Surf a tsunami?.. it's not really a possibility

Is it possible to surf a tsunami?: Not really. For one thing, a tsunami does not curl. For another, it tends to be moving too fast - more than 100 mph - as opposed to the typical surfing wave speed of 35 mph. Still, Hawaii officials say a tsunami warning years ago drew more than 400 surfers off Oahu's North Shore. State officials there have distributed a DVD through local surf shops warning against even attempting such a stunt.

Some more key facts about tsunamis...

Often a tsunami is incorrectly referred to as a tidal wave, which, strictly speaking, describes the periodic movement of water associated with the rise and fall of the tides. Oceanographers call tsunamis seismic seawaves because they are usually caused by a sudden rise or fall of part of the earth's crust under or near the ocean. Less powerful tsunami waves can also be triggered by volcanic activity. They are most common in the Pacific Ocean.

A tsunami is not a single wave, but a series of waves that can travel across the ocean at speeds of more than 800 km (500 miles) an hour. In the deep ocean, hundreds of miles (km) can separate wave crests; many people have lost their lives during tsunamis after returning home thinking the waves had stopped.

As the tsunami enters the shallows of coastlines in its path, its velocity slows but its height increases. A tsunami that is just a few centimetres or metres high from trough to crest can rear up to heights of 30 to 50 metres as it hits the shore, striking with devastating force. For those on shore there is little warning of a tsunami's approach. The first indication is often a sharp swell, not unlike an ordinary storm swell.

In 1883, a tsunami following the eruption of Krakatoa volcano between the Indonesian islands of Java and Sumatra killed 36,000. The tsunami's passage was traced as far away as Panama. In July 1998, two undersea quakes measuring 7.0 created three tsunamis that killed at least 2,100 near the town of Aitape on the north coast of Papua New Guinea. Villagers said the massive walls of water, which washed two kilometres (1.2 miles) inland, sounded like a jet fighter landing.

Is a tsunami the same thing as a tidal wave?

No. It has nothing to do with tides, which are caused by the gravitational pull of the moon. The word tsunami (pronounced tsoo-nah'-mee) is composed of the Japanese words "tsu" (which means harbor) and "nami" (which means "wave"). Tsunamis can be generated by earthquakes, volcanic eruptions or underwater landslides.

A Phuket resort succumbs to the tsunami in 2004

The combo photo above taken 26 December 2004 shows (top-L) Phuket's Chedi resort staff preparing for the day as the first swell edges toward the lawn, followed by the arrival of the second and third waves (top-R and bottom-L) respectively, which engulfed the hotel restaurant and its surrounding gardens, and the final photo showing the water at its crest, flooding the whole area.

Is the SE Asia Earthquake/Tsunami the worst natural disaster of all time?

No. In October 1887 the Yellow River overflowed its banks in China, killing some 900,000 people. It's not even the worst natural disaster in the last 30 years. The 1976 Tangshan earthquake in China killed at least 255,000 people, and maybe more than 500,000. This is, however, the highest death toll from a tsunami. Previously the record was 27,000 people who drowned when a tsunami estimated to be 80 to 110 feet high hit a Japanese village in the middle of a religious festival in 1896. Fishermen at sea didn't notice the deadly wave as it passed beneath their boats. They returned to a shore strewn with corpses.

Did the SE Asia earthquake really affect the Earth's rotation?

Yes. This quake was strong enough to affect the Earth's rotation slightly. It also redistributed Earth's mass, moving the North Pole 1 inch and causing the length of a day to shrink permanently by 3-millionths of a second, according to geophysicist Richard Gross of NASA's Jet Propulsion Laboratory.

A giant whirlpool swirls off the coast of Japan near a port in Oarai, Ibaraki Prefecture after the
Japan earthquake on Friday 11 March 2011 © Kyodo News/AP

More about tsunamis

A tsunami can be generated by ANY disturbance that displaces a large water mass from its equilibrium position. Submarine landslides, which often occur during a large earthquake, can also create a tsunami. During a submarine landslide, the equilibrium sea level is altered by sediment moving along the sea floor. Gravitational forces then propagate the tsunami given the initial perturbation of the sea level. Similarly, a violent marine volcanic eruption can create an impulsive force that displaces the water column and generates a tsunami.

Above water landslides and space born objects can disturb the water from above the surface. The falling debris displaces the water from its equilibrium position and produces a tsunami. Unlike ocean-wide tsunamis caused by some earthquakes, tsunamis generated by non-seismic mechanisms usually dissipate quickly and rarely affect coastlines far from the source area.

Tsunamis are characterized as shallow-water waves. Shallow-water waves are different from wind-generated waves, the waves many of us have observed at the beach. Wind-generated waves usually have period (time between two successional waves) of five to twenty seconds and a wavelength (distance between two successional waves) of about 100 to 200 meters (300 to 600 ft).

A tsunami can have a period in the range of ten minutes to two hours and a wavelength in excess of 300 miles (500 km). It is because of their long wavelengths that tsunamis behave as shallow-water waves. A wave is characterized as a shallow-water wave when the ratio between the water depth and its wavelength gets very small. The speed of ashallow-water wave is equal to the square root of the product of the acceleration of gravity (32ft/sec/sec or 980cm/sec/sec) and the depth of the water. The rate at which a wave loses its energy is inversely related to its wavelength.

Since a tsunami has a very large wavelength, it will lose little energy as it propagates. Hence in very deep water, a tsunami will travel at high speeds and travel great transoceanic distances with limited energy loss. For example, when the ocean is 20,000 feet (6100 m) deep, unnoticed tsunami travel about 550 miles per hour (890 km/hr), the speed of a jet airplane. And they can move from one side of the Pacific Ocean to the other side in less than one day.

As a tsunami leaves the deep water of the open sea and propagates into the more shallow waters near the coast, it undergoes a transformation. Since the speed of the tsunami is related to the water depth, as the depth of the water decreases, the speed of the tsunami diminishes. The change of total energy of the tsunami remains constant. Therefore, the speed of the tsunami decreases as it enters shallower water, and the height of the wave grows. Because of this "shoaling" effect, a tsunami that was imperceptible in deep water may grow to be several feet or more in height.

When a tsunami finally reaches the shore, it may appear as a rapidly rising or falling tide, a series of breaking waves, or even a bore. Reefs, bays, entrances to rivers, undersea features and the slope of the beach all help to modify the tsunami as it approaches the shore. Tsunamis rarely become great, towering breaking waves. Sometimes the tsunami may break far offshore. Or it may form into a bore: a step-like wave with a steep breaking front. A bore can happen if the tsunami moves from deep water into a shallow bay or river.

The water level on shore can rise many feet. In extreme cases, water level can rise to more than 50 feet (15 m) for tsunamis of distant origin and over 100 feet (30 m) for tsunami generated near the earthquake's epicenter. The first wave may not be the largest in the series of waves. One coastal area may see no damaging wave activity while in another area destructive waves can be large and violent.

The flooding of an area can extend inland by 1000 feet (305 m) or more, covering large expanses of land with water and debris. Flooding tsunami waves tend to carry loose objects and people out to sea when they retreat. Tsunamis may reach a maximum vertical height onshore above sea level, called a runup height, of 30 meters (98 ft). A notable exception is the landslide-generated tsunami in Lituya Bay, Alaska in 1958, which produced a 525 meter (1722 ft) wave.

Tsunami information courtesy of www.tsunami.org