Glaciers are awe-inspiring geological formations that have defined landscapes all over the world, including Colorado. A glacier is formed when snow accumulates for many years until thick ice is formed, at least a portion of which lasts year-round. For this collection of ice to be named a glacier, it must be continuously in motion under the influence of its own weight and gravity. An “average” estimate for the motion of a glacier is around ten inches per day, though there is a huge variance. During glacial surges, glaciers can even move upwards of 100 feet in one day!

Arapahoe Glacier

The historical movement of glaciers has carved many valleys in Colorado. Valley glaciers form at higher elevations and flow down through valleys, carving and shaping them over potentially thousands of years. While glaciers can be viewed as forces of destruction, they also create room for new life and habitat. Valley glaciers were a key part of forming our beloved Eagle Valley, which is now being shaped by the Eagle River. When exploring a valley, big or small, a U-shape is a tell-tale sign that it was formed by a glacier long ago.

The great valley glaciers of Colorado’s rich geologic history have since melted, but the United States Geological Survey still lists sixteen named glaciers in Colorado. However, like many glaciers across the globe, those in Colorado are retreating at an accelerated rate because of climate change. In glaciology, the term retreat means melting is occurring faster than new snow and ice can accumulate. 

As a result of warming temperatures, many of Colorado’s glaciers are no longer considered active by glaciologists, as they have retreated to a point where they no longer move (<0.1 km²) or are suspected to have ceased moving. Even if not technically a glacier, these ice features can still be quite impressive. Most active glaciers in Colorado are cirque glaciers, which, similar to an alpine glacier, form high in the mountains and flow downslope. Their main distinction is that they form in bowl-like depressions with steep headwalls, or cirques, which capture windblown snow and avalanches and can provide some shelter from sunlight.

Andrews Glacier

Rock glaciers are a separately classified but even more climate-resilient type of glacier formation found in Colorado. These form when rocks accumulate on top of typical ice glaciers, or when snow melts and refreezes enough over the years that it integrates with a rocky slope and causes movement. Either way, these glaciers are more resistant in the face of our warming climate as the outer layers of rock protect the ice from sun and heat. As a result, there are significantly more remaining; according to Colorado State, there are over 3500 rock glaciers estimated to be in Colorado. While rock glaciers might not awaken as much wonder in spectators, they contribute to mountain ecosystems by providing cooler habitat for alpine critters and potential water sources.

For those intrigued by glaciers, exploring Colorado's remaining glaciers, active or not, offers a chance to witness these magnificent formations firsthand. Places like Andrews Glacier and Arapahoe Glacier offer breathtaking hiking experiences. However, appreciating their legacy doesn’t always require direct observation. Colorado’s valleys and mountains tell the geologic story of the profound influence glaciers had on this landscape. 

As glaciers continue to retreat, it’s essential to cherish those that remain and acknowledge the role of glaciers shaping our world. By taking action to mitigate climate change, we can create the best possible odds for future generations to experience these wonders as well.

Gabi Watkins is a naturalist at Walking Mountains Science Center who loves to traverse across moving ice.