Hidden water reservoir discovered beneath the Cascade mountains

Oregon’s Cascade Range is not just a scenic landscape of volcanic peaks – it also hides a massive underground aquifer filled with water. 

Scientists from the University of Oregon and their collaborators have mapped this extensive water storage beneath the central Oregon Cascades and found it to be at least 81 cubic kilometers in size. 

This discovery is significant because it reveals a water resource nearly three times the capacity of Lake Mead and more than half the volume of Lake Tahoe, reshaping our understanding of regional water supplies and volcanic processes.

“Big water tower” beneath the Cascades

The newly mapped aquifer lies beneath volcanic rocks at the crest of the central Cascades, acting like a giant, continental-sized lake stored in the mountains.

“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 the University of Oregon and lead author of the study.

Karlstrom and his team suggest that similar large volcanic aquifers likely exist elsewhere in the Cascade Range, potentially making it one of the largest aquifer systems of its kind in the world.

Evolution of the Cascade landscape

The discovery emerged from research originally aimed at understanding the evolution of the Cascades landscape and the movement of water through it. During this investigation, the team uncovered critical information about the sheer volume of water stored underground and how it relates to volcanic activity in the region.

“We initially set out to better understand how the Cascade landscape has evolved over time, and how water moves through it,” explained co-author Gordon Grant, a geologist with the U.S. Forest Service. 

“But in doing so, 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.”

This research enhances our understanding of the region’s geology and water resources, particularly as climate change drives increased droughts and reduces snowpack – a primary source of recharge for the aquifer.

Mapping the water underground 

To gauge the size of the aquifer, researchers tapped into historical geothermal drilling data from the 1980s and 1990s. Those earlier projects, aimed at finding geothermal energy sources, had drilled deep into the earth and recorded temperatures at various depths. 

By analyzing these temperature records, Karlstrom’s team could infer how water moves through the volcanic rocks.

Normally, rock temperatures increase with depth, but groundwater flowing downward keeps deeper rocks cooler. By identifying where temperatures start to rise again in these drill holes, the team estimated how far groundwater penetrates, and thus, mapped out the aquifer’s volume.

Unlike past methods that only measured water coming out of springs or streams, this approach looked deep underground to reveal a far larger water reserve than previously thought. 

Due to gaps in the data – since the original drill holes weren’t intended for mapping groundwater – the 81 cubic kilometer estimate is likely a lower bound, and the actual volume could be even greater.

Volcanic hazards and future risks

The presence of such a large volume of water at high elevations affects not only water supply but also volcanic activity. When magma interacts with groundwater, it can lead to more explosive volcanic eruptions, which change landscapes and impact air quality. 

Understanding the size and flow of this aquifer helps scientists assess potential volcanic hazards in the Cascades.

However, the aquifer’s future is uncertain. It relies on snowpack for recharge, and climate change threatens to reduce the snow that feeds it. Warmer temperatures mean less snow and more rain, which can affect how much water is absorbed and stored underground.

“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 warned.

Managing a precious resource

While discovering this vast aquifer is encouraging, it also raises important questions about sustainability. As climate change alters precipitation patterns and reduces snowpack, the amount of water recharging the aquifer could decline. 

Scientists like Gordon Grant and Leif Karlstrom are now focused on understanding these dynamics to manage the resource effectively.

“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.”

The discovery underscores the vital role of scientific research in uncovering hidden resources and informs strategies for water management amid a changing climate. 

As experts continue to study this “big water tower” beneath the Cascades, they aim to ensure that it remains a reliable resource for the region while also monitoring the interactions between groundwater and volcanic activity.

The study is published in the journal Proceedings of the National Academy of Sciences.

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