A tsunami's depth is largely determined by the depth of the ocean it's traveling through. In the open ocean, a tsunami wave can have a wavelength (distance from crest to crest) of hundreds of kilometers, but its amplitude (height) might be only a meter or less. However, the entire water column is in motion, meaning the tsunami wave extends from the surface all the way to the seabed. So, in the open ocean, tsunamis go as deep as the ocean floor.
Here's a more detailed breakdown:
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Open Ocean: In the deep ocean, tsunamis can travel at speeds of up to 800 kilometers per hour (500 miles per hour), with wavelengths of hundreds of kilometers but heights of less than a meter. The wave's energy extends throughout the entire water column, reaching the ocean floor, which can be several kilometers deep.
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Coastal Areas: As a tsunami approaches the coast and enters shallower water, its speed decreases, its wavelength shortens, and its height dramatically increases. This is where the destructive power of a tsunami becomes evident. While the depth of the wave is still the entire water depth, the impact is concentrated in the coastal zone. The inundation depth, which is how far inland the water reaches, depends on factors like the topography of the land.
- Flat Terrain: On flat coastal plains, a tsunami can surge inland for significant distances, potentially exceeding 1.6 kilometers (1 mile) or more.
- Hilly Terrain: Hilly or mountainous terrain can limit the inland penetration of a tsunami, reducing it to a few hundred meters as the wave loses energy more quickly.
In summary, tsunamis extend to the ocean floor in the open ocean. Near the coast, the entire water column is still in motion, but the destructive impact is more related to the inundation depth, or how far inland the wave travels.
