Tsunami

A tsunami is a series of waves created when a body of water, such as an ocean, is rapidly displaced. Earthquakes, mass movements above or below water, some volcanic eruptions and other underwater explosions, landslides, underwater earthquakes, large asteroid impacts and testing with nuclear weapons at sea all have the potential to generate a tsunami. The effects of a tsunami can be devastating due to the immense volumes of water and energy involved. Since meteorites are small, they will not generate a tsunami. The Greek historian Thucydides was the first to relate tsunamis to submarine quakes, but understanding of the nature of tsunamis remained slim until the 20th century and is the subject of ongoing research. Many early geological, geographic, oceanographic etc; texts refer to "Seismic sea waves" - these are now referred to as "tsunami." Some meteorological storm conditions - deep depressions causing cyclones, hurricanes; can generate a storm surge which can be several metres above normal tide levels. This is due to the low atmospheric pressure within the centre of the depression. As these storm surges come ashore the surge can resemble a tsunami, inundating vast areas of land. These are not tsunami. Such a storm surge inundated Burma (Myanmar) in May 2008.

Causes

A tsunami can be generated when converging or destructive plate boundaries abruptly move and vertically displace the overlying water. It is very unlikely that they can form at divergent (constructive) or conservative plate boundaries. This is because constructive or conservative boundaries do not generally disturb the vertical displacement of the water column. Subduction zone related earthquakes generate the majority of all tsunamis. A tsunami has a much smaller amplitude (wave height) offshore, and a very long wavelength (often hundreds of kilometers long), which is why they generally pass unnoticed at sea, forming only a slight swell usually about 300 mm above the normal sea surface. A tsunami can occur at any state of the tide and even at low tide will still inundate coastal areas if the incoming waves surge high enough.

Characteristics

While everyday wind waves have a wavelength (from crest to crest) of about 100 m (300 ft) and a height of roughly 2 m (7 ft), a tsunami in the deep ocean has a wavelength of about 200 km (120 miles). This wave travels at well over 800 km/h (500 mph), but due to the enormous wavelength the wave oscillation at any given point takes 20 or 30 minutes to complete a cycle and has an amplitude of only about 1 m (3 ft). This makes tsunamis difficult to detect over deep water. Their passage usually goes unnoticed by ships. As the tsunami approaches the coast and the waters become shallow, the wave is compressed and its forward travel slows below 80 km/h (50 mph). Its wavelength diminishes to less than 20 km (12 miles) and its amplitude grows enormously, producing a distinctly visible wave. Since the wave still has a wavelength on the order of several km (a few miles), the tsunami may take minutes to ramp up to full height, with victims seeing a massive deluge of rising ocean rather than a cataclysmic wall of water. Open bays and coastlines adjacent to very deep water may shape the tsunami further into a step-like wave with a steep breaking front.

Signs of an approaching Tsunami

There is often no advance warning of an approaching tsunami. However, since earthquakes are often a cause of tsunami, any earthquake occurring near a body of water may generate a tsunami if it occurs at shallow depth, is of moderate or high magnitude, and the water volume and depth is sufficient. If the first part of a tsunami to reach land is a trough (draw back) rather than a crest of the wave, the water along the shoreline may recede dramatically, exposing areas that are normally always submerged. This can serve as an advance warning of the approaching tsunami which will rush in faster than it is possible to run. If a person is in a coastal area where the sea suddenly draws back (many survivors report an accompanying sucking sound), their only real chance of survival is to run for high ground or seek the high floors of high rise buildings.

Warnings and prevention

A tsunami cannot be prevented or precisely predicted - even if the right magnitude of an earthquake occurs in the right location. Geologists, Oceanographers and Seismologist analyse each earthquake and based upon many factors may or may not issue a tsunami warning. However, there are some warning signs of an impending tsunami, and there are many systems being developed and in use to reduce the damage from tsunami. One of the most important systems that is used and constantly monitored are bottom pressure sensors. These are anchored and attached to buoys. Sensors on the equipment constantly monitor the pressure of the overlying water column.

The End!

2008 Summer Olympics

The 2008 Summer Olympic Games, officially known as the Games of the XXIX Olympiad, is a major international multi-sport event which is being celebrated in Beijing, People's Republic of China from August 8 to August 24, 2008 and followed by the 2008 Summer Paralympics from September 6 to September 17. 10,500 athletes are expected to compete in 302 events in 28 sports, one event more than was on the schedule of the 2004 games.

Beijing National Stadium

The centrepiece of the 2008 Summer Olympics will be the Beijing National Stadium, nicknamed the "Bird nest" because of its nest-like skeletal structure. Construction of the venue began on December 24, 2003. The Guangdong Olympic Stadium was originally planned, constructed, and completed in 2001 for the Games, but a decision was made to construct a new stadium in Beijing. Government officials engaged architects worldwide in a design competition. A Swiss firm, Herzog & de Meuron Architekten AG, collaborated with China Architecture Design & Research Group to win the competition. The stadium features a lattice-like concrete skeleton forming the stadium bowl and will have a seating capacity of over 90,000 people during the Olympics. Architects originally described the overall design as resembling a bird nest with an immense ocular—an opening with a retractable roof over the stadium. However, in 2004, the idea of retractable roof was abandoned for economic and safety reasons. The Beijing National Stadium will be the site of the opening and closing ceremonies, as well as the athletics events and soccer finals. Most recently, the Beijing Olympic Village opened on July 16, 2008 and to the public on July 26, 2008.

Mascots

The 2008 Olympic Mascots are the five Fuwa (literally "good luck dolls" initially known as Friendlies in English). The Fuwa consist of five members that incorporate fish, giant panda, fire, Tibetan antelope, and swallow designs. The Fuwa each have as their primary colour, one of the colours of the five Olympic Rings that stand for the five continents. The five Fuwa are named Beibei, Jingjing, Huanhuan, Yingying, and Nini. When the first syllable of each of the five names are said together, the result is the phrase (Beijing huanying ni) which means "Beijing welcomes you".

Sports

The program for the Beijing 2008 Games is quite similar to that of the Athens Games held in 2004. The 2008 Olympics will see the return of 28 sports, and will hold 302 events (165 men’s events, 127 women’s events, and 10 mixed events), one event more in total than in Athens. Overall 9 new events will be held, which include 2 from the new cycling discipline of BMX. Women will compete in the 3000 m steeplechase for the first time. In addition, marathon swimming events for men and women, over the distance of 10 kilometres, will be added to the swimming discipline. Team events (men and women) in table tennis will replace the doubles events. In fencing, women's team foil and women's team sabre will replace men's team foil and women's team epee. The Beijing Organizing Committee have released pictograms of the 35 Olympic disciplines. This set of sport icons is named the beauty of seal characters, due to each pictogram's likeness to Chinese seal script.
The End!