hotspot, huh? Well, really, that’s not a huge record. There’s not that much to worry about, is there?
Except for the fact that the Yellowstone hotspot has been busy. And it’s been around for MILLIONS of years.
Yellowstone hotspot eruptions can be tracked from their current location in the corner where Wyoming, Montana, & Idaho meet, all the way back in a southwest direction nearly to the northeast corner of California — as many as a dozen or more! The oldest known eruption dates to at least 16-18 million years ago.


previous yellowstone

Location of some of the previous Yellowstone-hotspot calderas, with ages indicated.
Credit: Kelvin Case at English Wikipedia, CC BY 3.0,


A different version of the map, showing other areal features, including a few members of the Cascade volcanic chain, and the Columbia Flood Basalts, a trap eruption which may or may not be associated with the hotspot.
Credit: Lori Snyder, Department of Geology, University of Wisconsin-Eau Claire, via USGS

Also realize that the Rocky Mountains orogeny (mountain-building) ended some 55 million years ago, meaning they were already formed before the Yellowstone hotspot got to them…yet, aside from some resurgent domes, etc., there are essentially NO mountains in the hotspot track — at least within the megacalderas.
The mantle plume/hotspot is NOT moving relative to the Earth’s surface overall, nor with respect to the Earth’s core. Plate tectonics creates the appearance that it is moving, when it is really the North American plate moving across the hotspot. The track of past calderas punched through the plate is therefore an inverse record of the direction of movement of the North American plate. The North American Plate is moving roughly southwest to west-southwest, with slight changes in direction over time. This accounts for the direction and slight curvature of the caldera track.

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

155 thoughts on “Kiss Your Ash Goodbye: The Yellowstone Supervolcano, Part IV, A Vulcanology Primer By Stephanie Osborn

  1. Gee, wouldn’t it be nice to have an orbital civilization from which humans could sit up there looking down on these major earthshattering events instead of being limited to observing from inside them?

    1. Or, imagine a setting that is far so far in the future that the next eruption is a ancient history.

        1. Oh, it wouldn’t kill everybody or you wouldn’t have a story. But you could play it several ways. (total collapse, civilization breaker, culture group destroyer, skin-of-teeth survival with help from rest of solar system, horrible disaster mitigated by heroic efforts, etc.) Depends on the social development at the time of the eruptions, which would be a big part of the backstory of the setting.

          1. Pov of the species colonizing the planet centuries later and finding they were not first

            1. that also works. Of course, the last one didn’t kill all the hominids either, so you can have an evolved species as well. There’s a lot of possibilities.

  2. Wait, is Island Park inside the caldera? I thought it was outside . . . (No, non-Idahoans, it involves no Island, just everybody’s family vacation cabin.) No, wait, different caldera. Okay then, never mind.

    I need a good topo map. Wonder how difficult the internet’s made getting one these days? (Used to be Fish and Game had them, physically, last time I checked it was buy and download a file . . . but my printer can’t print at a decent size.)

    Seems like I should be able to see the pinker 10-7 caldera right out my door . . . what am I looking for? Or is it mostly erroded and destroyed by younger uplift mountains and basalt flows? I should have learned this stuff instead of ignoring Dad on road trips . . .

    1. Island Park is one of three overlapping calderas. We can determine the caldera rims in areas where they were not obliterated by subsequent eruptions, and match them with the ages of the tuff strata.

      So at least parts of the Island Park caldera are outside the most recent (and obbvious) Yellowstone caldera.

    2. I’ve been been using various mapping programs to get a topo view, though I can only print B&W. The US government uses ESRI, and you’ll either get an older image (the NOAA hazard map uses satellite data for my area from 2011 or so), or while more modern, inciweb dot nwcg dot gov will get you a lower resolution view a few years old (my place is as of summer 2016).

      Not sure how good the topo data (if any) is in Google Maps. Inciweb seems to be pretty good for my area; found a virtual elevation marker on my property that I wasn’t aware of. OTOH, if you want good sat imagery, go with Google. I could see the solar panels on my tent trailer…

      1. There is some topographical data in Google Maps, otherwise its 3D view wouldn’t work. Unfortunately, there is no topographical mode that will display elevation contour lines, nor a convenient way to find elevation at a point (which Google Earth will do).

        1. The version in the hazard map will give the USGS USA Topographic data. Unfortunately, it won’t give you a scale. On the gripping hand, it will give lat and longitude. Not so useful as printed, but online it’s pretty good.

          (Note, the warnings for this cover the western US. I’m not sure how far east it covers, and haven’t been able to find the eastern version. Still, you get topo (and doppler radar) for the country.

