Many Juneau residents were relieved to learn that offshore tsunamis, like the one anticipated Tuesday morning in the Gulf of Alaska, pose little threat to communities not situated on the coast.
But a different type of tsunami, one generated by a nearby earthquake or landslide, for example, could quickly pose a problem.
The biggest threats to Juneau will come with no warning, according to Tom Mattice, Juneau’s emergency programs manager.
“We recognize here in the city that our greatest threat is from a localized tsunami. That’s going to be a no-notification event,” Mattice said. “That would be a landslide, whether submarine or above ground into a nearby body of water creating an event that’s not going to go past buoys and it’s not going to be an hour from now, it’s going to be minutes or seconds.”
Juneau does not have a tsunami warning system, like in Sitka and Kodiak where sirens blared Tuesday.
Juneau has never qualified for federal funding for those systems because our offshore tsunami threat is low.
“If an earthquake is big enough to knock you down, then you should consider going to higher ground,” Mattice said, back in October. “If an earthquake is longer than 20 seconds or more, it’s estimated to be greater than a 6.0, and if you live in an area that you feel is compromised, you should seek higher ground.”
In October, the city released a report modeling worst-case scenarios for tsunami events in Juneau. Mattice said Juneau residents — especially those who live near the water — should be familiar with two maps on the city website, which show the probable impact of inshore tsunami waves.
One map predicts the highest potential flooding after an offshore tsunami caused by an earthquake.
The other does the same, but for waves from an inshore tsunami caused by submarine landslide or a seiche, or when water in an enclosed area sloshes back-and-forth as if it were being carried in a bucket of water.
The offshore tsunami map shows up to 16 feet of flooding around much of Gastineau Channel. The inshore tsunami map predicts up to 50 feet of flooding along the channel.
“The most important thing for people to recognize in Juneau is, you need to look at the maps, you need to know where the affected areas are and if you feel an earthquake, you need to take it upon yourself to evacuate,” he said.
While Juneau hasn’t experienced any tsunamis in recent memory, areas nearby have.
Lituya Bay is known for being a tsunami prone area.
In 1958, an earthquake triggered a landslide that forced a huge wave out the mouth of the bay, sinking two fishing boats.
Skagway experienced a landslide-generated tsunami in 1994 that killed one person and caused more than $25 million in damage.
View the city’s tsunami inundation maps:
