Rainfall controls cascade mountains’ erosion and bedrock uplift patters

The pattern of rainfall in the Washington Cascades strongly affects long-term erosion rates in the mountain range and may cause bedrock to be pulled up towards the Earth’s surface faster in some places than others, according to a National Science Foundation (NSF)-funded study published in this week’s issue of the journal Nature. The results are the first convincing evidence of such effects, on mountain-range scales.

“The data strongly suggest that precipitation controls erosion rates across the Cascades, and that the regional climate may also exert a strong control on the distribution and scale of tectonic rock uplift and deformation of the range,” said Peter Reiners, lead author of the study and a geologist at Yale University.

“Geologists usually think of erosion wearing away mountains,” says David Fountain, program director in NSF’s division of earth sciences, which funded the research. “These results, however, show us that erosion can be an important player in uplift of mountain ranges, especially in mountainous regions that receive heavy precipitation.”

Using a dating method that determines when and how fast erosion brings bedrock toward the surface of the Earth, Reiners and his co-researchers found evidence to support long-standing theories about the interplay of climate, erosion and tectonics.

“People have thought the scale and pattern of rock uplift is mostly controlled by deep, plate-tectonic forces,” he said. “Based on our findings, the pattern of bedrock uplift is closely tied to climate through erosion.”

Rainfall is heavy in parts of the Pacific Northwest because mountains in the region cast enormous rain shadows. Moist air moving east from the Pacific rises and cools as it encounters the ranges, dumping large amounts of rain and snow on the west side of the Cascades, where it rains about 10 times more than in most places in Washington. The east sides and the summits are relatively dry.

Co-authors of the paper include Todd Ehlers of the University of Michigan and Sara Mitchell and David Montgomery of the University of Washington.

Media Contacts:
NSF: Cheryl Dybas, 703-292-7734, cdybas@nsf.gov
Yale University: Jacqueline Weaver, 203-432-8555, jacqueline.weaver@yale.edu
NSF Program Contact: David Fountain, dfountai@nsf.gov

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