            1. And now I see that they have improved things in Google Maps. If you go to the menu (the three horizontal bars stacked atop each other, at the upper left) and choose Terrain it will show labelled contour lines plus some relief shading.

  3. I do not like seeing tuff from CA, WA, OR, and WY in the Texas Panhandle. We’ve got enough of a mess with the stuff from NM, thank you very much. 🙂

    On a slightly more serious note, after I visited the Ashfall State Fossil Bed in Nebraska on a hot, windy day (glad I didn’t wear contact lenses!), Yellowstone has given me the willies. The way all those poor critters died… ugh. Miserable way to go.

    1. Yup. Talk about ASFB in the book. Think it’ll be mentioned in an upcoming blog installment.

      Texas is just in one of those places where the major supervolcanoes are gonna dump ash on ya. Of course, so is Colorado, Wyoming, Nebraska, New Mexico…yeah, don’t worry, I won’t go on.

      1. Mask, goggles, asbestos raincoat, shovel.
        If the ashfall is deeper than the house is tall, you’re not going to save the house. Of course by then it’s too late to leave.

        1. True.
          Asbestos ain’t good for the health neither.

          I’m thinking that TX is far enough away not to have to worry with that ash depth. Closer in…well, never mind.

            1. Texas yes, and Arkansas had ’em too. But I’m not aware of any ancient volcanoes in Alabama (which is where I’ve lived for the last several decades). There may possibly be a newly-discovered volcanic complex in northern Georgia, which isn’t that far away from me, but the vast majority of Alabama was an inland sea for much of its existence. We got a carp-ton of sedimentary rocks, some metamorphic rocks too, but the only igneous rocks I know of are in the northeastern quadrant of the state, in the tail end of the Appalachian chain, where the mountain cores are apt to contain plutons.

              I’ll have to dig deeper because now I’m curious, but the info I have to hand shows any volcanic activity to be either east or west of here.

              1. Robert Adams invented some volcano in the southern Appalachians for his Horseclans series. I don’t know if he had any basis in reality for it or not.

                1. If you have access to Scientific American you might check out the article, When Was the Last Time Volcanoes Erupted on the East Coast? by David Biello (January 2, 2014). 

                  1. I read it, and have a few concerns about certain things in the article.
                    But it sounds to me less like a true volcanic eruption and more of a “the fresh pluton found a teeny crack” kind of situation. Granted, that’s still a volcano of sorts. But also 50My ago, and in Virginia.

                    1. It does seem to be a one off, so I put in my, ‘That is an idea, I wonder if anything further will come of it.’ mental file.

                2. Actually, it was a volcano because of either a nuclear explosion or a meteor impact in the future between “now” and “then”, IIRC.

              2. Having dug into the whole “southern Appalachian volcanoes” bit, insofar as I can tell, there’s no such aminal and never was.

                FWIW the Appalachians are largely fold mountains: anticline/syncline, with a few faults where the fold stresses proved stronger than the rocks.

                Arkansas, however, DID have volcanoes, and produced the diamond fields there. The cause was rifting in the plate. I have yet to ascertain if any of that was concurrent with the Reelfoot Rift, or another rifting event.

                1. …There IS a very excellently-crafted and entertaining April Fools Joke that any number of more gullible website managers have picked up and run with, however. (Think Dante’s Peak looming over Gatlinburg.)

                  1. I lived in east Tennessee in Blount County on the edge of the Great Smokeys for two years (1970-72). A Dante’s Peak looming over Gatlinburg? Really? In all the times I visited the the area I never noticed it. When The Daughter took me back up there for the Eclipse last year it still wasn’t to be seen.

                    I guess I’ll have to tell The Daughter we need to go back and explore the area some more. Yes, that’s it. Oh thank you very much kind lady for giving me an excuse to go to the mountains.

                    1. Have fun with the excuse, but no no no. It was an April Fool’s joke, and the end of the article patently yelled, “APRIL FOOL!”
                      Let me go find the article so y’all can get a kick out of it too. It’s really well done. They use all the right terminology, and I had to go elsewhere and verify that indeed the composition is all sedimentary with some metamorphism from the folding.

                    2. Well, that’s the reason I threw out Arkansas. That’s not that far from me as the crow flies, and I know there was a LOT of vulcanism there, and Alabama and Arkansas both start with A…

                  2. Did you not see my tongue so firmly planted in my cheek that it nearly broke through? Oh, I guess not. 😉

                    1. The fact that I just found myself placed on a mailing list for a Tin Foil Hat Brigade (TM) e-newsletter (Moon Landing Hoax! Mars Face! Aliens Among Us! UFOs!!!!!!!) at the same time as I got the notification of your comment probably affected that a bit…

                    2. I’ve been doing a bit of lurking in the chans, and discovered the flat earthers. Run Away!!!!!!!!

                2. I’ve read that Arkansas diamonds are from a volcano aged around 95 million years ago. Too late for the formation of the Reelfoot rift or the Southern Oklahoma Aulacogen, which are related to the breakup of Rodinia. The location is about midway between the two, in the Oachita mountains which rose later as Pangea was assembling. The timing suggests it is related to spreading in the Gulf of Mexico. There is a lot of extended continental crust under the Gulf, and that province would have been very wide, like the modern Basin and Range.

