Failure of Wash. volcano runoff could be catastrophic

Kyle Iboshi | KGW Staff

Show Caption Hide Caption Spirit Lake in danger of overflowing Spirit Lake in danger of overflowing

PORTLAND, Ore. — A tunnel dug to help drain a lake whose natural outlet was blocked when Mount St. Helens erupted in 1980 is narrowing. Experts say if it fails, Interstate 5 in Washington state could be inundated.

The Spirit Lake Tunnel was built after the 1980 Mount St. Helens eruption, when ash and debris blocked the lake's natural outlet into a local creek.

When lake levels began to rise, the U.S. Army Corps of Engineers bored a 1.6-mile tunnel through bedrock to provide Spirit Lake a new outlet.

The tunnel opened in 1985. Last fall and spring, inspections found that the tunnel floor was rising. Geologists say shifting rock formations under the surface are to blame.

"The bottom of the tunnel is actually pushing up into the tunnel and deforming the shape," said Chris Budai, project engineer for the U.S. Army Corps of Engineers.

In October 2013, the tunnel had an opening of eight feet, six inches. One year later, the tunnel was constricted to seven feet, one inch.

In April of 2015, the uplift reduced the opening to six feet, eight inches.

"That was a pretty gross and significant movement that I had not seen in the 30 years I've been inspecting the tunnel," Budai said.

If the tunnel were to collapse, the lake could fill up and overflow, causing a catastrophe.

In a recent report, the U.S. Army Corps wrote that "this worst case possibility would destroy all transportation routes" to the west of the lake, in southern Washington along the Cowlitz Valley, including Interstate-5 and the main North-South rail lines.

The tunnel still has a ways to go before it can no longer drain the lake, said Budai.

"I don't think that is imminent," he said. "We have time."

The Army Corp of Engineers, which inspects and maintains the tunnel for the U.S. Forest Service, is now working on designs to fix the problem.

It hopes to make emergency repairs to the tunnel by later this year. So far, there is no price tag on the fix.

Two Washington senators and a congresswoman have raised serious concerns about the problem.

"Complete failure of this tunnel in the shadow of Mount St. Helens could be catastrophic to Washington state on multiple levels," Sen. Patty Murray (D-WA), Sen. Maria Cantwell (D-WA) and Rep. Jaime Herrera Beutler (R-WA) wrote in a joint letter to the head of various federal agencies.