From January 14th to 15th, 2022, Tonga, an island country located in the southwest Pacific Ocean, experienced continuous violent underwater volcanic eruptions. A huge amount of gas and smoke erupted from the seabed, and after reaching the surface through the sea water at a depth of four or five kilometers, a mushroom cloud with a diameter of nearly 500 kilometers was formed like a nuclear explosion, and it went straight to an altitude of more than 20 kilometers, enough to block the sun. The electrostatic discharge height of mushroom clouds is twice as high as the height of the most violent thunderstorms on Earth, producing massive amounts of volcanic lightning. In the 15 minutes after the volcano’s initial eruption, lightning detection networks and satellites recorded more than 60,000 lightning strikes, equivalent to nearly 70 strikes per second, and few conventional thunderstorms can match. The Tonga volcanic eruption has the characteristics of high intensity, high energy, and high gas column (up to the middle of the stratosphere). The gas components are mainly water vapor, sulfur dioxide, hydrogen sulfide, and relatively low content of carbon dioxide. The main climate effect is Lowers surface temperature, destroys the ozone layer and forms acid rain.
When the Tonga volcano erupted, the movement was very loud, and the island where it was located was blown up, and the loud noise spread throughout the countries around Tonga. In Fiji, 800 kilometers away, people thought there was a big explosion nearby. People in New Zealand, 1,700 kilometers away, and Australia, 2,300 kilometers away, also heard the sound. Even weather forecasters in Alaska, North America, more than 8,000 kilometers away, said they heard a loud noise from the Tonga volcano. The outbreak on January 14, 2022 was small in scale. Compared with the big outbreak the next day, it could only be regarded as a warm-up exercise, but it had already caused a rare spectacle. It is estimated to be the largest volcanic eruption in nearly 30 years, following the 1991 eruption of Mount Pinatubo in the Philippines.
Tonga volcano eruption triggers tsunami
Mushroom cloud nearly 500 kilometers in diameter formed when Tonga volcano erupted
A rapidly radiating white ring can be easily seen in satellite images of the volcano’s perimeter, indicating that the massive shock wave from the eruption expanded through the air and appeared much earlier than the mushroom cloud column. Data from the National Weather Service showed that air pressure from the eruption slammed into the ocean’s surface and traveled faster than the speed of sound. Atmospheric shock waves traveled halfway across the Earth. The first round crossed the Pacific Ocean from west to east, traveling about 13,000 kilometers to southern New England, USA; the second round moved in the opposite direction, traveling nearly 27,000 kilometers west.
After the Tonga volcano erupted, it also formed a tsunami that swept across the Pacific Ocean. Around Tonga, Fiji, New Zealand, and Australia experienced high winds and waves, and even the distant coastal areas of Japan, the United States, Canada, Peru and Chile were also rough. It stands to reason that the waves caused by the tsunami in the source area are the highest, and the waves are lower the farther away. But the Tonga volcanic tsunami did the opposite. The tsunami waves on the coasts of Japan, the United States, and Canada were about one meter high, and the waves in Peru and Chile in South America were about two meters high, which was higher than the tsunami generated near the volcano. In addition, the tsunami triggered by the eruption appeared much earlier than the normal arrival time of an earthquake tsunami. The waves of a small tsunami were detected about three hours before the normal tsunami’s arrival in Japan, and also several hours earlier along the coasts of the United States, Canada, Mexico, Peru and Chile.
The appearance of the tsunami phenomenon across the continent is the strangest phenomenon among the tsunamis caused by the eruption of Tonga’s volcanoes. We know that tsunamis caused by earthquakes etc. only occur in the sea area and ocean where the earthquake occurred. For example, the tsunamis caused by the Chile earthquake on May 21, 1960 and the East Japan earthquake on March 11, 2011 both occurred in the Pacific Ocean. The tsunami caused by the 2004 Indonesia earthquake mainly affected the Indian Ocean. In addition to causing tsunamis in the Pacific Ocean, the Tonga eruption also caused a tsunami in the Atlantic Ocean. Scientists have also detected small tsunami waves about 10 centimeters high in the Caribbean Sea in Central America, which is separated from the Pacific Ocean by the Central American Isthmus, which belongs to the Atlantic Ocean.
