Ancient Lake on the Eel River
Science magazines are abuzz with the news that there was a 30 mile lake on the upper reaches of the Eel River around 20,000 years ago. It was caused by an enormous landslide. The lake occurred East of Harris and is estimated to have lasted around 1,000 years.
According to the California Institute of Technology news release,
“Perhaps of most interest, the presence of this landslide dam also provides an explanation for the results of previous research on the genetics of steelhead trout in the Eel River,” says Mackey, referring to a 1999 study by the U.S. Forest Service. In that study, researchers found a striking relationship between two types of ocean-going steelhead in the river—a genetic similarity not seen among summer-run and winter-run steelhead in other nearby rivers.
An interbreeding of the two fish, in a process known as genetic introgression, may have occurred among the fish brought together while the river was dammed, Mackey says. “The dam likely would have been impassable to the fish migrating upstream, meaning both ecotypes would have been forced to spawn and inadvertently interbreed downstream of the dam,” he explains. “This period of gene flow between the two types of steelhead can explain the genetic similarity observed today.”
Once the dam burst, the fish would have reoccupied their preferred spawning grounds and resumed different genetic trajectories, he adds.
“The damming of the river was a dramatic, punctuated affair that greatly altered the landscape,” says coauthor Joshua J. Roering, an associate professor of geological sciences at the University of Oregon. “Although current physical evidence for the landslide dam and paleolake is subtle, its effects are recorded in the Pacific Ocean and persist in the genetic makeup of today’s Eel River steelhead. It’s rare for scientists to be able to connect the dots between such diverse and widely felt phenomena.”
The lake formed by the landslide, researchers theorize, covered about 12 square miles. After the dam was breached, the flow of water would have generated one of North America’s largest landslide-dam outburst floods.
Map indicates general area of Lake. The slide that blocked the Eel came from Neafus Peak.
UPDATE: and this.