How climate change causes earthquakes

How climate change causes earthquakes

Written by Evan Howell Edited by Andrea Thompson

The Sangre de Cristo Mountains in southern Colorado jut out abruptly from the flat San Luis Valley. The fault system that gives the mountain its name shaped this impressive geographical transition over millions of years and still rattles the area from time to time today. The new study suggests that the melting of alpine glaciers thousands of years ago may also have increased the frequency of earthquakes in the region by relieving pressure on faults.

We don’t usually associate Earth’s atmosphere or surface climate with the movement of plates miles deep in the Earth’s mysterious bulk. However, new research published in 2016 shows that geology, The study provides rare evidence of how rising temperatures, such as those occurring today, can actually cause fault activity. Researchers warn that other glaciated and earthquake-prone areas could face similar risks as temperatures continue to rise. “Seismic activity may increase in areas where glaciers are retreating or where hydrological changes occur over active faults,” said study co-author Sean Gallen, a geologist at Colorado State University. he says.

About 25 to 28 million years ago, the interior of western North America began to break apart, forming the Rio Grande Rift. As the land slowly opened, the San Luis Basin subsided and the Sangre de Cristo Mountains arched skyward, creating vertical shifts of up to 9.2 kilometers between the two sides. Then, starting about 2.6 million years ago, global temperatures plummeted, and the summit of Sangre de Cristos was filled with glaciers. Glaciation reached its peak during the Last Glacial Maximum about 20,000 years ago, carving a dramatic U-shaped valley and depositing moraines, piles of rubble marking the farthest reaches of the ice.

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Increasing or decreasing surface mass can change the stress on the Earth’s crust. For example, when a mountain rises, the earth’s crust bends under its weight, like a diving board when a person stands on top of it. Even if the mountains are worn down and crumbled over countless hours, the earth will rise again. This process is called isotropic rebound and can cause small-scale seismic activity. That’s why older mountain ranges such as the Appalachians still occasionally rumble.

Galen and co-author Cecilia Hurtado, also of Colorado State University, wondered if the removal of glacier mass could similarly affect seismic activity. They hypothesized that melting glaciers could change stress on faults, reducing stress on the Earth’s crust and accelerating earthquakes in the short term.

Although computers can model this behavior fairly easily, Galen says testing the concept in nature is the most important criterion. However, there are few places where concrete evidence has been preserved. As an example, the Teton Fault in Wyoming has experienced increased seismic activity as the Yellowstone ice sheet melts. Jessica Thompson-Jove, a geologist with the U.S. Geological Survey who was not involved in the study, said the new study raises the possibility that the phenomenon is more common than scientists thought. He says he has made it clear. “This is pretty unique,” Jobe says of the study. “They’re trying to link climate and fault activity, and this is a great place to do that because we have information from both datasets. That’s not always the case.”

To support their hypothesis, Hurtado and Galen built a computer model based on the natural features of the Sangre de Cristo landscape, such as moraines and fault scarps that resemble cracks in the Earth’s skin. , provided 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 researchers compared these models with real-world evidence and proposed that Ice Age glaciers “clamped” fault systems, suppressing earthquakes. Less than 20,000 years ago, the glaciers began to melt, lifting their weight and releasing the accumulated stress. This caused a dramatic five-fold increase in earthquake frequency and was a phase of increased seismic activity compared to pre-glacial maximum levels, which would continue until the glacier finally retreated.

Eric Leonard, a geologist emeritus at the University of Colorado who was not involved in the study, said melting of even relatively small glaciers in Sangre de Cristos could have had a significant impact on fault activity. I agree with that. However, he added that the age of the fault plane is uncertain, which affects the accuracy of when the earthquake occurred. Galen acknowledged that more accurate and expensive methods of dating fault planes could improve the earthquake timeline. But he and Hurtado are confident that these findings confirm earlier research in the American West. “What we have here is compelling evidence,” Galen said.

The study authors also warned that regions with active faults and large ice and water loads – currently shrinking as the planet warms – could face more earthquakes in the future. are.

Leonard said that a rise in temperature of just 3 degrees Celsius (5.4 degrees Fahrenheit) has melted most of the ice in Sangre de Cristos, so tectonic regions such as the Himalayas, Andes and Alaska are experiencing even larger ice masses today. He added that there are concerns that there may be. . “Does this significantly increase the risk?” he muses. “I don’t know, but it’s certainly possible.”