Size of TsunamiTsunamis have an extremely longwavelength (wavelength is the distancebetween the crest (top) of one wave and thecrest of the next wave) -- up to severalhundred miles long. The period (the timebetween two successive waves) is also verylong -- about an hour in deep water.In the deep sea, a tsunamis height can beonly about 1 m (3 feet) tall. Tsunamis areoften barely visible when they are in thedeep sea. This makes tsunami detection inthe deep sea very difficult.
A tsunami can travel at wellover 970 kph (600 mph) in theopen ocean - as fast as a jet flies.It can take only a few hours fora tsunami to travel across anentire ocean. A regular wave(generated by the wind) travelsat up to about 90 km/hr.
•Tsunami is should not be known as tidalwaves. Tsunamis are sometimes incorrectlycalled "tidal waves" -- tsunamis are not causedby the tides (tides are caused by thegravitational force of the moon on the sea).Regular waves are caused by the wind.•If the first part of a tsunami to reach land is atrough—called a drawback—rather than awave crest, the water along the shorelinerecedes dramatically, exposing normallysubmerged areas.
•Most tsunamis, about 80 percent, happen within thePacific Ocean’s “Ring of Fire,” a geologically activearea where tectonic shifts make volcanoes andearthquakes common.•A tsunami may be less than a foot (30 centimeters)in height on the surface of the open ocean, which iswhy they are not noticed by sailors. But thepowerful shock wave of energy travels rapidlythrough the ocean as fast as a commercial jet. Once atsunami reaches shallow water near the coast, it isslowed down. The top of the wave moves faster thanthe bottom, causing the sea to rise dramatically.
•Geological features such as reefs, bays, riverentrances, and undersea formations may dissipatethe energy of a tsunami. In some places a tsunamimay cause the sea to rise vertically only a fewinches or feet•Flooding can extend inland by a thousand feet (300meters) or more. The enormous energy of atsunami can lift giant boulders, flip vehicles, anddemolish houses. Knowledge of the history oftsunamis in your area is a good indicator of what islikely to happen in a future tsunami event.•The 2004 Indian Ocean tsunami could rank as themost devastating on record. More than 200,000people lost their lives, many of them washed out tosea.
• An earthquake is a natural tsunami warning. If you feel a strongquake do not stay in a place where you are exposed to a tsunami. Ifyou hear of an earthquake be aware of the possibility of a tsunamiand listen to the radio or television for additional information.Remember that an earthquake can trigger killer waves thousands ofmiles across the ocean many hours after the event generated atsunami.•Witnesses have reported that an approaching tsunami is sometimespreceded by a noticeable fall or rise in the water level. If you see theocean receding unusually rapidly or far its a good sign that a bigwave is on its way. Go to high ground immediately.•Many people were killed by the Indian Ocean tsunami because theywent down to the beach to view the retreating ocean exposing theseafloor. Experts believe that a receding ocean may give people asmuch as five minutes warning to evacuate the area.• Remember that a tsunami is a series of waves and that the firstwave may not be the most dangerous. The danger from a tsunami canlast for several hours after the arrival of the first wave. A tsunamiwave train may come as a series of surges that are five minutes to anhour apart. The cycle may be marked by a repeated retreat andadvance of the ocean.
•Survivors of the Indian Ocean tsunami reported that thesea surged out as fast and as powerfully as it came ashore.Many people were seen being swept out to sea when theocean retreated.•A tsunami surge may be small at one point of the shoreand large at another point a short distance away. Do notassume that because there is minimal sign of a tsunami inone place it will be like that everywhere else.• Tsunamis can travel up rivers and streams that lead tothe ocean. Stay away from rivers and streams that lead tothe ocean as you would stay away from the beach andocean if there is a tsunami.• Its always a good idea to keep a store of emergencysupplies that include sufficient medications, water, andother essentials sufficient for at least 72 hours. Tsunami,earthquake, hurricane—an emergency can develop withlittle or no warning.
Plan for a Tsunami• Develop a Family Disaster Plan• Learn about tsunami risk in your community• If you are visiting an area at risk from tsunamis, check with the hotel, motel, or campground operators for tsunami evacuation information• Plan an evacuation route from your home, school, workplace, or any other place youll be where tsunamis present a risk.
• Practice your evacuation route• Use a NOAA Weather Radio with a tone-alert feature to keep you informed of local watches and warnings. • Discuss tsunami with your family• Assemble a Disaster Supplies Kit
How to Protect Your Property• Avoid building or living in buildings within several hundred feet of the coastline. These areas are more likely to experience damage from tsunamis, strong winds, or coastal storms. Make a list of items to bring inside in the event of a tsunami. A list will help you remember anything that can be swept away by tsunami waters.• Elevate coastal homes. Most tsunami waves are less than 10 feet. Elevating your house will help reduce damage to your property from most tsunamis.• Follow flood preparedness precautions. Tsunamis are large amounts of water that crash onto the coastline, creating floods.• Have an engineer check your home and advise about ways to make it more resistant to tsunami water. There may be ways to divert waves away from your property. Improperly built walls could make your situation worse. Consult with a professional for advice.
What to Do After a Tsunami• Continue listening to a NOAA Weather Radio, Coast Guard emergency frequency station, or other reliable source for emergency information• Help injured or trapped persons• Use the telephone only for emergency calls• Stay out of the building if waters remain around it• Examine walls, floors, doors, staircases, and windows to make sure that the building is not in danger of collapsing.• Inspect foundations for cracks or other damage
• Look for fire hazards. • Check for gas leaks• Look for electrical system damage. • Check food supplies. Any food that has come in contact with flood waters may be contaminated and should be thrown out.