                  1. I looked into that when I was writing Rock and Roll: The New Madrid Fault System, and the information I had indicated it was most likely too young, yes. But evidently there is a lot about the system that is not fully understood, and that might change that. Of course the Aulacogen is the other half of the “Y,” and may extend quite some distance.


                    1. If you have specific sources for information on the Arkansas volcanic field, I’d be very interested. Most of what I found pertained to the turf wars that sprang up between rival owners.

                    2. I have to make a correction. Spreading in the Gulf of Mexico had ceased by about 140-130 million years ago. By then the Yucatan Block had detached itself from South America and the young oceanic ridge in the Gulf became inactive. A new ridge formed south of the Yucatan.

                      The Murfreesboro, AR diamonds are from a lamproite pipe, similar to kimberlite. Kimberlite only erupts through Archean crust, and the Arkansas crust isn’t old enough. The word kimberlite is often used to refer to any diamond pipe, but is technically incorrect in many cases.

                      So spreading cannot explain Arkansas volcanics. There have been attempts to link this to a proposed Bermuda hotspot. The problem is Bermuda is not part of a long chain of volcanic islands, so there is no hotspot track. There is no obvious reason for Bermuda to have formed where it is, and 30+ million years of seafloor spreading would place its hotspot far to the east. But Arkansas would have been in that vicinity 95 million years ago. There are also 115 million year old volcanics in Kansas which could be related. But as of now they are not well understood.

                    3. If memory serves, and granted, it does not always, I recollect that the Arkansas vulcanism was officially “explained” by one or another rifting events, but it’s been a year since I researched and wrote that book, so (excuse the pun) my memory is probably somewhat faulty. I suspect, however, that the confusion over what caused the vulcanism is one reason I was never fully willing to throw out any possible connection to the Reelfoot Rift. By the time you got done with the Keweenawan and Reelfoot Rifts, the whole region was fairly riddled with crustal rips/cracks anyway.

                      And since we don’t fully understand kimberlite and its related rocks, add another question mark to the tally.

                      Given the fact that, per current geologic theory, supercontinents tend to breed their own destruction by insulating the mantle and creating hotspots, and the resulting upwelling/outflow from those hotspots breaks up the crust and carries it away, it’s arguable to use the hotspot from the breakup as A (maybe not the only, but A) potential source for the lamproite.

                      I think the gist of it is, “We just don’t really know.”

          1. I would think that for significant portions of the country if you survived the initial event and ash-falls your would still have a challenge staying alive until the next time crops came in.

            1. Yes, it won’t be fun. And the “breadbasket” will be the areas hardest hit by the deeper ash falls. Contrary to popular belief, raw volcanic ash is not fertile and not good for plants. The material has to be chemically weathered before it can turn into the rich soil common to volcanic regions.

              More, the ranching and animal husbandry industries will get hit hard, too. Animals tend not to want to wear filter masks, and to want to roam freely, and that’s a sure combo for large numbers of animals dying from inhaling the ash (which will be discussed in more detail next week if memory serves).

              1. Doubt that the ash itself would do much good for the fish either. Then there is the possibility of certain chemicals which might not be nice to have in concentration in the water during the breakdown period.

                When The Daughter was a preschooler she already knew she wanted to be a scientist. She first flirted with the idea of being a Volcanologist.
                She would talk about moving to the bay of Naples and studying Mount Vesuvius. Once she discovered its existence, Solfatara was added to her list.  The children’s book you mentioned last week, Hill of Fire, about the boy who discovered a volcano (Paricutin) growing in the family corn field was one of the many books related to the subject she took out of the library.

              2. Probably depends on the dose. The year after Mt.St.Helens, my farming relatives in north-central Montana had a year like no other — winter wheat yields in their area normally top out at 65 bushels/acre. That next season, they got as high as 120 bu/ac.. Of course their ashfall maxed out at about half an inch deep, so it was more like a big dose of micro-nutrients than a soil replacement.

          2. I have friends who think Arizona will be “okay” when Yellowstone pops again, then I see that Tucson falls in the borders of three of the four ashfalls on the first map.

              1. I notice the San Fransisco peaks splash entry did not contain the word “extinct,” which I had always thought it was. Of course the Pinacate field is even closer, and the splash says that it might go active on the Mexico side of the border.

