Acehtsunami

 A tsunami (pronounced soo-nahm-ee) is a series of huge waves that happen after an undersea trouble, such as an earthquake or volcano eruption. (Tsunami is from the Japanese word for harbor wave.) The waves travel in all directions from the area of disorder, much like the ripples that happen after throwing a rock. The waves may travel in the open sea as fast as 450 miles per hour. As the big waves approach shallow waters along the coast they grow to a great height and crash into the shore. They can be as high as 100 feet. They can cause a lot of destruction on the shore. They are sometimes mistakenly called “tidal waves,” but tsunami have nothing to do with the tides.

Hawaii is the state at greatest risk for a tsunami. They get about one a year, with a damaging tsunami happening about every seven years. Alaska is also at high risk. California, Oregon and Washington experience a destructive tsunami about every 18 years.

Did you know:

In 1964, an Alaskan earthquake generated a tsunami with waves between 10 and 20 feet high along parts of the California, Oregon and Washington coasts.

In 1946, a tsunami with waves of 20 to 32 feet crashed into Hilo, Hawaii, flooding the downtown area.

 
DAMAGE TO BOATS

A tsunami can be generated by any commotion that displaces a large water mass from its equilibrium location. In the case of earthquake-generated tsunamis, the water column is troubled by the uplift or subsidence of the sea floor. Submarine landslides, which often accompany large earthquakes, as well as collapse of volcanic edifices, can also disturb the overlying water column as sediment and rock slump downslope and are redistribute across the sea floor. Equally, a violent submarine volcanic eruption can create an impetuous force that uplifts the water column and generates a tsunami. Conversely, supermarine landslides and cosmic-body impact disturb the water from above, as momentum from falling debris is transferred to the water into which the debris falls. Usually speaking, tsuna-mis generated from these mechanisms, unlike the Pacific-wide tsunamis caused by some earthquakes, dissipate quickly and not often affect coastlines distant from the source area. What happens to a tsunami as it approaches land?

As a tsunami leaves the deep water of the open ocean and travels into the shallower water near the coast, it transform. If you read the “How do tsunamis differ from other water waves?” section, you discovered that a tsunami travels at a speed that is connected to the water depth — hence, as the water depth decreases, the tsunami slows.The tsunami’s energy flux, which is reliant on both its wave speed and wave height, remains nearly constant. Consequently, as the tsunami’s speed diminish as it travels into shallower water, its height grows. Because of this shoaling effect, a tsunami, unnoticeable at sea, may grow to be several meters or more in height near the coast. When it finally reaches the coast, a tsunami may appear as a quickly rising or falling tide, a series of breaking waves, or even a bore.

As a tsunami approaches shore, we’ve learned in the “What happens to a tsunami as it move towards to land?” section that it begins to slow and grow in height. Just like other water waves, tsunamis begin to lose energy as they rush onto land — part of the wave energy is reflected offshore, while the shoreward-propagating wave energy is dissipated through bottom friction and confusion. Despite these losses, tsunamis still reach the coast with tremendous amounts of energy. Tsunamis have great erosional potential, stripping beaches of sand that may have taken years to accumulate and undermining trees and other coastal vegetation. Capable of inundate, or flooding, hundreds of meters inland past the typical high-water level, the fast-moving water related with the inundating tsunami can crush homes and other coastal structures. Tsuna-mis may reach a maximum vertical height onshore above sea level, often called a run-up height, of 10, 20, and even 30 meters.