The largest mountain range in Oregon, the majestic Cascades stretch from British Columbia, Canada, to Northern California.
Scientists from University of Oregon (UO) and partners recently discovered a hidden gem beneath the Cascade range that is desperately needed in the West: water in volumes much higher than had previously been estimated.
After mapping the amount of water underneath volcanic rocks that lie at the central crest of the mountain range, the scientists discovered an aquifer many times bigger than was once believed — a minimum of 81 cubic kilometers, or nearly three times the full capacity of Lake Mead, the overdrawn reservoir on the Colorado River that supplies drinking water to California, Nevada and Arizona, a press release from UO said.
“It is a continental-size lake stored in the rocks at the top of the mountains, like a big water tower,” said Leif Karlstrom, an Earth scientist at UO who led the study along with collaborators from Oregon State University, Duke University, Fort Lewis College, the University of Wisconsin, the U.S. Geological Survey and the U.S. Forest Service. “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 findings have implications for how scientists and policymakers view the region’s water, which has become an increasingly urgent concern across the West as climate change reduces the amount of snowpack, intensifies drought and puts a strain on limited resources.
The discovery also affects our understanding of the area’s volcanic hazards. When magma interacts with large volumes of water it often causes explosive eruptions that send ash and gas spewing into the air, as opposed to eruptions with slower lava flows.
Most Oregonians depend on water originating in the Cascades. The City of Eugene’s drinking water, for example, is supplied by the McKenzie River, which starts high up in the mountains at spring-fed Clear Lake.
However, the discovery of an underground aquifer of that size was surprising.
“We initially set out to better understand how the Cascade landscape has evolved over time, and how water moves through it,” said co-author of the study Gordon Grant, a geologist with the U.S. Forest Service, in the press release. “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.”
Rivers in the western Cascades have carved out deep valleys surrounded by steep slopes. Meanwhile, the high Cascades are flatter and dotted with lakes and lava flow topography.
Built up by millions of years of volcanic activity, the exposed rocks of the high Cascades are much younger than those of their western counterparts. This makes the transition zone of the high and western Cascades around Santiam Pass a natural laboratory for comprehending how Oregon’s landscape has been shaped by volcanoes.
“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 in the press release.
To get a better idea of how water flows through different volcanic zones, the researchers referenced projects started in the 1980s and 1990s. Scientists had previously drilled deep into the Earth to measure temperatures at varying depths during their search for geothermal energy sources associated with the abundance of hot springs found in the mountain landscape.
Rocks typically get hotter as you dig deeper into the ground. However, water percolating downward changes the temperature gradient, making kilometer-deep rocks the same temperature as those at the surface.
Karlstrom and the research team analyzed where the temperature began to rise again inside the deep drill holes, which allowed them to infer the depth of the groundwater’s infiltration through cracks in the rock. This gave them the information they needed to map the aquifer’s volume.
Earlier estimates of Cascades water availability took mountain springs at face value, only measuring stream and river discharge. But since the holes Karlstrom and colleagues used hadn’t been drilled with the intention of mapping groundwater, not all areas where scientists might prefer to collect data were covered. This means the new estimate might not reflect the actual volume of the aquifer, which might be even bigger.
Karlstrom cautioned that, while the aquifer being much larger than once thought was encouraging, it remains a limited resource that needs further study and must be carefully stewarded.
“It is a big, active groundwater reservoir up there right now, but its longevity and resilience to change is set by the availability of recharging waters,” Karlstrom explained.
The aquifer is primarily replenished by snow, and with high Cascades snowpack predicted to decrease rapidly in the coming decades — precipitation is increasingly expected to be in the form of rain — it may impact how much recharge feeds the aquifer. It is likely resilient to small fluctuations from year to year, but many consecutive years of low rainfall or an absence of snowpack would likely lead to changes to the aquifer’s water level.
“This region has been handed a geological gift, but we really are only beginning to understand it,” Grant said in the press release. “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.”
The study, “State shifts in the deep Critical Zone drive landscape evolution in volcanic terrains,” was published in the journal Proceedings of the National Academy of Sciences.
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