Atop the Oregon Cascades, a University of Oregon team finds a huge buried aquifer¶
I’ve always had a love for the massive spring-fed rivers in Oregon. I actually got married along the Metolius River, and have done many hikes along the Fall River and Mckenzie River. These rivers are always ice cold (~40F), and keep a consistent flow year round.
I recently heard about a University of Oregon team that did some additional research on the aquifer that feeds these rivers:
Scientists from the University of Oregon and their partners have mapped the amount of water stored beneath volcanic rocks at the crest of the central Oregon Cascades and found an aquifer many times larger than previously estimated — at least 81 cubic kilometers.
That’s almost three times the maximum capacity of Lake Mead, the currently overdrawn reservoir along the Colorado River that supplies water to California, Arizona and Nevada, and greater than half the volume of Lake Tahoe.
They used previous known quantities of the water outflow, and combined it with previous drilling for geothermal test wells in order to more accurately map the area and depth of the water. Normal ground gets hotter as you go down, but the area here stays the same temperature, which lets them understand how deep the water goes.
To better understand the flow of water through different volcanic zones, the team took advantage of projects begun in the 1980s and 90s. Past scientists had drilled deep into the ground and measured temperatures at different depths as part of the search for geothermal energy resources associated with the many hot springs that pepper the Cascades landscape.
Normally, rocks get hotter as you go deeper into the earth. But water percolating downward disrupts the temperature gradient, making rocks a kilometer deep the same temperature as rocks at the surface.
By analyzing where the temperature starts to pick up again in these deep drill holes, Karlstrom and his colleagues could infer how deeply groundwater was infiltrating through cracks in the volcanic rocks. That allowed them to map the volume of the aquifer.
Previous estimates of water availability in the Cascades took the springs at face value, measuring river and stream discharge. Instead, Karlstrom and his colleagues went deeper — literally. But since those holes weren’t originally drilled with the intent of mapping groundwater, they don’t cover every area where one might like to collect such data. So the new estimate of the size of the aquifer is a lower bound, and the actual volume might be even bigger still.
I also heard an interview with the researchers on a local outdoors podcast that I enjoy, and recommend listening.