Southern Colorado’s Sangre de Cristo Mountains, known for their dramatic rise from the flat San Luis Valley, have long been shaped by tectonic activity and glacial forces. Now, a groundbreaking study in Geology suggests that the melting of alpine glaciers thousands of years ago may have significantly increased earthquake frequency in the region by relieving pressure on the underlying fault system.
The research connects Earth’s changing climate to tectonic movements, a rare link that sheds light on how warming temperatures like those seen today might trigger fault activity. “Areas where glaciers are retreating or where hydrologic changes occur over active faults could experience elevated earthquake activity,” explained study co-author Sean Gallen, a geologist at Colorado State University.
The Geology of the Sangre de Cristo Fault
The Sangre de Cristo fault system, which created the sharp transition between the mountains and the San Luis Valley, has been active for millions of years. Around 25-28 million years ago, the Rio Grande Rift began to form, slowly separating the San Luis Basin from the mountains. This tectonic activity created a vertical displacement of up to 9.2 kilometers.
Fast forward to about 2.6 million years ago, glaciation took hold, culminating in the Last Glacial Maximum around 20,000 years ago. During this time, glaciers carved valleys and deposited moraines, reshaping the mountainous landscape. As global temperatures rose and the glaciers melted, the weight pressing on the fault system decreased, potentially triggering a fivefold increase in seismic activity, according to the study.
Evidence of Glacial Influence on Earthquakes
Gallen and his co-author Cecilia Hurtado used high-resolution lidar and satellite imagery to map features such as fault scarps and glacial moraines. These data, combined with computer models, suggest that Ice Age glaciers acted as a “clamp” on the fault, suppressing seismic activity. As the glaciers receded, the stress released from the fault likely caused a dramatic uptick in earthquake frequency, a period of heightened seismicity that may have lasted for thousands of years.
Jessica Thompson Jobe, a geologist with the U.S. Geological Survey, praised the study’s innovative approach, noting its rarity in linking climate changes with fault activity. “It’s a great example of using both climate and tectonic datasets to understand a complex relationship,” she said.
Implications for Modern Glaciated Regions
The study’s findings have significant implications for other tectonically active regions with large ice masses, such as the Himalayas, Andes, and Alaska. Even relatively small temperature increases, such as the three-degree Celsius rise that melted most of the Sangre de Cristos’ ice, could trigger heightened earthquake risks in these areas.
Eric Leonard, a geologist emeritus at Colorado College, echoed the study’s concerns, pointing to the potential hazards posed by shrinking glaciers in tectonically active regions. While precise dating of faulted surfaces in the Sangre de Cristos remains a challenge, Leonard and other experts agree that the research highlights a compelling connection between climate and seismic activity.
As global temperatures continue to rise, the melting of ice and water loads over active faults may create additional risks for communities in quake-prone regions, reinforcing the importance of understanding and preparing for these evolving hazards.