Global tsunami alert: Why do some tsunamis hit in minutes while others take hours?

A massive 8.8 magnitude earthquake hit the eastern coast of Russia in Kamchatka Peninsula on July 30, recording the sixth strongest ever recorded. Evacuation warnings have been issued across the Pacific. As residents move to higher ground, leaving the coastal zones, they wait for the tsunami to strike. There are speculations about the prospective height of the wave and speed with which it will strike, reviving a crucial question: why do some tsunamis hit the coastline in minutes while others take hours to arrive?

The earthquake hit at 4:15 am local time in Russia, and within minutes, 13-foot-long waves were observed along the coastlines, prompting widespread evacuation. Soon after, Japan, Hawaii, the U.S. West Coast, Mexico, and parts of South America issued tsunami advisories with warnings, expecting the tsunami to reach the coast within 3-20 hours of the initial tremors.

Tsunami travel time

The travel time of the Tsunami depends on its speed, which is directly proportional to the depth and the distance from the epicentre. The deeper the water, the faster the waves. It can reach up to the speed of a jet in deep water (500 mph), while in shallow water it slows to the speed of (20-30mph). Coastal areas near the quake, like parts of Kamchatka and the Kuril Islands, saw waves arrive in under 15 minutes. The areas close to the epicentre of the earthquake are likely to face the Tsunami first. The rupture direction of the waves, ie the energy release, also influences which regions are hit the hardest. Japan’s northern coast was directly in the wave’s path and recorded wave activity with 0.4-meter-long waves in under an hour.

Where has the Tsunami reached?

The Tsunami hit Russia's Kamchatka within minutes of the earthquake, and waves up to 4 meters were observed.

"Unfortunately, there are some people injured during the seismic event. Some were hurt while running outside, and one patient jumped out of a window. A woman was also injured inside the new airport terminal,” Oleg Melnikov, the regional health minister, quoted by TASS.

The wave activity reached Hokkaido, Japan, within an hour, with 0.4-meter-long waves. Evacuation alerts were issued for over 900,000 residents. It is expected to hit Hawaii and Alaska within 5-7 hours, and California and Mexico within 10-14 hours. Ports and harbours remain on alert, and emergency services have asked citizens to stay on higher ground.