Hells Canyon South Kirkwood

Hells Canyon is the deepest gorge in North America. But until now, no one had defined how, when, and why it formed.

Ever since he first visited the canyon on a geology field trip in 2010, Matthew Morriss has wanted to find out. Now completing his Ph.D., in geology at the University of Oregon, Morriss has discovered that a combination of faulting, river piracy, and the drainage of a giant lake in Idaho are all factors that sculpted Hells Canyon into its present form. His research is funded by the National Science Foundation.

“People have been sniffing around the idea of a fault defining Hells Canyon for decades,” Morriss said. “But because the river has eroded much of the traditional evidence of a big fault—features known as “breccia” and “slickensides” — evidence has been hard to find.”

Working with a collaborator at University of Washington, Phil Schoettle-Greene, Morriss found that the Columbia River basalts on the Idaho side of the canyon were about 3,000 feet higher than equivalent flows on the Oregon side.

“Then, when I hiked from Heavens Gate in the Seven Devils down to the Snake River, I could physically document that there were high elevation basalts in the Seven Devils but there were no basalts that were equivalent on the Oregon side,” Morriss said.

“It really seemed to be a “normal” fault, where the Oregon side had dropped down relative to Idaho and the Seven Devils,” he said. “There’s other evidence for a fault, too—the strata on the east side of Hells Canyon tilt back a little bit toward the east, which is exactly what you’d expect if there is a normal fault where Hells canyon is today.”

Faults, or breaks in the earth’s crust where one side has moved relative to the other, generally produce straight-line features. And Hells Canyon, especially from about Copperfield to Pittsburg Landing, is about as straight as any geologic feature can get. Faults are also zones of weakness in the Earth’s crust—and easily eroded. Rivers are notorious for carving their valleys and canyons through these straight-line zones of weak and broken rock. So it makes perfect sense that the Snake River would excavate Hells Canyon along the Hells Canyon fault.

How the Snake River began flowing north as it eroded Hells Canyon is another fascinating part of the story.

Morriss noted that 10 million years ago a much smaller stream—perhaps an ancestral version of today’s Pine Creek that now runs from Cornucopia to the Snake—flowed north along the same course as today’s Snake River. A different stream flowed south from somewhere around Farewell Bend into Lake Idaho — a very large lake that occupied much of the Boise area and present Snake River Plain. Lake Idaho extended north to Ontario and the Farewell Bend area. Those light-colored sedimentary layers that you see along Interstate 84 as you near Ontario are 4 to 10 million year old Lake Idaho sediments.

Because the gradient of the north-flowing stream was steeper, its waters had more erosive power. Four to five million years ago, its canyon may have been a substantial gorge resembling the modern Imnaha Canyon, Morriss said. Through a process of stream capture (also known as stream piracy) the powerful northbound creek eroded farther and farther into the drainage of the smaller southbound stream, eventually “capturing” its channel and tributaries. By about 4 million years ago, the southbound stream had been replaced by a northbound drainage – the eventual Snake River.

At some point, perhaps 4 to 3.5 million years ago, this ambitious northbound stream tapped into the huge water supply of Lake Idaho. This event probably occurred somewhere around the present location of Oxbow, Oregon.

“We don’t know whether it was sudden event or gradual, or whether the capture of Lake Idaho occurred because of an unusually high lake level,” Morriss said. “ It could have been a catastrophic event like the Ice Age floods. It might have been gradual. There’s no specific evidence either way.”

With the capture of Lake Idaho’s waters, the modern Snake River was born. This newly formed river had a huge watershed, from the Tetons in Wyoming to parts of Nevada and most of Idaho. “That enormous drainage system and the volume of water that it poured into the Snake fueled the further erosion of the canyon,” Morriss said.

How rapidly did the newly inaugurated Snake River cut its canyon? To find out, Morriss resorted to both old-fashioned and new-fangled technologies.

“When I did the big hike from the Seven Devils down to the river, I collected rock samples from the top to the bottom,” he said. Those samples will enable Morriss to determine how rapidly the rocks in Hells Canyon were uplifted from depth and reached the surface. The rate of uplift seems rapid. Rocks that are now high on the Idaho side of Hells Canyon were more than a half-mile beneath the earth’s surface only 8 million years ago, according to uranium + thorium/helium dating of apatite crystals. * (See Sidebar)

While the landscape rose, the river cut its canyon. But how fast, and when did serious down cutting begin? For that, Morriss resorted to caving.

Caves form at the level of the water table. In Hells Canyon that means river level. During floods, the Snake River would flood the river-level caves, depositing sediments inside the caverns. Then, as the river cut down farther, new caverns would form and the older caves would be left stranded where floodwater would never reach. If Morriss could determine how old the sediments were in the stranded caves, he could tell how long ago the Snake River’s channel was at that elevation.

