26 December 2004 - The Indian Ocean tsunami

During the afternoon on the 26th of December of 2004, the earth shook on the island of Sumatra, part of Indonesia, in the third largest earthquake ever recorded, a magnitude 9.2. Soon after, a wave rose up to 30 meters (100 feet) high as it ran aground on coastal areas in Indonesia, Thailand, India. Several hours later, waves ran aground in east Africa, causing further devastation. All told, 230,000 people died and millions had their lives upturned. The earthquake had lasted longer than any previously recorded at almost 10 minutes and the tsunami that followed had affected an entire ocean basin and was the first major megathrust earthquake since the 1960s.

What is a tsunami?

Tsunamis happen when the seafloor is rapidly lifted by an earthquake. The overlying water is also raised creating a wave displacing enormous amounts of amounts. In the deep ocean, this wave would be barely noticeable because tsunamis have a wavelength up to 200 kilometers in the deep ocean, and are only a few inches tall. Normal ocean waves with wavelengths of a few dozen meters. However, as the tsunami arrives in the shallow water near the coastline, the wave slows down and the water piles up forming a much tall wave. This is what those on the shore experience. Tsunamis can happen anywhere a large thrust fault lies underwater -- Japan (the source of the word tsunami), the Carribean, the Mediterranean, Indonesia, southern California, amongst others.

Visualization of tsunami runups

Tsunami runup is the maximum height above sea level that a tsunami reaches at landfall. Runup provides a good proxy for the "size" of a tsunami at a location. This polar plot shows the travel time to each measurement of tsunami runup, and the direction from the epicenter of the earthquake. The size of each point shows the number of fatalities and the color shows the runup.
Sources:
  • NOAA Historical Tsunami Database
  • Bilham, R., Engdahl, R., Feldl, N. & Satyabala, S. P. Partial and complete rupture of the Indo-Andaman Plate boundary 1847–2004. Seismol. Res. Lett. 76, 299–311 (2005)