Signs of a hidden threat: preparing for the really big one - Salish Current
September 6, 2023
Signs of a hidden threat: preparing for the really big one
Adam M. Sowards

In the event of a major earthquake along the Cascadia subduction zone, a tsunami’s multiple waves would inundate many shoreline areas, including most of the land visible looking south from Samish Overlook in the Blanchard State Forest. (Adam M. Sowards / Salish Current photo © 2023)

September 6, 2023
Signs of a hidden threat: preparing for the really big one
Adam M. Sowards

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Travelers moving south on Chuckanut Drive began noticing a new sign earlier this summer. With a bright orange background, a blue wave and a warning — Entering Tsunami Hazard Zone — it is hard to miss among the green trees.

It grabs attention just before motorists and cyclists cross the bridge over Colony Creek that takes them out of the mountains and onto the floodplain. Similar signs have appeared in other designated tsunami zones, too.

These signs are relatively new additions from the Washington Emergency Management Division’s Tsunami Program, joining other signs that direct people to evacuate or head inland or to higher ground in case of a tsunami. County emergency managers worked with state officials to bring the new signs to more places along the state’s coastlines. 

The signs enhance messaging and bring “a greater awareness of the location of the inundation zone to the general public,” according to Elyssa Tappero, tsunami program manager for the Washington Emergency Management Division. Skagit County has been placing them along state highways as part of a multiphase program to prepare the public in case of this kind of emergency.

“Those signs freaked me out,” said Summer Ray, who lives and works in Bow. “When did they decide to hang those up? … Why now of all times?” Without any further explanation offered, the signs made her uneasy.

Tsunamis should create some unease; they are serious, and people often misunderstand tsunami risks. The tsunami to prepare for is not a 100-foot wave that will crash over Chuckanut Manor (elevation 39 feet). The Strait of Juan de Fuca reduces the energy of waves.

New signs along local roads alert travelers to the possibility of tsunami. (Adam M. Sowards / Salish Current photo © 2023)

“But they’re very fast-moving waves with strong, strong currents. Very forceful,” said Corina Allen, chief hazards geologist for the Washington Geological Survey in the Department of Natural Resources (DNR). “They’re not a cresting wave like you imagine … they’re sort of like a wall of water, much like flooding. They’re filled with debris. They’re brown. They’re dirty. They’re roaring. And they are very destructive.”

Pay attention

Understanding this and what to do about it requires information and attention. The signs are a start. 

Most adults living here have experienced an earthquake. But no one in Northwest Washington remembers a tsunami from their lifetime. Yet they have hit before and will again. 

Indigenous stories recount earthquakes and floods that are pegged to 1700 and some even older. Deposits in Seattle indicate a major tsunami hit the region about 1,000 years ago. When, where and how dangerous the next one will be cannot be pinpointed. But it is all but assured. 

The Northwest faces tsunami risks from three types of earthquakes.

deep earthquake does not produce a tsunami on its own but might generate landslides and lead secondarily to a tsunami. This happened in Tacoma in 1949, for instance, flooding homes and damaging bridges.

In a crustal fault earthquake, surfaces rupture and disrupt water bodies, creating a localized tsunami. These faults crisscross Puget Sound. 

The third type is, according to Allen, “the really big one.”

Off the Pacific Coast from northern California to British Columbia is the Cascadia subduction zone, a fault between continental and oceanic plates. The ocean plates are denser and move beneath the continental plates, building friction. When that friction gets too much, an earthquake will release the stress. Subduction zone earthquakes can exceed a magnitude nine (M9). This would produce a tsunami that could devastate coastal communities. 

The big earthquake used to model these future scenarios would last three to six minutes. “That earthquake that we’re going to feel is going to be the largest, most notable, dramatic thing that most of us have ever had happen in our lives,” said Brendan Cowan, San Juan County’s director of emergency management. “So there’s no missing it.”

It’s local

According to estimates, the first wave would arrive at Bellingham a little over two hours after the earthquake begins. Waves and stronger currents might last longer than 14 hours. It is common that the first wave is not the largest, and the receding waves cause damage also.

Dramatic video simulations by the DNR for Bellingham Bay and the San Juan Islands show how those areas might be inundated by tsunami after a hypothetical 9.0 magnitude earthquake on the Cascade subduction zone.

Tsunamis, like most natural hazards, depend on local conditions, and preparation requires clear messaging. Southwest Washington would be the first to be hit by a tsunami generated by the Cascadia earthquake, so the state focused on developing plans and posting signs there first. Emergency managers have been increasing attention elsewhere, including inland shores like those in Northwest Washington.

The statewide tsunami siren network was completed in 2021. The first All-Hazard Alert Broadcast (AHAB) siren in Whatcom County was installed at Sandy Point in 2006; Skagit County started putting up its sirens about six years ago. They are not suitable for every place, so San Juan County does not use AHABs.

Maps produced by several state agencies in 2022 estimate the walking distance time needed to escape the tsunami zone. The darkest areas indicate an hour or more; the lightest, 10 minutes.

Signs help, too — and because they do not rely on a power source may withstand earthquake damage better than AHABs. The signs pointing to evacuation routes started showing up around 2016. The bright new signs announcing tsunami zone boundaries are even more recent.

Adding signs is part of a phased program in Skagit County, according to Hans Kahl, the county’s emergency management coordinator. It coincides with grant funding to help with costs to post them. More signs are coming along with a public educational campaign next year.

