This is a multi-channel composite map of the Fengyun-3 E star on January 15 provided by the China Meteorological Administration. The figure shows that the texture structure of the ash mushroom cloud formed during the eruption of the Tonga volcano is clearly visible, forming an umbrella-shaped cloud with a diameter of nearly 500 kilometers, and a circular shock wave appears around the umbrella-shaped cloud, spreading around it. Xinhua News Agency (Photo courtesy of China Meteorological Administration)
Beijing, 19 Jan (Xinhua) -- On 19 January, xinhua daily telegraph published an article entitled "Why is the volcano of Tonga 'as fierce as fire'?" report.
The off-white gas and volcanic ash produced by the violent eruptions form a super-huge mushroom cloud, like a "flower of death" slowly blooming in space; the clearly visible ring-like shock wave spreads around, and the violently fluctuating sea water triggers a transoceanic tsunami - the scene of the eruption of the Tonga volcano captured by satellites from many countries is shocking and heart-wrenching.
The crater is like a steaming round cauldron. Xinhua Daily Telegraph reporter Zhang Jiansong took a photo
The volcanic eruption in Tonga has brought great disasters to the local people, and the search and rescue work is of global concern. Why was this eruption so violent?
The New Zealand Navy ship Wellington (left) sets sail for Tonga from Devonport Military Port in Auckland on 18 January. The New Zealand Ministry of Defense said on the 18th that two rescue ships of the New Zealand Navy have departed for Tonga on the same day, preparing to provide Tonga with freshwater-based relief materials. Xinhua News Agency (Photo courtesy of New Zealand Ministry of Defence)
Tonga volcano located in the Pacific Rim "Ring of Fire"
The Pacific Ring of Fire, also known as the Pacific Ring of Fire, is an area of frequent earthquakes and volcanic eruptions around the Pacific Ocean, with a total length of about 40,000 kilometers and a horseshoe shape. Ninety percent of the world's earthquakes, 81 percent of major earthquakes, and 75 percent of volcanic eruptions occur around the Pacific Rim.
According to Zhang Jinchang, Qiu Qiang, Yang Xiaodong, Zhou Zhiyuan and other researchers at the South China Sea Institute of Oceanology of the Chinese Academy of Sciences, Tonga Volcano is located at the southwest end of the "Ring of Fire" around the Pacific Ocean. Due to the active plate movement, the geological structure of the area is complex, and volcanic and seismic disasters are frequent. But also located on the Pacific Rim "Ring of Fire", why is the Hawaiian volcano calm and gentle, while the Tonga volcano is as fierce as fire?
Schematic diagram of the Pacific Rim "Ring of Fire" (courtesy of the interviewee)
Zhang Jinchang explained that this is because the two volcanoes belong to different types of submarine volcanoes. Submarine volcanoes can be roughly divided into three types: ocean ridge volcanoes, trench volcanoes, and ocean basin volcanoes.
Ridge volcanoes are formed in the mid-ocean ridge, which is the boundary of the expansion of the oceanic plates and the place where the oceanic crust grows. Volcanoes of this type erupt along the mid-ocean ridge, forming long mountain ranges.
Trench volcanoes are formed in trenches, which are the boundaries where plates converge and where the oceanic crust subducts and dies. This type of volcano is distributed along the trench and takes on an arc-like volcanic island arc, such as The Krakatoa Volcano in Indonesia.
Ocean basin volcanoes are formed in the ocean basin, belong to the volcanoes inside the ocean plate, and are the places where magma erupts from mantle hot spots, mainly including submarine volcanic chains, flat-topped seamounts, ocean floor plateaus, etc., such as the Mauna Loa Volcano in Hawaii, USA.
"Hawaiian volcanoes and Tonga volcanoes are both active volcanoes that erupt from time to time, but the two volcanoes are of different types. Hawaii is a ocean basin volcano and Tonga is a trench volcano. Due to different geological origins, Hawaii volcanoes are weaker in dynamics and have relatively little material energy, so they are milder. Zhang Jinchang said.
