Scientists have successfully mapped the underground water stored beneath volcanic rocks at the top of the central Oregon Cascades, revealing an aquifer far larger than anyone had previously thought—at least 81 cubic kilometers. This discovery carries significant implications for how scientists and policymakers approach water resources in the region, particularly as climate change is causing snowpack levels to drop, droughts to become more severe, and resources to become increasingly limited across the Western United States.
Although the Oregon Cascade Range mountains may not contain gold, they are rich in another vital resource: water.
Researchers from the University of Oregon, alongside collaborators, have identified a vast underground aquifer beneath the volcanic formations at the summit of the central Oregon Cascades, finding it to be significantly larger than earlier estimates—at least 81 cubic kilometers.
This volume of water is nearly three times greater than the maximum capacity of Lake Mead, the heavily depleted reservoir located along the Colorado River that provides water for California, Arizona, and Nevada. It is also more than half the volume of Lake Tahoe.
The implications of this discovery are crucial for scientists and policymakers alike, particularly as the issues of water scarcity become increasingly pressing in the Western United States due to factors like lowered snowpack, intensified drought conditions, and limited water resources.
Additionally, this research enhances our understanding of volcanic risks in the region. When magma interacts with abundant water, it is more likely to trigger explosive eruptions that send ash and gases into the atmosphere, rather than producing slower lava flows.
“It’s like a vast continental lake trapped within the rocks at the mountain peaks, functioning like a large water reservoir,” stated Leif Karlstrom, a UO earth scientist who led the study in collaboration with researchers from Oregon State University, Fort Lewis College, Duke University, the University of Wisconsin, the U.S. Forest Service, and the U.S. Geological Survey.
“Moreover, the presence of similar large volcanic aquifers north of the Columbia Gorge and around Mount Shasta suggests that the Cascade Range might host the largest aquifer of its kind globally.”
The findings were published on January 13 in the journal Proceedings of the National Academy of Sciences.
Most residents of Oregon depend on water sourced from the Cascades. For instance, the McKenzie River, which provides the majority of drinking water for Eugene, originates from high-up in the mountains at Clear Lake, a spring-fed body of water. However, the discovery of the aquifer’s extensive size was unexpected.
“Our original goal was to gain a clearer understanding of the evolution of the Cascade landscape over time and how water flows through it,” explained co-author Gordon Grant, a geologist with the Forest Service. “During our basic research, we uncovered significant findings of considerable public interest: the remarkable volume of water actively stored in the Cascades and how water movements are interconnected with volcanic hazards.”
The western Cascades are known for their steep slopes and deep valleys that rivers have carved out. In contrast, the higher portions of the Cascades are flatter, interspersed with lakes and volcanic features like lava flows. The Cascade Range itself has formed over millions of years through volcanic activity, resulting in the volcanic rocks in the high Cascades being considerably younger than those found in the western part.
Consequently, the transition zone that lies between the western and high Cascades around Santiam Pass serves as a natural laboratory, shedding light on how volcanic forces have influenced Oregon’s scenery.
“What drives our research is not just the visible differences in the landscapes. It’s the distinct ways in which water traverses these areas,” Karlstrom commented.
To gain a deeper insight into how water flows through various volcanic regions, the team utilized earlier projects initiated in the 1980s and 1990s. Past researchers had drilled deep into the ground to measure temperatures at different depths, exploring geothermal energy linked to the myriad of hot springs scattered across the Cascades.
Typically, temperature increases with depth into the earth. However, water moving downwards alters this temperature gradient, allowing rocks a kilometer deep to maintain temperatures similar to those at the surface.
By studying the temperature patterns in the deep boreholes, Karlstrom and his team could deduce the depth at which groundwater was infiltrating through the volcanic rock fissures, helping them to map the volume of the aquifer.
Previous assessments of the Cascades’ water reserves simply focused on spring volumes and measured river or stream flow. In contrast, Karlstrom and his colleagues aimed deeper—both literally and figuratively. However, since the drill holes were not originally established for this groundwater mapping purpose, they do not encompass all potential data collection sites. As a result, the newly proposed size of the aquifer is a minimum estimation, and its actual volume could be even larger.
While the discovery of such a significant aquifer is promising, Karlstrom warns that it remains a finite resource that requires careful management and additional research.
“There is an active groundwater reservoir in place, but its sustainability and ability to withstand changes depend on how much replenishing water is available,” he mentioned.
The aquifer primarily receives its supply from snowfall, and projections indicate that snowpack levels in the high Cascades may significantly decline over the next few decades. Additionally, more precipitation is likely to occur as rain, which could affect the recharge levels for the high Cascade aquifer. While the aquifer may withstand small fluctuations in annual rainfall, prolonged periods of insufficient rain or snowpack could pose greater risks.
“This area is fortunate to have received a geological treasure, but we’re just starting to grasp its complexities,” Grant noted. “If we experience years without snow or several consecutive seasons of inadequate rainfall, what consequences will that bring? These are the vital questions we must now tackle.”
This research was funded by the National Science Foundation and the U.S. Forest Service.
