The CRUEL Physics behind Tsunamis!

Tsunami waves that form in the open ocean travel at high speeds but are barely noticeable. Now the wave is approaching the shore where the water depth decreases. Surprisingly, the wave that initially seemed harmless suddenly gains a huge amplitude. A devastating tsunami. The slow-moving ocean beds sometimes interact like this. One tectonic plate sliding under another. Notice the bulging upper layer. How long will this motion continue? These stuck wooden pieces demonstrate what happens. Let's keep on tightening them. But after some point of time... Boom! Similar to the experiment, the ocean beds release all the accumulated energy in a short period of time. This is how tsunami waves are formed. If by magic you could drain the entire ocean, you would clearly see different pieces of the Earth's surface. They are called tectonic plates. The Earth's surface is made up of different tectonic plates moving relative to each other. Precisely seven major tectonic plates. The molten lava in the Earth's core circulates continuously due to convective heat transfer. The tectonic plates float on the molten core like ice floats on water. Due to the continuous motion of lava, the tectonic plates are constantly moving. For example, in this animation, two tectonic plates are diverging away and a rift valley is being formed. The East African Rift Valley is a great example of this kind of motion. Now look at this tectonic plate movement. Here the plates are converging. This kind of interaction can result in the formation of mountains, trenches and sometimes active volcanoes. The best example of this kind of converging motion is Cascade Range, northwestern USA. The movement of tectonic plates is very slow, just a few inches per year. Now an interesting observation. Mark dots on all the earthquake-prone areas of the globe. You will find that they all lie in regions where two tectonic plates meet. Yes, the relative motion between two tectonic plates and associated energy release results in earthquakes. When an earthquake happens deep in the ocean, it may lead to a tsunami. The tectonic plate movement that causes the tsunami is very interesting. It's called subduction zone movement. We've already seen this kind of converging movement, but this time it happens underwater. In this movement, strain energy accumulates in the top tectonic plate over time. Here the continental crust bulges upward and the oceanic plate sinks beneath it. This happens because the oceanic plate is much denser than the continental crust. You may observe one interesting feature of the continental crust. It bends inward, resulting in the formation of huge trenches along the tectonic plate boundary. Look at the beautiful trenches formed on the ocean floor of the Pacific Ocean. But how long does this energy accumulation continue? Some subduction zones store energy for centuries. In other subduction zones, the strain energy is released gradually over time. This slow-slip event does not result in a tsunami. However, in some regions, like the Japan Trench and the Chile-Peru Trench, the energy is released in a fraction of a second. Such earthquakes definitely result in a tsunami wave. The wave so generated will have a speed of more than 200 km per hour, but is barely noticeable due to its low amplitude. Tsunami waves typically have an amplitude of less than half a meter, but a wavelength measuring hundreds of kilometers. However, when the wave approaches the shoreline, the story changes. What's the impact of the decreasing water depth on the wave?