Schematic diagram of the subduction zone and volcanoes in Tonga (courtesy of the interviewee)
The global impact remains to be seen and studied
The giant "mushroom cloud" produced by the eruption of The Tonga volcano is shocking.
According to Zhang Jinchang, this is because the eruption of submarine volcanoes will produce a large amount of gas, mainly from the deep part of the earth's water vapor, carbon dioxide, sulfur dioxide and some volatile substances, as well as a large number of volcanic clastic materials and hot lava spewed out, condensed in the air into volcanic ash, volcanic bombs and volcanic debris.
Submarine volcanic eruptions will undoubtedly have a huge impact on the environment of the hydrosphere, biosphere, atmosphere and other multi-layer layers. It is reported that in the most recent eruption of The Doba Volcano on the Indonesian island of Sumatra, the sulfide combined with water molecules in the air to form acid rain, resulting in a large amount of damage to vegetation. High-temperature, toxic volcanic ash landed in large areas in the surrounding area, causing large-scale human and animal casualties.
In addition, volcanic ash enters and stays in the stratosphere in the atmosphere, and the material in the ash reflects sunlight, causing less sunlight to enter the surface, resulting in widespread cooling. At the same time, the particulate matter from volcanic eruptions falls into the vast ocean, providing fertilizer for marine algae, promoting the growth of seaweed, enhancing their absorption of carbon dioxide, a greenhouse gas, and also cooling the earth.
"However, volcanic eruptions release carbon dioxide that was buried deep in the earth and warm the earth. However, what kind of climate change the volcanic eruptions bring to the world in time and space still needs continuous scientific observation and further research. Zhang Jinchang said.
According to the U.S. Geological Survey, the eruption was equivalent to a magnitude 5.8 earthquake, but it produced an oceanic tsunami beyond imagination. The specific mechanism of the current tsunami is not clear, most likely due to the large-scale collapse of the volcanic mountain caused by the volcanic eruption, coupled with the dual effect of the shock wave, resulting in the transoceanic tsunami.
A volcano in Rabaul, Papua New Guinea, in the South Pacific. Xinhua Daily Telegraph reporter Zhang Jiansong took a photo
"Dive belt processing plant"
Why does the Pacific Rim have a "Ring of Fire"? Because this area is located in the area where the Pacific Plate meets the Eurasian Plate, the Australian Plate and the American Plate, it is the "subduction zone processing plant" on Earth.
Subduction zone refers to the tectonic zone in which the oceanic plate subducts under the continental plate, which is the place where the earth's surface material and deep material meet and energy are exchanged.
According to Academician Wang Pinxian of the School of Oceanography and Earth Sciences of Tongji University in the book "Earth System and Evolution", when the oceanic plate subducts, sedimentary rocks, basalt and seawater will be brought into the depths of the mantle. With the increase of the subduction depth, the subduction plate continues to deteriorate and dehydrate. Eventually, when the subduction plate piece reaches a depth of 80 km, the hornblende decomposes, releasing water and other volatile substances, lowering the mantle solid phase line, causing the mantle to melt, magmatic upwelling, and forming a volcanic arc along the subduction zone through volcanic eruptions and magmatic activity.
Specifically, there are two cases: if the oceanic plate subducts below the continental plate, a continental arc is formed, such as the Cascadia Mountains on the west coast of North America and the Andes Mountains on the west coast of South America; if the subduction zone occurs in the ocean, the oceanic plate subducts towards the ocean plate, forming an ocean arc, such as the Izu-Ogasawara-Mariana Island arc in the western Pacific Ocean, which stretches for 2800 kilometers.