In this regard, the scientists explained that this shows that the huge shock wave generated by the volcanic eruption expands in the air, and it can also spread across the land. The original tsunami triggered by the Tonga eruption was a shock wave tsunami, and this very rare “global shock wave” circled the entire planet at the speed of sound. The Tonga volcanic eruption is eye-opening, breaking people’s inherent thinking mode about tsunami generation, and broadening the horizons of tsunami research. Needless to say, such shock wave tsunamis caused by volcanic eruptions must have occurred many times before, but due to the lack of advanced observation methods at the time, they have never been detected.
The volcanic eruption was huge, releasing an energy equivalent to 1,000 Hiroshima atomic bombs. Communication between Tonga and the outside world was interrupted for several days due to damaged submarine cables and volcanic ash obscuring satellite signals. It is reported that the volcanic eruption affected more than 80% of Tonga’s population. The United Nations Satellite Center analyzed the disaster situation and released a comparison of satellite images of multiple islands before and after the disaster on social media. In the picture, the entire island in the north after the eruption and the new island formed in 2014 sank below the sea surface, and the surrounding 285 hectares of land almost “disappeared”. The satellite monitoring of the damage on the island of Tonga’s Nomuka in the cloud-free area showed that almost all buildings were covered in volcanic ash, of which 41 buildings were confirmed to be damaged. Short-term shortages of food and drinking water have brought disaster to the locals. In the longer term, the follow-up issues from this crisis are more challenging.
In addition to worrying about the safety of Tonga residents, many people have also begun to worry about whether Tonga’s volcanic activity will have a wider impact, such as affecting the global climate, and even causing the summer to disappear in 2022? Judging from the latest satellite monitoring data, the volcanic ash emitted by this volcanic eruption is mainly concentrated in the southern hemisphere, with a maximum height of about 28 kilometers, which has reached the middle and lower layers of the stratosphere and will definitely have a certain impact on the climate. Its cooling effect causes a slight cooling in winter. But it is estimated that only about 400,000 tons of sulfur dioxide entered the stratosphere during the eruption, about one-fifth of the impact of the Pinatubo eruption. These values are still far from having an impact on the global climate. If there is no larger-scale eruption in the future, it can be judged that this volcanic activity is unlikely to affect the global temperature, and it is not enough to cause a global “year without summer”. Currently, the Tonga volcano is still active, and based on statistical analysis of historical volcanic events, the current eruption could last for weeks or months. Whether there will be a larger outbreak in the future requires further monitoring.
Satellite images of Tonga volcano eruption
Schematic diagram of tsunami caused by volcanic eruption
Tonga’s chief geologist Kula pointed out that the energy released by this volcanic eruption is about 7 times that of December 20, 2021, indicating that the crater in the area has awakened, and the active period of the eruption can last for weeks or even years. It is still unclear. has reached its peak. If the volcano erupts again, Tonga will be devastated by a chain of disasters including tsunamis, heavy rains, floods and strong winds. The eruption was the equivalent of a magnitude 5.8 earthquake, according to estimates by the U.S. Geological Survey. At present, the specific mechanism of tsunami generation is still unclear. It is likely to be due to the large-scale collapse of volcanic mountains caused by volcanic eruptions, coupled with the dual effects of atmospheric shock waves. Next, scientists will carry out further multidisciplinary exploration of seafloor geophysics, hoping to solve this mystery.
The interior of the earth is a concentric ring structure, which is divided into the core, the mantle and the crust from the center to the surface. Although the core temperature exceeds 4300 ° C and can melt any substance, the core still exists in a solid form due to the sufficient pressure. The mantle layer outside the core is a viscous fluid with a higher temperature, and the outer mantle layer is a cold and hard rock layer. Heat convection occurs as the hot material below the mantle flows upwards into the rock layer and cools. Thermal convection can not only cause the slow movement of mantle material, but also cause the crustal layer above the mantle to gradually move, forming plate drift.
