Hells Canyon, The Deepest River Gorge In The US, Was Created Incredibly Recently

Everything’s bigger in the US, they say, and that apparently includes its river gorges. But don't be fooled by its grand size – this geological giant is a fresh-faced whippersnapper by Earth’s standards.

Hells Canyon runs down the western flank of the US, snaking along the border of eastern Oregon and western Idaho before ending in Washington state. 

With a maximum depth of 2,436 meters (7,993 feet), it's the deepest river gorge in the entirety of North America (as far as we know). Even the Grand Canyon, with a depth of 1,857 meters (6,093 feet), can’t rival this.

Such a depth could suggest that it’s been whittled away by erosion for an extremely long time. However, as revealed by new research, Hells Canyon is relatively young.

In a new study, geologists reveal evidence that the river gorge was rapidly carved just a couple of million years ago. By studying cave-bound river deposits and feeding that data into computer models, the researchers pieced together the powerful geological forces that shaped the canyon. 

They concluded the river gorge was created ~2.1 million years ago when a major shift in the Snake River’s path caused it to join the Columbia River system. This change expanded the river’s drainage area and gave it much more erosive power. As a result, Hells Canyon was quickly carved into the landscape, along with a series of steep drops in nearby streams. 

All of this happened relatively recently and surprisingly fast on a geological timescale. To put it in perspective, the Grand Canyon was carved by the Colorado River over the past 5 to 6 million years, although parts of the canyon are made of rocks that have been there for 1.8 billion years. Despite having the advantage of age, the Grand Canyon can't compete with the depth of Hells Canyon.

Today, Hells Canyon is a place where geological time meets human ambition. In the 1960s and ‘70s, the Hells Canyon Dam complex was built to soak up the immense hydropower potential that flowed with the river. The project was controversial from the get-go, igniting debates over whether public or private interests should control the dams and who would profit from the power they generated.

The question of hydroelectric dams in Hells Canyon continues to stir tempers. Ultimately, private utility company Idaho Power was granted the license to construct three dams: Brownlee, Oxbow, and Hells Canyon Dam. While they brought electricity to thousands, the dams also blocked salmon migration and reshaped ecosystems that had thrived for millennia. 

Lastly, we should point out, Hells Canyon is often dubbed the deepest gorge in North America, but that might not be strictly accurate. 

Beneath thousands of meters of ice on Alaska’s Ruth Glacier, there’s a feature known as the “Great Gorge”. It’s big, but its precise size is unknown. In a study last year, scientists used a new measuring technique and found it was 2,465 meters (8,087 feet) deep, give or take 65 meters (213 feet) either way. This estimate would make it either slightly shallower or possibly even deeper than Hells Canyon. At the very least, it's a worthy rival.

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