The ocean is the cradle of life, providing rich conditions and endless resources for the birth, evolution and reproduction of life on earth. It can be said that the origin and development of human life and civilization are closely dependent on the ocean and have an indissoluble relationship with the ocean.
However, there are unpredictable storms, and whenever the natural marine environment undergoes abnormal or drastic changes, human beings will also face various unexpected disasters.
Marine disasters mainly include catastrophic waves, sea ice, red tides, tsunamis and storm surges. Among them, tsunamis, as one of the most dangerous marine disasters in the world, are rare, but once they occur, they will bring huge losses to human society, which cannot be underestimated.
Tsunami (Figure: Bug.com)
Tsunami formation
A tsunami is a huge, catastrophic wave. Large-scale, abrupt upward and downward movements of the seabed, including submarine volcanic eruptions, submarine landslides and undersea earthquakes, can cause destructive waves and trigger tsunamis.
Submarine earthquakes are a high-frequency cause of tsunamis, usually the source of the submarine within 50 kilometers below the seabed and the magnitude of 6.5 on the Richter scale or more will cause the seabed topography to rise and fall sharply, resulting in strong disturbance of seawater. The mechanisms are in the form of "descending" tsunamis and "uplifting" tsunamis.
"Descending" tsunami refers to a large-scale sharp decline in the seabed crust caused by certain tectonic earthquakes, and the seawater rushes towards the space of the staggered subsidence, and after encountering resistance on the seabed, it turns back to the sea surface to produce compression waves, forming long-wave large waves, which propagate and spread around. This tsunami initially manifests itself as an unusual low tide on the coast.
"Uplift" tsunamis are caused by certain tectonic earthquakes that cause a large and sharp rise in the crust of the seabed, and the sea water rises and spreads from the source area to the surroundings, forming turbulent waves. This tsunami can first manifest itself as an abnormal high tide phenomenon on the coast.
Tsunami hits coastal buildings (Picture from Figureworm.com)
Tsunamis have wave velocities of up to 700 to 800 kilometers per hour and can cross oceans in a matter of hours. Its wavelength can reach hundreds of kilometers and travel thousands of kilometers with little energy loss. In the deep ocean, although the tsunami wave height is only tens of centimeters, after reaching the shallow water area of the coast, the wavelength is shortened and the wave height increases sharply, up to tens of meters, thus forming a "water wall" containing huge energy, which can destroy the embankment and submerge the land, which is extremely destructive.
At present, the tsunami zone around the world is roughly in line with the seismic zone. About 260 destructive tsunamis have been recorded, an average of about one in six or seven years, and about 80 per cent of earthquakes and tsunamis occur in the Pacific Rim alone.
Self-help guide
On December 22, 2015, the United Nations General Assembly unanimously adopted a resolution officially designating November 5 as "World Tsunami Day" to raise awareness of tsunami preparedness and reduce disaster losses.
As a large coastal country, China has more than 50 coastal cities and countless major projects built by the sea. Once a tsunami occurs, it will bring unimaginable consequences and impacts to the mainland's economy and society.
Therefore, in the face of the huge risk of tsunami disasters, the mainland has gradually strengthened the tsunami disaster monitoring and early warning system and built a perfect tsunami disaster prevention and mitigation mechanism. As individuals, we need to grasp the tsunami dynamics in time, understand escape skills, take early precautions, and evacuate in time to ensure the safety of our lives and property.
Ships before the tsunami (Picture from Tuworm.com)
In coastal areas, earthquakes are the most obvious precursor to tsunamis. If residents notice strong shaking on the ground, please do not approach the seaside or the mouth of a river. In addition, if you find that the tide suddenly rises and falls, the sea level drops significantly, or there are huge waves, it is necessary to evacuate the beach as quickly as possible.
Before the tsunami, the abnormal retreat of the sea often leaves fish, shrimp and other marine animals in the shallows, and the scene is spectacular. At this time, do not go to collect fish or watch the excitement, but quickly leave the coast and move to higher inland places.
When a tsunami makes landfall, everyone should quickly evacuate to a safe area high above the ground and far from the shore, and choose tall and sturdy buildings, hillsides, trees, etc. as shelters.
If you fall into the water, do not raise your hands to struggle, reduce your body movements, strive to float on the surface, grasp floating objects such as wooden boards if possible, and pay attention to avoid collision with other hard objects. If the sea temperature is low, do not take off your clothes. Do not drink seawater to prevent hallucinations. Move as close as possible to other people who have fallen into the water, which makes it easier to help each other and easier for rescuers to detect due to crowds.
After the tsunami warning is issued, ships sailing at sea are not allowed to return to the harbor. With sufficient time, boats mainly sail to the open sea before the tsunami. If it is too late, everyone has to evacuate the ships moored in the harbor.
The tsunami was menacing and the consequences unpredictable. Therefore, no matter when and where, once the tsunami warning information is released, everyone needs to take it seriously, take active precautions, and not take it lightly.
Source: Xinhuanet National Emergency Broadcasting Network
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