On January 15, the south Pacific island nation of Tonga erupted violently, attracting worldwide attention. The eruption of the volcano not only formed a mushroom cloud with a height of 20 kilometers, but also triggered tsunamis in many parts of the world.
Source: Taaniela Kula_ TGS
In the face of the sudden volcanic eruption, many netizens have raised concerns.
We specially invited Dong Hanwen, institute of geology of the Chinese Academy of Geological Sciences and a well-known geological science blogger, to interpret the Tonga volcano for everyone.
Effects of volcanic eruptions in Tonga
Q1: "Will the eruption of the Tonga volcano have any effect on the mainland?"
During this volcanic eruption, many cities on the mainland detected changes in air pressure, but this change in air pressure was very small and negligible. In addition, although tsunamis have been observed in Australia, New Zealand, Japan and other countries, the surge height of tsunamis is not particularly high. The continental shelf is very flat, the coastline is very long, and even if a tsunami occurs, the surge height will not be too high. Therefore, at present, everyone does not have to worry too much about the impact of this volcanic eruption on the mainland.
Changes in air pressure were detected in several cities on the mainland
Image source: weibo.com
A total of 19 fishing boats capsized or sank in the harbors of Kochi Prefecture, Japan, with no casualties reported
Source: The Paper
Q2: "Will there be any impact on the global climate?"
Volcanic ash from eruptions obscures the sky and causes some degree of cooling in the range of the volcano (about 400-500 km). Although the intensity of the volcanic eruption in Tonga has affected the world, its eruption time is relatively short, and the concentration of sulfur dioxide rushing into the lower stratosphere is relatively limited, and it is not yet up to the extent of affecting the global climate. In addition, the northern hemisphere prevails in the westerly belt, the southern hemisphere prevails in the easterly belt, and the northern and southern hemispheres are relatively independent, so it is unlikely to affect the continents and the impact on the global climate is also very small.
Source: China Meteorological Administration
Although the volcanic eruption of Tonga did not have a direct measurable impact on the global climate, it has other ways of influencing the climate. As a volcano in the low latitude region of the South Pacific, this eruption will have a significant impact on the local and high-latitude land in the southern hemisphere; second, the volcanic eruption site is near the key enso region, which may affect the radiative forcing through the parasol effect, causing local cooling and possibly promoting el Niño events. However, an El Niño event itself could lead to years of small global warming, which may partially offset the cooling of the volcano's parasol effect region overall.
The effects of volcanic eruptions on the equatorial Middle East Pacific SST can be seen in promoting the formation of El Niño events
Image source: weibo
Q3: "I heard that volcanic ash shields about 10%-13% of the world's sunshine, will it have an impact on agriculture?"
Here, we have to debunk the rumors. The key to volcanic eruptions is sulfur dioxide. Volcanic ash particles are relatively large, difficult to rise to the high stratosphere, generally in the troposphere, they are easily carried down by raindrops or thunderstorms, settling to the ground.
Volcanic eruption process
Image source: Satellite photo
Once sulfur dioxide enters the stratosphere, it may become small particles of sulfate that persist in the stratosphere for months or even years, obscuring sunlight. But the eruption produced only about 400,000 tons of sulfur dioxide, two percent of Mount Pinatubo last cut about a thousandth of the earth's sunlight and reduced the global average temperature by 0.5 degrees Celsius. Therefore, the sulfur dioxide produced by the Tonga volcano will be weaker in reducing sunlight and will not have an impact on agriculture.
In 1991-1993, it cooled down significantly due to Mount Pinatubo
Whether the Tonga volcano will continue to erupt and whether it will cause further effects remains to be seen.
In fact, volcanic eruptions are not only graded in intensity, but volcanoes around the world have different styles and personalities.
Types of volcanoes
Most people divide volcanoes into the following three types according to their activity:
- An extinct volcano that almost no longer erupts
- Active volcanoes that are often erupted or are expected to erupt
- A dormant volcano that has erupted in history but has long been relatively stationary
However, the differences between volcanoes are far more than that, and even the way they erupt is different, far from the scene that people imagine or the comic book "magma soaring into the sky like a giant firework".
A scene of volcanic eruption in a regular impression
Image source: tenor.com
The type of outbreak
Most types of eruptions are named after a volcano because scientists tend to observe an eruption from among the most famous volcanoes.
- Hawaiian eruptions
This type of volcanic eruption is represented by volcanoes on the island of Hawaii, characterized by rare violent explosions, and is one of the calmest in volcanic eruptive activity.
Low-viscosity basalt magma spills out of the crater or rift in the mountainside and flows slowly downwards, and I am afraid that the chocolate lava cake that will leak out of the inner pulp after poking a crack is the inspiration for this.
Image source: Little Bear Emoji Jun Weibo
This type of eruption is not prone to casualties, and most of the deaths are the result of artificial forced approaches to the film. However, the flowing magma will destroy the surrounding farmland villages, causing some property damage.
December 20, 2020
Eruption of Kilauea Volcano in Hawaii
Image source: weather.com
- Stonebori eruptions
This type of eruption is represented by the Stonbury Volcano on the Italian island of Aeolian. Volcanic slag, boulders and volcanic bombs are continuously ejected to tens to hundreds of meters in height, and then a large amount of pyroclastic debris falls back into the crater and is ejected again.
