Coastlines

• The word tsunami is a Japanese word, translated as "harbour wave". It is not a tidal wave.
• Tsunamis are usually caused by underwater earthquakes which result in massive displacement of water. They can also be caused by landslides displacing water, or even asteroid impacts.
• Tsunamis can travel thousands of kilometres before reaching land. Tsunamis can wipe out an entire city and kill a large number of people, particularly in countries where many people dwell and make their livingclose to the coast.
• Tsunamis occur most often along countries which border the Pacific "Rim of Fire", or "Ring of Fire'. One end of this region of high seismic and volcanic activity begins at New Zealand, heading northwest to Indonesia (completely bypassing Australia) and then west to Papua New Guinea and Indonesia, northeast along the Asian coastline, east to North America and then south along the western North American coastline. Roughly horse-shoe shaped, the Ring of Fire extends about 40,000km long, and tsunamis can be generated anywhere along this rim.
• Some tsunamis can be very large. In coastal areas their height can be as great as 10 to 30 m high, whilst the largest tsunami ever recorded was 524 metres high, or just over half a kilometre (Alaska, 1958).
• Tsunamis in excess of 100m high are called megatsunamis.
• All low lying coastal areas can be struck by tsunamis.
• A tsunami is actually made up of a series of waves which may arrive every 10 to 60 minutes. Often the first wave may not be the largest. The danger from a tsunami can last for several hours after the arrival of the first wave. Tsunami waves typically do not curl and break, so you should never try to surf a tsunami.
• Tsunamis can travel through deep water as fast as 950kph. However, their amplitude (height) is only about 1 meter with a wavelength of 200-300m. In deep water, a tsunami would be just barely perceptible, if at all.
• Sometimes a tsunami may cause the water near the coast to recede dramatically, exposing land which is usually submerged. This is a sure sign of an impending tsunami.
• There is no limit as to when a tsunami can hit - morning, noon, night, etc.
• In the Indonesian or "Boxing Day" Tsunami of December, 2004, waves reached heights of over 30 meters in Banda Aceh, evidenced by the complete stripping of the very tallest palm trees. In a minor tsunami, the waves may be only millimeters high.
• Some types of animals have an innate sixth sense which enables them to detect when a tsunami is going to occur: they will then head inland in the opposite direction.
• Tsunamis are accompanied by a loud roaring sound, described by witnesses as being similar to the sound of a train or aircraft.
• Once a tsunami reaches the shore, its wave length may be as much as 100km, compared to ordinary ocean waves of some 100 metres in length.
• After reaching shallower waters, tsunami lose their forward speed and hugely gain amplitude; their forward momentum is not lost by much, however.
• Unlike wind waves which "break" and move water in mostly a circular motion, tsunami waves have forward moving inertia, which carries the entire volume of the wave inland at high speed, much like a hurricane's storm surge.
• Depending on the severity, casualties can range from hundreds of thousands to none. In a catastrophic tsunami, the waves can be over 30m/98ft high. Moving faster than anyone can run, they churn a horrid mix of debris, from cars to pieces of homes, bodies and whatever else is not cemented to the ground; people are either crushed to death or drowned.
• Some types of animals have an innate sixth sense which enables them to detect when a tsunami is going to occur: they will then head inland in the opposite direction.
• Tsunamis do not have to be a certain height but have to be caused by a earthquake or something that is nothing to do with tides to be called a tsunami.
• On July 12, 1993 a magnitude 7.8 earthquake in the Sea of Japan produced tsunami that totally destroyed the southern half of Okushiri Island. Waves were greater than 30 feet and some could have been 100 feet. The earthquake was about 50 miles offshore and the tsunami arrived within minutes. 120 people died.
• In the USA, the states most at risk for Tsunami are California, Hawaii, Oregon and Washington.
• On 28 March 1964 an extremely large earthquake (magnitude 8.4) struck Alaska. It caused tsunami waves that were very destructive in southeastern Alaska, in Vancouver Island, Canada, and in the States of Washington, California and Hawaii. Waves ranged in size from 6 to 21 feet. The tsunami killed more than 120 people and damages costing more than $106 million. It was the costliest tsunami ever to strike the Western United States and Canada.
• Although a large asteroid impact is highly unlikely, scientists studying the possibility have decided that a moderately large asteroid or about 5-6 km in diameter falling in the middle of the Atlantic Ocean, would generate a tsunami that would travel all the way to the Appalachian Mountains in the upper two-thirds of the United States. Coastal cities would be wiped out by such a tsunami.

The terms sea defense and coastal protection are used to mean, respectively, defense against flooding and erosion. The term coastal defence is the more traditional term, but coastal management has become more popular as the field has expanded to include techniques that allow erosion to claim land.

Hard engineering is generally defined as controlled disruption of natural processes by using man-made structures. It is sometimes considered to be the use of concrete breakwalls to limit the amount of coastal erosion on a being or a cliff-face where land is being absorbed by the sea or steel sheet piling to stabilize shorelines and achieve safety along the coastline to limit the amount of sand being transported by longshore drift.

Soft engineering is the use of ecological principles and practices to reduce erosion and achieve the stabilization and safety of shorelines and the area surrounding rivers, while enhancing habitat, improving aesthetics, and saving money. Soft engineering is achieved by using vegetation and other materials to soften the land-water interface, thereby improving ecological features without compromising the engineered integrity of the shoreline or river edges.