An enormous underground water store containing three times the volume of Lake Mead has been discovered hidden underneath the Oregon Cascades.
This huge aquifer, stored underneath volcanic rocks deep within the mountains, contains some 19.4 cubic miles of water, or roughly 21,400,000,000,000 gallons, according to a new paper in the journal Proceedings of the National Academy of Sciences.
Scientists have known that this aquifer existed for a while but it wasn't until now that it was known quite how much water it held: Three times the total capacity of Lake Mead, and over half the volume of Lake Tahoe in California.
"It is a continental-size lake stored in the rocks at the top of the mountains, like a big water tower," study co-author Leif Karlstrom, an earth scientist at the University of Oregon, said in a statement.
"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."
An aquifer is an underground layer of rock or soil that can store water, acting as a natural reservoir and providing water to springs, wells, and other water sources. They are typically made up of porous materials like sandstone, gravel or fractured rock, allowing water to flow through them.
Much of Oregon's drinking water, as well as water for agriculture and industry, is fed by aquifers high up in the Cascades. Aquifers act as natural water storage systems, buffering against periods of drought or reduced snowfall. This is particularly important as the snowpack in the Cascades, a major source of surface water, becomes less reliable due to warming temperatures.
"We initially set out to better understand how the Cascade landscape has evolved over time, and how water moves through it," study co-author Gordon Grant, a geologist with the Forest Service, said in the statement.
"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 researchers describe how they measured the temperatures at different depths around the Cascades to determine how deep water flowed through the rocks in different volcanic zones.
The formation of the Cascade Range was primarily driven by the interaction of tectonic plates along the western edge of North America, with the small Juan de Fuca Plate being pushed beneath the larger North American Plate at a convergent plate boundary known as the Cascadia Subduction Zone.
The magma generated by this subduction rises to the surface, creating a chain of volcanoes. Some of the most well-known volcanic peaks in the Cascades include Mount Rainier, Mount St. Helens, Mount Hood, and Mount Shasta.
"What motivates our work is that it's not just how these landscapes look different topographically. It's that water moves through them in really different ways," Karlstrom said.
As water in the ground reduces the temperature of the surrounding rocks, measuring temperature allowed the researchers to map out the volume of the aquifer. The researchers say that the true volume of the stored water may even be larger than they measured.
This is good news, considering reduced snowpack and changing rainfall patterns in the face of climate change. However, this aquifer is still a limited resource, and therefore, can still be depleted.
"This region has been handed a geological gift, but we really are only beginning to understand it," Grant said. "If we don't have any snow, or if we have a run of bad winters where we don't get any rain, what's that going to mean? Those are the key questions we're now having to focus on."
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References
Karlstrom, L., Klema, N., Grant, G. E., Finn, C., Sullivan, P. L., Cooley, S., Simpson, A., Fasth, B., Cashman, K., Ferrier, K., Ball, L., & McKay, D. (2025). State shifts in the deep critical zone drive landscape evolution in volcanic terrains. Proceedings of the National Academy of Sciences of the United States of America, 122(3). https://doi.org/10.1073/pnas.2415155122
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