What some media reports have referred to as an "inland tsunami" occurred on January 16, 2009, at Lake Roosevelt National Recreation Area in eastern Washington State—and this impressive wave was not the first of its kind at the lake.
While the term "tsunami" may technically be a misnomer for this event, the results were very similar. According to a report by Adam Kelsey, Acting Chief Ranger at the park, homeowners in the Mill Canyon area contacted the park and reported that their docks had been destroyed by a large wave.
Responding rangers found that a section of hillside approximately 17 acres in size across from Breezy Bay had broken free. The subsequent landslide had fallen into the water, creating a wave that was about 30 feet high when it hit the shore about a thousand yards across the lake. A park press release provides some details:
The wave damaged or destroyed several private docks located at Breezy Bay, Moccasin Bay, Sunset Point and Arrowhead Point. Several vessels moored in the area were also swamped and left beached on land. The water reached one residence before receding and came just to the foundations of several others.
The full extent of the damage caused by the landslide is not yet known, but damage to property has been documented as far as a mile and a half downstream, and significant resource damage and erosion to the shoreline occurred as far as three miles downstream.
The park has issued a general safety warning due to the debris in the water, which is making navigation difficult. Boaters in the area have been advised to use extreme caution when boating from Cayuse Cove to Breezy Bay on the Spokane River. Along with ice deposits in the lake, there are now large trees, dock parts, and sediment deposits in yet unknown locations that have made safe navigation difficult. Due to uncertainty about conditions near the slide, people are also being advised to avoid approaching the site by land, since the ground will be quite unstable for some time and sinkholes and falling debris may occur.
You may be wondering why homeowners were calling national park rangers about damage to private docks. Isn't this a National Recreation Area?
In this case, the answer may be that the NPS was simply the easiest agency to contact, even if the problem was technically outside its purview. A little background on the area will help you put this situation in perspective.
In 1941, Grand Coulee Dam was built on the Columbia River as part of the Columbia River Basin project, creating a 130-mile long lake named for President Franklin D. Roosevelt. The lake level is controlled by the Bureau of Reclamation; the recreation area on and around the lake was originally called Coulee Dam Recreation Area, and was renamed Lake Roosevelt National Recreation Area in 1997. It's managed under a cooperative agreement described in a park publication:
Lake Roosevelt's shoreline totals more than five hundred miles of cliffs and gentle slopes. Today, the Park Service manages 61 percent of the narrow strip of federal land along the shoreline of Lake Roosevelt and 58 percent of the total water surface area. The Colville Confederated Tribes and the Spokane Tribe of Indians manage most of the remainder of the land and water. Reclamation retains management of the dam, its immediate area, and a few other locations considered necessary for reservoir operations. Management of the reservoir and its resources is complicated by the fact that nine federal agencies, two tribes, four state agencies, six counties, and four cities have interests in various aspects of this essentially linear resource
And you thought your job was complicated!
Landslides are not respecters of bureaucracy, and waves caused by those events have occurred in the past at Lake Roosevelt. Some of them were very impressive indeed.
The Washington State Enhanced Hazard Mitigation Plan includes a section on Tsunamis, which notes:
Landslides into Lake Roosevelt in eastern Washington generated numerous tsunamis from 1944 to 1953 after Grand Coulee Dam created the lake on the Columbia River. Most tsunamis generated large waves (30 to 60 feet in height) that struck the opposite shore of the lake, with some waves observed miles from the source.
Stevens County, Washington, has its own "Multi-Hazard Mitigation Plan" which also lists some dramatic landslides in years past:
April 1944 - A four-to-five million cubic yard landslide from Reed Terrace generated a 30-foot wave, 5,000 feet away on the opposite shore of the lake about 98 miles above Grand Coulee Dam.
April 1952 – A 15 million-cubic-yard landslide three miles below the Kettle Falls Bridge created a 65-foot wave that struck the opposite shore of the lake. People observed some waves six miles up the lake.
February 1953 – A series of landslides about 100 miles upstream from Grand Coulee Dam generated a number of waves that crossed the lake and hit the opposite shore 16 feet above lake level. On average, observed waves crossed the 5,000-foot-wide lake in about 90 seconds.
April-August 1953 – Landslides originating in Reed Terrace caused waves in the lake at least 11 different times. The largest wave to hit the opposite shore was 65 feet high and observed six miles away. Velocity of one of the series of waves was about 45 miles per hour.
A U. S. Geological Survey report provides a little further insight into these events:
... the shores of Roosevelt Lake have been subject to several hundred landslides since the reservoir began to be filled during construction of Grand Coulee Dam during the 1930’s and early 1940’s. The greatest percentage of landslide activity occurred during initial filling of the reservoir, but many slope failures also have been caused by intermittent drawdown of the reservoir level. In addition, occasional slope failures have occurred as natural phenomena, related more to wet winters than to fluctuation of the reservoir.
A park representative I spoke with speculated that recent wet snow may indeed have been a factor in the most recent incident.
It's been over half a century since a really major landslide at Lake Roosevelt, but I'm not sure I'd want any waterfront property in this area. This is probably one spot where the cry "surf's up" would not be considered good news!