▶️ Little Did I Know: What’s a Tuya?


The other weekend, I went up to Hoodoo to do my first night skiing in decades and I was reminded about this crazy-looking rock formation that to me, looked like a mesa.

It’s called Hayrick Butte and my research led me to ask “What’s a Tuya?”

Not “What’s it to ya?” but “What’s a Tuya?”

And COCC Geology Professor Hal Wershow did me the favor of answering that very question for me.

“So Hayrick Butte is actually a pretty rare type of volcano known as a Tuya. It’s spelled T-U-Y-A and globally there’s a bunch of them in northern British Columbia. There are some in Antarctica and there’s, I think some in Russia or Siberia. There’s not a lot of them and yet we’ve got a whole bunch right here in Central Oregon which is pretty cool.”

I come to find out that Hayrick Butte, that thing you see when sitting on the chair…is a volcano eruption under a massive sheet of ice.

“So this goes back to the last Ice Age. There would have been an ice sheet covering most of the Central Oregon Cascades. Which is pretty cool to think about. I mean, today we’ve got some cool glaciers, but there used to be just ice everywhere. So we’ve got a big thick ice sheet and there’s a volcano erupting underneath. It makes sense. We have volcanoes erupting all the time here.”

When a volcano erupts under a glacier, it goes through four distinct phases.

“Stage one is, it’s gonna melt a pocket of water into the bottom of the ice. Think of like almost a watery cave inside the glacier, and at that point you’ve got lava that’s erupting into this big pocket of water. This is no different than what we see today in the middle of the ocean when lava erupts at the bottom of the sea floor.”

Stage two happens when the heat from the molten lava creates an upward vent through the ice and the leftover water creates a lake down below.

“What ends up happening is we start melting a hole through the glacier. Let’s say it was 2000 feet thick. Eventually, we melt all the way through to the top and it opens up. You still have ice everywhere, so imagine like a plug that’s been taken out of the ice and now there’s gonna be a lake inside there ’cause we melted it.”

As lava erupts through water, it becomes very explosive. But eventually, the lava’s patience is rewarded and it begins to grow beyond the water in the lake.

“This is stage three. This is where everything changes ’cause now instead of erupting underwater, where you’ve got the water available to act as an explosive agent and blast things to bits, now it’s just normal lava oozing out, and what we know with lava, it’s basically like a liquid and it spreads out flat.”

Ah, okay. So now I can see why I thought it was a mesa. A mesa is an isolated, flat topped feature, only a Tuya is more specific.

“It’s spreading out flat but it can’t go very far ’cause it runs into ice walls we got ice walls on each side it runs into them and stops. So one, this is how we get that flatness. It’s no longer explosive – it’s just oozing out, but two, we also get some cool stuff going on with the rocks and this is how geologists would recognize these things in the field.”

The rocks found around a Tuya are similar to obsidian in that they come from the lava cooling so fast that it can’t form crystals, so it leaves a glassy type surface.

And the fact that that can all be viewed from a chairlift is one of the myriad of things that I love about Central Oregon.


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