How a set of rare inland tsunamis rocked Lake Roosevelt

Washingtonians breathed a sigh of relief when an 8.8-magnitude earthquake in Russia brought only small waves to the coast without triggering destructive tsunamis.

But what many might not know is that two tsunami waves already hit the state just last November — 300 miles inland.

When most people think of a tsunami, they picture giant ocean waves crashing into coastal cities. But more often than not, tsunamis in Washington are triggered by landslides, and most of them occur at Lake Roosevelt.

The giant Columbia River reservoir behind the Grand Coulee Dam covers almost 125 square miles, as it reaches nearly to the Canadian border. After construction of the dam was finished in 1941, the waters behind it became a national recreation area that attracts more than 1.5 million visitors a year.

On Nov. 17, at approximately 7:45 a.m. and again at 4:13 p.m., two large landslides occurred on Reed Terrace, a steep slope of pines, shrubs and grasses. The landslides hollowed out part of the riverbank measuring 850 feet wide and 180 feet high.

Miles Oliver, who lives near the site, was sitting on his porch late in the day when he heard and felt a deep rumbling from the ground.

“I thought in my head, ‘I don’t remember being able to hear the train from across the river,’ ” he said. “Then I automatically realized that doesn’t make any sense.”

Although posts on social media described a 30-foot wave hitting the shore, a recently published report by the Washington Department of Natural Resources estimates the waves were smaller, about 11 to 14 feet above lake level.

Using evidence left from the tsunami, like scars on nearby trees, flattened grass, displaced debris and unusual seismic disturbances recorded that day, DNR estimated the wave’s impacts reached as far as two to three miles from the slope.

“When we talk about tsunami hazards, this area in Eastern Washington is actually the most prone and has the most events,” said Alex Dolcimascolo, a tsunami hazards geologist with the Washington Geological Survey involved in the research.

Historically many landslides in the area were caused by the raising and lowering of the lake’s level from the dam.

Between 1894 and 1953, 19 slides were recorded near Reed Terrace, an area on the west bank of the river a few miles south of Kettle Falls, Stevens County, and the Highway 20 bridge over the river. One of the largest tsunamis was in April 1952, when a landslide produced a 65-foot-tall wave. It was the largest wave recorded anywhere on Lake Roosevelt.

Since strict limits on water-level drawdown began to be enforced in the late 1950s, the Reed Terrace area stopped causing major tsunamis. But the other areas kept sloughing into the lake.

In January 2009, a 17-acre landslide unleashed a 30-foot wave into Breezy Bay, damaging private docks and vessels for at least 1.5 miles downstream from the site.

Later that year, a large landslide near the Blue Creek drainage launched a wave approximately 12 feet high by the time it hit Porcupine Campground. No one was severely injured, although numerous people were swept into the water. The wave damaged log booms, docks, a swim platform and other park facilities, causing about $250,000 worth of damage.

Researchers haven’t determined the exact cause of last November’s landslides, but they don’t directly attribute it to the dam, as it was not being filled or drained at the time.

Instead, discoloration in the hill’s slope indicates wet soil may be the culprit.

“We think that there was some groundwater within the landslide itself that kind of caused a disturbance,” Dolcimascolo said.

The damage from November’s slides didn’t just impact Mother Nature — many private docks and shores were not spared from the wave’s reach.

A dock and several fish pens from Sherman Fish Hatchery were dislodged by the waves. The tsunamis also damaged the Ricky Point Sail Club’s dock and shoreline located directly across from the slide.

Eric Weatherman, a marine contractor for the U.S. Bureau of Reclamation who has a boat ramp about three miles upstream from the tsunami location, said the day after the tsunamis, he took his boat to Reed Terrace to survey the damage.

The lake was laden with the remnants of large trees, some 70 to 80 feet tall, lodged in the lake bed or floating atop the water. Chunks of dirt still trickled from the crumbling ledge. As he approached the shore south of the slide, he saw vegetation and other debris lodged between the standing trees about 100 yards from the water.

“Imagine how big a wave it took to do this, to rise 100 yards up into the woods up there, unearth the trees and the brush and the shrub and everything, and bring them all back down,” Weatherman said. “You could definitely see the water line 20 and 30 feet up in the existing trees that were able to withstand the pressure.”

Weatherman has lived his entire life working on Lake Roosevelt, previously residing on its shorelines about a mile and a half from the site.

He even has an old picture of his kids and grandkids smiling as they climb the site of the very slide that fell in November.

Today, looking at the photo turns his stomach.

“That was a real wake-up call,” he said. “I hope before anything happens, maybe we decide to make a priority of surveying those potential areas and spending the effort to identify them ahead of time.”

If the Reed Terrace landslide happened during a summer day with lots of visitors, the damage wouldn’t just be material.

When last year’s tsunami hit, the cold November conditions meant the closest recreational area, Colville Flats Beach, was empty save for a few fishers. But in the summer, the beach’s shores fill with visitors.

An unexpected massive wave carrying sludges of debris could be perilous for a crowd of beachgoers, even deadly.

“Luckily the people who were here were on a shoreline or on a boat, and they had enough warning that they could pay attention,” said Lake Roosevelt National Recreation Area spokesperson Denise Bausch. “If this had been as packed as it can be, then we might have actually had some injuries.”

Brandon Hatch is a Kettle Falls resident who frequently fishes in the reservoir. In his years on the water, he’s witnessed chunks of sediment fall from the slide area, even as soon as this past week.

“It was jaw-dropping,” he said. “There was a wave, but it looked like a bomb with the silt.”

He grew up by the ocean in Western Washington, so he’s familiar with the protocol for handling tsunamis. But he can’t say the same for other residents who’ve lived inland their entire lives.

“I guarantee you that there would have been a multitude of people that didn’t know how to handle the wave,” Hatch said. “They just wouldn’t have that knowledge. Why would they?”

“This is Mother Nature doing what Mother Nature does.”