The tsunami recently swept into populated areas on the shores of a number of islands in the South Pacific, following the eruption of an underwater volcano on the island of Tonga, causing material damage and prompting some residents to flee to safer areas.

Video clips, circulated by social media pioneers, showed tidal waves sweeping land in Nuku Alofa, the capital of the Kingdom of Tonga, which is located two thousand kilometers northeast of New Zealand, and in Pago Pago, the capital of American Samoa, which is located to the east of Tonga.

Friday, January 14, 2022, the volcano, located 65 kilometers north of the capital of Tonga, erupted, releasing a cloud of ash, steam and gas into the air that extended for a distance of 20 kilometers.

The Geological Survey of Tonga stated that the volcano witnessed an intermittent eruption in late December, but indicated that the eruption that occurred on Friday was 7 times stronger than its last eruption.

Etymology

A tsunami is a series of single strong waves that hit the shore with a time difference between minutes and hours, and are not sensed inside the water, as their height often does not exceed a meter before they approach the shore.

The word "tsunami" in Japanese means beach waves or harbor waves, and the origin of this name goes back to the Japanese fishermen who were wading through the sea in their search for fishing, and when they return to the shore sometimes they find that the port from which they started has been completely destroyed, although they did not feel these waves The destroyer coming from the sea when they were in his view.

These waves result from a sudden and violent movement of large quantities of water under the influence of tremendous pressure from the bottom of the ocean water body or the sea, and it is often the result of a high-intensity earthquake that causes violent movement of the tectonic plates (the earth plates) with the resulting enormous air pressure or revolution A large-scale volcanic or landslide deep in the water body.

The controversy raged among scientists about the difference between these two phenomena, but the progress of scientific research allowed monitoring the radical difference between them, both in terms of the climatic origin of the tidal wave and the geology of the tsunami, or in terms of the waves' formation and behavior.

its reasons

The movements of tectonic plates and plates are the main factor in the occurrence of a tsunami. In the midst of our preoccupation with life, the earth moves from under us at a constant pace, as the stars, planets and moons move above us.

Scientists believe that the Earth was a single continent called Pangea, and it split into plates that converged and diverged between themselves until it reached its current form consisting of 7 continents, and what confirms this theory that the borders of the continents are compatible with each other like a puzzle.

Scientists predict that the continents, after 200 million years, will converge again and return to their previous era "Pangia" and in a scene that may seem surreal and surprising: This clip shows the movement of the continents through time in their separation and then coalescing again in the future.

Scientists divided the Earth's surface into 12 tectonic plates. These plates move 3 different movements at a rate of 1-2 inches annually, which are: convergent, divergent, or horizontal movements.

Some natural disasters such as volcanoes and earthquakes result from plate tectonic movements.

To visualize the movement of the plates, imagine that both your hands represent a tectonic plate, place one palm opposite the other palm and bring them close to touch, this will be a convergent movement. forward and the other back.

Convergent movements cause volcanoes or the formation of mountains. When the plates converge, one plate may fall under the other, so if one plate is more dense than its counterpart, it will fall under it, then the pressure under the surface will rise as a result of this fall. As the temperature rises, they, in turn, stimulate the melting of minerals and rocks below the surface.

The molten rock is called “magma” and it comes out from the ground to the surface from the crater of the volcano as a result of the high pressure and temperature, and after its exit it is called “lava.” The opposite movements may sometimes be accompanied by severe earthquakes (earthquakes).

The so-called "Ring of Fire" - located in the Pacific Ocean - contains the largest number of active volcanoes on the Earth's surface, with nearly 500 active volcanoes, and Indonesia alone contains 76 active volcanoes.

The reciprocal movement of the tectonic plates caused the Indonesian tsunami, as the Indonesian-Australian plate slipped under the Eurasian plate, which led to severe pressure resulting in high waves, according to a press statement to the British Guardian website.

tidal waves

Tsunami waves form large in the depth of the sea and flourish and swarm thanks to the strong winds, while tsunami waves remain hidden and are hardly perceptible until they reach the coasts, and their intensity has nothing to do with the strength of the wind.

On the other hand, the impact of a tidal wave on land does not exceed a few metres, while tsunami waves can penetrate the land several kilometers depending on the nature of the beaches and the level of their height above sea level.

The phenomenon of tsunami is characterized by the fact that the speed of its waves spread sometimes reaches 800 kilometers per hour, and the scope of this spread may exceed the area of ​​an entire ocean, sometimes in one day.

