Secrets Beneath: Uncovering the Vast Buried Aquifer of the Oregon Cascades

Oregon’s Cascade Range may not harbor gold, but it conceals another valuable asset in plentiful supply: water. Researchers from the University of Oregon and their collaborators have charted the quantity of water sequestered beneath volcanic formations at the peak of the central Oregon Cascades, uncovering an aquifer significantly larger than earlier projections—amounting to no less than 81 cubic kilometers.

This volume is nearly thrice that of Lake Mead, the currently overexploited reservoir along the Colorado River supplying water to California, Arizona, and Nevada, and exceeds half the capacity of Lake Tahoe. The team presents their findings in a research paper released on Jan. 13 in the journal Proceedings of the National Academy of Sciences.

This discovery impacts how researchers and policy officials perceive water resources in the area—an issue that is becoming increasingly urgent across the Western United States as climate change reduces snow accumulation, exacerbates drought, and challenges limited supplies.

Additionally, it influences our comprehension of volcanic threats in the region. Magma interacting with substantial amounts of water frequently leads to explosive eruptions that propel ash and gas into the atmosphere, rather than eruptions characterized by slow-moving lava flows.

“It represents a continental-scale lake stored within the rocks atop the mountains, functioning like a large water reservoir,” stated Leif Karlstrom, a UO earth scientist who spearheaded the study alongside partners from Oregon State University, Fort Lewis College, Duke University, the University of Wisconsin, the U.S. Forest Service, and the U.S. Geological Survey.

“The existence of similar substantial volcanic aquifers north of the Columbia Gorge and around Mount Shasta likely renders the Cascade Range the largest of its kind globally.”

The majority of residents in Oregon depend on water sourced from the Cascades. For instance, the McKenzie River, which serves as the primary source of drinking water for Eugene, originates from the high mountains at the spring-fed Clear Lake. However, the revelation of this underground aquifer’s magnitude was unexpected.

“Our original goal was to gain a deeper understanding of the evolution of the Cascade terrain over time and the dynamics of water movement within it,” commented study co-author Gordon Grant, a geologist affiliated with the Forest Service.

“Yet, during this fundamental research, we uncovered significant insights that matter to people: the astonishing volume of water actively stored in the Cascades and the interconnectedness of water movement with the hazards presented by volcanic activity.”

The western Cascades are defined by steep inclines and deep canyons forged by river erosion. In contrast, the high Cascades are more level, dotted with lakes and volcanic formations such as lava flows. The Cascade Range has been developed through volcanic activity over millions of years, resulting in the exposed rocks in the high Cascades being significantly younger than those in the western Cascades.

Consequently, the transition area between the western and high Cascades surrounding Santiam Pass serves as a natural laboratory for comprehending how volcanoes have influenced Oregon’s geographic features.

“What drives our research is not just the different topographical appearances of these landscapes but also the fact that water traverses through them in vastly distinct manners,” Karlstrom stated.

To enhance the understanding of water flow through various volcanic regions, the research team utilized projects initiated in the 1980s and 90s. Previous researchers had drilled deep into the ground and assessed temperatures at varying depths as part of the exploration for geothermal energy resources linked to the numerous hot springs scattered throughout the Cascade region.

As a general rule, rocks increase in temperature as one penetrates deeper into the Earth. However, the infiltration of water disrupts this temperature gradient, causing rocks a kilometer deep to exhibit the same temperature as surface rocks.

By evaluating where the temperature begins to rise again in these deep boreholes, Karlstrom and his associates were able to deduce the extent of groundwater infiltration through fissures in the volcanic rocks. This enabled them to map the aquifer’s volume.

Prior estimates of water availability in the Cascades took the springs at face value, assessing the flow from rivers and streams. In contrast, Karlstrom and his team dug deeper—literally. However, since these holes were not originally drilled with the aim of mapping groundwater, they do not encompass every locality where such data collection would be desirable. Thus, the new estimate of the aquifer’s size serves as a lower limit, and the true volume may be even more substantial.

Although it’s promising to discover that the aquifer is much larger than once thought, Karlstrom cautions that it remains a finite resource that must be managed prudently and demands further research.

“It constitutes a substantial, dynamic groundwater reservoir currently present, but its sustainability and ability to endure change is dependent on the availability of replenishing waters,” he remarked.

The aquifer is predominantly replenished by snowfall, and snowpack in the high Cascades is projected to decrease significantly in the forthcoming decades. A greater proportion of precipitation is anticipated to manifest as rain, potentially affecting the recharge feeding the high Cascade aquifer. While it is likely resilient to minor year-to-year variances, multiple consecutive years of low rainfall or absent snowpack would likely tell a different story.

“This region has been given…

“a geological treasure, yet we are truly just starting to grasp its complexities,” Grant remarked. “If we lack snow, or if we experience a streak of harsh winters with little rainfall, what implications will that have? These are the critical inquiries that we must now concentrate on.”