The volcanic eruption of Tonga affects geometry

Recently, a large-scale volcanic eruption occurred in the South Pacific island country of Tonga, causing a tsunami that affected the entire Pacific coastal region, and many countries issued tsunami warnings, causing global concern about the follow-up impact of the disaster.

Tonga is located on the subduction boundary of the southwest Pacific Plate, in the strong area of crustal activity in the Pacific Ring Seismic Belt, with the Tonga Trench, which is the "second deepest on earth". Based on such a special geological location, the region is prone to volcanoes and earthquakes. The eruption of the Hong Aha Apay Island volcano has been very active in history, with small eruptions in the past 100 years in 1912, 1937, 1988, 2009 and 2014.

Judging the impact of a volcanic eruption is first of all its intensity. According to reports, the volcanic column of the Tonga volcano is more than 20 kilometers high, combined with the sound of the volcanic eruption and the scale of the tsunami, the preliminary judgment is that its volcanic eruption index (VEI) may be between 5-6 levels. VEI measures the intensity of a volcanic eruption based on factors such as the volume of debris ejected by the volcano, the height at which ash exceeds the summit or enters the atmosphere, and the type of eruption. There are 8 levels in total, and for each level increased, the corresponding energy will increase by 10 times. Eruptions above VEI6 are relatively rare, and the largest recorded eruption of Mount Tambora in Indonesia in 1815 was VEI7, when the volcanic ash spewed out spread around the world with the flow of the atmosphere, resulting in an average temperature drop of about 0.5 degrees Celsius throughout the earth, and 1816 was also called "summerless year" in Europe and the United States.

Second, it depends on how long it lasts. Generally speaking, volcanic eruptions require three conditions: one is the material basis, that is, the magma inside the earth; the second is the eruption channel; and the third is the eruption power, that is, the energy that can cause the magma to erupt from the earth's interior along the channel from the earth's interior to the surface. How long a volcanic eruption can last also depends on these three conditions. Volcanic eruptions are mostly intermittent, such as the recently concluded volcanic eruption on the island of La Palma in Spain, which lasted intermittently for nearly 3 months. It is not yet possible to judge how long the Tonga eruption will last, and it requires continuous attention.

Volcanic eruptions are commonplace on Earth, but they need to be closely watched if they are close to human activity areas. The Hong Aha Apay Island volcano is located on the bottom of the sea, the eruption first caused a tsunami in the local area, from the report can see that not only the local air and water sources are polluted, communications and transportation are also affected, resulting in aircraft can not land, large ships can not approach, water supply has become a current concern. In addition, after the eruption, tsunami warnings were triggered in neighboring countries, such as Fiji, New Zealand and Australia, Japan, the United States, etc. were also affected. According to the latest monitoring results of the Tsunami Warning Center of the Ministry of Natural Resources of China, tsunami waves were monitored in the coastal waters of China in the early morning of the 16th, and the maximum tsunami wave amplitude was about 20 centimeters, although the impact was small, but the coastal areas of southeast China also needed to strengthen precautions.

In addition, volcanic eruptions may also have potential impacts on the climate. After the volcanic eruption of sulfur dioxide enters the stratosphere above the surface, it forms a sulfate aerosol through chemical reactions, thereby blocking solar radiation, playing an "umbrella effect" and changing the climate. In 1991, the Philippine volcano Pinatobo erupted, spewing about 20 million tons of sulfur dioxide into the stratosphere, and the "parasol effect" caused the Earth to enter a cold winter for the next two years. At present, the sulphur dioxide spewed by the Tonga volcano is only 400,000 tons, which is only equivalent to 2% of the amount of Pinatubo volcano, and it is too early to draw conclusions about the geometric impact on the global climate, and there may be local cooling, which requires further continuous observation.

Natural disasters know no borders, and responding to large-scale volcanic eruptions requires enhanced prediction, preparedness and response. At present, accurate prediction of volcanic eruptions is a worldwide problem. As earth science develops into deep space, deep earth, and deep sea, scientists are expected to have a deeper understanding of the active crustal activity of volcanoes.

(The author is an associate researcher at the Institute of Geology, Chinese Academy of Geological Sciences)

Author: Dong Hanwen

Source: People's Daily