Tsunami Preparedness Week: Are you in a tsunami zone?
In the event of a tsunami warning, you need to know if your location is in a tsunami zone. While the risk of a tsunami is very real for many Alaskans, it isn't necessarily a concern everywhere in the state.
The largest tsunami threat in Alaska are the coastal areas facing the Pacific Ocean. There are however other coastal areas of the state that could be impacted by a tsunami during specific events, including areas in Southeast and the Pribilof Islands.
A tsunami is defined as a series of extremely long waves, sometimes hundreds of miles apart, caused by a large and sudden displacement of the ocean. Tsunamis radiate out from the central point of origin and can travel across an entire ocean basin. As tsunamis reach the coast, they can cause an influx of water and strong currents that can last days.
Tsunami Preparedness Week: What is a Tsunami?
The most common cause of tsunamis are earthquakes. According to the National Weather Service, Alaska is the most seismic-prone region of the U.S., home to 10 of the 15 largest earthquakes in U.S. history. Lituya Bay in Southeast Alaska experienced the biggest tsunami in recorded history, 1,720 feet high at its peak, caused by a magnitude 7.8 earthquake-generated landslide in 1958.
The threat goes beyond record-setting singular events, Alaska's coastal communities live in the most serious tsunami threat in the United States according to the Alaska Department of Natural Resources. This is due to the area being along a subduction zone, where the Pacific Plate subducts under the North American Plate. Geologists say this occurs due to the constant movement of the Earth's crust, which forces one tectonic plate to go under the other, in a term known as subduction. This collision causes earthquakes which create a vertical displacement of water, creating tsunamis that pose a threat locally and across the Pacific Basin.
During the 1964 earthquake, the resulting tsunami proved to be the most deadly part of the event. Records provided by the Alaska Department of Natural Resources detail that of the 131 people who lost their lives, 122 of those were a result of the tsunami caused by the quake. As far away as Oregon and California the tsunami from the earthquake claimed lives, providing a sobering example of the impacts that can be felt hundreds and even thousands of miles from the initial earthquake.
The Pacific-facing Aleutian Islands and Pribilof Islands are at risk of both local and distant tsunamis. The area shaded in red in the map illustrates the areas at greatest risk of a tsunami impact. While the impacts can be felt from activity thousands of miles away, local seismic activity in the Aleutian islands can be caused by earthquakes, volcanoes and landslides.
Deep water and direct access to the open water give locations like Homer, Seward, and Kodiak a high risk for tsunamis. The Alaska Earthquake Center has been working to create tsunami inundation mapping interface for communities most at risk for a tsunami, click here to find yours.
Southeast Alaska is a tricky area. While a good portion of the region is surrounded by water, the threat mainly pertains to Pacific-facing communities. Communities such as Sitka or Yakutat face the danger of an ocean-crossing wave as well as a locally triggered tsunami. Areas farther from the Pacific face the danger from potential local tsunamis from geologic events like landslides.
The Cook Inlet region, including Anchorage, is an interesting study on potential tsunami danger. While the threat of earthquakes is very real in Anchorage, the threat of a tsunami is not. The water of the inlet is just too shallow and the inlet offers the right amount of protection to keep Anchorage safe from a potential tsunami. It would take a major volcanic eruption or major landslide in the right area to generate any significant waves, and even that is extremely unlikely.
For a list of areas at risk for local and distant tsunamis in Alaska, click here for more information provided by the Department of Homeland Security & Emergency Management. You can also find out about the risk for other areas in the U.S. here.
If you find yourself in a tsunami zone, always have a plan in place and know what to do when the alarms sound. If you're unsure and near the coast and you feel the ground shaking to the point that you can stand up, head inland or to higher ground.
Copyright 2019 KTVA. All rights reserved.