Ocean waves of the type monitored by the Disasters Charter are most typically tsunamis, but storms with strong winds can also cause hazardous coastal waves.
Tsunamis are seismic sea waves and typically occur as a result of underwater earthquakes or volcanic eruptions, but they can also be caused by other external factors; such as ice calving from glaciers or meteorites. Tsunamis are tall waves which can extend as high as tens of metres, and are enerated by activity at sea. These waves extend over land when they reach coastal areas and can impact with deadly force and leave flooding in their wake.
The majority of tsunamis occur in the Pacific Ocean's "Ring of Fire", a wide area stretching roughly from the western coast of South, Central and North America and then across to the eastern coast of Russia, China, and the entirety of Japan, the Philippines and many islands in the south Pacific Ocean. Tectonic plates meet in this ring, and as such it as a geologically active region.
Satellites are useful in imaging the aftermath of a tsunami, using optical and radar data to identify damage and flooded areas.
Japan - Minamisoma - Observed inundation extent as of March 12, 2011
Source: RapidEye and TerraSAR-X
RapidEye, DLR - Map produced by ZKI
Tsunami affected areas - Rikuzentakata - Iwate Prefecture, Japan
Acquired: Pre-disaster: 29/09/2010;
GeoEye, NASA - Map produced by ImageCat