Published Aug 17, 2023 by Yereth Rosen

There is a persistent belief that Anchorage, snug at the head of narrow Cook Inlet, is too far away from the open ocean to be at risk from tsunamis.

That is false, according to a newly released hazard-mapping report from the University of Alaska Fairbanks’ Alaska Earthquake Center and the state Division of Geological and Geophysical Surveys. The report provides the first-ever tsunami innundation analysis for Alaska’s largest city and the upper part of the inlet, a region where such hazards were previously overlooked.

“There is a rare but real tsunami threat to that area, and we describe why it is possible and all the hypothetical tsunami scenarios are outlined in our report,” said lead author Elena Suleimani, a tsunami modeler with the Alaska Earthquake Center, which is part of UAF’s Geophysical Institute.

The report, the product of years of study and modeling work, shows how a particular combination of high tides and earthquake conditions could send walls of water into certain low-lying areas in and around Alaska’s largest city.

If a 1964-style earthquake ripped through the Gulf of Alaska off the Kenai Peninsula precisely when an extreme high tide was building in Cook Inlet, a tsunami could arrive four to five hours later, inundating low-lying areas from part of downtown Anchorage to sections of the Matanuska-Susitna Borough to communities along Turnagain Arm, the new study found.

Worst-case scenarios for Anchorage and Upper Cook Inlet, according to the new study, include flooding coastal Anchorage areas like Westchester Lagoon on the edge of the downtown area and along Knik Arm up to the mouths of the Matanuska and Susitna rivers, which lie past existing highway bridges. These scenarios also include up to 72 hours of dangerous waves and currents. Hotspots for flooding hazards include the vitally important Port of Alaska, the Campbell Lake area in South Anchorage and the sections of Girdwood and Hope that are closest to Turnagain Arm.

While the magnitude 9.2 quake that struck Alaska in 1964 was the second-most powerful on record in North America, analysis of seismic data collected over the past two decades shows that Southcentral Alaska has experienced even more powerful quakes in the last 1,500 years, according to the study.

Published Aug 17, 2023

The Earth’s surface north of the Arctic Circle, which includes nearly a third of Alaska, is warming 3-4 times faster than the global average. Alaska as a whole is warming twice as fast as the lower 48 states. As is true for most of the manifestations of anthropogenic climate change, moreover, the extremes of temperature are growing faster than the averages: the highest-ever temperature north of the Arctic Circle—100.4°F—was recorded in Verkhoyansk, Siberia, in June 2020; Anchorage reached an all-time high of 90°F on July 4, 2019; and Utqiavgik, Alaska, the northernmost U.S. city, reached an all-time winter high of 40°F in December 2022.

The reasons warming is so fast in the Far North are quite well understood scientifically. The most important factor is the ice-snow-albedo feedback, in which warming reduces the area of land and water covered by ice and snow, which means less reflectivity and more absorption of incident solar energy at the surface, hence further warming.