Tsunami Risk in Turnagain Arm
Girdwood sits near the head of Turnagain Arm, a narrow, shallow waterway where tides are already among the most extreme in North America. That same geography means a tsunami here is unlikely, but not impossible. Scientists distinguish between two very different kinds of risk: a major subduction-zone earthquake, which is statistically rare, and a landslide-triggered wave, which is a more immediate and ongoing concern due to unstable slopes nearby. Understanding both helps our community stay prepared without being alarmed.
What Could Cause a Tsunami in Turnagain Arm?
There are two distinct ways a tsunami could reach Turnagain Arm:
- A major earthquake. Alaska sits on one of the most active subduction zones in the world. A large earthquake similar to the 1964 Good Friday Earthquake could generate a tsunami that reaches Upper Cook Inlet, including Turnagain Arm, several hours after the shaking stops.
- A local landslide. Several slopes around Prince William Sound and the Chugach region are known to be geologically unstable, including the slope above Portage Lake. A sudden slope failure could generate a large, fast-moving wave with very little warning – in some cases, just minutes. This is considered the more immediate hazard for our area.
What a Tsunami Could Mean for Girdwood
Modeling from the Alaska Earthquake Center and the State of Alaska’s Division of Geological & Geophysical Surveys shows two main ways Girdwood could be affected:
- Flooding in low-lying areas. A significant wave would push water up the Arm, with the greatest impact on the lower, flatter sections of the community closest to the water. View the AEC Inundation Map for Turnagain Arm.
- Disruption to the Seward Highway. Because the highway closely follows the low-lying edge of Turnagain Arm, sections could be inundated during a worst-case event. This could temporarily cut off road access to and from Girdwood, and if the highway sustains significant damage, it may take time before all sections reopen.
Tsunami Warnings and Evacuations
A tsunami threatening Turnagain Arm doesn’t always start with shaking you’d notice. Because a damaging wave can be triggered by an earthquake far from Girdwood, you may not feel anything before an official alert is issued. Warnings are sent through wireless emergency alerts to cell phones, NOAA Weather Radio, local radio and TV, and in some areas, outdoor sirens. If you receive a tsunami warning through any of these channels, move to higher ground immediately. For an explanation of the different tsunami alert levels and what each one means for you, see the National Weather Service’s Tsunami Alerts Guide.
Local and state emergency management agencies have mapped evacuation routes and safe zones specifically for Girdwood. For full details, download the Official Tsunami Evacuation Brochure for the Girdwood/Anchorage area, produced by the Alaska Earthquake Center. It includes a safety map with Girdwood’s evacuation line, local emergency contacts, and guidance on what to do before, during, and after an event.
Community Resilience and Preparedness
A tsunami event could leave Girdwood temporarily cut off – by road, by power, or both – just as past events like the 1990s avalanche closures and the 2018 earthquake rockslides have done. Being self-sufficient for at least a week is the best protection while routes are checked and repaired.
- Store seven days of food and water for every person and pet in the household. The CDC recommends one gallon of drinking water per person, per day, plus one ounce per pound of body weight per day for pets.
- Plan for cooking without power. Have a BBQ or camp stove with extra fuel canisters on hand, and know which freezer items you’d use first if the power is out for several days.
- Test your emergency food in advance so you know it’s something your household will actually eat during a stressful event.
- Have reliable emergency lighting, such as rechargeable or solar lights, and a headlamp with fresh batteries for every household member. Keep them somewhere accessible, like by the bed or front door.
- Keep a spare headlamp in your vehicle, in case a tsunami warning happens while you’re on the road or away from home.