According to the news released by Indonesia's National Disaster Management Agency, at 21:27 Jakarta time on 22nd, 2018 Banten Province and southern Lampung Province near the Sunda Strait were hit by a tsunami. As of December 27, the Sunda tsunami had killed 430 people, left 159 missing, and injured 1,459 people. Rescue and evacuation efforts are underway, and the number of casualties may rise further.
01 Geological Background
The Sunda Strait is located between Java Island and Sumatra Island . It is part of the Sunda Island Arc Convergence Zone. It is the normal subduction of the Indian Ocean-Australian plate towards the northern Java Island and the oblique subduction towards Sumatra Island. The northwest-trending Sumatra dextral strike-slip fault zone connects the Sunda Strait to the Andaman Transform Zone in the Andaman Sea.
The western part of the Sunda Strait is located in the extensional step area of the Sumatra right-lateral strike-slip fault zone. A number of nearly north-south normal faults have developed in the step area, which may have led to the extremely developed Quaternary volcanic activity in the area. .
Except for the nearly northwest-trending Java subduction zone and the Sumatra fault zone in the south, the Sunda Strait and adjacent areas have no active faults near the strait, and the moderately strong seismic activity recorded by instruments is weak. However, Quaternary active volcanoes are widely distributed in the area.
When the tsunami occurred, there was no moderate or strong earthquake of magnitude 6 or above nearby. Preliminary judgment is that the tsunami was caused by the eruption of the Krakatoa volcano in the Sunda Strait. Krakatoa is a volcanic island group formed by multiple volcanic eruptions, with a maximum altitude of more than 800 meters and a water area of approximately 10.5 square kilometers.
According to records, the eruption of Krakatau volcano in 1883 triggered a tsunami. It is said that hundreds of villages and cities were destroyed at that time, and more than 30,000 people were killed. The current eruption of Krakatau volcano began in 1927, when the volcanic cone was still below sea level. Since 2013, the cone of Krakatoa has been above the water and is still growing.
At present, the altitude of Krakatau volcano is 338 meters. The volcano erupted on June 20, 2016, and February 19, 2017 respectively. It began activity in the form of an explosion on June 29, 2018. The pyroclastic material produced by the explosion landed within 1 kilometer around the volcano. Since July 23, 2018, activity of white hot material (magma) has been observed near the coast.
Krakatoa volcano erupted again at 9:30 on December 22, 2018. The eruption column was 300-1500 meters higher than the edge of the crater. Seismic activity continued, with a maximum amplitude of 58 mm. This happened after a long period of time. Tsunami. As of December 23, 2018, the volcano alert level is still Level II, and the 2 kilometers around the crater is a danger zone.
Japan divides the volcanic eruption alert into five levels based on volcanic activity, and divides the "scope of alert" and the "disaster prevention response that should be taken" by disaster prevention departments, residents, etc. into five stages to publish indicators.
02 Expert interpretation
Tsunami can be generated by earthquakes, volcanic eruptions, submarine landslides or destructive waves caused by meteorological changes. Generally speaking, tsunamis caused by earthquakes are more common than those caused by volcanic eruptions. Although the eruption of Krakatau volcano was limited in scale, with the height of the eruption column being only 300-1500 meters, because the volcano is located offshore, the volcanic eruption caused the volcanic cone to collapse, forming a submarine landslide and inducing a tsunami, while the tide (full moon) Activities may have increased the intensity of this tsunami event.
Director of the Volcano Research Center of the China Earthquake Administration and researcher at the Institute of Geology of the China Earthquake Administration Xu Jiandong interpreted the Indonesian tsunami and pointed out: : It is preliminarily inferred that the tsunami was caused by the eruption of the Krakatau volcano in the Sunda Strait. The specific process is that the volcanic eruption caused the collapse of the volcanic cone, forming a submarine landslide, which induced a tsunami, and tidal (full moon) activity aggravated the intensity of this tsunami event.
"This volcanic eruption is a small-scale eruption. Volcanic eruptions of this magnitude rarely cause tsunamis. At the same time, they do not directly cause tsunamis, but are caused by the formation of submarine landslides, which are secondary disasters caused by volcanic eruptions. However, this tsunami reflects the local lack of preparedness for secondary disasters caused by volcanic eruptions, and also reminds our country that "it is imperative to strengthen volcanic early warning capabilities."
