Volcanic eruptions are extremely violent and spectacular but also quite dangerous geological activities.
Currently, there are an average of 50 to 60 volcanic eruptions worldwide each year. Modern volcanic eruptions can benefit humanity by providing fertile soil, air, minerals, building materials, energy, and other resources. However, they also bring immense disasters and suffering to people. Since the 1920s, many countries have conducted monitoring and research on volcanic activity and implemented corresponding disaster prevention and mitigation measures.
(1) Formation of Volcanoes
The formation of volcanoes involves a series of physical and chemical processes.
Partial melting of mantle rocks beneath the Earth’s crust occurs under certain conditions, and the molten material separates from the parent rock. This molten material, or magma, moves upward through pores or fractures and accumulates in magma chambers. When the strength of the overlying layers is insufficient to prevent the magma from continuing its upward movement, the magma rises to the surface through weak zones. During this ascent, volatile components dissolved in the magma gradually exsolve, forming bubbles. As the volume fraction of bubbles increases, they rapidly release, leading to explosive eruptions.
(2) Types of Volcanoes
Volcanoes can be classified in many ways, including by their activity status, as follows:
- Active Volcanoes These are volcanoes that are currently erupting or have periodic eruptions. They are in an active phase. Examples include Hawaii’s volcanoes in the United States and Mount Bromo in Indonesia. In China, the most notable recent volcanic activity is from the Qixing Mountain in the Tatun Volcano Group in Taiwan.
- Extinct Volcanoes These are volcanoes that erupted in prehistoric times but have shown no activity in recorded history. Such volcanoes have lost their ability to erupt. An example is the volcanic cones of the Datong Volcano Group in Shanxi, China, which are remnants of extinct volcanoes. These volcanoes may appear intact or only have partial remnants.
- Dormant Volcanoes These volcanoes have erupted in historical times but have been inactive for a long period. They remain in good shape and still have the potential to erupt, or it cannot be determined if they have lost this ability.
There is no strict scientific standard to determine if a volcano is “dead” or “alive.” Some volcanologists propose an improved definition of an active volcano based on the interval between eruptions of many active volcanoes and the last eruption time of extinguished volcanoes. However, the distinction between “dead” or “alive” remains relative. Some “extinct” volcanoes that haven’t erupted for 10,000 years or more can potentially become active again.
(3) Distribution of Active Volcanoes Worldwide
There are about 500 active volcanoes worldwide, and their distribution follows certain patterns. Most volcanoes are located at plate boundaries, with some within plate interiors.
- Active Volcanoes at Plate Boundaries Plate tectonics theory divides the Earth’s surface into several rigid lithospheric plates. Most volcanoes are concentrated at plate boundaries. The significance of plate tectonics in volcanic research is that it connects many seemingly isolated phenomena into a cohesive whole. The four major volcanic belts at plate boundaries include:
- The Pacific Ring of Fire:
This includes many famous volcanoes such as Ojos del Salado in South America, Mount St. Helens, Lassen Peak, and Mount Rainier in North America, the Japanese islands, and numerous volcanic islands from the Ryukyu Islands to Taiwan in China. The most active volcanic regions are the Philippines and Indonesia, with notable volcanoes like Krakatoa, Mount Pinatubo, and Taal Volcano. - The Mid-Atlantic Ridge Volcanic Belt:
This belt has volcanoes primarily along the Mid-Atlantic Ridge, with most eruptions occurring underwater and thus less noticeable. Notable active volcanoes include Hekla and Laki. - The East African Rift Volcanic Belt:
Volcanic activity is frequent here, especially since the late Cenozoic. The current volcanic activity centers include the western rift system at the Uganda-Rwanda-Zaire border, with the still-active Nyiragongo Volcano, the Afar Depression in Ethiopia with the Erta Ale and Afdera volcanoes, and the Natron Lake area in Tanzania with the Lengai Volcano. - The Alpine-Himalayan Volcanic Belt:
This belt has an uneven distribution of volcanoes, including famous ones like Vesuvius, Etna, Vulcano, and Stromboli. Volcanic activity is weak in the central section but intensifies in the eastern section along the northern slopes of the Himalayas, with notable volcanoes like the Makran, Kardarshi, Kokoxili, and Tengchong volcano groups.
- Volcanoes within Plate Interiors Some volcanoes are far from plate boundaries, such as the Hawaiian volcanoes, located more than 3200 km from the nearest plate boundary. Researchers suggest these volcanoes sit above a hotspot that melts rock to produce magma, which rises to the surface and erupts.