“I’ve crawled through more than 50 caves in Hells Canyon, Morriss said. I’ve found sediments in two of them above Big Bar, and I’ll be exploring more caves this year.”

How do you figure out how long a cobble or a grain of sand has been hidden in a cave? By using a technique called “cosmogenic radionuclide dating” which determines how long since that sample was last exposed to sunlight and cosmic rays. Morriss’ cave samples are presently being analyzed at Purdue University.

Morriss’ research supports the long-held notion that Hells Canyon, and the Snake River’s present course are relatively young, geologically speaking. The Snake River began flowing along its present course probably about 4 million years ago, aided and abetted by the drainage of Lake Idaho.

The Hells Canyon fault, like the Wallowa fault, was probably most active about 14 to about 4 million years ago. Today, both faults seem to offer little threat of earthquakes, although small quakes of magnitude two and three occur every few years. But the Hells Canyon fault did offer an easy, straight channel for an opportunistic river, and a canyon that’s a Wallowa County treasure, if not a national icon.

Hells Canyon is the deepest gorge in North America. But until now, no one had defined how, when, and why it formed. Ever since he first visited the canyon on a geology field trip in 2010, Matthew Morriss has wanted to find out. Morriss, now completing his Ph.D. in geology at the a University of Oregon, has discovered that a combination of faulting, river piracy, and the drainage of a giant lake in Idaho are all factors that sculpted Hells Canyon into its present form. His research is funded by the National Science Foundation.

“People have been sniffing around the idea of a fault defining Hells Canyon for decades,” Morris said. “But because the river has eroded much of the traditional evidence of a big fault—features known as “breccia” and “slickensides” — evidence has been hard to find.”

Working with a collaborator at University of Washington, Phil Schoettle-Greene, Morriss found that the Columbia River basalts on the Idaho side of the canyon were about 3,000 feet higher than equivalent flows on the Oregon side.

“Then, when I hiked from Heavens Gate in the Seven Devils down to the Snake River, I could physically document that there were high elevation basalts in the Seven Devils but there were no basalts that were equivalent on the Oregon side,” Morriss said.

“It really seemed to be a “normal” fault, where the Oregon side had dropped down relative to Idaho and the Seven Devils,” he said. “There’s other evidence for a fault, too—the strata on the east side of Hells Canyon tilt back a little bit toward the east, which is exactly what you’d expect if there is a normal fault where Hells canyon is today.”

Faults, or breaks in the earth’s crust where one side has moved relative to the other, generally produce straight-line features. And Hells Canyon, especially from about Copperfield to Pittsburg Landing, is about as straight as any geologic feature can get. Faults are also zones of weakness in the Earth’s crust—and easily eroded. Rivers are notorious for carving their valleys and canyons through these straight-line zones of weak and broken rock. So it makes perfect sense that the Snake River would excavate Hells Canyon along the Hells Canyon fault.

How the Snake River began flowing north as it eroded Hells Canyon is another fascinating part of the story.

Morriss noted that 10 million years ago a much smaller stream—perhaps an ancestral version of today’s Pine Creek that now runs from Cornucopia to the Snake—flowed north along the same course as today’s Snake River. A different stream flowed south from somewhere around Farewell Bend into Lake Idaho — a very large lake that occupied much of the Boise area and present Snake River Plain. Lake Idaho extended north to Ontario and the Farewell Bend area. Those light-colored sedimentary layers that you see along Interstate 84 as you near Ontario are 4 to 10 million year old Lake Idaho sediments.

Because the gradient of the north-flowing stream was steeper, its waters had more erosive power. Four to five million years ago, its canyon may have been a substantial gorge resembling the modern Imnaha Canyon, Morriss said. Through a process of stream capture (also known as stream piracy) the powerful northbound creek eroded farther and farther into the drainage of the smaller southbound stream, eventually “capturing” its channel and tributaries. By about 4 million years ago, the southbound stream had been replaced by a northbound drainage – the eventual Snake River.

At some point, perhaps 4 to 3.5 million years ago, this ambitious northbound stream tapped into the huge water supply of Lake Idaho. This event probably occurred somewhere around the present location of Oxbow, Oregon.

“We don’t know whether it was sudden event or gradual, or whether the capture of Lake Idaho occurred because of an unusually high lake level,” Morriss said. “ It could have been a catastrophic event like the Ice Age floods. It might have been gradual. There’s no specific evidence either way.”

