Flash interactive
Produced by the American Museum of Natural History, November 2005.
This interactive allows users to click through the steps of tsunami generation, propagation, and inundation. Text and animated diagrams explain the science behind tsunami wave motion.
Visual: Cutaway illustration of an ocean overlying a subduction zone plate boundary.
Underwater earthquakes cause most tsunamis.
Visual: The continental plate lifts upward, launching a bulge of water that falls back into the ocean.
During a subduction earthquake, one tectonic plate thrusts upward several meters. This launches a massive volume of water upward. The water falls back into the ocean from gravity.
Visual: A giant waveform rolls across the ocean's surface.
A tsunami is energy traveling rapidly through water. The tsunami's energy is the sum of the plate's upward thrust and gravity's downward pull. This energy spreads as a wave.
Visual: The energy underneath the tsunami wave is represented by a gradient that is strong at the top and weaker near the ocean floor.
A tsunami's energy affects water to the seafloor. The depth of water a wave affects is half its wavelength (distance peak to peak). Since one tsunami wave can be 200 kilometers long, its energy extends to the ocean floor.
Visual: Surface-wind waves are shown in comparison to the tsunami wave. Their energy gradient extends only a short distance down from the water's surface.
Most ordinary ocean waves are caused by wind. With typical wavelengths around 100 m, their energy is very shallow.
Visual: The tsunami wave rolls toward shore. It gets taller and narrower.
As a tsunami approaches shore, its energy stays constant but its shape changes. Decreasing water depth increases the wave's amplitude (height) and decreases its wavelength.
Visual: The taller, narrower tsunami wave floods shore.
The tsunami loses energy to friction with the rising seafloor. The wave slows, creating a pileup of water. The tsunami floods the coast to a runup (level) based on the wave's energy and local topography.