Stay Informed: Knowing how tsunamis occur will help you recognize their warning signs. Tsunamis are most often caused by earthquakes beneath the sea floor. As deep sea waves created by the quake approach land, the shallower waters leave less room for the waves' energy to disperse. As a result, the waters rise, sometimes as waves as high as 100 feet, but more often as a powerful, fast-moving flood with strong currents. Tsunamis of either sort are extremely dangerous for coastal areas.
Move to Higher Ground: Tsunamis can result from local or distant events. Local event tsunamis are likely to be very fast moving. If you are near a shoreline and feel a strong earthquake, evacuate to higher ground immediately. Other immediate warning signs include water pulling away from the shore and a loud ocean roar.
Authorities may respond to more distant events by issuing a series of advisories about tsunami risks. A tsunami watch means that a tsunami has not yet been verified, but an earthquake or other event has made one possible. When a tsunami watch is in effect, use a battery-powered radio to keep up with the latest information. Gather your family, collect your disaster kit, and prepare to evacuate to higher ground.
A tsunami warning means that a tsunami is on its way. Evacuate immediately to higher ground or inland areas. Do not go to coastal areas to watch for the tsunami, regardless of their elevation. If it is too late to evacuate, go to an upper level of a sturdy building or the highest ground you can access as soon as possible.
Additional severe activity may follow initial quakes and early waves, so remain at a higher elevation until the tsunami threat has completely passed. Local officials will issue an "all clear" advisory when appropriate.
Once the all clear has been given, use caution or seek professional help when returning to your home, as damage or dangers — such as live wires, electrical shorts, gas leaks, and sewage — may not be immediately visible.
Upon returning, you should check your food and water supplies. Use your emergency water or boil tap water before drinking until you are told the water supply is safe. Food that came in contact with floodwaters may be contaminated and should be discarded.