03 Current situation in my country
"Volcanoes are a natural phenomenon that are closely related to our lives. , Various volcanic activities occur every day around the world. The volcanic activity cycle is at least a hundred years long. Even if there is no eruption, we should still take precautions. "
China is a country with many volcanoes, with 186,000 square kilometers of new volcanoes. There are thousands of volcanoes of various sizes, and there are at least 14 proven active volcanoes, including Wudalianchi volcano, Changbaishan Tianchi volcano, etc., mainly distributed in Northeast China, the Tibetan Plateau, and southwest China. Among them, the most recent eruption was the Ashkule volcano in Yutian, Xinjiang, which erupted in 1951.
my country officially built and started operating the China National Volcano Monitoring Network Center in 2006, and established 6 volcanoes including Tianchi volcano in Changbai Mountain in Jilin, Longgang volcano, Tengchong volcano in Yunnan, Wudalianchi volcano in Heilongjiang, Jingbohu volcano and Hainan Qiongbei volcano. Active volcanoes are included in the China Volcano Monitoring Network.
my country's existing volcano monitoring technology has been in line with international standards. With the deepening of volcanic research and the improvement of national strength, more active volcanoes will be monitored in the future.
04 Popular Science Tips
Will a volcanic eruption cause a tsunami?
Tsunamis can be generated by earthquakes, volcanic eruptions, submarine landslides or destructive waves generated by meteorological changes. Generally speaking, tsunamis caused by earthquakes are more common than those caused by volcanic eruptions.
People have the impression that tsunamis are mostly caused by earthquakes. For example, the 2004 Indian Ocean tsunami and the 2011 Japanese tsunami were both caused by earthquakes. The former is due to an earthquake with a magnitude of 9.3 that occurred on the seabed north of Indonesia Sumatra, while the latter is due to an earthquake with a magnitude of 8.9 that occurred in the Pacific waters near Japan.
What is extraordinary about this Indonesian Sunda Strait tsunami is that before the tsunami, there was no local earthquake. It was the volcanic eruption that caused the collapse of the volcanic cone, causing a submarine landslide. The disturbance to the water body during the landslide caused the caused the tsunami.
Solid lava flowing after a volcanic eruption
05 Disaster reduction measures
Identification of high-risk volcanoes and volcanic hazard zoning map
How to reduce volcanic disasters from a scientific perspective? The first step is to identify high-risk volcanoes. For these high-risk volcanoes, the basic work is to prepare a volcanic hazard zoning map. This map should clearly indicate the distribution range of different eruptions in the history of high-risk volcanoes and the different types of eruptions that may occur in the future. Disaster scope, probability and intensity.
What have these volcanoes done in history, what is their current behavior, and what will be the likely course of volcanic activity in the future. Scientists interpret volcanoes and their activities so that other members of society can prepare for such hazards and respond appropriately to reduce casualties and property damage.
Government and Administrative Management Behavior
The next step is how to properly transform the awareness of volcano scientists into public awareness and influence the behavior of government and administrative decision-making.
Under the guidance of volcano scientists, relevant government departments should formulate emergency plans in a timely manner and continuously improve them. When volcanic danger occurs, government officials, businesses, people, disaster relief personnel, and journalists should take appropriate emergency measures. And through the media and popular science education institutions, the public can understand some volcanoes and volcano-related knowledge.
Volcanic knowledge that the public should know
So, as a public living in high-risk volcanic areas, what volcanic knowledge do we need to know? First of all, people should understand the past and present basic activities of nearby volcanoes.
For example: the location, shape, eruption center of the volcano, previous eruption forms and some eruption parameters such as size, intensity, eruption volume, affected areas and eruption frequency.The public should understand the timeliness of eruption forecasts, understand the role and limitations of scientific research, and know that sometimes precursory phenomena of volcanic eruptions do not necessarily lead to volcanic eruptions.
How scientists help the public obtain necessary information
Teaching the public about volcanoes should be a long-term process. During the dormant period of volcanic eruptions, it is easiest to start in places where volcano observatories and scientific staff are stationed. And communicating relevant information to governments through regular communications will be critical in the face of future volcanic emergencies.
Volcan monitoring station staff inspected the volcanic lava tunnel Sili Cave
In view of the lack of examples of volcanic eruptions in modern times in my country but the existence of several very dangerous active volcanoes, the current volcanic education for the Chinese public should first focus on strengthening volcanoes Focus on the volcano research work of scientists, learn from foreign advanced results, and improve the overall level of volcano research in our country as soon as possible.
In addition, through our article, you must have learned about tsunamis, volcanoes and how to reduce volcanic disasters from the Indonesian Sunda tsunami incident.
Changbai Mountain Tianchi
Data sources: China Earthquake Administration official website, Institute of Geology of China Earthquake Administration, Sina.com, Japan Meteorological Agency, "City and Disaster Reduction" magazine, Jilin Provincial Earthquake Administration Baishan Volcano Monitoring Station
