So, let's talk about this volcanic eruption in Tonga first.
1. Tonga is located in a volcanic-prone area.
Tonga is located on the famous "ring of fire" around the Pacific Ocean, which is a part of the highly active volcanic arc of Tonga-Kemadek Islands (see figure 1), and is a frequent area for earthquakes and volcanoes. At present, there are 6 large and small volcanoes 16 in Tonga, including 2 active volcanoes 12. (Note that a volcano that has been inactive for more than 10,000 years can be called an extinct volcano. Therefore, volcanic eruption can be said to be common in Tonga.
2. The volcano in Tonga is a subduction volcano.
Tonga, located at the intersection of the Indian Ocean-Australia plate and the Pacific plate, is a part of the subduction zone extending from northeast New Zealand to Fiji. Here, the Pacific plate dives westward under the Australian plate, forming the second abyss on the earth-Tonga Trench, with a water depth of nearly 10800 meters. The volcanoes in this area are called trench volcanoes or subduction volcanoes. Figure 2 is a schematic diagram of three types of volcanoes on the earth, and subduction volcanoes are framed with red lines on the right side of the figure.
When the ocean plate subducts, it will bring sedimentary rocks, basalt and seawater deep into the mantle. With the increase of subduction depth, the subduction plate is constantly metamorphic and dehydrated. The gas released by the subduction plate accelerated the melting of the mantle of the upper compression plate, formed magma upwelling, and finally formed the volcanic arc of the subduction volcano along the subduction zone. It is not difficult to understand from the formation mechanism that the eruption of subducted volcanoes is often accompanied by high-pressure gas. The volcano in Tonga is such a volcano. (Because the subduction zone constantly devours the old plates and spits out new rocks through volcanic eruption, it is not unreasonable for some people to say that the subduction zone is the recycling factory of the earth. )
3. Unusual submarine volcano
65438+ 10 15, the volcanic eruption occurred near two uninhabited islands, Hunga-Ha'apai and Hunga-Tonga, 65km north of Nukuwalofa, the capital of Tonga. The island is about 100 meters above sea level. The huge volcano is hidden under the waves on the island, about 1800 meters high and about 20 kilometers wide. The center of the crater is a depression with a diameter of about 5 kilometers. See figure 3.
The dotted line in the figure is the approximate edge line of the crater, and the center of the middle crater is the deepest, about 150-200 meters underwater. Two small islands, namely Hunga-Ha'apai and Hunga-Tonga, are actually located at the edge of this huge crater.
This volcano has erupted frequently in the past few decades, but the eruption scale is not large. The last two times were in 2009 and 201415, both of which occurred at the edge of the crater. The eruption in 2009 formed a volcanic cone (labeled as the 2009 cone). The volcanic cone (marked as cone 20 15 in the figure) generated by the eruption of 20 14/ 15 connected the original two henga islands, forming the present combined island with a length of about 5 kilometers.
Before this explosion, there were two medium-sized eruptions at 202 1, 13, and on February 20, 2022, volcanic ash cloud columns as high as 17 km were generated, and a joint island was formed at 20 14/ 15. The volcanic eruption in June 5438 +65438 10+May 2022 was explosive, so we called it eruption to distinguish it from the general eruption.
4. How strong was the outbreak?
The eruption of Tonga volcano has attracted global attention for two reasons. First, the epidemic is extremely fierce. Second, there are some differences in this outbreak, and some phenomena need further explanation by scientists.
So, how powerful is this outbreak? We look at it from the following aspects.
explosive sound
The explosion can be heard not only in Fiji, Samoa and other neighboring island countries, but also in New Zealand, 2000 kilometers away. Incredibly, a series of explosions or rumblings were heard in Anchorage, Alaska, and Yukon, Canada, almost 10,000 kilometers away, which lasted for dozens of minutes.
shock wave
The satellite captured the scene that the powerful shock wave generated by the explosion spread in the Pacific Ocean. Weather stations in New Zealand and Australia recorded considerable pressure fluctuations. Even in Switzerland and Britain, fluctuations in air pressure have been measured. The shock wave seems to go around the earth several times, because it was recorded four times in Japan and Utah and at least twice in other parts of the United States. This is also very rare.
Volcanic cloud column
The mushroom-shaped volcanic cloud column formed by volcanic ash and steam generated by volcanic eruption is 20km high and 260km in diameter (some people say it is 500km). Volcanic ash particles and harmful gases enter the stratosphere of the atmosphere until they are 39 kilometers above the ground.
Earthquake/tsunami
The volcanic eruption triggered a tsunami in Tonga and its neighbors Fiji and Samoa. Tsunami waves travel thousands of kilometers to New Zealand and Australia. Many places, including New Zealand, Japan, Alaska and California, the Russian Far East, Chile and Peru, have reported destructive tsunamis to varying degrees.
As for the height or intensity of tsunami waves, there is no exact unified statement at present. There are also some inconsistencies in the media reports. A tidal recorder in Nuku 'alofa, the capital of Tonga, was damaged after recording the waves of1.5m. Some media said that the tsunami wave height was1.5m.. This is obviously underestimated. The highest height of tsunami wave confirmed by Tonga government is 15m. This seems to confirm the devastating disaster brought by the tsunami to several nearby islands. But it is not consistent with the data measured by several neighboring island countries. I believe that experts will have further research on this.