                I seriously doubt having a wall on the border will deter the ash fall from crossing…

                  1. Interestingly, the cause seems to be another (much smaller) hotspot. It’s notable that the extinct volcanoes are on the west side of the field, and the currently dormant volcanoes are on the east side. And yes, I do mean dormant — Sunset Crater cinder cone last erupted in 1085AD.

                  2. “These future eruptions may provide spectacular volcanic displays but should pose little hazard because of their small size and the relative remoteness of the area.”

                    I think the residents of Flagstaff, Winslow, and especially the Hopi and Navajo Reservations may take exception to that sentence.

                    1. I may have misspoke; it appears the 10 cm ashfall depth of Sunset crater is well(ish) to the northwest of the other large hole in the ground of the Flagstaff/Winslow area: Meteor Crater. I’m sure Meteor Crater has to have some evidence of previous San Fransisco field eruptions, but not enough to pop up in a casual Google search.


              2. Jumping into a different science, the home page for that map has a very pretty picture of the 4m scope on Kitt Peak.

  4. Another one to consider is the La Garita Caldera in CO.

    And there’s always Toba, which may have caused the human bottleneck.

    1. La Garita was discussed last week, if memory serves.
      Toba is mentioned in the book.
      There are enough supervolcanoes in the world that at a certain point, one is left to simply list them, else the book — intended to discuss Yellowstone specifically — loses focus.

  5. This has been an interesting series of posts, since they discuss things from my home region. I lived for years in Southern Oregon (on both sides of the Cascades), about an hour away from Crater Lake. We used to have a lovely view of Mt Shasta to the south, and we took occasional trips to the Lava Beds National Monument in Northern California. We even got a little ashfall from St. Helens!
    So remnants of volcanic activity have been a part of my life since…forever. But nothing on the scale of Yellowstone!

    1. I’m glad you’re enjoying it. I think there is one more blog post in the series, but I do recommend checking out the ebook. There’s more in it than I can reasonably cram in a blog series.

      And yes, I’ve been in your neck of the woods. I’ve been to Mt. Mazama and down to the Shasta/Redding area, though I didn’t have time to hit the lava beds. That said, I’ve walked or ridden horseback over a really large number of volcanoes from Shasta north to the Seattle area. (Did not get to “do” any of the ‘canos in the Seattle area, but at least saw them, though cloud cover made it iffy.) Did a bunch in the Deschutes Nat’l Forest/Bend area.

  6. One quick clarification on the tuff stratum map: The ONLY eruption depicted on that map where “only tuff” is NOT the rule, is the St. Helens eruption. That is truly the ashfall extent. Any tuff deposits are apt to be so close in to the mountain itself that it could not be depicted to scale on that map.

  7. Also, Thanks for the definition of “Tuffs.” I keep seeing the word in relation to the Tucson Mountains Chaos, but had no idea what they we’re talking about.

    The last time I spent any serious time looking at geology was in the 8th grade or so.

    1. Glad to do it, and thrilled someone learned something new.

      Strictly speaking, tuff strata can be formed from concreting materials as well, but it’s been my experience that what’s being referenced by the term is usually welded.

  8. Once again, I would like to thank Our Esteemed Hostess for inviting Stephanie Osborn, The Interstellar Woman of Mystery to take the floor.

                  1. And the docs have booked me in for another CT scan this afternoon. (That’s pretty quick) I’ve also spoken with a respiratory specialist who wants me to pop by in 2-3 months to the clinic, for the (happily not immediately dangerous) pulmonary embolism they found during the last CT scan… (it’s being treated with warfarin pills, which doesn’t transfer to baby via breastfeeding.)

                    1. Shadow, I’d get a second opinion on that one. Pulmonary embolism is nothing I want to fool with.

                    2. Basically, “Are we sure this can be left for 2-3 months? What are the options and associated risks for dealing with it quicker?”

            1. Yike!

              Have one of the guys pick up one of those cheap Chinese laser thermometers. They work great for mapping surgical infections, at least if they’re near the surface.

              You can also use them when cooking, for quick checks of childrens’ temperatures, checking the temperature of the air conditioner or heater from across the room, or annoying animals. (some spiders will chase the red dot just like cats…) (and so will some goldfish…)

  9. Woah. BIG. Good thing it won’t reach my house for another few million years. 😀

    [Wonderful series. Come back soon!]

    1. Given I don’t know your area, I couldn’t say. I do know somebody on faceplant was commenting as how they hoped it took out…was it Chicago…? When in fact Yellowstone is moving roughly NE and is already considerably north of Chicago, so it will eventually be in Canada, I suppose.