All of these measures are designed to raise awareness and guide people in case of tsunamis. The state, working with national and local leaders, aims to keep messaging as uniform as possible.

Local conditions create differences, though.

“In our community,” said Cowan of San Juan County, “our warning system is that you just felt a very large earthquake.” 

To prepare residents and visitors in San Juan County, brown signs direct people to head to higher ground. They also include a QR code to provide more focused messages about local conditions and resources, including maps of places likely to be at risk. According to Cowan, this provides a more localized message. 

“We have a lot of higher bank waterfront that’s not super-vulnerable to tsunami,” explained Cowan. The wave might be 15 to 20 feet high, which will certainly damage property, but the news is good for people. “Here in the islands, getting 20 feet or … 30 feet above sea level is not usually very far away.” Cowan thinks that means the county should be able to make sure nobody dies.

On the flats

The situation is different along the shorelines of Samish, Padilla and Fidalgo bays. There, flatness contrasts with the San Juans’ high banks.

This geography is obvious to anyone standing on a dike looking miles inland with no real obstruction but an occasional farmhouse and barn. 

The precariousness is illustrated even more clearly in maps produced by several state agencies in 2022 that estimate the walking distance time needed to escape the tsunami zone. They use walking time because the large earthquake that would produce the tsunami would likely damage roads or bridges. Walking may be the only way out.

Edison, for example, sits in the heart of the tsunami zone. The model used to make the walking-distance map predicted an hour-long walk to get to safety. Few places along Northwest Washington’s coast are so vulnerable or so distant from safe ground.

At Terramar Brewing and Distilling (elevation 7 feet), about 50 feet from Edison Slough and 2,500 feet from Samish Bay and in the heart of the 60-minute zone, Kat Zuanich is not too concerned. 

“I’m not afraid of a tsunami here, because I don’t think we’d take most of the impact,” said Zuanich.

She once owned a home in Bow, and now just works there. Recently, the flooding has gotten worse; that is what draws her attention. “I don’t think tsunamis are the biggest threat to Skagit Valley,” she said. “I think there’s a whole lot more.”

A dike along Samish Bay just west of Edison shows how little stands in the way of a tsunami. (Adam M. Sowards / Salish Current photo © 2023)

The flooding concern is common in the Samish River delta. 

Flooding worries

“Mostly, you just worry about the Samish River if anything. If you’re worrying about water, you’re worrying about flooding,” said Ray, one of Zuanich’s coworkers.

Brian Rusk, one of the co-owners of Bow Sanctuary (elevation 8 feet) located just inside the tsunami zone in Blanchard, agreed.

“Considering all the different sort of natural hazards we have in this area, tsunami is definitely one of them, but flooding is a much more real hazard that we worry about,” said Rusk.

The business’s buildings and gardens are about 500 feet from Colony Creek and less than 1,000 feet from Samish Bay. Floods have come in each of the last two years.

People know that floods are more common, but the geological models show that tsunamis will produce “significant inundation” around Puget Sound, especially in low-lying river valleys, said Allen. This modeling is relatively new and too few people know about it. “It takes a long time and a lot of effort from state and local emergency managers and educators” to inform the public, said Allen.

Floods occur often in a human lifetime; tsunamis like those expected by a Cascadia earthquake do not. “They happen every few hundred years to thousands of years depending on what the source is for the tsunami,” said Allen. This makes tsunamis “kind of this hidden threat that many people don’t think about, especially within the Puget Sound.”

Tsunami dreams

Still, the signs might be making a difference. 

Donna King lives just above the tsunami zone boundary near the Chuckanut sign. She rarely thought of the tsunami risk, she said, “until they put those big scary signs up.” Once a month, she might hear the tsunami test siren that blares just across the road from Bow Sanctuary where she works as administrative staff.

That regular sound was noticeable, but now tsunamis have even entered her subconscious. King recently dreamed about directing people to safety during a tsunami. “I was telling everybody, ‘Don’t go that way because the bridge will be out’,” she said. “So my anxiety is, you know, how would I get home?” 

The best plan of action in the event of a tsunami? Higher ground! (Courtesy image)

The signs prompt diverent reactions, even in the same person. On the one hand, they increase anxiety about the possibility of a disaster. On the other hand, they suggest preparedness. “I think they’re ready,” said King. “We’re going to get it one of these days.” The sign increased her awareness and helped her devise a plan that she did not have before. 

The signs and attention are meant to prepare people, especially visitors, for the certainty of a tsunami, if not the precise timing and magnitude of it.

But at times, fatalism settles in. Rusk said, “If the tsunami comes, then maybe it was sort of meant to be.”

Still, making a plan is smart. Ray has an informal one. She lives at one end of Bow Hill Road near the tsunami zone boundary; at the other end, up the hill, is the Skagit Casino Resort (elevation 262 feet). 

“I’m going to go up and get myself a cocktail and play slots,” she said with laugh. “You know, smoke ’em while you got ’em. “

The message from the state’s hazards geologist is also poetic but more serious: “If it’s long, if it’s strong, be gone,” said Allen. “Meaning, if it’s a long duration earthquake, if it’s very strong shaking, that’s your sign that you need to be gone.”

In many places that will mean scrambling up to higher ground. But in flat areas, it means going inland, sometimes quite a distance. In the Samish River Delta, the Leaving Tsunami Hazard Zone sign — in white and blue instead of the bright orange — is three to four miles from the shore. Its placement, amid fields far from saltwater, signals the potential scale of danger and serves as its own warning — if only we take it seriously.

— Reported by Adam M. Sowards

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