What is a Tsunami? How does it form?

SALT LAKE CITY (ABC4) — While Utah is landlocked and deals more with earthquakes than tsunamis, the news of the 8.8 magnitude earthquake off the Russian coast spread quickly.

Tsunami alerts were posted and issued for the coastal regions of our neighboring states like Oregon and California. Evacuations were underway for coastal regions of the Hawaiian island Tuesday night, where a lot of Utahns visit or now live. 

What is a Tsunami?

A Tsunami is a series of waves generated by a sudden displacement of the ocean, which in this case, was the large earthquake off the coast of Russia. While earthquakes are the most common trigger volcanic eruptions, landslides and meteorites have also been known to initiate a tsunami. 

Tsunamis are not related to tidal waves. A tsunami is a series of powerful, long ocean waves that form when energy expands in all directions after in this case, the earthquake occurred. The distance between tsunami wave crests is very long, and forecasters refer to these wavelengths in coastal areas will tracking tsunami movement.

Tsunami waves travel hundreds of miles up to speeds of over 500 miles per hour and some of controlling factors of tsunamis revolve around earthquake magnitude, earthquake type and earthquake depth. While in the open ocean tsunami waves may not be noticeable with small wave heights, the series of waves builds and builds and change when they approach land. Waves become larger when they hit a shallow sea floor near the coast as energy is forced upward, so you get destructive and damaging waves.

There’s an initial drawback before waves crash when water is pulled from the coast, but when these powerful waves reach land, you get multiple waves crashing onshore and spreading inland. The force of this water is extremely dangerous for people and animals and can often be devastating to property with widespread damage. 

Courtesy: Alana Brophy with ABC4

To put the intensity of tsunami warnings into perspective, this was the urgent messaging from the National Weather Service Office Honolulu office:

“EACH INDIVIDUAL WAVE CREST CAN LAST 5 TO 15 MINUTES OR MORE AND EXTENSIVELY FLOOD COASTAL AREAS. THE DANGER CAN CONTINUE FOR MANY HOURS AFTER THE INITIAL WAVE AS SUBSEQUENT WAVES ARRIVE. TSUNAMI WAVE HEIGHTS CANNOT BE PREDICTED AND THE FIRST WAVE MAY NOT BE THE LARGEST. TSUNAMI WAVES EFFICIENTLY WRAP AROUND ISLANDS.

ALL SHORES ARE AT RISK NO MATTER WHICH DIRECTION THEY FACE. THE TROUGH OF A TSUNAMI WAVE MAY TEMPORARILY EXPOSE THE SEAFLOOR BUT THE AREA WILL QUICKLY FLOOD AGAIN. EXTREMELY STRONG AND UNUSUAL NEARSHORE CURRENTS CAN ACCOMPANY A TSUNAMI. DEBRIS PICKED UP AND CARRIED BY A TSUNAMI AMPLIFIES ITS DESTRUCTIVE POWER. SIMULTANEOUS HIGH TIDES OR HIGH SURF CAN SIGNIFICANTLY INCREASE THE TSUNAMI HAZARD.”

For continuing coverage of this developing weather situation, stay with the ABC 4WARN Weather Team.