With the capture of Lake Idaho’s waters, the modern Snake River was born. This newly formed river had a huge watershed, from the Tetons in Wyoming to parts of Nevada and most of Idaho. “That enormous drainage system and the volume of water that it poured into the Snake fueled the further erosion of the canyon,” Morriss said.

How rapidly did the newly inaugurated Snake River cut its canyon? To find out, Morriss resorted to both old-fashioned and new-fangled technologies.

“When I did the big hike from the Seven Devils down to the river, I collected rock samples from the top to the bottom,” he said. Those samples will enable Morriss to determine how rapidly the rocks in Hells Canyon were uplifted from depth and reached the surface. The rate of uplift seems rapid. Rocks that are now high on the Idaho side of Hells Canyon were more than a half-mile beneath the earth’s surface only 8 million years ago, according to uranium + thorium/helium dating of apatite crystals. * (See Sidebar)

While the landscape rose, the river cut its canyon. But how fast, and when did serious down cutting begin? For that, Morriss resorted to caving.

Caves form at the level of the water table. In Hells Canyon that means river level. During floods, the Snake River would flood the river-level caves, depositing sediments inside the caverns. Then, as the river cut down farther, new caverns would form and the older caves would be left stranded where floodwater would never reach. If Morriss could determine how old the sediments were in the stranded caves, he could tell how long ago the Snake River’s channel was at that elevation.

“I’ve crawled through more than 50 caves in Hells Canyon, Morriss said. I’ve found sediments in two of them above Big Bar, and I’ll be exploring more caves this year.”

How do you figure out how long a cobble or a grain of sand has been hidden in a cave? By using a technique called “cosmogenic radionuclide dating” which determines how long since that sample was last exposed to sunlight and cosmic rays. Morriss’ cave samples are presently being analyzed at Purdue University.

Morriss’ research supports the long-held notion that Hells Canyon, and the Snake River’s present course are relatively young, geologically speaking. The Snake River began flowing along its present course probably about 4 million years ago, aided and abetted by the drainage of Lake Idaho.

The Hells Canyon fault, like the Wallowa fault, was probably most active about 14 to about 4 million years ago. Today, both faults seem to offer little threat of earthquakes, although small quakes of magnitude 2 and 3 occur every few years. But the Hells Canyon fault did offer an easy, straight channel for an opportunistic river, and a canyon that’s a Wallowa County treasure, if not a national icon.

Hells Canyon is the deepest gorge in North America. But until now, no one had defined how, when, and why it formed. Ever since he first visited the canyon on a geology field trip in 2010, Matthew Morriss has wanted to find out. Morriss, now completing his Ph.D. in geology at the a University of Oregon, has discovered that a combination of faulting, river piracy, and the drainage of a giant lake in Idaho are all factors that sculpted Hells Canyon into its present form. His research is funded by the National Science Foundation.

“People have been sniffing around the idea of a fault defining Hells Canyon for decades,” Morris said. “But because the river has eroded much of the traditional evidence of a big fault—features known as “breccia” and “slickensides” — evidence has been hard to find.”

Working with a collaborator at University of Washington, Phil Schoettle-Greene, Morriss found that the Columbia River basalts on the Idaho side of the canyon were about 3,000 feet higher than equivalent flows on the Oregon side.

“Then, when I hiked from Heavens Gate in the Seven Devils down to the Snake River, I could physically document that there were high elevation basalts in the Seven Devils but there were no basalts that were equivalent on the Oregon side,” Morriss said.

“It really seemed to be a “normal” fault, where the Oregon side had dropped down relative to Idaho and the Seven Devils,” he said. “There’s other evidence for a fault, too—the strata on the east side of Hells Canyon tilt back a little bit toward the east, which is exactly what you’d expect if there is a normal fault where Hells canyon is today.”

Faults, or breaks in the earth’s crust where one side has moved relative to the other, generally produce straight-line features. And Hells Canyon, especially from about Copperfield to Pittsburg Landing, is about as straight as any geologic feature can get. Faults are also zones of weakness in the Earth’s crust—and easily eroded. Rivers are notorious for carving their valleys and canyons through these straight-line zones of weak and broken rock. So it makes perfect sense that the Snake River would excavate Hells Canyon along the Hells Canyon fault.

How the Snake River began flowing north as it eroded Hells Canyon is another fascinating part of the story.

Morris noted that 10 million years ago a much smaller stream—perhaps an ancestral version of today’s Pine Creek that now runs from Cornucopia to the Snake—flowed north along the same course as today’s Snake River. A different stream flowed south from somewhere around Farewell Bend into Lake Idaho — a very large lake that occupied much of the Boise area and present Snake River Plain. Lake Idaho extended north to Ontario and the Farewell Bend area. Those light-colored sedimentary layers that you see along Interstate 84 as you near Ontario are 4 to 10 million year old Lake Idaho sediments.

