Transcription
Arches National Park contains the largest concentration of natural stone arches anywhere in the world. More than 2,000 documented arches dot this landscape, along with an assortment of balanced rocks, fins, spiers, and other spectacular red rock formations. From the photogenic isolation of Delicate Arch to the seemingly impossible span of Landscape Arch, from the precarious solidity of Balanced Rock to the towering duality of Double Arch, it is yet another outstanding addition to the already mesmerizing Utah Canyon Country. And all of this in a park of just 76,000 acres. It really is spectacular and wonderful to look at. There's a reason millions of people visit this park every year. But today, I want to share with you how it all got that way.
Hello and welcome to National Park Diaries. My name is Cameron, and this is a channel dedicated entirely to telling stories from the world's protected places. I tell educational, informative stories about National Parks, public lands, and protected areas, all with the goal of helping you understand and hopefully come to love these places as much as I do. If that is something you are interested in, there are a couple ways you can help support what I'm trying to do here. One of them is like all the YouTube stuff: like, subscribe, hit the little bell thing, leave a comment. All of that lets YouTube know that people actually like what I'm doing here and helps these stories reach more people. If you're really excited though about what I'm doing and want to support me more directly, I also have a Patreon, which you can check out at patreon.com/nationalparkdiaries. Got a lot of cool stuff over there, lots of good perks, all for as low as two dollars per month. This channel is entirely fan-funded, and I truly appreciate your support. It goes a long way to help keep this whole thing running.
All right, now let's figure out how Arches got all of those arches. So, like with most other unique geological phenomena, you need a certain combination of ingredients. In this case, our first ingredient is salt. Probably not what you were expecting, but let me explain. About 300 million years ago, this area of what would become Utah was subject to nearly 30 different cycles of ocean advancing and retreating. And each time the ocean advanced and retreated, salt water became concentrated in what was known as the Paradox Basin. And because it was a basin, water had no outlet to leave. It eventually just evaporated away. But because it was salty ocean water, when the water evaporated away, it left behind a massive deposit of salt. 5,000 feet worth of it. Enough to fill a YouTube comment section, for sure.
Then you fast forward a few million more years, and you've got some mountain building activity in this area. And with mountains comes erosion, because as rain falls on those mountains, it carries sediment way, and that sediment has to be deposited somewhere. This is known as deposition. So, deposition occurred in the Paradox Basin on top of all that salt that was deposited millions of years earlier. Eventually, that sediment is going to solidify to form rocks: sedimentary rocks. So now you've got rocks on top of salt. Two ingredients.
Now, here's the thing with salt. When you've collected enough of it in one location, like what happened in the Paradox Basin millions of years ago, it doesn't really behave like you'd expect when subjected to immense geological forces, like piling a few million years' worth of rocks on top of it. When that happens, the pressures and forces acting on the salt actually cause it to flow. It's a, it's a solid, yes, but it has these properties that cause it to act all weird and over insanely long geologic time scales, yeah, it flows. Think of like a glacier. Same relative concept. Anyway, so yeah, the salt is flowing underground, and then it runs into these deep-lying faults within the Earth's crust. Can't go through the faults, so instead, this mass of salt is just pushed upward, causing a salt dome.
Now, as the salt moves upward, again, it has this flow property, but the rock above it does not have this flow property. Rocks don't flow, they break. And that's exactly what happened. As the salt pushed upward, it caused the rock above it to break and fracture in these parallel, vertical fissures. So now we've got this salt dome with these vertically fissured rocks above it. Eventually, the rock on top of those rocks – this is a lot of rocks, I know – but those rocks, the top layers, are going to erode until eventually the rock layer with the vertical fissures is exposed to the surface. You can imagine what happens next. Water infiltrates those vertical fissures all the way down to the big old pile of salt below. And because salt dissolves in water, the big old pile of salt begins to disappear. But now it's no longer holding up those vertically fissured rocks above it, and everything just begins to collapse. And this is how we ended up with what is today known as Salt Valley.
When you're driving on the main road through Arches National Park, you're driving through Salt Valley, and it's on the edges of Salt Valley where we see most of the arches in the park. You can see this really well on Google Earth, actually. The reason you'll find most of the arches on the edge of this valley is because that's actually where you'll find the remnants of those vertically fissured rocks. Down in the middle of the valley, that's kind of where everything collapsed, so you don't really see anything down there. But yeah, out on the edges, the last vestiges of those vertical fissures can still be seen today. You'll notice them as these massive, deeply red-colored fins. What happened was those fissures, again, being exposed to the surface, allowed slightly acidic rainwater to infiltrate into the rock, which widened the fissures and the cracks and ultimately created the fins.
And the type of rock here is important too. That's an ingredient we haven't really talked about yet. Most of the arches in the park are found in a rock layer known as the Entrada Sandstone, which has these nice spherical granules of sand and which is very porous. It has a lot of tiny holes in it, lots of pores, make it really easy for water to infiltrate the rock and erode it and continue opening up those cracks and fissures.
Now let's finish this thing off by finally forming some actual arches, because there's another type of rock that's important here as well. Below the Entrada Sandstone, where all the arches form because the rock is really porous and erodible, lies a rock layer known as the Carmel formation. It has some sand in it too, but it also has clay. Clay grains are much smaller than sand grains, and thus do not allow as much water to infiltrate into the rock and erode it away. As a result, water ends up just kind of pooling on top of the Carmel formation, where it can further eat away at and erode the Entrada Sandstone above it. You can start to see how these arches come together now. The water sits and pools, infiltrates the pores of the Entrada Sandstone, begins to form a little opening, exposing more rock to erosion. The opening becomes wider, rinse and repeat, until you get a window, a tiny little window in the rock that will eventually become an arch.
Now, after that opening gets big enough, it's not just the acidic water wearing away at the sandstone anymore. You've got some wind action thrown in there, as it carries sand grains off the ground and blasts the rocks, chipping away further at the newly created opening, basically like a sand blaster. Once things get far enough off the ground too, gravity can even take over, as the weight of the rock becomes too much to support itself, and these massive chunks can just fall off and enlarge the opening even further. This was actually captured on film at Landscape Arch in 1991. And that's how all these arches formed. Some familiar geological processes, yes, but a unique combination of ingredients.
Now, two important things to remember here. As with basically every other geological thing I talked about on this channel before, this isn't happening overnight. Geologic wonderlands like Arches take millions of years to form, and we happen to be lucky enough to exist at just the right time in Earth's history to witness these magnificent natural creations. In that same vein, these arches are not permanent. As sturdy and strong as they look today, the same forces that shaped them will eventually tear them down. See the collapse of Wall Arch in 2008. Time waits for no arch, and erosion will eventually bring down the arches of Arches National Park, no matter how much we like putting them on Instagram.
And I hate to end on a sour note, but that is everything I have for you today about the formation of Arches National Park. Have you ever been? Do you have a favorite arch? Let me know down in the comments below. Be sure to like, subscribe, and hit the little bell thing so you don't miss an episode. Check out my Patreon and follow me on Instagram if you would like. That's where I post trip and channel updates, and it's the easiest way to get in touch with me. Thanks so much for watching. I'll see you next time. Goodbye.