Huge waves, crossed waves and tsunami waves

Feb 15, 2007 15:09 GMT  ·  By

Thousands of boats, for fishing, transport, oil tanks, have to face many times huge waves that can trigger catastrophes, thus sailors and ship builders must manage a lot of knowledge about these phenomena.

Waves have different energies, frequencies, and speeds. Two waves which follow one another can unite at a given moment in a sole larger and stronger one.

Sometimes, several waves moving in the same direction can join, forming a giant wave.

They can last two-three minutes and vanish after that like they would have never existed.

During sea storms, when the waves move towards the same direction reaching much larger heights, the union of two waves can give birth to 30 m (100 feet) high waves, in front of which nothing can resist. Wind power, water temperature, air temperature, storm frequencies, marine currents, the topography (shape) of the sea bottom, are some of the factors that influence the emergence and size of the waves.

But even the best computers cannot predict to a ship commander when he will encounter such a wave. For example, in 1942, off the British coast an extremely violent storm started. At that moment, "Queen Mary" ship was floating 700 miles (1200 km) off the storm's place. On its deck 15,000 British troops were waiting to land to fight in Europe against Nazi Germany.

Suddenly, a huge wave hit the boat like a shot, along all its length. Soon after, "Daily Mail" informed that "Queen Mary ship, having a length of over 300 m and a displacement of 81237 tons, tilted so much that the top of its chimney almost touched the water! The crew's members, some of them working on the ship from its first drive, were convinced that their ship could not set to right. A little more, and the water would have entered through the broken windows, and Queen Mary would have perished for ever in the waters of the Atlantic, together with the 15,000 troops on its board".

In April 1970, the Italian ship "Michelangelo", with a displacement of 44,000 tons, and 775 passengers onboard, is surprised by a violent storm in the middle of the Atlantic. Suddenly, a huge wave fully hit the ship, damaging it severely. The wave flooded the front part of the ship, twisting the ship's skeleton, breaking all the windows till 25 m height over the floating level. Tons of water entered inside the ship through the broken windows. Two passengers and one of the crew's members were thrown forever into the sea and tens of passengers suffered severe traumatisms.

The ship tilted like a nutshell. When the ship was tugged and brought to New York's harbor, people were amazed that it was the opera of one wave.

The oceanographer Blair Kinsman describes these giants of the seas: "Imagine you are on the command deck of a ship. And imagine a mass of green-black water, as high as a 7-8 levels block and with a length of about one km (0.6 miles), which suddenly appears in front of you and approaches with a speed of roughly 100 km (60 miles) per hour. This gigantic beast is rising over you, like it would be alive, roaring, howling, and them disappears ?"

We have described the storm waves. But even more dangerous are the crossed waves.

In 1965, two ships were swallowed by the sea due to these waves.

Let's say that two waves, one 10 m tall, and the other 15 m tall move in the same direction at constant distance one from the other. At a point, the configuration of the sea bed changes the moving direction of one of the waves. The two waves rush at each other from different parts.

A ship hit by such a wave stands no chance ?

These are offshore waves, but now there are also the well known and infamous tsunami (in Japanese "harbour wave") waves (photo), which emerge as a result of submarine earthquakes, submarine volcanic blasts, landslides, large meteorite impacts or testing with nuclear weapons at sea.

Out in the sea, they can hardly be detected, because they are just a few meters tall, only that they propagate with over 500 km (300 miles) per hour. Normal large waves decrease their height close to the shore (they break).

But when tsunami waves reach the shore, they join and can reach heights of 30 m. At this height and speed, it's easy to understand the damages they can produce: the people do not even have time to react. There's no need to detail the tsunami waves provoked by a submarine earthquake on December, 26, 2004, which killed around 300,000 people.