A tsunami is a powerful and destructive sea wave. When an earthquake occurs under the sea, it causes violent undulations in the water due to the seismic waves' energy, forming powerful waves that move forward, submerging coastal areas one by one in a disaster known as a tsunami.
In many Western languages, a tsunami is called "tsunami," a word derived from Japanese "津波," meaning "harbor wave" ("津" means "harbor"). This also indicates that Japan is a country frequently hit by tsunamis. Currently, humans can only observe and predict sudden catastrophic changes such as earthquakes, volcanoes, and tsunamis to prevent or reduce the losses they cause; we cannot yet stop them from happening.
Tsunamis are typically caused by submarine earthquakes with their epicenters less than 50 kilometers below the sea floor and measuring over 6.5 on the Richter scale. The wavelength of a tsunami is larger than the maximum depth of the ocean, and its propagation near the seabed is not significantly impeded. Regardless of the ocean's depth, the wave can travel across it. A tsunami travels at about 500 to 1,000 kilometers per hour in the ocean, and the distance between adjacent wave crests may be as far as 500 to 650 kilometers. When the tsunami wave enters the continental shelf, the depth becomes shallower, causing a sudden increase in wave height. This wave motion creates tidal waves with heights reaching tens of meters, forming a "water wall."
The oscillations caused by earthquakes differ from the waves on the sea surface. Normal sea waves only fluctuate within a certain depth of the water layer, while the water fluctuations caused by earthquakes involve the entire water column from the sea surface to the seabed. Additionally, underwater volcanic eruptions, landslides, and man-made underwater nuclear explosions can also cause tsunamis. Moreover, meteor impacts can also cause tsunamis, with "water walls" reaching up to hundreds of feet. Meteor-induced tsunamis can occur in any body of water, not necessarily along tectonic zones, though they may only happen once every thousand years.
There is a significant difference between tsunamis and waves or tides generated by wind. A gentle breeze over the ocean creates relatively short waves, generating currents limited to shallow water layers. Strong winds can stir up waves over 3 meters high across vast oceans but cannot disturb deeper waters. Tides sweep across the globe twice daily, producing ocean currents similar to those of tsunamis that reach the ocean bottom. However, unlike tides which are caused by the gravitational pull of the moon or sun, tsunamis are driven by underwater earthquakes, volcanic eruptions, meteor impacts, or underwater landslides. Tsunami waves can travel faster than 700 kilometers per hour in deep water, easily keeping pace with a Boeing 747 aircraft. Despite their speed, tsunamis are not dangerous in deep water, where individual waves less than a few meters high can span over 750 kilometers in length, creating such a subtle slope on the sea surface that these waves usually pass unnoticed in deep water. Tsunamis quietly and imperceptibly traverse the ocean, but unexpectedly in shallow water, they can reach catastrophic heights.
Tsunamis are powerful and destructive waves caused by major activities like underwater earthquakes, volcanic eruptions, or underwater collapses and landslides. During an earthquake, the ocean floor fractures, and parts of the strata suddenly rise or sink, causing the entire water column from the seabed to the sea surface to violently "shake." This "shaking" differs greatly from regular sea waves, which usually only fluctuate near the surface and involve little depth, with their amplitude quickly decaying with water depth. In contrast, the "shaking" caused by earthquakes involves the entire water column from the seabed to the surface, containing astonishing amounts of energy.
During a tsunami, the towering waves can reach heights of several meters to dozens of meters, forming a "water wall." Additionally, tsunami wavelengths are very large, capable of traveling thousands of kilometers with minimal energy loss. For this reason, when a tsunami reaches the shore, the "water wall" can surge onto land, posing a severe threat to human life and property.
How to survive a tsunami:
1. Earthquakes are the most obvious precursors to tsunamis. If you feel strong vibrations, stay away from the coast and river mouths. If you hear reports of nearby earthquakes, prepare for a tsunami, paying attention to TV and radio news. Remember, tsunamis sometimes reach places over a thousand kilometers away from the epicenter hours after the earthquake occurs.
2. Ships at sea should avoid returning to the harbor upon hearing a tsunami warning. The fluctuations and turbulence caused by tsunamis in harbors are extremely dangerous. If there is enough time, ship owners should take their vessels out to open sea before the tsunami arrives. If there isn't enough time to leave the harbor, everyone should evacuate from ships moored in the harbor.
3. When a tsunami hits the shore, the sea level often rises or drops noticeably. If you see the sea retreating abnormally fast, immediately evacuate to higher inland areas.
4. Everyone should have an emergency kit with enough medication, drinking water, and other necessities for 72 hours. This applies to tsunamis, earthquakes, and all sudden disasters.