The Nenana River originates near here, north of the Alaska Range, and flows through the mountains south of the range. (Courtesy Photo | Ned Rozell)

The Nenana River originates near here, north of the Alaska Range, and flows through the mountains south of the range. (Courtesy Photo | Ned Rozell)

Rivers U-turn through Alaska range

The ‘unusual’ feature that makes bananas cheaper in Fairbanks.

By Ned Rozell

Alaska’s landscape has an unusual feature that allows us to enjoy cheap bananas in Fairbanks and other things that make life better in the subarctic.

The Nenana River, born on the south side of the Alaska Range, makes a U-turn and flows north through the mountains. With it comes a wide, low corridor that has favored construction of both the Alaska Railroad and the Parks Highway.

“Ordinarily, a mountain range is a pretty good barrier,” said Don Triplehorn, a man curious about many things and a professor emeritus at the University of Alaska Fairbanks. He once described the curious behavior of the Nenana.

“It flows out to the south, downhill as any decent river should, but then it turns west and then north, past McKinley,” Triplehorn said “That’s really unusual.”

[River Piracy strikes the Yukon]

And the Nenana River isn’t the only major waterway cutting through the Alaska Range. The Delta River does the same thing, originating south of the Alaska Range but then flowing north through the mountains.

“These are rivers that cut across one of the highest mountain ranges in the world,” Triplehorn said. “The broad, low passes that come with them are convenient routes for highways, pipelines and microwave stations, as well as people, plants, and animals.”

Why do these two major rivers seem to defy logic by cutting through mountains? Triplehorn put forth a theory suggested by his friend and geologist Tom Hamilton of Anchorage — that glacial ice flowing northward across the range scoured the broad, almost flat valleys through which the rivers flow.

The Delta River flows through and past Alaska Range peaks. (Courtesy Photo | Ned Rozell)

The Delta River flows through and past Alaska Range peaks. (Courtesy Photo | Ned Rozell)

The Alaska Range rose about 6 million years ago, Triplehorn said. During the last 2 million years or so, Earth went through a major ice age, and the Alaska Range south of Fairbanks looked something like the Greenland ice cap.

Since moisture came from the south then as it often does now, the high point of the ice shifted southward. Ice could then flow away from the high point, and in a few instances it flowed northward, scouring valleys across the buried mountains. As the glaciers receded, meltwater streams that were to become the Nenana and Delta flowed northward down the valleys, maintaining their paths after the ice sheet disappeared.

[A village grave that led to a virus breakthrough]

There are differing theories of why the rivers cut through the Alaska Range, but textbook concepts on why rivers run through mountain ranges don’t explain the courses of the Nenana and Delta rivers, Triplehorn said.

Whatever the reason for the Delta and the Nenana, life here would be different without them. Without the passes, Fairbanks probably wouldn’t exist, because human settlement north of the Alaska Range probably would have been on the Yukon River and its tributaries.

And, we need no tunnels to cross the Alaska Range, like the thousands who pass through Colorado’s Eisenhower Tunnel that accommodates interstate route 70 at 11,000 feet. Our expansive passes through the Alaska Range have for thousands of years allowed the easy movement of people, animals, oil, and trucks carrying bananas.

“It’s a good example of how geography and geology create history,” Triplehorn said.

• Since the late 1970s, the University of Alaska Fairbanks’ Geophysical Institute has provided this column free in cooperation with the UAF research community. Ned Rozell is a science writer for the Geophysical Institute. A version of this column appeared in 2007.

More in News

This 2020 electron microscope image provided by the National Institute of Allergy and Infectious Diseases - Rocky Mountain Laboratories shows SARS-CoV-2 virus particles which causes COVID-19, isolated from a patient in the U.S., emerging from the surface of cells cultured in a lab. On Monday, Oct. 5, 2020, the top U.S. public health agency said that coronavirus can spread greater distances through the air than 6 feet, particularly in poorly ventilated and enclosed spaces. But agency officials continued to say such spread is uncommon, and current social distancing guidelines still make sense. (NIAID-RML via AP)
COVID at a glance for Friday, Jan. 22

The most recent state and local numbers.

A Coast Guard Station Juneau 45-foot Response Boat-Medium patrols Auke Bay during an exercise in 2018. A response boat similar to the one in the photo was struck by a laser near Ketchikan on Saturday, Jan. 17, prompting an investigation into the crime. (Lt. Brian Dykens / U.S. Coast Guard)
Coast Guard wants information after laser pointed at boat

“Laser strikes jeopardize the safety of our boat crews…”

The valleys of Jim River and Prospect Creek in northern Alaska, where an official thermometer registered Alaska’s all-time low of minus 80 degrees F on Jan. 23, 1971. Photo by Ned Rozell
Alaska’s all-time cold record turns 50

The camp was there to house workers building the trans-Alaska pipeline

This 2020 electron microscope image provided by the National Institute of Allergy and Infectious Diseases - Rocky Mountain Laboratories shows SARS-CoV-2 virus particles which causes COVID-19, isolated from a patient in the U.S., emerging from the surface of cells cultured in a lab. On Monday, Oct. 5, 2020, the top U.S. public health agency said that coronavirus can spread greater distances through the air than 6 feet, particularly in poorly ventilated and enclosed spaces. But agency officials continued to say such spread is uncommon, and current social distancing guidelines still make sense. (NIAID-RML via AP)
COVID at a glance for Thursday, Jan. 21

The most recent state and local numbers.

Gov. Mike Dunleavy addresses the public during a virtual town hall on Sept. 15, 2020 in Alaska. ( Courtesy Photo / Austin McDaniel, Office of the Governor)
Dunleavy pitches dividend change amid legislative splits

No clear direction has emerged from lawmakers.

Joar Leifseth Ulsom, right, wearing a bib with ExxonMobil lettering on it, congratulates Peter Kaiser on his win in the Iditarod Trail Sled Dog Race in Nome, Alaska. The world’s most famous sled dog race has lost another major sponsor as the Iditarod prepares for a scaled-back version of this year’s race because of the pandemic, officials said Thursday, Jan. 21, 2021. ExxonMobil confirmed to The Associated Press that the oil giant will drop its sponsorship of the race. (Marc Lester / Anchorage Daily News)
ExxonMobil becomes latest sponsor to sever Iditarod ties

The world’s most famous sled dog race has lost another major sponsor.

Has it always been a police car? (Michael Penn / Juneau Empire)
Police calls for Friday, Jan. 22, 2021

This report contains public information from law enforcement and public safety agencies.

This electron microscope image made available and color-enhanced by the National Institute of Allergy and Infectious Diseases Integrated Research Facility in Fort Detrick, Md., shows Novel Coronavirus SARS-CoV-2 virus particles, orange, isolated from a patient.	(THE CANADIAN PRESS/AP-NIAID/National Institutes of Health)
State reports 24 COVID-19 deaths

Only 1 of the deaths happened recently, according to the state.

Most Read