An ocean scientist explains the physics of these destructive waves
Deep displacement. Most waves are generated by wind as it blows over the ocean’s surface, transferring energy to and displacing the water. Tsunami waves travel fast. No matter the cause of a tsunami, after the water is displaced, waves propagate outward in all directions – similarly to when a stone is thrown Destruction on land.
Once a tsunami forms, its speed depends on the depth of the ocean. In the deep ocean, a tsunami can move as fast as a jet plane, over 500 mph, and its wavelength, the distance from crest to crest, may be hundreds of miles.
An increase in wave amplitude results in “shoaling” when waves, including tsunamis, run from deep to shallow water. This is significant in coastal regions. This phenomena occurs because of the force from the seabed as it becomes shallower. This slows down the wave: the shallower the water, the slower the wave.
Why do we study tsunamis in science?
Students can investigate tsunamis to discover the impacts of Earth’s systems on humans. Teachers can use these potentially deadly waves and other natural hazards to bring relevance to science concepts such as plate tectonics, acceleration and speed, force and motion, energy transfer, and the physics of waves.
Why do tsunamis cause shoaling?
If we look at the natural causes of this phenomenon, we’ll realize the shoaling process is strictly related to the wave ” amplitude “. An increase in wave amplitude results in “shoaling” when waves, including tsunamis, run from deep to shallow water. This is significant in coastal regions.
About 80% of tsunamis are generated by powerful earthquakes (particularly those beneath the sea floor); the remaining 20% result from large landslides, volcanic eruptions, and less frequently (fortunately) meteorite impacts. They are sometimes referred to, incorrectly, as tidal waves. Tides result from astronomical forces.
While researching we ran into the question “What determines the amount of shoaling caused by a tsunami?”.
The amount of shoaling by a tsunami is described by the term ‘ run-up ’, which is the height of the wave crest above normal sea level at its highest point inland before it dissipates. Run-up, wave speed and slope of land at the coast all contribute towards the damage caused.
The form of the adjacent geography to deep water (open bays and coastline), can shape the tsunami into a step-like wave with a steep braking face. The wave height as it crashes upon a shore depends almost entirely upon the submarine topography offshore. Steeper shorelines produce higher tsunami waves.
How do tsunamis move the ocean?
Sound waves, radio waves, even “the wave” in a stadium all have something in common with the waves that move across oceans. It takes an external force to start a wave, like dropping a rock into a pond or waves blowing across the sea. In the case of tsunamis, the forces involved are large — and their effects can be correspondingly massive.
Another thing we wondered was; is a tsunami a wave?
Tsunamis are just long waves — really long waves. But what is a wave? Sound waves, radio waves, even “the wave” in a stadium all have something in common with the waves that move across oceans. It takes an external force to start a wave, like dropping a rock into a pond or waves blowing across the sea.
What happens to a tsunami wave when it enters the ocean?
Shoaling happens because waves experience force from the seabed as the water gets shallower. This slows down the wave – the shallower the water, the slower the wave. In deep water, a tsunami moves very fast and has a long wavelength and a small amplitude. As it enters shallower water, it slows down and the wavelength decreases.
How does the speed of a tsunami depend on its wavelength?
The speed of shallow-water waves, including tsunamis, is independent of their wavelength, but is dependent on water depth in the following way: Speed = √ (g. depth) (g = gravitational constant, 9.8m/s 2; depth in metres) In the case of tsunamis, the wavelength is many times greater than water depth, even in oceans more than 4000m deep.