Preliminary assessment
This volcanic eruption destroyed the submarine cable connecting Tonga with the outside world and cut off Tonga's contact with the outside world. This has brought some difficulties to the evaluation of this volcanic activity. It is preliminarily estimated that the volcanic eruption index (VEI) of this volcanic eruption is 5, that is to say, it is estimated that 1 cubic kilometer of volcanic material was erupted. The energy released by it was originally estimated to be10 million tons of TNT equivalent, and later it was said to be 4 million to18 million TNT equivalent. If compared with the TNT equivalent of Hiroshima atomic bomb 1.5 million tons, it is 266- 1.2 times. However, unlike the atomic bomb, the main disasters caused by this volcanic eruption are tsunami and volcanic ash, not shock waves.
This is the strongest volcanic eruption in the world in the past 30 years since the eruption of Mount Pinatubo in the Philippines in 199 1, and it is also the once-in-a-thousand eruption of this volcano (the last one was 1 100).
Fortunately, although the outbreak was extremely violent, it only lasted 10 minutes. And it is estimated that there will not be another big explosion of the same intensity in the near future. In addition, because the amount of volcanic ash particles and sulfur dioxide entering the stratosphere is relatively small, it is estimated that it is not enough to cause obvious changes in the global climate.
image data
There happened to be three satellites nearby when the explosion happened, which photographed the extremely precious and shocking explosion process.
(Click here to view dynamic pictures)
5. Why is it so violent?
The scene of the explosion was extremely shocking and caused many discussions. The uniqueness of this eruption is that the magma is not ejected but exploded, which is an explosive eruption. Experts believe that there are two reasons for the explosion: first, the magma of the subducting volcano is often accompanied by high-pressure gas. Second, the location of the volcanic eruption is obviously not at the edge of the crater, but somewhere in the middle of the crater, underwater. The deepest point there is150-200m, and the underwater pressure can reach about 15-20 atmospheres.
It is conceivable that when a huge amount of high-temperature magma rushed out of the crater with high-pressure volcanic gas, seawater could not form a stable protective layer outside the magma to slowly cool the magma, so the magma and seawater formed a chain reaction: the high-temperature magma directly contacted with water and gas in a large area, causing a violent explosion, further tearing the magma into more fragments, and the new magma fragments exposed the fresh high-temperature inner surface to water, and the explosion was repeated, forming a chain reaction. It can be guessed that the location of the explosion is at an appropriate depth, and the underwater pressure here is not enough to completely stop the underwater explosion, but it is enough to make the underwater explosion accumulate energy, and finally reach a weapon-grade extremely violent explosion, rushing out of the water, ejecting a large number of volcanic particles, and producing a sonic boom close to supersonic speed. This is the huge volcanic mushroom cloud and huge shock wave that we see and hear.
Subsequently, the explosion caused the top of the crater to collapse inward, triggering a tsunami. At the same time, the collapse of the crater increased the impact of seawater and shortened the duration of the explosion. We saw that the island of Hongjia-Tonga-Hongjia-Habai combination split again after the volcanic eruption, which should be the evidence of crater collapse.
6. Impact on global climate
Perhaps people are more concerned about the impact of this volcanic activity on the global climate. Strong large-scale volcanic eruption will reduce the global average temperature and even trigger the so-called "volcanic winter". This is because volcanic eruptions contain volcanic ash, water vapor and sulfur dioxide. If these substances are in the troposphere of the atmosphere, they will fall back to the ground with the rain. However, once these substances enter the stratosphere of the atmosphere, they will form aerosols with sulfuric acid beads as the core and stay in the stratosphere for a long time. If there are enough aerosols, they will reflect some sunlight (back into space) and absorb some solar radiation energy. In this way, the solar energy received by the earth's surface is reduced, and the temperature is correspondingly reduced. Therefore, how much sulfur dioxide gas enters the stratosphere can be used to evaluate the impact on temperature change.
We can compare the eruption of Mount Pinatubo 30 years ago (199 1).
Pinatubo * * * ejects 10 cubic kilometers of volcanic objects; Tonga volcano is 1 cubic kilometer this time (10% of the former);
After the eruption of Mount Pinatubo, about 20 million tons of sulfur dioxide gas entered the stratosphere. This time Tonga volcano is only 400,000 tons (2% of the former);
The eruption of Mount Pinatubo caused the global temperature to drop by an average of about 0.4℃ for about two years. According to experts' estimation, the eruption of Tonga volcano will not have a significant impact on the global temperature, but it may reduce the temperature in the southern hemisphere by about 0. 1℃ in a short time (about half a year).
Purple sunset
At present, although the amount of aerosol in the stratosphere is not enough to affect the global temperature change, it still scatters sunlight, especially blue light. Therefore, experts predict that colorful sunrises and sunsets, even purple sunsets, will appear in the southern hemisphere in the next few months.
I have never seen a purple sunset. Out of curiosity, I went to a seaside in Sydney for a few days to watch the sunset. I wonder if these photos below are the so-called purple sunset.
7. Conclusion
It is said that there are at least 500 active volcanoes in the world, and dozens of volcanoes erupt every day, but most of them are ignored.
Volcanoes and earthquakes are both manifestations of the vitality of the earth. It is said that 80% of the earth's surface is related to volcanic eruptions. The earth is getting colder, and volcanic and seismic activities are gradually decreasing. Once the volcanic and seismic activities on the earth stop, the earth will "die". This day will come, but there are still millions or even billions of years from today.