Because the gradient of the north-flowing stream was steeper, its waters had more erosive power. Four to five million years ago, its canyon may have been a substantial gorge resembling the modern Imnaha Canyon, Morris said. Through a process of stream capture (also known as stream piracy) the powerful northbound creek eroded farther and farther into the drainage of the smaller southbound stream, eventually “capturing” its channel and tributaries. By about 4 million years ago, the southbound stream had been replaced by a northbound drainage – the eventual Snake River.

At some point, perhaps 4 to 3.5 million years ago, this ambitious northbound stream tapped into the huge water supply of Lake Idaho. This event probably occurred somewhere around the present location of Oxbow, Oregon.

“We don’t know whether it was sudden event or gradual, or whether the capture of Lake Idaho occurred because of an unusually high lake level,” Morriss said. “ It could have been a catastrophic event like the Ice Age floods. It might have been gradual. There’s no specific evidence either way.”

With the capture of Lake Idaho’s waters, the modern Snake River was born. This newly formed river had a huge watershed, from the Tetons in Wyoming to parts of Nevada and most of Idaho. “That enormous drainage system and the volume of water that it poured into the Snake fueled the further erosion of the canyon,” Morriss said.

How rapidly did the newly inaugurated Snake River cut its canyon? To find out, Morriss resorted to both old-fashioned and new-fangled technologies.

“When I did the big hike from the Seven Devils down to the river, I collected rock samples from the top to the bottom,” he said. Those samples will enable Morriss to determine how rapidly the rocks in Hells Canyon were uplifted from depth and reached the surface. The rate of uplift seems rapid. Rocks that are now high on the Idaho side of Hells Canyon were more than a half-mile beneath the earth’s surface only 8 million years ago, according to uranium + thorium/helium dating of apatite crystals. * (See Sidebar)

While the landscape rose, the river cut its canyon. But how fast, and when did serious down cutting begin? For that, Morriss resorted to caving.

Caves form at the level of the water table. In Hells Canyon that means river level. During floods, the Snake River would flood the river-level caves, depositing sediments inside the caverns. Then, as the river cut down farther, new caverns would form and the older caves would be left stranded where floodwater would never reach. If Morriss could determine how old the sediments were in the stranded caves, he could tell how long ago the Snake River’s channel was at that elevation.

“I’ve crawled through more than 50 caves in Hells Canyon, Morriss said. I’ve found sediments in two of them above Big Bar, and I’ll be exploring more caves this year.”

How do you figure out how long a cobble or a grain of sand has been hidden in a cave? By using a technique called “cosmogenic radionuclide dating” which determines how long since that sample was last exposed to sunlight and cosmic rays. Morriss’ cave samples are presently being analyzed at Purdue University.

Morriss’ research supports the long-held notion that Hells Canyon, and the Snake River’s present course are relatively young, geologically speaking. The Snake River began flowing along its present course probably about 4 million years ago, aided and abetted by the drainage of Lake Idaho.

The Hells Canyon fault, like the Wallowa fault, was probably most active about 14 to about 4 million years ago. Today, both faults seem to offer little threat of earthquakes, although small quakes of magnitude 2 and 3 occur every few years. But the Hells Canyon fault did offer an easy, straight channel for an opportunistic river, and a canyon that’s a Wallowa County treasure, if not a national icon.

Hells Canyon is the deepest gorge in North America. But until now, no one had defined how, when, and why it formed.

Ever since he first visited the canyon on a geology field trip in 2010, Matthew Morriss has wanted to find out. Morriss, now completing his Ph.D. in geology at the a University of Oregon, has discovered that a combination of faulting, river piracy, and the drainage of a giant lake in Idaho are all factors that sculpted Hells Canyon into its present form. His research is funded by the National Science Foundation.

“People have been sniffing around the idea of a fault defining Hells Canyon for decades,” Morris said. “But because the river has eroded much of the traditional evidence of a big fault—features known as “breccia” and “slickensides”-- evidence has been hard to find.”

Working with a collaborator at University of Washington, Phil Schoettle-Greene, Morriss found that the Columbia River basalts on the Idaho side of the canyon were about 3,000 feet higher than equivalent flows on the Oregon side.

“Then, when I hiked from Heavens Gate in the Seven Devils down to the Snake River, I could physically document that there were high elevation basalts in the Seven Devils but there were no basalts that were equivalent on the Oregon side,” Morriss said.

