It could hold at least 81 cubic kilometers of water — roughly 3 times the capacity of Lake Mead

Oregon’s Cascade Range mountains might not hold gold, but they store another precious resource in abundance: water.
Scientists from the University of Oregon and their partners have mapped the amount of water stored beneath volcanic rocks at the crest of the central Oregon Cascades and found an aquifer many times larger than previously estimated — at least 81 cubic kilometers.
That’s almost three times the maximum capacity of Lake Mead, the currently overdrawn reservoir along the Colorado River that supplies water to California, Arizona and Nevada, and greater than half the volume of Lake Tahoe.
The finding has implications for the way scientists and policymakers think about water in the region — an increasingly urgent issue across the Western United States as climate change reduces snowpack, intensifies drought and strains limited resources.
It also shapes our understanding of volcanic hazards in the area. Magma interacting with lots of water often leads to explosive eruptions that blast ash and gas into the air, rather than eruptions with slower-moving lava flows.
 

“It is a continental-size lake stored in the rocks at the top of the mountains, like a big water tower,” said Leif Karlstrom, a UO earth scientist who led the study alongside collaborators from Oregon State University, Fort Lewis College, Duke University, the University of Wisconsin, the U.S. Forest Service and the U.S. Geological Survey. 

“That there are similar large volcanic aquifers north of the Columbia Gorge and near Mount Shasta likely make the Cascade Range the largest aquifer of its kind in the world.”  
The team reported the findings in a paper published Jan. 13 in the journal Proceedings of the National Academy of Sciences. 
Most Oregonians rely on water that originates from the Cascades.  For example, the McKenzie River, which supplies most of Eugene’s drinking water, begins high in the mountains at the spring-fed Clear Lake. But the discovery of this underground aquifer’s size was a surprise.

“We initially set out to better understand how the Cascade landscape has evolved over time, and how water moves through it,” said study co-author Gordon Grant, a geologist with the Forest Service. “But in conducting this basic research, we discovered important things that people care about: the incredible volume of water in active storage in the Cascades and also how the movement of water and the hazards posed by volcanoes are linked together.” 
The western Cascades are characterized by steep slopes and deep valleys carved out by rivers. The high Cascades, meanwhile, are flatter, dotted with lakes and volcanic topography such as lava flows. The Cascade Range has been built up by volcanic activity over millions of years, making the exposed rocks in the high Cascades much younger than those in the western Cascades. 
This content is taken from University of Oregon

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"Atop the Oregon Cascades, a UO team finds a huge buried aquifer", MachPrinciple, February 14, 2025, https://machprinciple.com/post/Atop-the-Oregon-Cascades-a-UO-team-finds-a-huge-buried-aquifer