Tsunamis are large waves triggered by underwater occurrences such as; earthquakes, underwater volcanoes and landslides. Tsunamis are also described as a series of waves that may be close together or up to an hour apart. They can come in the form of a very large wave, or as a surge of water. The first wave is generally smaller than the second or third.

The 1964 Alaskan earthquake was the cause of the Port Alberni's tsunami. The earthquake happened in the Prince William Sound region of Alaska and had a magnitude of 9.2 on the Richter scale. Plate tectonics were the cause of the earthquake. The Pacific plate is subducting beneath the North American plate however when there is too much friction, the plates will build up energy and when one plate finally slips under the other the release of the energy causes an earthquake.

The entire event lasted four minutes in duration and was the cause of the tsunami that travelled from Alaska to British Columbia at a speed of about 830 km/h. The tsunami also caused damage down the coast of Oregon and as far south as California. The Alberni Inlet had a funnel effect on the tsunami and the waves witnessed in Port Alberni were two and a half times larger than the waves experienced at Tofino or Ucluelet.

Three waves reached Port Alberni between the hours of 12:20 am and 3:30 am on March 28, 1964. The waves raced up the Somass River at a velocity of 50 km/h. The second and most destructive wave hit Port Alberni at approximately 2 am and caused the power to go off from the waterfront mills. The third wave which was the largest came in at about 3:30 am, however the tide had gone down creating little further damage.

Two hundred and sixty homes were damaged by the tsunami, 60 of them extensively. Damages on Vancouver Island were estimated at about $10 million CDN (1964) however, more importantly, no one was seriously hurt in Port Alberni.