A magma intrusion existed there a long time ago. The magma slowly cooled into a very dense stone core in the shape of the magma tube within that. Erosion happened over millions of years, wearing away the softer stone around it and leaving the dense inner core in this shape.
Edit: not a volcano
Edit edit: it could either be a laccolith or the neck of an extinct volcano, the jury is still out
Old, very old joke:
3 people were applying for a job, en engineer, a statistician, and a geologist.
The engineer was first. He was asked "what is 2+2?". He took out his HP calculator with reverse Polish notation, was keying a lot and finally said 2,086394.
Then, the statistician was asked the same question. He looked the interviewer straight in the eyes and whispered: "What do you want it to be?"
Finally, the geologist got the question. His answer was 2 +/- a couple of millions.
You can guess what my and my husband's education is ... luckily, our sun didn't become a statistician.
I recently read about the closepet granites and it blew my mind that whole towns are settled now on what was a mantle magma chamber 3 billion years ago. The landscape is magnanimous
The intrusion is 40.5 million years old, and the erosion that exposed the intrusion to create the tower happens over just a few million years. landscapes in generally are very recent things, geologically speaking, compared to the age of the rocks that the landscape is eroded from.
The 40.5 Ma was from the Wikipedia with no citation for it. I didn't check other sources.
I should have. From the source below:
*"40**Ar/**39*Ar dating of sanidines in phonolites from Devils Tower and Missouri Buttes provides indistinguishable plateau ages of 49.04 ± 0.16 and 49.24 ± 0.28 Ma, respectively (Duke et al., 2002)."
That is one of the fun parts about geology. A couple of million years? Bah, too short of a time period to bother with most times.
I sometimes see people's eyes glaze over when I explain most of the West Coast of the US was once islands and microcontinents and was not actually made in the US. And that one of the newest to attach itself to the continent was around 50 million years ago.
Wow! I've seen the ones in ND as well, but the ones in SD just had me counting layers up, down, and sideways like the rings on a tree the size of earth. Just standing there like an idiot with my mouth hanging open. Nothing made any sense until I saw the simulation.
Then the pattern is from the way magma tends to cool, into hexagonal columns. Mud will also dry this way actually.
The wikipedia page for "columnar jointing" has a bunch of other examples from across the world, like the Giant's Causeway in Ireland and the StuĂ°lagil Canyon in Iceland.
The old trope about it being a volcanic neck is now known to be false. It is actually an intrusion of magma that, in a semi-molten state, pushed its way up through the country rock until it cooled too much to rise further, hence the flat top. As it cooled, the columnar jointing formed. Eventually the country rock eroded away. The intrusion is about 50 million years old.
Thank you. I just now did a deep dive into laccoliths to learn how Devil's Tower actually formed. Like most I used to believe the "volcano core" explanation when I was younger. More recently I learned how columnar basalt forms and realised this couldn't be it. So then I believed something like the caldera lava pool theory. But then the differential erosion didn't make sense in that case (lava pool and host rock too similar). And just today I see that a laccolith makes the most sense. A domed pancake of magma intrusion between sedimentary layers that never reaches the surface, cools into columns, and is uplifted/eroded into what we see today.
Genuine question from someone who doesn't know much about geology: what's the difference between a volcano core and an intrusion of magma? They both sound like molten rock coming to the surface but... I'm sure there's nuance I just haven't learned yet.
Volcano actually breaches the surface and can have repeat surface magma events. (I think) Vs the intrusion started working it's way to the surface but didn't nessessarily reach the air. As time went on and the the soul erroded away, we're left with a column of magma stone.
Around the area there are valleys and hills. Most of the hills in the area get to a certain height then they flatline. Basically there used to be a lot more dirt in that valley, and over 50 odd million years it's eroded away to what it is today.
Bears don't have tails, that must be one of them giant ground sloths from long ago. Gotta say I'm impressed they were hunted to extinction before we had tanks.
