Erosion caused by glaciation during ice ages can, in the right circumstances, wear down mountains faster than plate tectonics can build them, a new study measuring all the material leaving and entering a mountain range over a million years has found.
Researchers studied the St. Elias Mountains on the Alaskan coast and found that erosion accelerated sharply about one million years ago when global climate cooling triggered stronger and more persistent ice ages than times past.
"Humans often see mountain ranges as static, unyielding parts of the landscape," said co-chief scientist John Jaeger from University of Florida.
"But our work has shown that they are actively evolving along with, and responding to, Earth's climate, which just shows how truly dynamic and coupled this planet is," Jaeger added.
The study, conducted by a team of scientists from 10 countries, culminated more than a decade of fieldwork.
Researchers first used seismic equipment to image and map a huge fan of sediment in the deep sea in the Gulf of Alaska caused by erosion of the nearby mountains and took short sediment cores to understand the modern system.
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They then collected and dated almost 4 kilometers of sediment from the floor of the gulf and the Alaskan continental shelf, revealing millions of years of geologic history.
"It turned out most [sediments] were younger than we anticipated, and most rates (of sediment production and thus erosion) were higher than we anticipated," said lead author and co-chief scientist Sean Gulick from University of Texas.
"Since the big climate change during the mid-Pleistocene transition when we switched from short (about 40,000-years) ice ages to super-long (about 100,000-years) ice ages, erosion became much greater... In fact, there was more erosion than tectonics has replaced," Gulick added.
The study was published in the Proceedings of the National Academy of Sciences.