      I’m glad you’re enjoying the series, and much to my pleasure, Sarah has me guest here every now and then. I’m generally guest-posting a couple times a year, either with a series on my latest popular science ebook, or updating the solar activity.

  10. I have a question about those large-area falls of welded tuff on the maps… which is, basically, how do you get that so *far* from the actual eruption?

    Welded tuff (as you explain) is made from ash falling still partly or almost molten — so it has to be that hot where it falls, many (even hundreds) of miles away from the source. But how is it that it doesn’t cool and solidify on the way there, suspended in the air, in such small particles, over such a large distance..?
    Is the air *really* that hot, near the surface, over such an area?
    Is the ash swept over its welded-tuff “footprint” very fast, in something like a pyroclastic flow but maybe without the bigger “rocks” that a full-up one of those will sometimes involve?
    Some combination of those two?
    Or is the real answer closer to “we don’t know because nobody has ever seen anything enough like that to know, and thank all your lucky stars for that?”

    1. And this is where I must confess to ignorance. I am fairly knowledgeable about this stuff and have done a lot of research, but I am not, nor have I ever claimed to be, an expert in same. I know they’ve looked at that sort of thing in “standard” eruptions, and I know that the stuff is essentially superheated, and stays hot a surprisingly long way away. I also know that, while there have been lesser supervolcanic eruptions in recorded history and in prehistory (e.g. the Mazama eruption, which was seen by the local tribes and remembered in their legends and myths), they were all long before the advent of modern data-taking capabilities. (And yes, thank your lucky stars.)

      I know that when Mazama blew, the combo of lava/glacier left an entire freakin’ CLIFF of obsidian. Obsidian basically forms when the lava is flash-cooled. I’m still trying to figure out the thermodynamics of how an entire CLIFF of lava was flash-cooled to obsidian, even WITH glacier. There’s another one, even bigger apparently, at Yellowstone. My background is in physics (okay, astrophysics, but still physics — thermodynamics is thermodynamics), and I’m not wrapping my head around that one.

      I also know the pyroclastic flow from St. Helens not only flash-sublimated all the snow on the summit as well as several entire glaciers, it flash-evaporated part of Spirit Lake and the Toutle River, and still had the wherewithal to leave trees 20 miles away nothing but charred, blackened trunks. I know it most likely hit Mach on the way out. I know that the ash cloud went stratospheric inside 10 minutes, and continued pumping hot material upward for more than 10 hours. I know that something like 17-18 pyroclastic flows happened in the span of the first eruption. I know the ash cloud took only ~3hrs to reach Spokane, nearly 300mi away. I know the resulting hot lahar did a number on the wildlife in the Toutle River pretty much all the way to its outlet in the Columbia.

      And I know that the total volume was only about 0.05 cubic miles of rock, from a VEI-5 eruption, equivalent to “only” ~26MT.

      Now scale that up to a VEI-8. >240cu.mi of ejecta. Energy measured in hundreds of gigatons. Instead of a 10-20mi radius of devastation, a minimum 100mi radius — and that’s the conservative estimate.

      And since volcanic ash is basically just tiny slivers of obsidian — volcanic glass — and since glass is an insulator, it will hold heat a long time.

      And that’s the best answer I know to give you.

      1. If I draw from my knowledge of impact science, I can also tell you that there is a high probability that the molten ejecta of a large impact will come down still hot enough to set the local foliage on fire, and that the Chixulub impactor likely produced a “volcanic/nuclear/whateveryawannacallit winter” as much from the wildfire smoke as the debris it flung up.

        And it doesn’t have to be anything but tacky/sticky in order to “weld.” Goopy molten isn’t a requirement for it.

        1. Lassen National Volcanic Park has a lovely interpretive trail with a picture sign of a boulder ejecta from the early 20th-century eruption in front of that same boulder. They had to wait several days for the boulder to cool down enough to approach (of *course* there’s someone standing in front of it!) Probably the only reason it didn’t set everything on fire is that it’s high Sierras/Cascades scrubland.

          1. Exactly! Though some of the stuff in that area can be highly flammable; chaparral, if memory serves, is one of those.

            But yes, that doesn’t surprise me.

            I’m curious; how big was this boulder?

              1. Ho-lee cats.
                Heckuva lava bomb.

                I do wonder, though, if it wasn’t actually an ejecta fragment, given the sharp-ish angles. That is to say, a shattered but extant part of the mountain, thrown out under the force of the explosion. Happens not infrequently. True lava bombs tend to be much more rounded from the combo of aerodynamics and surface tension effects. Not always, but it’s a thought.

                Wouldn’t stop it being dang hot. Much of the solids in a pyroclastic flow are extant broken bits.

