Submerging below a 60-toot tsunami
Along the southwest coast of Washington State, almost 60 miles directly west of Olympia, lies Damon Point and the coastal community of Ocean Shores. This town is not a coastal community perched on a cliff overlooking the Pacific. No, it’s a flattish sort of town with a nice beach sloping to the ocean and about 20 feet of elevation in the center of town. But elevation is not particularly important — until you need it. The day it will be needed is most likely when a magnitude nine earthquake occurs along the Cascadia Subduction Zone. New earthquake modeling predicts the town of Ocean Shores will submerge beneath a 60-foot tsunami surge when this unfortunate day arrives.
Events leading to this type of disaster may possibly be described in hindsight as follows:
When the Cascadia fault zone ruptured, it initiated a series of events at the sea bottom. A large segment of the seafloor, resting on the North American plate, thrust upward about twenty meters, elevating the water above it. As the surface of the ocean rose to twenty meters above normal, the land along the coast dropped by about two meters. This dual-action happened almost instantaneously, and the net effect was a massive energy imbalance, which started self-correcting the moment it formed. The mountain of water collapsed under the influence of gravity, and a tsunami was born. This tsunami moved outward in every direction from the subduction zone. Powerful waves were on their way to Hawaii, Japan, Alaska, and the Oregon-Washington coast. (Excerpt from – Cascadia Unfolding)
It’s okay; the warning system will save us
It’s not okay. Modeling by the Washington State Department of Natural Resources predicts about a 20-minute window between a rupture on the Cascadia fault zone and tsunami landfall at Damon Point.
The National Tsunami Warning Center, in Palmer, Alaska, serves the continental United States, Alaska, and Canada. Palmer is just northeast of Anchorage, and it is statistically part of the Anchorage metropolitan complex. Palmer is also about 1,000 miles northwest of the Washington Coast, where a Cascadia earthquake would occur.
Seismic waves don’t instantaneously arrive at the Palmer Warning Center. They must travel there through the earth’s crust — a journey taking over four minutes. Even after the first waves reach the warning center, it takes time to process the data, locate an epicenter, and issue a warning. The reality is, the first and last warning residents may receive is violent shaking from the initial seismic waves. The clock starts ticking when the seismic shock arrives— a count-down is in progress, leaving no time to dilly dally.
Move to high ground
Anyone living or visiting the Pacific Northwest coast is familiar with the ubiquitous tsunami warning signs. Warnings are continuously issued along the coastal roads, giving you alerts when entering or leaving a tsunami hazard zone. There are also signs pointing to designated evacuation zones. In the event of a Cascadia tsunami, the evacuation plan is there, but time is not.
Before the tsunami hits, seismic waves rippling across the earth’s surface will bring down houses, rip up roads, and shake apart bridges. The roadways may or may not be passable. If the roads are blocked or destroyed, this leaves escape by foot as the last option. Unfortunately, Ocean Shores is many miles from the nearest safe high ground, and time is not on the side of those dashing for safety.
City planners are aware of these dangers and as ironic as it seems, shelter in place may be the solution. If your city cannot retreat to high ground, you face two options: bring high-ground to the city, or accept the risk and enjoy each day like it may be your last.
Evacuation towers are one of the options under consideration by some municipalities. But they won’t come cheap. The minimum height is sixty feet, and the structure must first withstand a magnitude nine earthquake without damage before it serves as a tsunami evacuation shelter. Needless to say, it will not be a source of enduring beauty in a quaint coastal town — think eyesore. But these are the planning decisions coastal communities must face.
Ocean Shores is not alone. Many other small communities nestled along the Oregon-Washington coast face a similar dilemma. The Cascadia Subduction Zone lies a mere fifty miles off the coast. The physics of destruction from a major earthquake along the Cascadia Fault allows for precious little lead time between rupture and the ensuing chaos. This fact does not mean each individual shouldn’t prepare; it merely means it can happen without warning.
The last major earthquake on the Cascadia Fault occurred on January 26th, 1700, at about nine in the evening. A major tsunami from a Cascadia earthquake has a reasonable chance of happening between now and 2220. Thus the risk is low, but the impact is high. Risk exposure to this type of disaster is what Washington and Oregon residents trade in exchange for the opportunity to live and work in the wild and beautiful Pacific Northwest.
Tsunamis (Source: Washington State Department of Natural Resources)
An Earthquake-Generated Tsunami Could Quickly Inundate Parts of Washington State, New Simulation Shows (By Jan Wesner Childs; The Weather Channel)