1. What does "tsunami" mean?

Tsunami is a Japanese word that means: “harbor wave”. Represented by two characters, the top character, “tsu”, means harbor, while the bottom character “nami” means wave.

2. How do tsunamis differ from other water waves?

One wave after another might have a period of about 10 seconds and a wavelength of 150m. A tsunami on the other hand can have a wavelength in excess of 100km and period on the order of one hour. As a result of their long wavelengths, tsunamis behave as shallow-water waves. A wave becomes a shallow-water wave when the ratio between the water depth and its wavelength gets very small. Shallow-water waves move at a speed that is equal to the square root of the product of the acceleration of gravity (9.8 m/s/s) and the water depth.
For example in the Pacific Ocean, where the typical water depth is about 4000 m, a tsunami travels at about 200m/s or over 700km/hr. Because the rate at which a wave loses its energy is inversely related to its wavelength. Tsunamis not only propagate at high speeds, they can also travel great, transoceanic distances with limited energy losses.

3. How do landslides, volcanic eruptions, and cosmic collisions generate tsunamis?

A tsunami can be generated by any disturbance that displaces a large water mass from its equilibrium position. Submarine landslides, which often accompany large earthquakes, as well as collapses of volcanic edifices, can also disturb the overlying water column. Similarly a violent submarine volcanic eruption can create an impulsive force that uplifts the water column and generates a tsunami.

4. What happen when a tsunami approaches land?

A tsunami travels at a speed that is related to the water depth; hence as the water depth decreases, the tsunami slows. Consequently, as the tsunami’s speed diminishes as it travels into shallower water, its height grows. When it finally reaches the coast, a tsunami may appear as a rapidly rising or falling tide, a series of breaking waves, or even a bore.

5. What happen when a tsunami encounters land?

When a tsunami approaches land it begins to slow and grow in height. Just like other water waves, tsunamis begin to lose energy as they rush onshore. Despite these losses, tsunamis still reach the coast with tremendous amounts of energy.
Tsunamis may reach a maximum vertical height onshore above sea level, often called a run-up height, of 10, 20, and even 30 meters.