By Ruby Pap
I’ll be honest with you; up until 10 years ago I didn’t know hardly anything about tsunamis. “Tidal waves,” as I called them, were mostly the stuff of storybooks and legends. I didn’t grow up along the coast, and was formally educated in the mountains of Colorado and the lakes of Michigan. Pearl Buck’s The Big Wave had an imprint in my mind, but my frame of reference really didn’t leave those pages.
Everything changed on Christmas day in 2004, when a magnitude 9.1 earthquake struck off the coast of Sumatra and caused the most destructive tsunami in history for that time, claiming an estimated 230,000 lives. Just a couple years into my fledgling career as a coastal planner in California, suddenly the conversation was all about tsunami science and planning. I began to learn a few things.
Now, just into my fourth year on Kaua‘i, and at the four-year anniversary of the devastating Tohuku tsunami in Japan, I have the opportunity to impart some of that knowledge on to you.
First things first, tsunamis are not tidal waves. They are multiple gigantic waves caused by underwater disturbances, including earthquakes, volcanic eruptions, landslides or even meteorites. Tsunamis can travel at speeds of hundreds of miles per hour and when they hit land, they can have waves as high as 100 feet or more. Tsunamis in Hawai‘i can be generated locally near the more seismically active Big Island or thousands of miles away in the Pacific Rim.
The recorded history of Hawaiian tsunamis shows that 26 large tsunamis have made landfall within the islands and eight have had significant damaging effects on Kaua‘i. Of note is the 1946 and 1957 Aleutian Island tsunamis where maximum runup recorded was 46 feet in Ha‘ena.
Geologic evidence recently discovered in the Makauwahi sink hole in Maha‘ulepu points to a super tsunami that hit Hawai‘i roughly 500 years ago from the Aleutian Islands.
Interestingly, in the less active period since 1964, tremendous coastal development has occurred on Kaua‘i, raising the risk of damage from future tsunamis.
Early warning and evacuation are key to staying safe. Tsunami warnings come from the Pacific Tsunami Warning Center. Sirens will go off and we may receive warnings by phone. The first step is to tune into local media to receive instructions. Never approach the ocean if you see it receding and suddenly exposing the ocean floor or fish.
In the case of a locally generated tsunami near the Big Island, we will only have 45 minutes notice so it is very important to move to higher ground immediately once notification is made. Tsunamis generated from elsewhere are detected with more advance warning — a few hours.
Last year, the Kaua‘i Civil Defense Agency completed a new set of tsunami evacuation maps, which are based on the latest scientific modeling by UH utilizing bathymetric or ocean floor mapping. Evacuation maps can be found at www.kauai.gov/civildefense and they are also published in the latest editions of the phone book.
Also, Kaua‘i Civil Defense recently deployed tsunami evacuation route signs along the roadways. Most important is to be aware, get to know the evacuation zones and have an emergency evacuation kit ready. Many of us have already been through an evacuation and know that it might be a while before we are cleared to go home. While it may seem like a pain to evacuate when no impacts actually occur, take comfort in knowing these systems are in place and we are as prepared as we can be when a damaging tsunami does strike.
- Ruby Pap is a Coastal Land Use Extension Agent at University of Hawai‘i Sea Grant College Program. She can be reached at firstname.lastname@example.org.