10/04/2026
Fun facts - thanks for posting Atlas Mirabilium:
It was one of Earth's largest known volcanic eruptions—and it happened in southwest Colorado.
Today, the area around Creede in the San Juan Mountains is not a towering volcano. La Garita is an extinct, deeply eroded caldera, so large and worn down that scientists took more than 30 years to fully work out its size.
About 28 million years ago, this place produced the Fish Canyon Tuff eruption, one of the most powerful known supervolcanic events in Earth’s history. The eruption released about 1,200 cubic miles (5,000 cubic kilometers) of volcanic material. It rated an 8 on the Volcanic Explosivity Index, the highest category on the scale. The deposit it left behind covered at least 11,000 square miles (28,000 square kilometers). Across that huge area, the Fish Canyon Tuff averaged about 330 feet (100 meters) thick.
For comparison, the 1980 Mount St. Helens eruption produced about 0.25 cubic miles (1 cubic kilometer) of material. La Garita’s Fish Canyon eruption wasn't just larger; it was thousands of times larger.
And yet the evidence is not a dramatic cone rising from the Colorado skyline. It is an enormous oblong caldera, about 22 by 47 miles (35 by 75 kilometers), shaped by collapse, time, and erosion.
The quiet landscape near Creede preserves the remains of a Colorado eruption so vast it left one of the largest known volcanic deposits on Earth.