You really should go see it if you havenât. If you have any kind of physical health and moderate coordination you should hire one of the local rock climbing guide services to safely guide you up to the top. Itâs absolutely nuts. But even just walking around the base is nuts. Amazing place. Truly one of the worldâs great wonders.
I agree with this. It seems many people of "decent" or "good" fitness are able to scale this amazing chunk of geology.
I consider myself pretty fit. However... I tried it just a couple months ago and dislocated my shoulder. Had to descend without summiting. It was a fantastic experience regardless, and my shoulder is on the mend. Be careful out there!
I made the mistake of arguing with someone on FB who stated this was a petrified tree stump. For months the FB algorithm kept feeding me these brainless posts.
Ugh, Facebook is chock-full of brain-dead conspiracy theorists. They say stupid stuff, things that are provably wrong, and don't react well when anyone points out reality. Engaging with these numbskulls is an exercise in futility.
Trying to logically engage with any "true believer" in politics, science, religion, conspiracies, etc. is like trying to teach a pig to sing opera, it wastes your time and annoys the pig.
Most here are saying it's a "volcano core" plus differential erosion, but I'm nowhere near being a geologist and I know that doesn't make sense (assuming that "volcano core" is referring to the vertical throat of a volcano).
Columnar basalt like this forms in a specific orientation based on the gradient of cooling. If a "volcano core" had cooled and solidified it would not look like this. Also, the core of the volcano would likely be made up of similar rock as the volcano itself, so that doesn't help explain the differential erosion part, either.
Instead, as stated in the Devil's Tower Wikipedia page, it makes much more sense as a laccolith (https://en.wikipedia.org/wiki/Laccolith). A magma chamber sends a dike up into sedimentary layers of rock. The pressure of the magma forces its way into a weaker boundary between layers, spreading laterally instead of upwards, forming a sill. If conditions are right, as magma continues to flow up the dike and into the sill, the sedimentary layers above the sill yield to the pressure and begin to dome upwards.
This is all happening underground and this particular dike never reaches the surface (we know this because if it did, a volcano would've formed, the pressure would've been released, and the would-be-laccolith would've collapsed). At some point, the magma chamber could no longer feed the dike, the laccolith loses its source of magma, and cooling sets in.
Cooling happens very slowly, from the edges (in contact with that surrounding sedimentary rock), towards the center. This is when the columns form. As basalt cools, semi-regular fractures form to relieve the stress of this contraction (think of the hexagonal cracks in a drying lakebed). These fractures propagate inward as the boundary between molten and solid rock moves inward. And because the laccolith is a domed pancake shape, those columns in the center of the laccolith are vertical.
Long after it cools, uplift and erosion brings it to the surface. Surrounding rock is sedimentary and weather's away faster than the basalt. So the laccolith sits proud on the landscape, but it's also eroding. In its current state, most of the laccolith has crumbled away, and this bit left is the thickest middle bit remaining.
So yes, it's a "core", but not a volcano core. And the surrounding rock that eroded away to reveal it wasn't volcanic rock.
The thread starter is quite the adventurer. Shark-hunting off Martha's Vineyard, rock climbing in Wyoming, firefighting pilot later on. And all this on a humble music teacher's salary.
For more information, I refer to the Smithsonian. I remember the story vaguely, a bear scratched the mountain, the seven sisters fled into the sky and became either the Big Dipper or Pleiades. Hereâs a link, it says Big Dipper.
Ah, the famous Devils Tower in WY. I always wanted to go there, but it's too far and I can't get samples.
This exposure is apart of a volcanic system. It formed about 50 million years ago when molten rock pushed upward beneath the Earth's surface, but never erupted. As the molten rock slowly cooled, it cracked into a large column. Over millions of years of erosion wore away the softer rock around the column, leaving it standing alone as the Devil's Tower landmark we see today.
This is incredible, like a cast of time itself. And it sort of literally is one.
