Tsunamis, also known as sea waves, are caused generally by earthquakes. It is a series of extremely long traveling ocean waves. These waves will propagate along the ocean floor with incredible speed and deceivingly small wave height.
"Tsunami waves are distinguished from ordinary ocean waves by their great length between wave crests, often exceeding 100 km(60 miles) or more in the deep ocean, and by the time between these crests, ranging from 10 minutes to an hour." (unesco.org)
Once the tsunami waves reach shallower areas, the waves will slow down and the wave height will increase exponentially until it can form a giant wall of water tens of meters in height. This effect can be amplified by submarine topography (bathymetry) or underwater landslides depending on the submarine soil composition. Conversely, its effects can be mitigated by effects of coral reefs and elevated topography.
BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH
Sources:
UNESCO Intergoernmental Oceanographic Commission & International Tsunami Information centre & Laboratoire de geophysique, France & U.S. National Oceaninc & Atmospheric Administration. "Great Waves." June. 2005.
[http://ioc3.unesco.org/itic/files/great_waves_en_2005_small.pdf]