      2. Oh, but the most fun questions are seldom the easiest, are they..?

        It sounds like the examples we have are pretty much in the “both/and” camp, especially with (as you say) the truly massive energy releases here. Even *as compared to*, say, Crater Lake/Mazama.
        And ash is small, which means probably(?) laminar-flow heat transfer to the air (= slower), and fluffy, whch means slower heat transfer too. But still…

        It even occurred to me that a *really* violent event could put even ash-fine particles on, basically, a ballistic trajectory (like impact ejecta), though that would basically mean “blowing off” something like cubic miles of lower atmosphere into the upper atmosphere (stratosphere or even higher) — and then that “express” cuts the heat-loss down to only radiation or almost so.
        But, wow.
        So possibly even that idea could be relevant here too (second comment)..?

        Also, at some depth of one-eruption ash-fall (tens of feet?) the heat capacity of the ash starts to rival the heat capacity OF THE ENTIRE ATMOSPHERE, the whole “column” top to bottom. Those pictures suggest… these eruptions might have got there, maybe even and then some. Wow, eek, and wow again.

        Maybe, whatever the mechanism or mechanisms really are, it boils down to, “relatively* non-violent can still be violent at this scale, no matter that you’re at the so-called “quiet” basaltic, fluid end of the volcano spectrum.
        Violent as in almost incomprehensibly violent, in our usual “watch little Mt. St. Helens explode, ooh ah” terms.

        That *cliff* of obsidian is… kinda dazzlingly amazing. Just guessing from the thremal diffusion lengths for a few seconds/minutes — seems to say, no, just no, not even close. (And of course it’s length ~ time squared.)
        I’ve got basically nothing to suggest on that one either.

        *Super* volcano, not cuddly nice like “regular” volcano.
        Maybe all this just underlines that point, yet again!

        1. Good. That means I got enough of the concept across to get you thinking about ramifications in some detail. Given I was brainstorming as I went, I wasn’t sure. Plus I also have to take the thermodynamics down to where I’m not spouting equations for the people who don’t do equations. But I really wasn’t sure if I was making sense on that one.

          But yes. The difference is akin to M80 and nuke. It is, literally, exponential.

          And yeah, I went to Mazama and the ranger was pointing out which peak around the rim was the honkin’ obsidian chunk and I sorta gaped at it and couldn’t get my head around the thermodynamics at all. Still can’t.

          1. Yes, most definitely on the “ramifications” here… you did get that across well!

            It’s just that they tend to, well, sneak up on you… like that basic, oh wait, how *did* that ash stay that hot, that long/far? Or the idea that at *some* depth of (fast) ashfall, you’re heating all the air as much or more as you’re cooling the ash.

            Somehow people expect, even without a lot of training/reading, “nuclear” stuff (for example) to be different. Falling rocks, or comet iceballs, maybe too, see that wonderful discussion in “Lucifer’s Hammer” for instance.
            But “ordinary” things like white-hot molten rock, they seem so ordinary that we forget how much scale matters.

            At some point, a difference in degree *becomes* a difference in kind.
            Then, just wildly, entirely *different*.

            And on that obsidian mountain… use “explosive self-mixing” to put bits of lava and ice/water in small enough pieces to cool/boil fast enough, then (magic goes here) somehow have the steam escape and let glass all fuse..? Still doesn’t sound so likely to me; but better than “magic instant heat transfer.”
            You were not the only one fumbling/brainstorming here on this…

            Looking happily forward to more of the same!

            1. You know, I’ve done so much in my life already, and stuck my nose into so many things like this. People keep telling me I need to write an autobiography or something, but 1) I don’t feel old enough (though they tell me to do it now while I can remember!), and 2) it seems awfully egotistical. I mean, I don’t really think of myself as any big deal — here in HSV, you trip over rocket scientists, walkin’ down the street — so I can’t imagine why somebody would want to read a book about me. But then I start talking about the stuff I’ve done and seen in the space program, and visiting Mazama and St. Helens and such like, and the people I’ve met (and how I met ’em) and suddenly there are people sitting around me listening and asking questions…

              I dunno.

              1. Ever read (any of) Charles Babbage’s “Passages From The Life of A Philosopher”..?

                I’ve never even seen the whole book, just snippets; it’s his (sort-of) autobiography, but the most interesting parts, beyond the Big Stuff like his work on the Difference Engine(s) and the Analytical Engine(s) and so on, are his “little” stories.

                Like inventing, and then deploying, what amounts to a Black Box for 1840s(?) railroads, and suggesting that things like that ought to be standard-use.

                Or even his account of a party trick, almost a bar-bet hustle, about cutting a small-diameter hole in a piece of glass (think window or bottle glass) with simple ordinary hand tools. (Hint, the method is just about the opposite of what one might expect. Spoilers available upon request, but he tells it better than ever I could.)

