Tsunami Guide

Tidal Water Waves: Tsunami Guide

Written by Don Huie

What is a Tsunami?

'Tsunami' is a Japanese word meaning "harbor wave." Tsunamis are giant waves that start because of volcanic eruptions or earthquakes that happen under the ocean. When an earthquake under the ocean causes plates in the Earth's crust to push against each other, this movement may displace the ocean water. Lava from an erupting underwater volcano causes a similar displacement of water. The water has no place to go; so it ripples out from the point of the displacement.

What Causes a Tsunami?

Large earthquakes and volcanic eruptions are more likely to cause a tsunami. However, not all earthquakes and volcanoes will cause tsunamis. Landslides and meteors can also cause tsunamis.

  • The shape of the ocean floor is one factor that can cause a tsunami.
  • The location and direction an earthquake moves are other factors that determine whether a tsunami happens.

How is a Tsunami Formed?

Fault lines are fractures in the Earth's crust, and many fault lines run under oceans. When tension builds at fault lines, eventually the tectonic plates shift to release the tension, causing an earthquake. If the movement of the plates shifts vertically, this may cause a tsunami due to the large displacement of water. Plates that shift only horizontally won't typically cause a tsunami.

  • The plate movement happens suddenly and quickly, which causes the ripple effect of the water.
  • Tsunami wavelength is considered to be a long wave, which means that it will move quickly across the ocean.
  • Tsunami speed slows when the wave reaches the coast because the ocean is shallower. The slower speed causes the wave to get higher.
  • Tsunamis might hit as a rapid tide, which means that the sea level rises quickly. Tsunamis might also hit as a wall of water, which would be the most destructive type of tsunami.

Where Do Tsunamis Happen?

Most tsunamis happen in the Pacific Ocean because there are many active earthquake zones under this ocean. Tsunamis can also happen in the Caribbean Sea and the Mediterranean Sea.

  • Coastal areas that face subduction zones have the highest risk for tsunamis. Subduction zones have a high potential for megathrust earthquakes, which are very big earthquakes.
  • Pacific Ocean countries with longer coastlines are more likely to experience a tsunami. Some of these countries include Chile and Japan.
  • Indonesia is the country with the highest rate of tsunamis.

Tsunami Preparedness

Tsunamis often happen quickly. For this reason, it's important to be prepared for a tsunami before it happens. If you are near the water and you feel an earthquake or you see the water pulling away from the shore quickly and you hear an ocean roar, move as fast as you can away from the shore.

  • Assemble a survival kit that includes one gallon of water per day for at least three days for everyone in your family, non-perishable food, a flashlight, extra batteries, medication, a first-aid kit, personal hygiene items, a cell phone with a charger, blankets, extra clothes, cash, and important personal documents.
  • Identify shelters where you can go for cover.
  • Listen for a tsunami warning siren and local advisories that will inform you of watches or warnings. A watch means that a tsunami hasn't been verified but that an event has occurred that makes one possible. A warning means that a tsunami is coming.
  • Follow evacuation orders if they arrive. Move away from coastal areas. Move to higher ground as quickly as possible.
  • If it's too late to evacuate, go to the highest level of a sturdy building or the highest ground you can find.
  • Stay in your safe place until the tsunami threat passes. There may be smaller earthquakes and waves that follow the first big one. Local officials will signal an all-clear when it's safe to move out of higher elevation areas.

Additional Resources