In the process of plate drift, earthquakes are sometimes triggered due to dislocation of the crust or geological collapse. In places where the crust is relatively weak, the magma in the mantle will be ejected along the gap under the action of pressure, forming a volcanic eruption. The magma erupted from the ground, merged into a boiling river and rushed forward until it gradually cooled. The physical and chemical reactions produced by magma can release toxic gases that rise like bubbles in water to the surface of the magma to burst, which is how magma is seen boiling.
Submarine volcanoes are all kinds of volcanoes formed at the bottom of shallow seas and oceans and are widely distributed. According to statistics, there are more than 20,000 submarine volcanoes in the world, and the bottom of the Pacific Ocean has more than half of them. Submarine volcanoes are mainly concentrated on the boundaries of the earth’s plates and are distributed in bands called “volcanic belts”. There are also some submarine volcanoes scattered in the ocean basin.
Submarine volcanoes can be roughly divided into three types: ridge volcanoes, trench volcanoes and ocean basin volcanoes. Among them, ridge volcanoes are formed on the mid-ocean ridge, which is the boundary of the expansion of the oceanic plate and the place where the oceanic crust is accreted. This type of volcano forms a long mountain range along the mid-ocean ridge. Trench volcanoes are formed in trenches, which are the boundaries of the convergence of plates and the place where the oceanic crust subducts and dies. Volcanoes of this type are distributed along ocean trenches, presenting arc-like volcanic island arcs. The oceanic basin volcanoes are formed in the oceanic basin and belong to the volcanoes inside the oceanic plate, mainly including submarine volcanic chains, flat-topped seamounts and oceanic plateaus.
Tonga is located at the southwestern end of the “Pacific Rim of Volcanic Seismic Belt”. The “Ring Pacific Volcanic Seismic Belt” is an area with frequent earthquakes and volcanic eruptions around the Pacific Ocean, with a total length of about 40,000 kilometers and a horseshoe shape. The active plate movement has resulted in a complex geological structure and frequent geological disasters in the region, which are concentrated in 90% of the world’s earthquakes, 81% of major earthquakes and 75% of volcanic eruptions. In fact, since the 20th century, the submarine volcanic activity of Hongahaapai Island has always been active. In recent years, the appearance of the island has been changed repeatedly with multiple eruptions. The rim of the massive underwater crater bulges. The massive eruption of the Tonga volcano is not surprising, given the huge underground magma chamber beneath the island.
Global Plate Tectonic Map
Both Tonga and Hawaii are active volcanoes that erupt from time to time, but they are of different types. The Tonga volcano is a trench volcano. During the subduction of the Pacific plate to the Indo-Australian plate (referring to the Indian and Australian plates), the Pacific plate continuously brings water and carbon seabed sediments and rocks into the deep part of the earth. High, the formation of molten magma, magma upwelling erupted to the bottom of the sea, violent and abnormal, as hot as fire, producing a large amount of gas. Hawaii is an ocean basin volcano with weak dynamics, relatively small material energy, and appears calm and gentle.
After reading this, some people may have doubts in their hearts: the vast oceans and seas are so vast, why can’t they extinguish the underwater volcanoes? Water can put out the fire, because the combustion of the fire requires a combustion-supporting material, and the water can isolate the combustion-supporting material and reduce the temperature, so that the fire can be reduced or even extinguished. The principle of volcanic eruption is that the internal pressure is too large, and the molten material above 1000 ℃ will be ejected to the earth’s surface at the moment of the eruption. Although seawater can reduce the temperature of volcanic magma to a certain extent, it cannot reduce the pressure inside the earth and prevent the eruption of volcanoes.
It is particularly worth mentioning that volcanic eruptions and volcanic disasters cannot simply be equated. Volcanic eruptions will have two consequences: one is harm, and the other is resources. There is no doubt that volcanic activity will bring huge disasters to human beings. However, the formation of energy sources such as geothermal, oil and natural gas is also related to volcanic activity. It is precisely because of volcanic activity that diamonds and various other mineral resources are formed. The formation of most metal deposits is inseparable from magmatic and volcanic activities, such as copper, titanium, nickel and rare earth elements in the mantle or crust are very low in content, and magmatic activities will enrich these elements and crystallize into Different minerals form corresponding deposits.