MINTO FLATS — Within a vast bowl bordered by blue hills, I rolled along on a trail scratched into ice by snowmachines. That deceptive basin — Minto Flats — is big enough to swallow Denali, if the big mountain happened to stumble in here and fall.

Just over a ridge west of Fairbanks, Minto Flats is an oval of swampy lowlands larger than Anchorage. The flats are a quiet expanse that has for longer than anyone’s memory produced moose, beavers and northern pike for local villagers. It has also intrigued oil and gas developers, as well as seismologists who know the self-healing surface hides the scars of large earthquakes.

As the sun rose over the flats and reflected off the wind sculpted snow, teams of sled dogs and their drivers passed me and my fatbike. I was one of three human-powered racers in a contest called the T-Dog. Competitors that day raced from the village of Minto — perched on a hill to the west of the flats — to Fairbanks, 100 miles away.

I signed up for the T-Dog to do something new, and to draw a new line on my map that crossed the flats.

Instead of dog mushers, a few bikers and a skier, in a few months Minto Flats will be loud with quacks, honks and splashes. Scientists once calculated 213 ducks per square mile existed here during one spring/summer breeding season. 

“Minto Flats constitutes one of the highest quality waterfowl nesting and staging habitats in Alaska, and possibly in North America,” wrote Alaska Department of Fish and Game biologists in the Minto Flats State Game Refuge Management Plan in 1992.

In 1961, a geologist named David Barnes of the U.S. Geological Survey in Menlo Park, California, described something extraordinary about the sprawling wetland: The force of gravity is not as strong in the center of Minto Flats as it is in the surrounding hills. That “gravity low,” achieved in part because the Earth isn’t a perfect sphere, means that the force holding dogsled runners to the snow there is a little weaker than on the ridges. It also means that Minto Flats is sinking. 

Scientists have calculated that the descending basin of Minto Flats is 56 miles long, 7.5 miles wide and 4.5 miles deep. That would allow the flats (if you scooped out all the muck) to swallow Denali, at 20,310 feet a little less than four miles tall.

The basin, however, is now full. Over millions of years, rivers have pumped in ground-up rock, filling Minto Flats with sediment and amplifying the effects of big earthquakes. Those include magnitude 7.2’s in both 1937 and 1947 and a 6 felt by many Fairbanks residents in 1995.

Carl Tape of the University of Alaska Fairbanks Geophysical Institute and his colleagues installed seismometers near Minto village and in spots along the adjacent Tanana River during the last 10 years. They have determined that earthquakes in Minto Flats and the larger Nenana Basin (of which it is a part) feel stronger to the observer than earthquakes that shake people standing on more solid ground.

That intensified earthquake shaking is typical of towns and cities built upon sedimentary basins, among them Tokyo, San Francisco and Los Angeles.

When the faults beneath Minto Flats slip, Fairbanks can rattle with a magnitude 7 earthquake. Other population centers adjacent to the flats are Minto village (150 people counted in the 2020 census), Manley Hot Springs (169) and Nenana (380).

In the middle of the flats in March, there seemed to be no one except those traversing it along a blue/white line of trail. Besides that big-sky feeling a person gets while driving across South Dakota, another sensation came to mind when biking Minto Flats: They are nice and flat.

It also helped that the snowmachine trails were hard as pavement. And that the 50 miles from Minto to the town of Nenana features a 40-foot elevation drop. From there, it’s slightly uphill to Fairbanks upon trails pressed into the frozen Tanana River by a few hundred Iditarod dogs in early March.

In 100-plus miles from the village of Minto to my home (to which I pedaled), the total elevation gain was just 56 feet. Add to that the imperceptible boost of riding through the flats where gravity wasn’t giving its best shot, I had no excuses not to make it home.

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 ned.rozell@alaska.edu is a science writer for the Geophysical Institute.

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