A spectacular Stonebori eruption
Photographed at the Fogu Volcano in Cape Verde, West Africa
Image source: scitechdaily.com
This is also a relatively gentle eruption, but it is relatively viscous compared to Hawaiian-style eruptive magma.
Since the volcanic channel is not affected by eruptive activity, the eruption system can continuously reset itself, allowing stonebori eruptions to last rhythmically for a long time, which is really like a continuous spray of fireworks.
In addition, due to the persistence of this small-scale eruption, Stunbury Volcano has been called the "Beacon of the Mediterranean".
- Vulcano eruptions
This eruption type is named after the island of Vulcano near Sicily, Italy. In volcanoes that erupt in this type, a thicker consolidated crust forms on the crater when calm, and gases accumulate under the consolidated crust.
So when eruptions occur, thick eruptive clouds containing volcanic ash rise from the summits of volcanic peaks, and these "cauliflower-like" eruptive clouds are usually dirty gray-black.
Vulcano eruption of Tauru Volcano in Papua New Guinea
Image source: wiki
In a Vulcano eruption, the gas being ejected can reach supersonic speeds and produce shock waves, so this eruption can be very noisy. Although it is a bit more intense than stoneboli eruptions, it is still a bluff in most cases and is not very harmful.
But it can't be taken lightly, because Vulcano eruptions produce a large number of "bread-skinned volcanic bombs", and if you get too close to the eruption, it is very dangerous to be hit by the lava condensed by these hard stones.
Bread-skinned volcanic bombs
- Pere type eruption
The name given to this type of eruption comes from the Pere Volcano in the French island of Martinique in the Caribbean Sea. The eruption of The Pere Volcano in 1902 was one of the worst natural disasters in history, causing enormous damage and killing more than 30,000 people.
A peregrine eruption is an intense volcanic eruption that produces high-viscosity magma. Its signature feature is the pyroclastic flow formed by fast-flowing hot gases, volcanic ash and pyroclastics, flowing down the slope.
In that eruption in 1902, a pyroclastic stream with a temperature of more than 1075 °C covered the entire city of Saint-Pierre in one minute, instantly igniting all the combustible materials, the first time human scientists have recognized the natural phenomenon of pyroclastic flow.
The volcano erupted in large amounts of smoke
Image source: he-earth-story.com
- Pliny eruptions
It is also sometimes called Vesuvian eruptions. The eruption of Mount Vesuvius in 79 AD was a typical Pliny eruption that destroyed Pompeii, 13 kilometers from the crater.
The Roman historian Pliny the Younger was a witness to the eruption, comparing the various types of volcanic eruptions that bear his name.
The most obvious feature of Pliny eruptions is the towering column of eruptions, where ash and pumice can be ejected into the stratosphere more than 10 kilometers above the ground and pushed away from the volcano by the wind.
And this solid material will eventually fall to the ground, and the entire city of Pompeii will be buried by pumice layers of pumice stone, which are an average of 7 meters thick.
Pliny eruption of Mount Ridot in 1990
Pliny eruptions are the most intense type of volcanic eruption known, often forming cone-crumbling craters.
A caldera in the Ecuadorian Andes Mountains
Image source: nationalgeographic.org| photographer: OBLIOT
- Sutersa eruptions
This is a type of eruption brought about by a special landform. In 1963-1967, a volcanic crater on the shallow seabed of southern Iceland erupted repeatedly, eventually forming a new volcanic island, Sutersay.
Sutersai eruptions are characterized by repeated eruptions, when hot basalt magma comes into contact with low-temperature seawater, and the temperature difference between the two leads to violent "water-lava" interactions that drive the explosion.
The eruption of Mount Sutessee on August 19, 1966
Image source: volcanocafe.wordpress.com
However, these major types of volcanic eruptions are not complete, because it does not mean that other types of eruptions do not occur in volcanoes.
In fact, people have always maintained a love and reverence for nature, and are still constantly observing the volcanic activity to try to understand it better and avoid the next "Pompeii apocalypse".
bibliography
[1] Becker, Robert John and Becker, Barbara (1998). "Volcanoes", p.133
[2] Scarth, Alwyn. La Catastrophe. Oxford. 2002: 207."
[3] How Volcanoes Work: Sakurajima Volcano". San Diego State University. [OL]. （http://sci.sdsu.edu/how_volcanoes_work/）
[4] Surtsey – The Birth of the Modern World, 2013 Nov.[OL]. (https://volcanocafe.wordpress.com/2013/11/13/surtsey-the-birth-of-the-modern-world/)
[5] Stephanie Pappas, Deadly Volcanic Flows Glide on Their Own Cushion of Air [OL]. (https://www.scientificamerican.com/article/deadly-volcanic-flows-glide-on-their-own-cushion-of-air/)
Author: Ding Zhongli & Wan San
Graphic editor: one person white, tinker bell
Video Editing: One Person White
Acknowledgements: Dong Hanwen, Institute of Geology, Chinese Academy of Geological Sciences, provided scientific guidance for this article
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