Hells Canyon, the deepest river gorge in the country, has always been a marvel for geologists, archeologists and travelers. But researchers are just now learning about the origins of the canyon -- and it's a lot younger than previously believed.
Carved by the Snake River, the canyon is nearly 8,000 feet deep (or roughly 2,000 feet deeper than the Grand Canyon) and straddles the border between Oregon and Idaho. However, unlike its national park counterpart that dates back at least 6 million years, Hells Canyon was sculpted rapidly just 2.1 million years ago, when a sudden landscape shift and melting glaciers caused an ancient lake to overflow, according to a new study.
Matthew Morriss, the study's lead author and a geologist with the Utah Geological Survey, studied Hells Canyon as a graduate student at the University of Oregon after an earlier field trip to the gorge intrigued him.
"I had always thought the Grand Canyon was the deepest it gets. It gets all the attention -- that one is a national park, right?" Morriss told SFGATE. "My initial thought after hearing that depth superlative was, 'Well, how old is it then?'"
Unfortunately, no one had a definitive answer. His professor at the time was able to tell him that the canyon was less than 16 million years old based on lava flows found along its rim. The question stuck with Morriss until he was able to revisit it as a graduate student.
But dating canyons is actually very difficult.
"If you go to the Grand Canyon or to Hells Canyon, what inspires so much awe is our sense of scale and space because a canyon is a big negative space right in the surface of the Earth," Morriss said. "So just in that definition, as a river carves a canyon, it kind of destroys the evidence of its past."
To date the canyon, Morriss had to look for river terraces or benches. These are places where the river used to sit at one period, and usually, rocks or sediment that can be accurately dated have been left behind. He soon found that the walls of the canyon were too steep and that the Snake River hadn't left behind any significant terraces.
Then, he turned to limestone caves. Caves often form at river level during interactions between groundwater and surface water and can also include sediment samples.
"I spent a very naive summer just looking around by myself, poking into any hole I could see in the landscape," Morriss said. "It was probably not the safest thing to do alone, and it wasn't very fruitful."
Seeking a guide, he turned to cave explorers with Gem State Grotto, a local chapter of the National Speleological Society. With new collaborators, he immediately found what he was looking for. In the very first cave the group explored (about 1,200 feet above the modern river), they found a wall of river gravel and sand where two cave channels intersected -- exactly what the team would need to start dating the canyon.
After exploring several other caves with mixed results, Morriss began dating the samples.
To figure out when the river swept these minerals into the caves, the research team applied a specialized dating method to sediment samples. Tucked beneath the surface, the minerals had been shielded from cosmic rays that would've slowly altered their chemistry if left exposed.
After years of research, including lots of postgraduate hours in his spare time, Morriss finally had an answer: 2.1 million years was his final estimate.
"It took a long time, and the process wasn't entirely linear, but that's the nature of science sometimes," he said. "It was tough."
While Morriss has answered his question, he said he believes that Hells Canyon still holds plenty of mysteries for the right scientist, from studies on the genetics of fish species that suddenly became less isolated to those focusing on splits in species that the growing gorge slowly separated.
"I'm just happy to be able to answer some of those questions about Hells Canyon," he said. "I was always a little jealous of all the attention the Grand Canyon gets when this other captivating landscape existed."