The 1946 tsunami in Hilo, Big Island. Contributed photo
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.