At around 12:10 p.m. Beijing time on January 15, 2022, a violent volcanic eruption occurred near 20.536° south latitude, longitude 175.382° west in the South Pacific island nation of Tonga,000, and the initial judgment was that the eruption intensity reached the volcanic eruption index level 5 or above, forming a volcanic ash column with a diameter of about 450 kilometers, and the volcanic ash mushroom cloud expanded at twice the speed of sound, affecting half the earth.
Figure 1 The eruption of The Tongahun Ahapay Volcano formed a huge cloud of volcanic ash (image from Doman et al 2022).
How big was the eruption in Tonga?
The volcanic eruption of Tongahun Ahapai Island spewed about 5 cubic kilometers of volcanic ash into the atmosphere, and a large amount of volcanic ash was sprayed into the air at an altitude of more than 30 kilometers, forming a column of volcanic ash with a diameter of about 450 kilometers, entering the stratosphere. As the ash drifts westward, small amounts of ash even reach an altitude of 39 kilometers. The impact of the Tonga volcano eruption is very strong, and the huge sound of the eruption can be heard in New Zealand 2,000 kilometers away.
NASA scholars in the United States believe that the energy released by the volcanic eruption in Tonga exceeds 10 million tons of TNT. Similarly, Richard Arculus, a prominent scholar at the Australian National University, believes that the eruption of the Tonga volcano released more than 1,000 atomic bombs from Hiroshima. Austrian scholars believe that the energy released by the eruption reached more than 50 million tons of TNT.
However, there is a clear difference between a nuclear bomb and a volcano. The energy density of nuclear bomb explosions is much higher than that of volcanic ash and soot. Volcanic ash and gases can form larger mushroom clouds. The comparison of the two requires caution.
Figure 2 A cloud of ash mushrooms formed by the eruption of a volcano in Tonga. (Image courtesy of Doman et al 2022)
Why did tonga have such a large volcanic eruption?
Tonga is located in the Tonga-Kemadek subduction zone in the western Pacific Ocean and is an important part of the Pacific Rim subduction zone.
The subduction zone along Tonga-Kemadek was formed by the Pacific Ocean turn about 52 million years ago. About 7 million years ago, this subduction zone underwent a major turn, with the plates retreating to form the Tonga Post-Arc Basin.
Figure 3 The Cenozoic subduction in the Western Pacific began about 52 million years ago (52 Ma). Slightly later than the collision era of the Tibetan Plateau (Sun and Zhang, 2020 Science Bulletin).
The Tongan subduction zone corresponds to a younger Pacific ocean crust and is much shallower than the Pacific Ocean outside Izu-Ogasawara-Mariana. Many places are above the carbonate compensation depth, especially the Louisville seamount chain, where the water depth is shallower and there is a large amount of carbonate subduction. Carbonates can lower the solid phase line of mantle peridot and form more magma, while carbon dioxide can cause violent eruptions of volcanoes, which is conducive to the formation of large volcanic eruptions.
Figure 4 The Tongahun Ahapay Volcano is located in the Tonga-Kemadek subduction zone in the western Pacific Ocean. (Above from Kutterolf 2012, below from Doman et al 2022)
Figure 5 The carbon dioxide content of volcanic rocks in the subduction island arc of Tonga is much higher than that of the Japanese island arc. （Plank and Manning, 2019）
What is the trend of volcanic eruptions in Tonga?
Figure 6 Satellite image of The Tongahun Ahapay before and after the eruption of the volcano (image from Doman et al 2022).
The Tonga eruption is an undersea volcanic eruption with its epicenters near Hunga Ha'apai and Hunga Tonga. The eruption completely destroyed the two small islands mentioned above.
The volcano is currently one of the most active in the world. According to New Zealand volcanologist Cronin and others, the volcano has a strong eruption every thousand years. The last violent eruption occurred in 1100 AD, 920 years ago. Each violent eruption produces multiple eruptions of different grades.
Prior to the eruption, the volcano erupted several times in 2009, 2014, 2015, 2019 and 2021. It is uncertain whether the January 15 eruption was the largest eruption of the volcano at its peak. However, it is certain that the volcano has entered an active period, and the potential future hazards are worthy of attention.
Destructive volcanic eruptions in history
The level of the Tonga eruption is close to that of Mount Pinatubo in the Philippines in 1991, but only 400,000 tons of sulfur dioxide erupted. According to simulations by the Pilot National Laboratory for Marine Science and Technology, the impact of the eruption on the environment was minimal.
Historically, volcanic eruptions have brought serious disasters to human society.
Mount Tambora is the largest volcanic eruption ever recorded, with an eruption of 100 cubic kilometers, which is a class 7 eruption.
The Krakatoa volcano erupted at a strong level of 6 and emitted 20 cubic kilometers, triggering a tsunami that killed more than 30,000 people.
The 1991 eruption of Pinatubo volcano was a Class 6 eruption with an eruption of 6 cubic kilometers and released about 20 million tons of sulfur dioxide, which led to a global cooling of about 0.5 degrees. Before the eruption of Mount Pinatubo, more than 40,000 people were evacuated because of forecasts, but it also killed 1,202 people.
Mount Vesuvius erupted, forming Pompeii. The key to the heavy casualties caused by the eruption was that the volcano was considered an extinct volcano at the time and the city was built at the foot of the mountain.
bibliography:
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3. Himawari-8 Real-time Web, 15 Jan 2020, Large volcanic Hunga Tonga-Hunga Ha'apai. https://ingvvulcani.com/2022/01/17/grande-eruzione-vulcano-hunga-tonga-hunga-haapai/.
4. Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations, Hunga Tonga -Hunga Haapai Erupts, https://earthobservatory.nasa.gov/images/149347/hunga-tonga-hunga-haapai-erupts
5. Sentinel 5 satellite observation, The big plume of SO2 emissions from Hunga Tonga -Hunga Haapai eruption reached Australia, ADAM Platform, https://adamplatform.eu/#info
6. r/Europe, Size of the explosion of the volcano in Tonga compared to France, https://www.reddit.com/r/europe/comments/s5mbcz/size_of_the_explosion_of_the_volcano_in_tonga/?utm_source=ifttt
Authors: Sun Weidong, Tian Fanfan, Xie Guozhi, Wang Kun, Sun Xiaole
Source: Institute of Oceanology, Chinese Academy of Sciences