Colorado is known for its beautiful remote wilderness areas and its high peaks. But it’s also home to one of the largest and most destructive volcanic events in Earth’s history. The story starts roughly 35 million years ago, when layers of lava, ash, and other debris erupted, creating a series of stratovolcanoes (like Mount St. Helens) that made up what’s called the San Juan Volcanic Field in the southwestern part of the state. Something more sinister was brewing, however, and 7 million years later, an underground build-up of extreme pressure and heat led to a supervolcano eruption, blasting debris from the center of a volcano near Creede, Colorado. If measuring the quantity of material released in the eruption, it was 1,000 times greater in extent than Mount Pinatubo in 1991. Layers of volcanic ash, or tuff, spread across the landscape. After ash from the supervolcano cooled and compacted, the volcano’s center caved in, leaving behind a 20×50-mile depression known as La Garita Caldera.
With the passing of time, the massive crater began to slowly fill in with ancient lakes, hot springs, and volcanic debris. Geologists suggest that activity from younger and smaller volcanoes eventually buried much of La Garita Caldera, especially the southern rim. These days, remnants of past volcanic activity can be seen across the San Juan mountain range in the form of ash layers, basalt, andesite and rhyolite (eruptive volcanic rock types), sculpted by wind, water and glaciers over the years, into the peaks we know today. We recently climbed on these remnants of ancient volcanic activity on the Wetterhorn (14,015 ft.) and Matterhorn (13,590 ft.) peaks in the San Juan mountains. As a scientist trained in the geological sciences, I cannot help but constantly be looking at the rocks and the surrounding landscape, imagining what it must have looked like millions of years ago. I cannot help but stand in wonder and awe at this ancient landscape beneath my feet.