- Distribution of Volcanoes in China China currently has no active volcanoes, but it was a volcanically active country in the Cenozoic era. Historical records indicate multiple volcanic eruptions, including at Wudalianchi and Changbai Mountain, with eruptions in the past 300 years. The most recent activity was the Ashi Volcano in the Kunlun Mountains, which erupted on May 27, 1951.
- Wudalianchi Volcano Group, Heilongjiang Province:
This is a famous Quaternary volcanic group in China, with 14 volcanoes. Recent volcanic activity includes Laoheishan and Huoshaoshan, with eruptions in 1719-1721, making it a historically documented active volcano in China. - Mudanjiang Volcano, Heilongjiang Province:
This volcanic group, located in Ning’an, Heilongjiang, consists of 13 volcanic craters and forms a composite volcano. The Holocene eruptions and lava flows created modern volcanic landscapes, forming the famous Mirror Lake volcanic scenic area. - Changbai Mountain Tianchi Volcano, Jilin Province:
This well-preserved Cenozoic composite volcano has historical records of multiple eruptions. The major eruption from 1199-1201 AD was the largest in the last 2000 years, with ashfall reaching as far as the Sea of Japan and northern Japan.
Volcanic Hazards
Every year, there are over 50 volcanic eruptions globally, with the major volcanic disasters occurring in island arcs and continental regions. Volcanic eruptions, along with the resulting explosions, ash, toxic gases, volcanic mudflows, and pyroclastic flows, pose significant threats to human life and property and have a profound impact on the human living environment.
For example, the 1781 eruption of the Laki volcano in Iceland released toxic gases and caused famine, reducing Iceland’s population by one-fifth. The 1815 eruption of Mount Tambora in Indonesia resulted in 92,000 deaths. In 1985, a moderate eruption of Colombia’s Nevado del Ruiz volcano caused 23,000 deaths. This disaster in Colombia prompted the international community to focus on disaster mitigation, leading to the “International Decade for Natural Disaster Reduction (1990-2000),” which was included in the resolution of the 42nd UN General Assembly in 1987. Besides direct volcanic losses, active volcanoes can also cause disasters during dormant periods. For instance, California’s Long Valley Caldera last erupted 600 years ago. In 1995, seismic activity led to high concentrations of carbon dioxide and helium in the soil beneath Mammoth Mountain, causing widespread pine tree deaths, which gradually spread to the neighboring Reds Meadow Valley.
(1) Types of Volcanic Disasters
Volcanic eruptions can cause both direct and indirect disasters, and often these two types of damage occur simultaneously during eruptions.
- Pyroclastic Flow Hazards Pyroclastic flows are mixtures of gas and volcanic debris. These are not water flows but high-density, high-temperature, high-speed currents of gas mixed with rock fragments, sweeping across the ground. The temperature of pyroclastic flows can reach 800°C, and their speed can be as high as 150-200 km/h. They can crush and incinerate anything in their path. Pyroclastic flows originate from explosive volcanic eruptions or the collapse of lava domes. They are one of the main volcanic killers due to their destructive and deadly nature. Because of their speed, they are difficult to evade. For example, the 1902 eruption of Mount Pelée in Martinique resulted in pyroclastic flows that devastated the city of St. Pierre, killing approximately 30,000 people. Incomplete statistics show that pyroclastic flows caused over 4,300 deaths in the 17th century, 4,766 in the 18th century, 19,732 in the 19th century, and more than 41,981 in the 20th century.
- Lava Flow Hazards Lava flows refer to molten rock that flows on the Earth’s surface. When it cools, it solidifies into rock formations, sometimes also called lava flows. The temperature of flowing lava typically ranges from 900 to 1200°C. If the lava contains a lot of gas, it can flow at lower temperatures. Acidic lava is viscous and doesn’t travel far, whereas large lava flows are usually basaltic. High temperature and steep slopes can increase the speed of lava flows to up to 65 km/h. The shape of lava flows depends on several factors, including lava composition (e.g., basalt, andesite, dacite, rhyolite), flow rate, topography, and environment. Lava flows can submerge villages, burn houses and forests, and block transportation routes. For instance, the 1783 eruption of the Laki volcano in Iceland produced lava that covered an area of 565 km², causing significant destruction. The population of Iceland decreased by one-fifth, and livestock numbers were halved. The 1906 eruption of Mount Vesuvius in Italy engulfed the town of Ottaviano, killing hundreds of people.
