Tsunamis
	Description
	Tsunamis, named from the Japanese term meaning 'harbour wave', are also known as seismic sea waves and are often erroneously referred to as 'tidal waves'. They are usually caused by submarine earthquakes, but may be caused by submarine volcanic eruptions or coastal landslips. In the oceans these waves cannot be detected as they are often over 100 miles in length and less than a metre in height, travelling at tremendous speed, reaching 300 to 500 knots. On entering shallow water the waves become shorter and higher. On coasts where there is a long fetch of shallow water with oceanic depths immediately to seaward, and in V-shaped harbour mouths, the waves can reach disastrous proportions. Waves having a height of 20 m from crest to trough have been reported. The first wave is seldom the highest and there is normally a succession of waves reaching a peak and then gradually disappearing. The time between crests is usually from 10 to 40 minutes. Sometimes the first noticeable part of the wave is the trough, causing an abnormal lowering of the water level. Mariners should regard such a sign as a warning that a tsunami may arrive within minutes and should take all possible precautions, proceeding to sea if at all feasible. Tsunamis travel for enormous distances, up to one-third of the circumference of the earth in the open waters of the Pacific Ocean. In 1960 a seismic disturbance of exceptional severity off the coast of Chile generated a tsunami which caused much damage and loss of life as far afield as Japan. Although large tsunamis cause grave havoc, small waves in shallow water can cause considerable damage by bumping a ship violently on a hard bottom. A ship in harbour, either becoming aware of a large earthquake in the vicinity, or observing sudden marked variations in sea level, or receiving warning of an approaching tsunami, should seek safety at sea in deep water, and set watch on the local port radio frequency . After tsunamis, abnormal ground swells and currents may be experienced for several days.
	International Pacific Tsunami Warning System
	Almost all of the countries bordering the Pacific Ocean participate in the International Pacific Tsunami Warning System and their seismic and tidal stations form a network covering that ocean. When a station detects an earthquake, it reports the occurrence to the Pacific Tsunami Warning Centre in Hawaii which then calls for any information available from other stations. As soon as the Centre has gathered enough information to locate the earthquake and to calculate its magnitude, it determines whether or not a tsunami is likely to be generated. If a tsunami is expected, tidal stations near the epicentre are required to report whether recorded mean sea level has changed or not. When the information from tidal stations has been evaluated, if a sizeable tsunami is expected, a warning is sent to all members of the system. If, however, an earthquake has a magnitude of 7.5 or greater on the Richter scale, preliminary alert messages are sent to the members indicating the probability of a tsunami and its estimated time of arrival at the various tidal stations. For ports where local Tsunami Warning Signals are used, the signals, if known, are given in Admiralty Sailing Directions.
	Tsunamis. Being Prepared
	A tsunami is a series of waves that may be dangerous and destructive. When you hear a tsunami warning, move at once to higher ground and stay there until local authorities say it is safe to return home. BEFORE Find out if your home is in a danger area. Know the height of your street above sea level and the distance of your street from the coast. Evacuation orders may be based on these numbers. Be familiar with the tsunami warning signs. Because tsunamis can be caused by an underwater disturbance or an earthquake, people living along the coast should consider an earthquake or a sizable ground rumbling as a warning signal. A noticeable rapid rise or fall in coastal waters is also a sign that a tsunami is approaching. Make sure all family members know how to respond to a tsunami. Make evacuation plans. Pick an inland location that is elevated. After an earthquake or other natural disaster, roads in and out of the vicinity may be blocked, so pick more than one evacuation route. Teach family members how and when to turn off gas, electricity, and water. Teach children how and when to call police or fire department, and which radio station to listen for official information. Have disaster supplies on hand. Flashlight and extra batteries  Portable, battery-operated radio and extra batteries  First aid kit and manual  Emergency food and water  Nonelectric can opener  Essential medicines  Cash and credit cards  Sturdy shoes  Develop an emergency communication plan. In case family members are separated from one another during a tsunami (a real possibility during the day when adults are at work and children are at school), have a plan for getting back together. Ask an out-of-state relative or friend to serve as the "family contact." After a disaster, often it's easier to call long distance. Make sure everyone knows the name, address, and phone number of the contact person. Contact your local emergency management office or American Red Cross chapter for more information on tsunamis.  DURING Listen to a radio or television to get the latest emergency information, and be ready to evacuate if asked to do so. If you hear an official tsunami warning or detect signs of a tsunami, evacuate at once. Climb to higher ground. A tsunami warning is issued when authorities are certain that a tsunami threat exists. Stay away from the beach. Never go down to the beach to watch a tsunami come in. If you can see the wave you are too close to escape it. Return home only after authorities advise it is safe to do so. A tsunami is a series of waves. Do not assume that one wave means that the danger over. The next wave may be larger than the first one. Stay out of the area. AFTER Stay tuned to a battery-operated radio for the latest emergency information. Help injured or trapped persons. Give first aid where appropriate. Do not move seriously injured persons unless they are in immediate danger of further injury. Call for help. Remember to help your neighbors who may require special assistance--infants, elderly people, and people with disabilities. Stay out of damaged buildings. Return home only when authorities say it is safe. Enter your home with caution. Use a flashlight when entering damaged buildings. Check for electrical shorts and live wires. Do not use appliances or lights until an electrician has checked the electrical system. Open windows and doors to help dry the building. Shovel mud while it is still moist to give walls and floors an opportunity to dry. Check food supplies and test drinking water. Fresh food that has come in contact with flood waters may be contaminated and should be thrown out. Have tap water tested by the local health department. INSPECTING UTILITIES IN A DAMAGED HOME Check for gas leaks--If you smell gas or hear a blowing or hissing noise, open a window and quickly leave the building. Turn off the gas at the outside main valve if you can and call the gas company from a neighbor's home. If you turn off the gas for any reason, it must be turned back on by a professional. Look for electrical system damage--If you see sparks or broken or frayed wires, or if you smell hot insulation, turn off the electricity at the main fuse box or circuit breaker. If you have to step in water to get to the fuse box or circuit breaker, call an electrician first for advice. Check for sewage and water lines damage--If you suspect sewage lines are damaged, avoid using toilets and call a plumber. If water pipes are damaged, contact the water company and avoid the water from the tap. You can obtain safe water by melting ice cubes.