April 1, 1946, was witness to a deadly tsunami earthquake generated south of Unimak Island with a moment magnitude of 8.6. that caused consequential events that lent to a number of deaths, mostly in Hilo, Hawaii.

The megathrust earthquake, that struck in the early morning hours, was generated 13,000 feet below the ocean’s surface just south of Unimak Island along the Aleutian Subduction Zone and thrust the seafloor upwards, causing undersea landslides, and generating a massive tsunami that quickly struck Unimak.

On the southwest corner sat the Scotch Cap Light, a navigation lighthouse manned by a five-man crew. The lighthouse was inundated and completely demolished by the sudden wave, thought to be as high as 138-feet. All five men at the lighthouse were killed. Consequentially, the tidal wave struck before the tsunami alert was sent out.

The large wave generated by the quake raced south at five hundred miles per hour through the Pacific unannounced. Four and a half hours later, the massive Tsunami was spotted by Navy Captain Wickland at just before 7 am, moments before it shallowed up and made landfall in Hilo Bay. 

Without warning, the initial wave rushed in and quickly receded draining the bay. Boats and flopping fish were left stranded in the bay until six additional waves in succession swept into the bay with devastating effect. The waves reaching over 30 feet and as much as 50 feet destroyed large portions of the city of Hilo and took as many as 159 lives. 

At Laupahoehoe, the schoolhouse was inundated, killing 25 students and a teacher.

Hawaiians have dubbed the 1946 tsunami as the “April Fools Tsunami” as many thought the reports of the tsunami was an April Fool’s practical joke.

The expansive destruction and loss of life prompted the creation of a warning system that would become the Pacific Tsunami Warning Center three years later in 1949.

The tsunami would travel further south and damage boats as far south as Chile.

Image-Scotch Cap Light-CG/Public Domain

Image-Residents fleeing Tsunami in Hilo. (Note wave in the background) Image-USGS