Bigger than Yellowstone

Nestled in the San Juan Mountains, there is ample evidence of one of the largest known volcanic eruptions on the planet: a caldera 22 miles wide and 62 miles long. It’s called the La Garita Caldera, and it rivals the Toba eruption in Indonesia and all Yellowstone eruptions. 

These are “supervolcanoes,” so comparing them to Italy’s Vesuvius or Washington’s Mount St. Helens is like comparing blowing out birthday candles to a hurricane. The Vesuvius and Mount St. Helens infamous eruptions were nothing short of devastating. Now, try to imagine a force much more powerful. 

Volcanoes can explode so violently that they completely empty their magma chambers and collapse in on themselves, leaving us beautiful spectacles like Crater Lake in Oregon. Eruptions are measured by ejecta — a terrible word which simply means the amount of volcanic stuff that launches out of the volcano. Supervolcanoes erupt at least 240 cubic miles of ejecta. 

Let’s use terrible math and analogies for scale. If Mount St. Helens’ ejecta in 1980 could all fit into a plastic, Wal-Mart kiddie pool, then the largest Yellowstone eruption would fill the Mountaineer Bowl to the brim. The La Garita eruption 28 million years ago would fill three Mountaineer Bowls. 

Peter Lipman of the United States Geological Survey said the eruption that left behind the La Garita Caldera killed everything within a hundred miles. A primitive, fuzzy rodent on modern-day Main Street in Gunnison likely did not make it. Wheeler Geologic Area in the La Garita Wilderness is an outcropping of volcanic ash from that massive eruption. It can only be accessed with a 4x4 vehicle or a hike.

The La Garita Caldera is only one of over a dozen calderas in the present-day San Juans. From Gunnison, Uncompahgre Peak on the horizon looks like a harmless cinnamon roll, but it is a glacially-eroded bit of a massive, violent volcanic complex. Lake City sits in a caldera. The town of Silverton also calls a caldera home. There is a Creede caldera alongside the La Garita. Cochetopa is a caldera. 

“They were big,” said Allen Stork, emeritus geology professor at Western Colorado University. Stork said these eruptions filled the Gunnison Basin to the top of W Mountain with ash. “We would have been under 800 feet of ash here in Gunnison,” he said. 

The evidence of these events are all around us. Tuff, a volcanic rock that forms from explosive eruptions, can be easily seen around Blue Mesa. The rock formations on the top of the hills that look like the bottom of a cupcake? That is called Blue Mesa Tuff. 

While our West Elk Volcano was eroding away after having more stereotypical lava and debris flows, the San Juans were ripping themselves apart as one of the most monumental volcanic fields on the planet.

In short, the Gunnison country’s scenic present has a violent past. This would not have been a fun place to live between 26 and 28 million years ago.