tsunamis

Tsunamis are long-wavelength ocean waves produced by rapid displacement of water, typically caused by undersea earthquakes at tectonic plate boundaries. They can also be generated by volcanic eruptions, submarine landslides, or asteroid impacts. In deep water, tsunami wavelengths may exceed 100 kilometers, with periods of 10 to 60 minutes, and they travel at high speeds (roughly 200–800 kilometers per hour) depending on water depth. Their wave height in the open ocean is often small, only a few tens of centimeters, making them difficult to detect far from shore.

As tsunamis approach shallower coastline, they slow and their amplitude increases due to shoaling, potentially producing waves tens of meters high that arrive as a series of waves over hours. The first wave is not always the largest; run-up height and flood extent can vary greatly by coast and seabed topography.

The most common cause is sudden vertical displacement of the seafloor during subduction-zone earthquakes, where one plate is forced over another. Other causes include volcanic explosions, flank collapses of volcanic islands, large submarine landslides, and, rarely, impacts from meteoroids. Tsunami propagation is influenced by ocean depth, coastline geometry, seafloor features, and bathymetric variations.

Detection and warning systems rely on seismic networks and sea-level sensors, including deep-ocean tsunami buoys and coastal tide gauges. Warnings are issued to evacuate low-lying areas; not all events produce warnings or landfall, but well-organized systems can significantly reduce casualties.

Notable tsunamis include the 2004 Indian Ocean event, which affected many countries around the rim of the Indian Ocean, and the 2011 Tōhoku tsunami in Japan, which caused extensive damage and led to a nuclear accident.