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If you go explore the Zagros Mountains of  Iran, you’ll find an astonishing sight: strange, multi-colored glaciers that don’t  melt, even in the heat of the summer. But, if you get caught in a rainstorm,  you can watch them start to dissolve away.

That’s because they’re made not of  ice, but of solid slabs of salt. And there’s another difference. Unlike  their much colder cousins, these salt glaciers don’t form here on the surface.  Instead, time, pressure, and buoyancy create them from deep underground.

Today, most of the Persian Gulf  sits on an ancient layer of salt. That salt came from seawater that evaporated  around 540 million years ago, early in the time period geologists call the Cambrian. Then, time happened.

Like, a lot of time. Unsurprisingly, a lot of stuff  has piled up on top of this layer of salt since it was first deposited. Enough to bury it four to ten  kilometers underground in most places.

And if this was normal rock, it  would probably stay down there. But, when conditions are just right,  the salt can begin to rise from its bed and kind of float towards the surface. That happens because of buoyancy, the  same force that floats ships in the ocean and causes bubbles to rise in the bath.

Picture that ancient salt layer  slowly getting buried by rock. As each new bit of rock piles  up, it adds more weight on top, pushing down on the salt, as  well as any other rock layers. All that force begins to squish down the rock, causing their layers to get denser over time.

But the salt actually stays at the same density, even as the layers above it get denser. That’s because rocks can contain  tiny, water-filled pores. When the rock is compressed,  those pores can be squeezed out kind of like squishing down a sponge.

A very heavy sponge. But rock salt doesn’t have these water-filled  pores, so it acts more like a brick. And bricks don’t squish.

Eventually, these different behaviors under  pressure result in salt layers that are less dense than the rock above them. And, thanks to buoyancy, less dense material  tends to rise to the top of a mixture. So if something gives the salt a path, like  a crack or mushy spot in the rock above, it begins to slowly float to the surface, kind of like mud squishing up through your toes.

This forms what’s known as a  diapir, a rock formation in which one layer is pierced upwards through another. It’s a process that can take millions of  years, but, if conditions remain right, the salt will eventually reach the surface. And there, it forms what’s called a salt  dome, essentially a big hill filled with salt.

There are about 200 such salt  domes in the Persian Gulf alone. But it’s when these domes leak, so to speak, that the spectacular salt glaciers form. The leaking salt is pushed out  like toothpaste from a tube, flowing and rolling over itself, forming  flows that spill into adjacent valleys.

These “glaciers” can be kilometers long  and filled with crevasses and ridges, just like their icy cousins. Meanwhile, impurities in the salt give  the glaciers their remarkable colors.   Of course, salt isn’t the most stable  stuff ever, and if the glacier gets wet, it can actually dissolve. But since much of the Persian Gulf is  a desert with very little rainfall, these glaciers can remain without washing away.

Other dry places, like Onion Creek in  Utah, are also home to salt glaciers. But if you want to see some of  the most spectacular examples, the Zagros Mountains seem like the place to be. Thanks for watching this episode of SciShow, which was brought to you  with the help of our patrons.

If you want to get involved, you can check  out patreon.com/scishow to get started. [♪ OUTRO].