The Risk Defined: How the tsunami warning system is working for Anchorage

New research released this week now shows the areas of Anchorage, Turnagain Arm, and Knik Arm that may need to evacuate during a tsunami alert
The Risk Defined: What to do when you get a tsunami warning — even in Anchorage
Published: Aug. 18, 2023 at 6:48 PM AKDT
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ANCHORAGE, Alaska (KTUU) - New research released this week now shows the areas of Anchorage, Turnagain Arm, and Knik Arm that may need to evacuate during a tsunami alert.

The National Tsunami Warning Center based in Palmer monitors earthquakes worldwide around the clock. Should there be an earthquake that has the potential to trigger a tsunami, an alert would be issued within minutes of the quake occurring.

How are tsunamis created

Destructive tsunami waves are born when the ocean is violently and suddenly moved.

In the case of a large mega-thrust earthquake, one tectonic plate is being forced under another, and when the land is lifted suddenly, a large earthquake will force the water to move in all directions, creating a series of waves. The waves extend from the bottom of the ocean floor to the surface and move in all directions — until the waves hit land.

“In just a matter of minutes, a destructive wave could reach coastal areas of Alaska and all the way down the U.S. West Coast,” National Tsunami Warning Coordinate Dave Snider said.

When the National Tsunami Warning Center will issue an alert

At the National Tsunami Warning Center, scientists check every quake. A computer sounds an alarm when a possible tsunami-creating event has taken place. Scientists are standing by, and move in and quickly to analyze each piece of data.

“What we want to do is find out, is this a big enough earthquake? Is a one that can move enough water? Is it in deep enough water? And then how much time do we have to tell people to get out of the way,” Snider said.

If the quake is in a place that will move the ocean — and big enough to create a tsunami — a warning or advisory is issued. But the initial details are still limited.

“From the time where the water changes above the earthquake, to the time that the water is reaching a dart buoy, or a coastal tide sensor could take 60 to 90 minutes. And that’s a long period not to know if there’s a damaging tsunami coming to your coastline,” Snider said.

Almost always, multiple updates will follow a tsunami alert because as more time goes on scientists get more details about the waves that have been created, allowing them to refine the forecast with more specific details.

But as new tsunami risk areas are defined like the Upper Cook Inlet, and new technology like cell phones are used, it’s possible to receive warnings not intended for your area. Snider said that is a work in process.

“It’s a tremendous amount of work to adapt something that is designed for the outer coast, and not for things like Cook Inlet, San Francisco Bay, Puget Sound, those are things that we don’t do well today. And we know that.” Snider said.

What to do if you get a tsunami alert

Snider said it is important to know your risk and plan — and practice — evacuation routes.

“If you get a notification on your phone that says, ‘tsunami warning,’ and you’re thinking, ‘Gosh, I’m not in a place that should be getting a tsunami,’ check. Confirm that that is a piece of information for you,” Snider said.

If you are on a coastline anywhere in Alaska, know where to go in case of a tsunami alert, Snider said. The general guidelines are to get 100 feet up and one mile inland from the shore.

Like any drill or alarm, it’s important to treat each alert like the real thing.

“We have to treat each one like it is the one until we know better,” Snider said.

What to do during a tsunami warning