Here, the remnants of the ancient oceanic crust of the Pacific Plate, because of its low temperature and high water depth, swooped beneath the young Philippine Plate, forming the deepest trench on Earth, the Mariana Trench, which has a water depth of nearly 11,000 meters. When the Pacific Plate swooped westward beneath the Australian Plate, it formed the second abyss on Earth, the Tonga Trench, with a water depth of nearly 10,800 meters.
If the subduction zone is likened to a factory, the raw materials are the oceanic crust and oceanic sediment, the product is magma and the land crust, and the waste products produced by the production process are the plates that have been subducted into the depths of the mantle after the dehydration and melting process. Scientists can further understand the production process in the depths of the "subduction zone processing plant" by in-depth analysis of the geochemical indicators of the material produced by volcanic eruptions.
Volcano monitoring facility in Rabaul, Papua New Guinea. Xinhua Daily Telegraph reporter Zhang Jiansong took a photo
Truly understand the Pacific Rim "Ring of Fire"
Like Tonga, the Pacific island nation of Papua New Guinea, located on the Pacific Rim "Ring of Fire", is also volcano-rich. Rabaul, the closest city to the New Britain Trench, is home to several active volcanoes.
In 1994, an active local volcano called Tavurvur erupted after more than half a century of silence, and a large amount of ash and hot gases instantly destroyed 80% of the entire city of Rabaul. Twenty years later, the vigorous active volcano erupted again, spewing large amounts of rock and ash into the air 18 kilometers above sea level, forcing multiple flights to take a detour.
In July 2015, the reporter followed the scientific expedition team of the Shanghai "Rainbow Fish" project to Rabaul and took the "Rankin" moored on the sea at the foot of the Tavurvur Volcano. From a distance, the volcano stands out. Because the surrounding peaks are verdant, only it is black and gray, and the crater is constantly emitting white smoke. At dusk, the crater is dotted with white clouds.
Rabaul has set up a special volcano monitoring station. Local monitors detailed the causes of the volcano and the monitoring equipment. In order to learn more about the volcano, the captain of the "Rankin" also led the expedition team to climb to the crater to inspect the site.
From the "Lanjin" to the foot of the volcano in a dinghy, the dark and delicate volcanic mud covered the beach, and in some places there was still steam, and the soles of the feet seemed to step on the "geothermal pad", so hot that they could not stand in one place for a long time, but the sea was warm and clear.
After the various substances spewed out by the volcano have cooled down, they are piled up on the volcano in a mess. Climbing up from the base of the mountain is like climbing a huge pile of rocks, and there is no mountain road to go. The volcano, which has just erupted, emits a strong smell of sulfur. Some of the crevices of the mountains are still steaming, and the stones are still hot to the touch; some magma has not yet formed stones after spewing out, only wrapped in a hard shell on the outside, and inside is a large lump of soft and soft substance; some materials form stones that are harder than iron, and the edges and corners are sharper than knives. At an altitude of more than 700 meters above sea level, we struggled to climb for more than two hours to finally reach the crater.
The black crater resembles a large, concave, circular cauldron. Standing on the edge of the cauldron and looking down, the pot is bottomless and steaming. The huge stone cracks are all steaming with white heat, sometimes large and small, the smell of sulfur is overwhelming, and the color of the stones around the cracks is obviously different. Witnessing the crater with their own eyes gave the expedition team a more realistic understanding of the Pacific "Ring of Fire".
However, Earth's own ability to repair is also amazing. In August 2016, when the reporter came to Rabaul again on the "Zhang Jian" research vessel, the volcano had stopped smoking, and its dark body had become soft and quiet, no longer appearing so abrupt between the surrounding mountains.
At present, the eruption of the "fiery" Tonga volcano indicates that the crater has awakened, and the eruption period may last for weeks or even years, and it is not clear whether it will reach the peak, let alone when it will be quiet. If it erupts again, Tonga risks being devastated by a "chain of disasters" such as tsunamis, torrential rains, floods and strong winds. Experts called on the international community to strengthen its assistance to the affected people in Tonga, while strengthening monitoring and preparing for more "disaster chains".