That’s right – it’s the only known eruption to score a 9 on the VEI.
(Edit: This was written a few months before news of the Wah-Wah Springs eruption broke.)
During a very unpleasant week, some 27-28 million years ago, La Garita blasted out double the amount of Yellowstone’s biggest eruption – enough material to fill Lake Michigan to the brim – with 5,000 times the energy released by mankind’s most powerful nuke.
What Caused It?
Basically, Earth’s “skin” was having a flare-up. Scientists call it the Mid-Tertiary Ignimbrite Flare-Up.
There was an active subduction zone to the west that triggered smaller volcanoes near the coast and somehow – scientists aren’t yet clear on the exact details – led to magma bodies in the shallow crust further inland.
The major eruption of La Garita wasn’t the only one in the region – in fact, La Garita would itself be active off and on for the next 1.5 million years – but this was certainly the biggest blast of any of them.
As well, multiple other volcanoes laid down ash sheets; two other calderas – Bachelor and Creede – nested inside the big one; and then glaciers moved in and started plowing and washing away the land we now call the San Juan volcanic field.
All in all, this region is very messed up and and yet is strange and very beautiful today.
Will It Erupt Again?
Wikipedia says La Garita is extinct.
What? You want a more authoritative answer on whether La Garita might suddenly end the world as we know it?
Okay. The US Geological Survey doesn’t say anything about it – at least, a Google search for “USGS,” “La Garita” and “extinct” came up empty.
Don’t panic, though. They are scientists, unwilling to say anything definite without data to back it up. It’s difficult for them to get data on La Garita because the big one was so long ago and the landscape has been altered so much since then, as is the fact that the plate tectonic situation is different today than it was 28 million years ago, and we are no longer in the midst of an ignimbrite flare-up.
They’re still trying to figure it all out.
It is significant that they know about La Garita; they’re studying it intensively; and yet it isn’t being monitored like Yellowstone, Crater Lake and other active volcanoes. I think that’s pretty reassuring.
So now we can all go back to worrying about Yellowstone. But not too much, really.