The bigger tsunamis that occur are caused by what scientists term "near earth objects" hitting Earth. Fortunately this tends to occur on a frequency of around once in every 100,000 years, although one hasn't happened for the last 200,000 years. Almost by accident geologists recently discovered a crater in the Barents Sea off the coast of Norway which was created by an asteroid thought to be 0.5 km in diameter which touched down at 30,000 km/h. In addition to the gigantic tsunami, which would have washed into both Russia and Canada, a mushroom cloud of vaporised sea and rock would have been tossed into the atmosphere, blasting a hole in the stratosphere and causing a "nuclear winter" which would have lasted several years and caused further loss of life from famine and cold.

In recent years technology has made it possible to identify approaching asteroids and comets. To date over 400 objects larger than 1km have been discovered which is thought to be around 10% of the total. In March this year scientists were given a scare by an asteroid which initially looked like it could be on track to get dangerously close to Earth in the year 2028. Luckily recomputation of its trajectory by NASA concluded that this was not the case.

Sixty-five million years ago 70% of all species living on Earth including the dinosaurs disappeared within a very short period. This mass extinction known as the K-T event is believed by many scientists to be caused by the impact of a 10km diameter asteroid hitting the Yucatan region of Mexico and causing the Chicxulub crater which has a diameter of 180km.

Whilst this might appear to be scare-mongering about rare tsunami events, if we get a little closer to reality we see that these events are in some ways far fetched but not as far from reality as originally perceived. On 7 July 1999 a meteorite caused a spectacular light and sound show for the people of Wellington, New Zealand as it hit our atmosphere and burnt up. In July 1993, a 31m tsunami hit a remote part of Japan. Had this hit Tokyo the death toll would have been far greater than 239, and insured losses would have been colossal.