New Tsunami Maps: Elfin Cove, Gustavus, and Hoonah
April 15, 2015

Ian Dickson

The Elfin Cove, Gustavus, and Hoonah maps are now available for download on the ADGGS website. The report is technical in places but still should make interesting reading for people who live or spend time in these communities or anywhere in Southeast Alaska.

Undersea landslides are one tsunami source we look at closely in this region. Sediments build up rapidly underwater in fjord environments. They can liquefy during earthquake shaking or, as in the case of a 1994 landslide-generated tsunami that claimed one life in Skagway, simply collapse under the additional pressure present during an extreme low tide. 

In July 2014, while we were preparing these maps, a magnitude six earthquake in Palma Bay triggered a landslide under Cross Sound that severed an ACS fiber optic cable and interrupted communications throughout Southeast Alaska. There was no tsunami, but the landslide highlighted the fact that even relatively modest earthquakes represent tsunami hazards for much of coastal Alaska.

We're grateful to ACS and their repair crew for sharing their data with us. Their information helped us to identify a likely source region for the landslide, though it would take a high resolution bathymetry survey to pinpoint the exact location.