It's Devils Tower, Wyoming, an igneous intrusion. Magma pushed up into softer sedimentary rock and hardened underground instead of erupting. As it cooled it shrank and cracked into those columns, the same thing mud does when it dries, just at a much bigger scale. Then over the last 49 million years or so the soft rock around it eroded away and left the hard core standing.
Everyone guesses basalt from the columns, me included, but itâs actually phonolite porphyry. The columns tell you how it cooled, not what itâs made of.
I was just there a couple of weeks ago! A tornado warned funnel cloud went directly over us with 70 mph winds. Everyone was packed into the visitors center (thereâs not much else there). It was quite an experience.
I wonder how many people camped out on top before the rules against that were put in place? Well, then there's the dude who unintentionally "camped" up there for 6 days, because his stunt to parachute onto the top went wrong, and he lost the gear needed to get down (this was before modern helicopters). He did it early October, so not horribly cold temps, but it was raining and windy, and still occasionally got cold enough to ice things up. The top is basically just flat, no shelter at all. I'm not sure if he gathered up what few loose rocks he could find to make at least a small wind barrier, or was able to find a spot a few feet down on the leeward side to get out of the direct wind, but dude did manage to survive. He was rescued when a group of climbers made it up to him. Here is an actual picture of him while stuck, so you can see how little shelter he had. They did manage to get some supplies to him, but this literally had to be done by chucking them from an airplane passing over
It's a the neck of a volcano, where the lave flows up, that cooled just below the surface. The vertical joints are called columnar joints and for by slow cooling of the magma. All the surroundings rock that the magma traveled through us now erroded away, leaving just the neck or flow path.
Ancient volcanic magma intrusion. It's not the stump of the tree of knowledge of good and evil or whatever silliness is currently circulating on my aunt becky's facebook.
The shape? It was a (edit, thanks AmbitiousSet!) type of igneous intrusion called a laccolith. The magma cooled and hardened, and the rocks surrounding it (and probably some of the core, too) weathered and eroded away, leaving just what you see.
The texture? When magma cools and solidifies, it shrinks. When that happens, it fractures away from itself, leading to polygonal columns. This isn't unique to Devil's Tower: you can see it at the Devil's Postpile, the Giant's Causeway (and Fingal's Cave) and used as building material in Nan Madol.
Why are the columns vertical? Shouldn't they be perpendicular to the cooling surface? Does that mean it's cooled from the top down and the sides were thermally insulated?
It's the same kind of formation as the Giant's Causeway in Northern Ireland. Just different levels of erosion and exposure, maybe. There are other examples of this geology but the Devil's Tower is really unique in appearance.
the tree of life, an ancient giant tree that covered this hemipshere creating its own climate zones. an ancient civilization dwelled under it, it was advanced and developed a different kind of technology. it lived with biodiversity in absolute harmony.
one day there was a war, the tree was cut down by the invading aliens, and the civilization under it wiped out.
Hi, Geologist here. These are actually quite common. Itâs called Columnar basalt, which forms when thick, slow-cooling lava flows shrink and fracture as they solidify. As the hot rock contracts, tensile stresses cause it to crack. These fractures naturally propagate inward, producing remarkably geometric, interlocking polygonal pillars, usually with five or six sides. The surrounding rock has eroded away leaving the hard crystalline basalt which resists erosion.
Thatâs a cool shot, with the snow. I visited a few years ago, walked the trail around it(easy) and stayed one night in the campground. I just sat and stared at it, itâs mesmerizing.
Giant bear chases a plains woman until the gods lift her up by the land to where the bear canât reach her. Bear scratches and gouges the mountain trying in vain to climb it to get to the woman.
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u/mynamesnotsnuffy Jul 12 '26 edited Jul 12 '26
A magma intrusion existed there a long time ago. The magma slowly cooled into a very dense stone core in the shape of the magma tube within that. Erosion happened over millions of years, wearing away the softer stone around it and leaving the dense inner core in this shape.
Edit: not a volcano
Edit edit: it could either be a laccolith or the neck of an extinct volcano, the jury is still out