                Interesting man… with an *amazing* fund of interesting stories.

                Maybe the “am I interesting enough to merit a self-portrait” is better asked as “do I have interestng enough stories to tell to fill a book” yet (even an e-book)?

                Every once in a while, though not on certain subjects (e.g. funding, and the perils of street musicians) I really do ask myself, What Would Babbage Do?
                [Someday, there ought to be a convention button for that…]

          2. Then there is the obsidian ridges around Newberry Crater. Plus Obsidian Falls on the PCT south of Scott Lake (hwy 242). They are the baby obsidian outcroppings found in Oregon.

            1. Holy. Cats.

              I never made it all the way to Newberry; I did wind up prowling one of its cinder cones — Pilot Butte, I think it was.

              But it seems Newberry has produced three obsidian flows, the biggest of which, imaginatively dubbed the “Big Obsidian flow,” per Wikipedia, “it is frequently cited as the largest Holocene obsidian formation in the United States, its area of 1.09 square miles (2.8 km^2) and volume of 0.031 cubic miles (0.13 km^3) actually place it fifth in the nation.”

              Okay, I may have to make it a hobby to try to figure out this means of producing honkin’ big chunks of obsidian in terms of the thermodynamics…

              1. “obsidian flows”
                (sub) cubic miles of glass
                from flash-cooled(?) lava..!

                Okay, this is officially a Scientific Mystery.
                (And, The Game Is Afoot.)

                  1. Yes, very much those, indeed.

                    And if the solution could only tell us how to flash-cool *optical* glass with *no stress* and no striations, *that* might be worth a shilling or two… beyond the budget of a consulting detective.

                    1. Oh, I don’t know that the “no stress or striations” would necessarily apply to the obsidian. I rather doubt anything that size had no stress fractures in it.

                      But yes. It would be nice.

                    2. If it formed the way you’ve been discussing, inclusions both solid and gaseous would seem a certainty.

              2. 😉 Having grown up in Oregon. Been to both Newberry Crater & Obsidian Falls (hike not very far, but is S T E E P), more than once. Lots of places in Oregon where picking up obsidian rock off the ground or chiseling it off an outcropping is NOT illegal; for the record, it is illegal in both these places (at least chiseling). I tend to take Obsidian rock as a given when volcanoes are involved; not the exception it appears to be.

                1. Obsidian, yes. It’s a given.
                  Honkin’ big hunks or piles of it, apparently not SO unusual as I thought.
                  I’m just tryin’ to figure out WHY, and HOW.

                  1. Chaotic thermal patterns? Massive cold front compression? I’m certainly not an expert, I’m just thinking of how a tornado can have areas of complete devastation next to untouched areas.

          3. Did you make it to the Medicine Lake obsidian flows, east of Shasta and south of the Lava Beds? They are so big, you can see the whole “river” of obsidian from Google maps.
            I never made it there myself– it’s rugged country.

            1. No, much though I wanted to explore that whole area, I was there to meet a friend and didn’t have time on that trip. By that time I was starting to have issues with my knees, though I was still going. Now, not so much. I’d hoped to do considerably more travel/exploring in my retirement years but it seems life has had other ideas.

  11. …Though I dunno if “fluffy” is quite the term for volcanic ash. That stuff is HEAVY! When my friends took me to St. Helens, we ascertained from the rangers how I could get a legal sample of the ash to take home, since the area around the volcano is a national monument out to some miles. So they told us to drive back along the Toutle until we passed a certain mile marker, and then we could park on the roadside, slip down a short trail to the riverbank, and get all the ash we wanted.

    I had a 0.5L water bottle I’d emptied, so we used that as a container. The river had cut down into the accumulated ash for geez, probably 20ft easy, maybe 30. And the “sand” was all ash. So we just scooped up ash and used our hands to funnel it into the bottle.

    The durn thing put my suitcase over weight on the airline trip home, and the bookshelf it sits on has to be one completely different from the petrified-wood bookends my parents gave me, because it would collapse the shelf if they were all on the same one.

    I readily see how a heavy ashfall can collapse buildings.

      1. Yeah, and my reply to your “I dunno” comment just got sent to Moderation Purgatory(tm), with about as much reason as Sarah’s You Need A New Browser to Post to Your Blog, ha ha!
        Wordpress delenda est… may now be an understatement.

        I can try to re-post that one, if you want to see it sooner…

        But meanwhile, my actual reply comment here:

        Yes, ash is just like a fluffy… ROCK. Because, made of it.
        Lower heat conductivity because little bubbles ‘n’ stuff.
        But still *rock*, as your bookcase sample proves.

