In the moments and initial hours following a Cascadia megathrust earthquake, it is important to know how to stay safe. The Center for Disease Control (CDC) has a good page on the subject. It covers topics like aftershocks, identifying injuries and building damage and checking on neighbors. But what happens when the dust settles?
Water and wastewater systems will be heavily impacted. For a time, faucets won’t flow, and pipes will run dry.
Hand washing, bathing, washing dishes and clothing, and obtaining fresh water for cooking, cleaning… and drinking will no longer be easy tasks. The I-5 corridor will go somewhere between one month and an entire year without water flowing from pipes. Those on the coast are expected to go between one and three years.
When the shaking stops, life in the impacted areas of the Pacific Northwest will feel as though it’s traveled back in time. Communities will be without working light switches, air conditioners, heaters, refrigerators, gas pumps, ATMs, stoves, and (gulp) electronics. Toilets won’t flush, many roads will be damaged, and bridges destroyed. Grocery store shelves will sit empty.
Even for those prepared to be self-sufficient for two weeks, the urge to evacuate the impacted area and head east to a place with running water, working electricity, and food on shelves will be undeniable. Before you decide that you’ll evacuate when the time comes, read about the potential obstacles to consider below.
Evacuating will most likely not be possible by car. Here is what the Cascadia Rising Exercise Scenario document states:
The Coast to the Valley
Most of the roads connecting coastal communities to the I-5 corridor may also suffer high damage due to extensive ground settlement. With few drivable routes from the coast to the I-5 corridor, coastal communities along U.S. 101 may be unable to self-evacuate.
The Valley to east of the Cascades
Roads connecting major urban areas in the I-5 corridor with infrastructure in eastern Oregon and eastern Washington may suffer little structural damage to the roads themselves. However, there are only a handful of eastbound routes that run through the steep, mountainous terrain of the Cascades, and many of these routes cross pre-existing landslides. The earthquake could trigger landslides that block or endanger these mountain passes.
The State of Oregon Cascadia subduction zone catastrophic earthquake and tsunami operations plan has a more critical view, stating that, “Landslides and earthquake damage will make all roads over the coast range and many in the I-5 corridor impassable.”
Traveling by bike or ATV will work for some, but most who head east will do so on foot. The chart listed here on the left shows the average time it would take for an average, healthy adult to make the journey by foot (with paths in good condition). These times are taken from Google Maps.
Children, individuals with physical and mental disabilities, those injured in the earthquake, the elderly, and anyone out of shape or ill may not be able to move at those speeds listed above. DOGAMI’s Beat the Wave images in the slideshow below provide average walking speeds for impaired vs unimpaired adults, children, and the elderly, as well as walking speeds based on terrain.
To be successful, travelers will need to somehow carry enough of the following supplies to make it to their destination.
Food
Water
Medical/First Aid
Sanitation
Sheltering
I don’t know about you, but walking over 100 miles isn’t something I do every week, especially up over a mountain with all the supplies listed above. If you plan to evacuate after the shaking stops, you and your loved ones might need to include a workout routine to train for “the main event”.
Cities east of the Cascades will have their own infrastructure issues to deal with, as the shaking is expected to break windows, knock items off shelves, and break pipes that may take weeks to fix. The cities will struggle to provide medical care, housing, food, sanitation, and other supplies to the influx of that many people.
Heading east through the Cascades is a problematic plan, considering that during four months (more or less) every year, they sit primed for the spread of wildfires. If you plan ahead to evacuate and then when the earthquake hits, the route is on fire, that’s a problem. In general, depending on evacuation as a plan means accepting a lot of additional risks and uncertainty. Visit Surviving Cascadia’s Summer Earthquakes and Volcanoes pages for more in-depth considerations.
There are dams throughout the state, which were built prior to knowledge of the CSZ—prior to understanding the hazards. Some of the dams are at risk of failure during shaking. Below are a few examples. I’ll gather more as I’m able to squeeze in research time.
Tillamook County
“Tillamook County has two (2) high-hazard dams, Barney Reservoir, located at the headwaters of the North Trask River, and the McGuire Dam, located at the headwaters of the Nestucca River… In the event of a Cascadia Subduction Earthquake, both dams have a very high probability of failure.” – Tillamook County Hazard Analysis
Coos County
“A recent seismic engineering investigation of the [Lower Pony Creek] Dam completed by a geotechnical consulting engineering firm identified a loose sand layer below the dam. It is likely this material may liquefy in a Cascadia Subduction Zone Earthquake. OWRD is currently doing an all-risks assessment to compare this dam to other HHPD-eligible dams in the state. Based on the preliminary investigation, there is a reasonable likelihood that the dam could fail in a Cascadia Earthquake… Under current conditions, failure appears to be likely in such an event and would result in catastrophic loss of life and also loss of all water supplies for 25,000 people.” – Coos County Multi-Jurisdictional Natural Hazards Mitigation Plan
Marion County
“Total failure of the Detroit Dam, with a full reservoir, would cause the smaller Big Cliff Dam to fail also and would inundate Gates, Mill City, Stayton, Aumsville, Turner, and Jefferson, as well as cause significant portions of Salem and Keizer to be flooded. Failure of the Detroit Dam is considered very low; however, if it were to fail, 65-70,000 people would be at risk, and damages could well exceed $500 million dollars… The County’s population has 326,110 residents covering 1,182.33 square miles.” – Marion County Emergency Operations Plan (EOP)
“In 2020, an updated seismic hazard analysis was completed for Detroit Dam to better understand the potential earthquake ground motions at the site. This hazard study has been used to analyze the performance of the spillway gates and found the risk to be higher than previously assessed. The performance of the spillway gates in an earthquake is a function of the potential ground motions due to an earthquake, the height of the gates above the dam foundation, and the water level acting on the gates at the time of an earthquake. Structural analysis of the spillway gates has shown there is a possibility for buckling of the spillway gate’s supporting arms resulting in an uncontrolled release of water from the dam.” – US Army Corps of Engineers: Detroit Dam IRRM Pool Restriction
Curry County
“The [Ferry Creek] dam is owned by the City of Brookings on the south coast. Based on a geotechnical investigation conducted as part of a feasibility study, the dam will experience severe deformation in a Cascadia subduction earthquake.” – Curry County Multi-Jurisdictional Natural Hazards Mitigation Plan
Since earthquakes don’t have a season, there is no way to know what the weather will be like when it happens. Evacuating in the winter will leave people exposed to dangerously low temps, wind, and snow. Red Cross has a good PDF and webpage on frostbite and hypothermia. Both would be good to read ahead of time if you are considering the evacuation plan. Summer heat requires additional breaks, water, and poses the additional risk of wildfires. Heat safety is another topic to research for the journey.
I don’t have any recommendations for this section, but rather just a thought to consider. If you are planning to walk 50 to 100 miles with supplies, maybe, pushing a cart of some kind, will others attempt to take the supplies from you? It will be hard to keep days worth of food and water hidden, and there will be some who are desperate.
Please take this information into consideration when you and your loved ones are creating your emergency plan. Eventually, helicopters, airplanes—and boats on the coast—will begin evacuating individuals out of the region, but that’s very unlikely to happen within the first 14 days following the earthquake and tsunami. If properly prepared, sheltering in place and waiting to be officially evacuated may be easier than going it alone. Both options, whatever you choose, will take planning.
Surviving Cascadia 