December 23, 2024
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How climate change can affect earthquakes
Climate change may affect seismic activity as melting glaciers reduce pressure on earthquake-prone faults
North Crestone Creek Valley, a U-shaped valley carved by ancient Colorado glaciers.
The Sangre De Cristo Mountains of southern Colorado rise abruptly from the flat expanse of the San Luis Valley. The mountains’ eponymous fault system carved this dramatic geographic transition over millions of years, and occasionally cracks the area. A new study suggests that the melting of Alpine glaciers thousands of years ago may also play a role the frequency of earthquakes in this area increased relieving pressure on the breakdown.
We don’t usually associate Earth’s atmosphere and surface climate with our planet’s inexorable plate movements. But new research, published in geology, provides rare evidence that warming temperatures (such as those occurring today) can trigger bug activity. As temperatures continue to rise, researchers warn that glaciers and other earthquake-prone regions may face similar risks. “Earthquake activity can be high in areas where glaciers are retreating or where changes in the hydrological cycle are occurring over active faults,” says Colorado State University geologist Sean Gallen, the study’s lead author.
About 25 million to 28 million years ago, the western interior of North America began to split apart, creating the Rio Grande Rift. As the earth slowly decompressed, the San Luis Basin sank as the Sangre de Cristo Range arched toward the sky, with a vertical displacement of 9.2 kilometers between the two sides. Then, beginning about 2.6 million years ago, global temperatures dropped, and the peaks of the Sangre de Cristos were filled with glacial ice. The glaciation ended about 20,000 years ago during the Last Glacial Maximum, carving dramatic U-shaped valleys and accumulating moraines, piles of debris that marked the farthest extent of the ice.
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West of the Sangre de Cristo Range, Colorado.
Adding or removing surface mass can change the stresses in the Earth’s crust. For example, when mountains rise, the earth’s crust bends under their weight, like a diving board when someone stands on it. As mountains erode and fall in inexplicable time, the earth rises again. This process, known as isostatic rebound, can cause minor seismic activity. That’s why relatively old constituencies like Appalachian still buzz from time to time.
Gallen and his co-author Cecilia Hurtado, also of Colorado State University, wondered if the removal of glacial mass could similarly affect seismic activity. They hypothesized that melting glaciers could change stresses on faults, accelerating earthquakes in the short term by reducing the load on the earth’s crust.
Computers can model this behavior fairly easily, but testing concepts in nature is the gold standard, Gallen says. There are few places where concrete evidence is preserved, however: in one example, Wyoming Teton fault saw more seismic activity as the Yellowstone ice cap melted. The new study reveals how this phenomenon may be more common than scientists think, says US Geological Survey geologist Jessica Thompson Jobe, who was not involved in the study. “It’s pretty unique,” Jobe says of the research. “They’re trying to link climate with bug activity, and it’s a great place to do that because you have information for both sets of data. That’s not always the case.”
To support their hypothesis, Hurtado and Gallen built computer models based on the raw features of the Sangre De Cristo landscape, such as moraines, as well as fault scarps that resemble splits in the Earth’s crust, which provide clues about the timing and location of prehistoric earthquakes. The researchers used high-resolution lidar (light detection and ranging) and satellite imagery to map these features. Finally, the team compared these models with real-world evidence, and proposed that Ice Age glaciers “blocked” the fault system and suppressed earthquakes. When the glaciers began to melt less than 20,000 years ago, the weight lifted and released the pent-up stress. This led to a dramatic fivefold increase in earthquake frequency, a phase of higher seismicity compared to pre-glacial maximum levels, which probably lasted until the glaciers finally retreated.
Sangre de Cristo fault scale (indicated by black arrows). The blue lines show the approximate ends of the last ice age glaciers.
Eric Leonard, a geologist emeritus at Colorado College who was not involved in the study, agrees that the melting of Sangre de Cristos’ relatively small glaciers could have a major impact on fault activity. He added, however, that the age of fault surfaces is uncertain, which affects the accuracy of earthquake timing. Gallen agreed that more accurate — and less expensive — methods for dating fault surfaces could improve the earthquake timeline. But he and Hurtado are confident that these findings reinforce earlier research in the American West. “What we have here is compelling evidence,” says Gallen.
The authors of the study also warn that regions with active faults and high ice or water loads – now shrinking as global temperatures rise – may experience more earthquakes in the future.
Leonard added that the three degrees Celsius (5.4 degrees Fahrenheit) increase in temperature melted most of the ice in the Sangre de Cristos, raising concerns in tectonically active areas around larger ice masses today, such as the Himalayas, the Andes and Alaska. . “Will that significantly add to the risks?” he meditates “I don’t know, but it definitely has potential.”
