What if a tsunami struck Hood Canal?

Last month's tsunami warning for the Northern California and Southern Oregon coasts, issued after a 7.0 earthquake struck west of Ferndale, California, saw panicked motorists lining the Pacific Coast Highway before the National Oceanic and Atmospheric Administration canceled the alarm.

The devastating effects of a tsunami are easy to imagine on coastal communities, but what about Hood Canal?

While Mason County doesn't have oceanfront land, our local fjord could face catastrophic flooding from a tsunami, according to the state Department of Natural Resources models.

DNR's tsunami hazard maps show two scenarios for the Hood Canal: one for the Cascadia subduction zone, looking at a 9.0 "megathrust" and another for a large Seattle event in the 7.3 to 7.5 range for the Seattle fault.

In both models, Belfair, sitting at the end of the canal, sees high water – as much as 13 feet at Theler wetlands and 6 feet at Belfair State Park in the Cascadia scenario, according to the model.

Daniel Eungard, a tsunami geologist and the tsunami program lead at the Washington Geological Survey, told the Journal the Seattle fault model is a recreation of an event that happened in 923 A.D. It's called a "maximum considered event," he said.

"You can build a scenario by looking at geological data and pick something truly extraordinary, but if that thing only happens once every 10,000 years, you kind of start to stretch the boundaries ... Do we need to plan for that?" he said.

If an earthquake similar to the Dec. 5 California temblor that triggered the tsunami warning happened off the Washington coast, there might be minimal impacts for Hood Canal, Eungard said.

"Some impacts to the outer coast of Washington, particularly Westport and Long Beach ... Very minimal impacts to the Puget Sound area and Hood Canal," he said.

"In terms of damaging inundation, I wouldn't anticipate that we would see a lot."

While water covering the Belfair Safeway might be far-fetched, a tsunami in Hood Canal would definitely affect mariners and anyone recreating close to shore, he said.

"Even if it's not a huge, super damaging event that just washes over the landscape, if you're at the beach and the wave comes up and drags you ... It only takes 6 inches of moving water to knock an adult off their feet," he said.

The geography of the canal also makes tsunami waves action last longer.

Tsunamis aren't just a singular wave; they are a series.

Once you get into the inner waterways, like Hood Canal, the waves are complex, Eungard said.

Waves can amplify each other.

They start pushing water into an area and it can't get out before the next wave comes in, he said.

"It causes a pile-up effect."

A tsunami simulation video on the DNR website shows the waves triggered in the Cascadia 9.0 event lasting for hours.

"When it hits Lynch Cove at the end of Hood Canal, because it's got nowhere else to go, that's where a lot of the energy is pushed into Belfair," Eungard said.

The second and third waves start stacking onto the previous wave for up to 12 hours, he said, until the wave action starts to settle down and allow the Hood Canal to naturally drain.

In the simulation, flood waters generally stay off U.S. Highway 101 except at Duckabush.

Bob Burbridge, with the county Department of Emergency Management, provided the Journal with a final draft of Mason County's All-Hazards Evacuation Plan, including tsunamis.

The Mason County Sheriff's Office and Shelton Police Department will be the primary agencies to lead a tsunami evacuation, according to the document.

"This plan is for unincorporated Mason County and the City of Shelton. However, mass evacuations will require multi-jurisdictional coordination. Whether directing traffic around the site of an accident or evacuating a geographic area, the principles remain the same: assess risk factors, plan an appropriate response, inform the public, and then implement the plan," the document states.

Burbridge said even with the DNR's Cascadia model, "It would appear that by the time the wave gets to the Union and Belfair area, it would be similar to a high tide and king tide."

He said he hopes to be hiking in the mountains when the big earthquake comes.