“It really seemed to be a “normal” fault, where the Oregon side had dropped down relative to Idaho and the Seven Devils,” he said. “There’s other evidence for a fault, too—the strata on the east side of Hells Canyon tilt back a little bit toward the east, which is exactly what you’d expect if there is a normal fault where Hells canyon is today.”

Faults, or breaks in the earth’s crust where one side has moved relative to the other, generally produce straight-line features. And Hells Canyon, especially from about Copperfield to Pittsburg Landing, is about as straight as any geologic feature can get. Faults are also zones of weakness in the Earth’s crust—and easily eroded. Rivers are notorious for carving their valleys and canyons through these straight-line zones of weak and broken rock. So it makes perfect sense that the Snake River would excavate Hells Canyon along the Hells Canyon fault.

How the Snake River began flowing north as it eroded Hells Canyon is another fascinating part of the story.

Morris noted that 10 million years ago a much smaller stream—perhaps an ancestral version of today’s Pine Creek that now runs from Cornucopia to the Snake—flowed north along the same course as today’s Snake River. A different stream flowed south from somewhere around Farewell Bend into Lake Idaho-- a very large lake that occupied much of the Boise area and present Snake River Plain. Lake Idaho extended north to Ontario and the Farewell Bend area. Those light-colored sedimentary layers that you see along Interstate 84 as you near Ontario are 4 to 10 million year old Lake Idaho sediments.

Because the gradient of the north-flowing stream was steeper, its waters had more erosive power. Four to five million years ago, its canyon may have been a substantial gorge resembling the modern Imnaha Canyon, Morris said. Through a process of stream capture (also known as stream piracy) the powerful northbound creek eroded farther and farther into the drainage of the smaller southbound stream, eventually “capturing” its channel and tributaries. By about 4 million years ago, the southbound stream had been replaced by a northbound drainage – the eventual Snake River.

At some point, perhaps 4 to 3.5 million years ago, this ambitious northbound stream tapped into the huge water supply of Lake Idaho. This event probably occurred somewhere around the present location of Oxbow, Oregon.

“We don’t know whether it was sudden event or gradual, or whether the capture of Lake Idaho occurred because of an unusually high lake level,” Morriss said. “ It could have been a catastrophic event like the Ice Age floods. It might have been gradual. There’s no specific evidence either way.”

With the capture of Lake Idaho’s waters, the modern Snake River was born. This newly formed river had a huge watershed, from the Tetons in Wyoming to parts of Nevada and most of Idaho. “That enormous drainage system and the volume of water that it poured into the Snake fueled the further erosion of the canyon,” Morriss said.

How rapidly did the newly inaugurated Snake River cut its canyon? To find out, Morriss resorted to both old-fashioned and new-fangled technologies.

“When I did the big hike from the Seven Devils down to the river, I collected rock samples from the top to the bottom,” he said. Those samples will enable Morriss to determine how rapidly the rocks in Hells Canyon were uplifted from depth and reached the surface. The rate of uplift seems rapid. Rocks that are now high on the Idaho side of Hells Canyon were more than a half-mile beneath the earth’s surface only 8 million years ago, according to uranium + thorium/helium dating of apatite crystals. * (See Sidebar)

While the landscape rose, the river cut its canyon. But how fast, and when did serious down cutting begin? For that, Morriss resorted to caving.

Caves form at the level of the water table. In Hells Canyon that means river level. During floods, the Snake River would flood the river-level caves, depositing sediments inside the caverns. Then, as the river cut down farther, new caverns would form and the older caves would be left stranded where floodwater would never reach. If Morriss could determine how old the sediments were in the stranded caves, he could tell how long ago the Snake River’s channel was at that elevation.

“I’ve crawled through more than 50 caves in Hells Canyon, Morriss said. I’ve found sediments in two of them above Big Bar, and I’ll be exploring more caves this year.”

How do you figure out how long a cobble or a grain of sand has been hidden in a cave? By using a technique called “cosmogenic radionuclide dating” which determines how long since that sample was last exposed to sunlight and cosmic rays. Morriss’ cave samples are presently being analyzed at Purdue University.

Morriss’ research supports the long-held notion that Hells Canyon, and the Snake River’s present course are relatively young, geologically speaking. The Snake River began flowing along its present course probably about 4 million years ago, aided and abetted by the drainage of Lake Idaho.

The Hells Canyon fault, like the Wallowa fault, was probably most active about 14 to about 4 million years ago. Today, both faults seem to offer little threat of earthquakes, although small quakes of magnitude 2 and 3 occur every few years. But the Hells Canyon fault did offer an easy, straight channel for an opportunistic river, and a canyon that’s a Wallowa County treasure, if not a national icon.

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