Geologists call the 2004 tsunami a "monster earthquake". The earthquake shaking lasted longer than usual. This was followed by mountains of waves that hit the beach at very high speeds.
What happened?
Giant waves occurred after an earthquake under the sea, about 100 kilometers west of the coast of Sumatra, at 07:59 local time. The epicenter was at a depth of about 30 kilometers below the sea floor. There are two colliding continental plates. The intense pressures then cause one plate to slide under the other plate. That happened on December 26, 2004, on a 1000 kilometer line. This is a very rare event.
The resulting earthquake lasted up to 10 minutes. Usually, an earthquake like this lasts only a few seconds. According to various calculations, the current earthquake strength reached 9.1 to 9.3 on the Richter scale, and was the second largest earthquake in the last 100 years. In 1960, an earthquake in Chile was recorded at a magnitude of 9.5 on the Richter scale.
Why do giant tsunami waves appear?
One of the continental plates shifted up to 15 meters, so it moved vertically. This caused the seabed to move up to 10 meters in some places. That is what makes the sea level at the location suddenly rise. The pushed water then forms a large wave, which travels at very high speed, as fast as a jet plane, and moves towards the shore. In deep ocean areas, this fast moving water is less pronounced on the surface. But towards the increasingly sloping coastal area, the waves will roll higher and higher. On the coast of Sumatra, the wave height has reached about 30 meters.