One of its features is the calm of the waves during their movement in the depth of the sea, their height often does not exceed one meter, but they quickly gain strength and strength as they approach the shore, and their height may reach more than 30 meters, and the successive waves also cause a rapid rise in the water level.

The tsunami phenomenon is also characterized by a decline in the water level and its receding in the minutes prior to the arrival of each wave, and this receding is more pronounced before the arrival of the first wave.

In addition, a tsunami is not caused - unlike traditional sea disturbances - from climatic influence such as storms and hurricanes, but is always a geological source.

automatic link

Strong earthquakes are often followed by issuing a warning of the possibility of a tsunami, and traditionally an earthquake is considered a tsunami if its intensity exceeds 6 degrees on the Richter scale.

There is no automatic correlation between the intensity of an earthquake and a tsunami, but the intensity of the earthquake is a necessary condition for a tsunami, but it is not sufficient alone.

Research has confirmed the existence of a close link between tsunami and seismic activity, as more than 80% of the tsunami cases recorded since the beginning of the twentieth century occurred in the Pacific Ocean, which is known for its intense seismic activity.

The history of mankind preserves writings describing tsunami-like phenomena that caused heavy losses, including a sea tide that struck the island of Crete in the Mediterranean in the twentieth century BC, and it is believed that it was the deep cause of the extinction of the Minoan civilization (arose at the beginning of the Bronze Age around 3000 BC).

During its emergence, a tsunami passes through 3 stages: generation, spreading, and then dumping.

Tsunami waves differ from ordinary sea waves in speed, size and losses that result from them. Their speed ranges between 500 and 700 km and sometimes 850 km/hour, and their height reaches 40 m.

The interval between two giant waves ranges from a few minutes to several hours.

The width of the conventional waves does not exceed a few meters, and the width of the tsunami wave is several kilometers.

Accordingly, the amount of water carried by these waves and the size of the loss resulting from them is not comparable to that of the usual counterpart.

Tsunami waves can cause damage far from the epicenter of the earthquake, as the effects of the waves of the Indian Ocean earthquake may extend to the coast of East Africa, and the waves of the Anchorage earthquake in Alaska in 1964 reached California, which is more than 2500 km from Alaska.

seismic belts

According to geologists, the tsunami phenomenon is related to the nature of the geological components of the areas affected by these earthquakes.

Understanding this topic requires entering into details related to the composition of the Earth and its components of the core, crust and mantle, and knowledge of the differences in the specific densities of the rocks that make up the Earth's crust, as well as studying the state of the permanent movement known to the Earth.

Geologists note that earthquakes do not spread randomly on the earth's map, but most of them are found in major belts.

The strongest of these belts is the so-called "Ring of Fire" belt that extends along the eastern coast of the Pacific Ocean, parallels the western Americas, Japan and the Philippines, and reaches Australia and New Zealand, accounting for about 68% of the world's earthquakes.

There is a second belt along the western coast of the Pacific Ocean, starting with the islands of Japan in the north to Indonesia in the south, passing through the arc of the islands of Taiwan.

The third belt, the "Alpine Belt", extends across Africa, Europe and Asia from the Atlas Mountains in North Africa, crossing the Mediterranean to include Italy, Greece and Turkey to China, and contains an estimated 21% of the world's earthquakes.

Earthquakes sometimes occur in areas unrelated to the three seismic belts, as was seen in the Cairo earthquake in October 1992.

through history

During the last century and the beginning of this century, the shores of the Pacific Ocean witnessed 796 cases of "tsunami", 17% of which occurred on Japanese beaches.

When tracking all the cases, it seems that what happened to Sumatra in 2004 was the most deadly in history.

October 28, 1707: An earthquake measuring 8.4 on the Richter scale sends waves up to 25 meters high in the Pacific Ocean, hitting Kyushu, Shikoku, and Honshu, damaging Osaka, damaging nearly 30,000 buildings and killing 30,000 people.

November 1, 1755: An 8.5-magnitude earthquake triggers a series of 3 huge waves that hit the coastal towns of western Portugal and southern Spain.

Its height reached 30 meters in some places.

This tsunami affected the waves even in Carlisle Bay in Barbados where people reported waves up to 1.5 meters in height.

The tsunami killed 60,000 people in Portugal, Spain and Morocco.

