Tsunamis (a Japanese word describing a “harbor wave”) are caused when a large amount of water is displaced in a short amount of time. In deep waters, tsunamis do not seem like a threat; however, once they reach shallow waters, they can cause catastrophic events to coastlines and nearby cities. Tsunamis are caused by geographical means such as earthquakes, volcanoes, landslides, and meteorite impacts.
There are several ways tsunamis could fabricate and a common misconception is that a tsunami is a tidal wave. “Tides are caused by the gravity of the Moon and Sun”; however, tsunamis have nothing to do with tides (Nakamura 152). Tsunamis are caused by the disturbance of the equilibrium position of a body of water. This could happen several ways, the most common being earthquakes. In subduction zones, tectonic plates grind against each other until they snap and create the event of an earthquake. As an earthquake occurs, the equilibrium position is displaced, creating waves forming as the unbalanced water mass acting under the influence of gravity attempts to gain its equilibrium. The vertical movements made from the earthquakes can occur at any faulted plate boundaries but “earthquake on the continental side of the subduction trench are particularly effective generating tsunamis” (Abdulsalam 154).
Moreover, tsunamis can be made by two different types of landslides- those occurring underwater and coastal landslides. Erosion and weathering on coastal landmasses can cause end pieces to fall and therefore causing a disturbance in the equilibrium position. Tsunamis often times occur during storms, where slumps acquire more water mass than they can carry and therefore fall off the coast along with leftover debris. For underwater landslides, smaller events such as a small earthquake or the collapse of a volcano can displace landmasses that then create tsunamis.
Furthermore, the eruption of a volcano above sea level causes tsunami by the debris it flings out called pyroclastic that can flow out to the sea. However, it is the volcanoes that erupt underwater that are more likely to cause a tsunami. Along with the debris that shoots out of the volcano, the gases expelled can also create a disturbance of the position of the water level. As the waves try to find a state of equilibrium, tsunamis are formed.
Perhaps the least frequent cause of tsunamis would be meteorite impact. Because they come from space, the force meteorites would fall into the water would be disastrous. The gravity of the impact can cause severe vertical movements made by “stony asteroids with diameters between about 200m and 2km” (Hills and Groda from Abdulsalam, 155).
All of these occurrences would initiate a wave or several waves that would have extremely long wavelengths that could cross the ocean from one side of the world to another without losing much energy throughout. At the location of the disturbance, otherwise an epicenter, a tsunami will spread in all directions. This could result in the waves spreading throughout the ocean or simultaneously rushing onshore to flood the lowered coast from landslides. Tsunamis that spread throughout the ocean can travel at fast rates; there have been recordings of a tsunami “produced by an earthquake along the coast of Chile in 1960 traveled across the Pacific Ocean, reaching Hawaii in about 15 hours and Japan less than 24 hours” (King). In deep waters, a tsunami may go unnoticed but once the tsunami reaches shallow water, it acquires the towering appearance that is widely known when tsunamis are described.
Tsunamis carry over land with the same force it traveled through the water; however, its physical state changes as it goes into shallow water. A tsunami’s speed will reduce significantly because it will rise in height. This phenomena is called the shoaling effect, where a wave that may have seem imperceptible in deep water grows several meters in height as it approaches the