The Big Lake

Flathead Lake often acts more like an ocean than a lake

By Kellyn Brown

A tsunami is possible on Flathead Lake. Tom Bansak, a research scientist at Flathead Lake Biological Station, said as much in a column published last year. The largest lake in the West is on a geological fault, which has resulted in periodical quakes.

Bansak pointed out that, technically, an event similar to a tsunami on a lake is called a seiche. The results, however, are similar.

“If there were major movement along the Mission Fault resulting in landslides or sudden lake bottom downdropping, waves of water would travel across the lake and then slosh back and forth,” Bansak wrote. “The size of the earthquake, downdropping or landslide would determine the size of the waves.”

Chances are, they would be large, because Flathead Lake often acts more like an ocean than a lake. It’s that big. And its vastness was apparent as I hopped on a friend’s boat earlier this month at Somers Bay.

What began as calm water quickly changed its mood. And as soon as we reached open water, the waves were splashing above the bow and soaking several members of our boating party who covered themselves in blankets. We headed to the aptly named Peaceful Bay and found some solace from the choppy waters and waited out the wind.

A friend of the captain wasn’t so lucky. He had chosen the wrong afternoon to try out his new sailboat. Soon we were heading back to Somers Bay and found him standing on the vessel paddling against the waves, his mast detached by the unrelenting wind. Despite his struggle, he had a smile on his face as we threw him a rope, saving him from a few hours of inching to shore.

After dropping the sailor off at his dock, we headed back out. This time, we went for it. The waves had appeared to die down a bit, and lunch on the opposite side of the lake was planned in advance. We pointed the boat east. The ride to Woods Bay was a little rough. Some passengers covered themselves in blankets again, but we made it to The Raven, hoping that after the lunch hour the waters would calm.

It’s not unusual for the lake to act this way, conditions changing drastically from one hour to the next. A few years ago, during the Spring Mack Days fishing tournament, five-foot swells forced all but one boat in the competition off the lake.

The lone holdout: “He’s someone who knows the lake,” Cindy Benson of the Confederated Salish and Kootenai Tribes told the Missoulian. “And he moved someplace so they were out of the worst of it.”

Biological station researchers have measured the lake’s complex currents. Flathead is so large that even the earth’s rotation influences how its water moves. Combine that with wind, stream inputs, water and air temperatures and lake conditions can change in a hurry.   

When we finished our lunch, the whitecaps had subsided, but smoke from the Copper King fire near Thompson Falls had blown in. We headed back west, as the sky darkened and visibility ebbed. When we reached the middle of the lake, neither other boats nor the shoreline was visible. Just calm water under a hot breeze.     

A passenger, looking out into the abyss, said, “It feels like we’re on the ocean.” She was right. The lake often acts like one.

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