An early-morning earthquake with the magnitude of 8.6 occurred south of the Aleutian Islands on April 1st, 1946. Earlier records indicated a magnitude of 7.4 but it was revised as further investigation took place.
Because the epicentre of earthquake was located in the ocean and a portion of the ocean floor shifted upwards along a fault line, it generated a powerful tsunami. In 1946, there was no tsunami warning system in place. Nobody knew a big wave was heading across the Pacific Ocean.
Areas Affected by the 1946 Aleutian Island Tsunami
- Unimak Island, Alaska
Within an hour, the first wave struck Unimak Island and the height was estimated to be at least 100 feet. Six years earlier, the U.S. Coast Guard had built a lighthouse at Scotch Cap on a cliff that was 40 feet above sea level. The structure was five stories high and built with reinforced steel and concrete. The tsunami washed out the lighthouse and killed all five crew members.
The tsunami continued to travel along the Pacific Ocean at a speed of 500 miles per hour, heading towards Hawaii.
- Kauai, Oahu, and Maui
Four and a half hours later, the north coast of Kauai was the first island struck by the tsunami. The maximum wave run-up was measured at 45 feet. Many homes and bridges were washed away. At least 14 people died. The shores of Oahu were battered with 36-foot waves and Maui experienced 33-foot waves.
- Big Island of Hawaii
The worst damage occurred on the big island of Hawaii. At the north end of the island, the maximum wave height was measured at 55 feet in the Pololu Valley. Further down the east coast, a schoolhouse in Laupahoehoe was smashed by the tsunami. The teacher and 25 students were killed.
Hilo on the Big Island of Hawaii suffered the worst property damage because it was a thriving port on the east coast. It was struck with a 32-foot wave that funnelled through Hilo Bay.
The entire waterfront was washed away. Buildings along the waterfront were smashed upon impact or tossed across the street. Bridges, highways and railway lines were washed out. Over one-third of Hilo was destroyed.
According to the Pacific Disaster Center, there were 159 people killed in Hilo and damage was estimated at $26 million (1946 dollars).
What was Learned from the 1946 Aleutian Island Tsunami
It was decided that a tsunami warning system was needed in the Pacific Ocean. In 1948, the U.S. Coast and Geodetic Survey established the Seismic Sea Wave Warning System. The name was later changed to the Pacific Tsunami Warning System.
Tsunamis are now detected through buoys in the ocean that are equipped with seismometers to pick up earthquakes and tide-gauges to detect sudden changes in wave height. The stations closest to the earthquake are the first to record new activity and broadcast alerts to the Pacific Tsunami Warning Center.
- Another disastrous tsunami destroyed Hilo on May 23rd, 1960 resulting from an earthquake in Valdivia Chile. At 9.5 on the Richter scale, it still holds the record as the world’s strongest earthquake.
- On March 28th, 1964, another tsunami hit Hilo as a result from a 9.2 earthquake that occurred in Prince William Sound in Alaska. There was no loss of lives in Hawaii, and the damage was estimated at $68,000 (1964 dollars).
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