        Maybe someday we can get orbit-made foamed rock, and metal, just like in all those stories. It’ll be lighter, but still not LIGHT.

        1. Well, I suppose “light” is relative.
          I actually found ash to be considerably heavier than pumice, and was fascinated to see pumice pebbles literally blowing along in a breeze. Not a gale, just a nice summer breeze.
          Never mind the piece I lifted in one hand and tossed to my friend, when the piece was three times the size of my head.
          It is, after all, a matter of density, or perhaps flux is a good way to put it. For a given volume, there is far more air in pumice than in ash.

          1. I have several small pumice boulders in my landscaping (which I’ve been slowly moving from the back yard to the front.) They’re not light, even if they would float. But definitely a lot less dense than tufa. (I also have a lovely chunk of gray-banded obsidian that got handed down to me. About the volume of a cantaloupe, though not that shape.)

            1. Again, the density of pumice will tend to vary. It all depends on how much gas was trapped in it and how “frothy” it was. I’m familiar with the stuff you’re talking about, and that was ALL I was familiar with until my trip to Mazama. Then I rather got my mind blown. Some of the stuff at Mazama was VERY frothy. Like I mentioned, pebbles blowing in the summer breeze frothy. That particular pebble was so light I could barely feel weight to it when I picked it up, and it appeared nearly translucent.

    1. Division One books, in order:
      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

      Not yet released:
      8) Phantoms (Oct 2018)
      9) Head Games (Winter 2019)
      10) Break, Break Houston (Spring 2019)
      and I’m brainstorming more.

      All are available for Kindle and Nook (mobi and epub) as well as print for those who prefer it.

      1. Also the Displaced Detective books are gradually being re-released by the new publisher. Books 3 & 4 are out in Kindle, and will soon be out in print and Nook. 5 & 6 coming soon!

          1. Me too. The first publisher was my “regular” publisher and they’re wonderful, but mostly do SF/F, and that series leans more mystery. The new publisher is putting it out through their mystery imprint, so it should hit the right readership.

        1. I snapped up all of those the FIRST time around…… I’m just hoping for another one.

          1. There are more in work. I’m currently trying to figure out the order in which I should put them, and that’s one of the main hold-ups. I have one already completed, but had planned to write another in between; now I’m not sure if I need to, or if I should just go ahead and put it out and the “in-between” one can happen later.

      2. Great to hear there are *10* books here or coming; all really good (to #4 so far) and with a distinct “Doc Smith” flavor at times.
        [tips hat]

        1. *bows* Thank you most kindly.
          I have read the Lensman series and a couple of the adjunct books and loved them, so yes, it doesn’t surprise me that you “read” Doc Smith in some of it. I’ve “been accused” of writing like Doc Smith and Heinlein both, as well as Conan Doyle, depending on what I’m writing at the time; I’m immensely honored by the comparisons, though I’m not sure they’re legit. But I’m having a grand old good time writing these books.

  12. Somewhat off topic Volcano question. How big of an impact is the East African Rift Valley going to have once it spreads far enough to erupt regularly? The Mid Atlantic Ridge is erupting fairly frequently but most of that is below a mile or more of ocean. Would the whole 3000 mile long or so rift all erupt at once or would smaller eruptions take place.

    1. I think the answer to this one is, “We don’t know yet.” This is one of those things that hasn’t really happened in modern times before, so we don’t have a full understanding of what to expect. I mean, after all, the Reelfoot Rift did much the same, but there was no vulcanism along it, apparently. Other rifts have had considerable vulcanism. This one, so far, has some, and the potential for a lot, but we can’t say until it happens.

    2. There can be much variation. When South America rifted from Africa the rift propagated from south to north. That could be due to variation in the thickness of the continental crust, or because the movement of the two continents wasn’t exactly perpendicular to the rift zone. That is, it opened like scissors. Also, the mantle/asthenosphere is not homogenous and varies in its ability to produce magma depending on what the upper mantle contains at a particular location. Water content, in particular, affects the melting point of the rock.

      The reason subduction zones produce volcanoes is the release of water trapped in the rock once the descending slab gets hot enough. The water, superheated and buoyant, alters the rock above it and rises into it. If the conditions are just right then it will reach the surface and erupt. What erupts depends on the type of rock it rises through.

      Rift zones produce magma by decompression melting. As the crust stretches and thins it allows hot rock beneath it to rise. This is because the mantle behaves like a very viscous fluid. The melting point is affected by pressure as well as temperature, and after it rises past a particular depth magma can begin to form. How much magma depends on what is in the rock, the proportions of various minerals and especially how much water. If the rock is particularly “dry” then little or no magma forms. You can still get a rift valley, but with no volcanoes in the rift.

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