According to National Parks Traveler, Tsunamis can happen as far inland as 200 miles on Lake Roosevelt. In 2009, Porcupine Bay, a bay just off of Lake Roosevelt, and the campground at Porcupine Bay was swamped with a tsunami within a matter of minutes. The 8 to 12-foot wave swept some campers out into the bay; however, no deaths or serious injuries were reported.
A landslide triggered the wave that damaged the shoreline and the campground. While earthquakes cause most tsunamis, as many as 15 percent may be triggered by landslides. Lake Roosevelt was created in 1941 when the dam was built, and the reservoir was filled behind Coulee Dam.
Porcupine Bay isn’t the first tsunami to hit the area, nor will it be the last. Looking at the region through Google Maps, you can see where many tsunamis have hit. So, what causes these tsunamis?
The Coulee Dam controls the water level. When the water levels change too quickly in a short amount of time, the soft soil deposits surrounding the lake become unstable. The changing water levels are often caused by the snow melt, which can vary widely from year to year.
The water seeps into the soil and creates gaps. These gaps can then trigger dangerous landslides when the water fills them in or is removed from them. According to their reports, Lake Roosevelt has had many landslides.
We don’t often think about tsunamis hitting inland and caused by landslides, however, more than earthquakes can trigger a landslide that can in turn trigger a tsunami. Combining all these variables, a tsunami can actually be triggered by a landslide at any time of the year.
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