In 1883: Karkatoa Island in Japan was known by a strong earthquake and crashing sea waves that left thousands of victims.

The tsunami waves extended to Australia, which is 4 thousand km from this island.

June 15, 1896: A tsunami occurred after a 7.6-magnitude earthquake struck the coast of Sanriku, Japan, and waves were reported to reach 38.2 meters in height and damaged more than 11,000 homes and killed 22,000, as well as the coast of China, killing 4,000. .

1933: An earthquake in San Rico, Japan, left 3,000 dead.

The first of April 1946: A violent earthquake struck Hawaii and Honolulu, leaving many destruction and victims, and the maximum wave height reached 35 m.

1952: Kamchaka, Russia, experienced a tsunami that left 5,000 people dead.

1958: A landslide occurred in Lituya Bay in Alaska and caused the longest tsunami in modern times. The wave reached a maximum height of 524 meters at that time, and was described as being similar to the explosion of an atomic bomb.

May 22, 1960: An earthquake measuring 8.3 on the Richter scale occurred on the beaches of Chile, causing losses to all coastal cities, bringing the death toll to more than two thousand.

The tsunami waves traveled thousands of kilometers to hit the coast of Hawaii and its effects to the islands of the Philippines.

October 9, 1963: The landslide caused 50 million cubic meters of water to exceed the Vaione dam in northern Italy, in a wave up to 250 meters high, causing floods and massive destruction in the Piave Valley below the dam.

260 million cubic meters of rock separated from the summit of Mount Tok on the border between Veneto and Friuli-Venezia Giulia, and fell into the reservoir of the dam.

This event killed two thousand people, nearly a third of the population of Longrone.

1964: The strongest earthquake ever recorded in North America struck Prince William Sound, Alaska, 74 miles southeast of Anchorage.

The earthquake measured 9.2 on the Richter scale, and caused the space needle in Seattle to vibrate 1,200 miles away as well, and it shattered all water and gas pipelines, and it lasted a full 4 minutes.

Once the tremors were over, the waters swelled and resulted in a series of tidal waves, giving local residents less time to prepare to evacuate, and the massive wave swept through coastal villages and wiped out a third of the population.

September 2, 1992: In Nicaragua, the maximum height of the tsunami waves was 10m, and resulted in many deaths.

1998: New Guinea experienced an earthquake that left 2,200 victims, with a maximum wave height of 15m.

December 26, 2004: An undersea earthquake, centered off the western coast of the Indonesian island of Sumatra, caused devastating tsunami waves along the coasts of land overlooking the Indian Ocean.

The most tragic tsunami in documented human history occurred when it reached more than 9 degrees on the Richter scale, and its devastating waves hit Indonesia, India, Sri Lanka and Thailand, leaving more than a quarter of a million people dead, more than 170,000 of them in Indonesia alone.

2006: A 6.3-magnitude earthquake hits the densely populated province of Java, killing 6,000 people and injuring 38,000.

It destroyed 157,000 homes and caused the displacement of 420,000 people.

2010: About 430 people were killed when a 7.8-magnitude earthquake triggered a tsunami that hit the isolated Mentawi region off the coast of Sumatra.

2011: A 9-magnitude earthquake hit the coast of Japan, and a tsunami swamped the northern and eastern coasts of the country, with waves reaching 40 meters above the surface, leaving more than 18,000 dead and missing, and a devastating environmental disaster due to the explosion of a nuclear reactor to generate power in the Fukushima region.

2015: A cliff collapse in Tan Fjord (southeast Alaska) caused a tsunami, reaching a height of 193 meters.

September 2018: Tsunami waves accompanied by an earthquake hit the Indonesian island of Sulawesi, killing 2,100 people.

December 22, 2018: Tsunami waves from the Pacific Ocean swept areas in the islands of Java and Sumatra (western Indonesia), killing about 400 people, in addition to hundreds of injured and dozens missing and about 12,000 people displaced due to the disaster.

The National Agency for Natural Disaster Management of Indonesia said that the tsunami was caused by an eruption of the Krakatau volcano on the island of Anak Krakatau, which caused landslides under the sea, i.e. in the "ocean crust".

October 18, 2021: The Journal of Geophysical Research: Solid Earth published a new study that reveals a method for predicting tsunamis before they occur. Researchers from Kyoto University in Japan show that tsunamis can be predicted even before they rise sea ​​level, by studying the magnetic fields that arise from these massive outbursts of waves.

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