- Volcanic Ash and Tephra Hazards Explosive volcanic eruptions can eject large amounts of volcanic debris, ash, and gases. The largest rock fragments usually fall within 3 km of the eruption vent, while volcanic ash is ejected into the atmosphere, forming a massive eruption column. This ash can bury houses, damage buildings and machinery, destroy crops, and endanger human lives and safety. Volcanic ash, composed of rock, mineral, and volcanic glass fragments less than 2 mm in diameter, is hard and insoluble in water, unlike soot. Hot volcanic ash rises rapidly with the air currents during eruptions, posing a threat to aviation safety. In the past 15 years, approximately eight commercial aircraft inadvertently flew into ash clouds, with several nearly crashing due to engine damage. Large-scale eruptions can release volcanic ash that remains in the stratosphere for extended periods, affecting the global climate. Volcanic ash can also harm respiratory systems of humans and animals. The 1991 eruption of Mount Pinatubo caused wet and heavy ash to fall in densely populated areas due to typhoon and rain, leading to about 200 deaths from collapsed roofs.
- Volcanic Gas Hazards Volcanic eruptions often release large amounts of gases, forming smoke columns that can reach several kilometers high. For example, the 1998 eruption of Mount Etna in Sicily produced a smoke column over 10,000 meters high. About 90% of volcanic gases are water vapor, mostly from heated surface water. Other gases include carbon dioxide, sulfur dioxide, hydrogen sulfide, and hydrochloric acid. Sulfur dioxide and hydrogen sulfide can cause greenhouse effects, and when they enter the atmosphere, they undergo photochemical reactions to form volcanic sulfuric aerosols, ultimately leading to surface temperature drops. Volcanic sulfides and halides can also create acid rain in the atmosphere, harming crops and the environment. In severe cases, they can cause mass animal deaths. Carbon dioxide, being heavier than air, can accumulate in low-lying areas, sometimes reaching suffocating concentrations. In 1986, a large release of carbon dioxide from Lake Nyos in Cameroon suffocated 1,700 people in the surrounding areas. The main environmental impact of hydrochloric acid is the destruction of the ozone layer, even forming “ozone holes.” This significantly damages ecosystems, exposing surface organisms to harmful ultraviolet radiation.
- Other Disasters Besides the direct hazards mentioned above, volcanic eruptions can cause indirect damage such as volcanic earthquakes, tsunamis, floods, mudflows, landslides, avalanches, toxic gas releases, and climate changes.
Utilization of Volcanic Resources
While volcanic eruptions can cause significant disasters, they also bring considerable benefits to society. The phosphorus-rich volcanic ash can make land fertile and increase agricultural yields. Geothermal energy, a clean and inexpensive renewable resource, is utilized in healthcare, tourism, residential heating, industrial processing, and power generation. In China, the Yangbajain geothermal field in Tibet has established the largest geothermal experimental base in the country, achieving remarkable success. Volcanic landscapes and the scenic beauty resulting from volcanic activity can boost tourism, bringing economic benefits to local areas. For instance, in 2004, UNESCO designated the Wudalianchi in Heilongjiang, China, as a world “geopark” due to its abundant volcanic resources and unique geological formations. Volcanic deposits also provide rich sources of diamonds, gold, silver, copper, lead, and zinc. Volcanic products can be used as construction materials and in various chemical and physical applications.
Measures for the Prevention and Mitigation of Volcanic Disasters
As understanding of volcanic hazards has deepened, efforts to mitigate their impacts have intensified. Volcanic activities and eruptions are significant geological processes driven by internal forces, often accompanied by distinctive geological phenomena such as abnormal seismic activity, crustal deformation, geochemical anomalies, geothermal anomalies, and volcanic eruptions. These phenomena offer scientists sufficient time to develop response strategies.
Volcanic monitoring involves two main aspects: fundamental geological investigations and the monitoring of volcanic activity.
(A) Volcanic Geological Investigations
Comprehensive and systematic investigations of volcanoes are foundational for volcanic monitoring. Geological surveys cover the morphology of the volcano, the geological structural background, the geochemical characteristics of rocks, geophysical properties, activity history, and eruption dynamics. Modern technologies such as GPS and GIS are used for high-resolution geological surveys of volcanic areas. In the late 1980s and early 1990s, Chinese scientists conducted systematic geological surveys of volcanoes like Tianchi in Changbai Mountain, Tengchong, and Wudalianchi. They completed a 1:10,000 scale volcanic geological map of Wudalianchi’s Laoheishan and Huoshaoshan, predicting potential eruption sites and creating corresponding hazard maps. By analyzing the composition of volcanic rocks, petrology, geochemistry, and isotope dating, they divided the Cenozoic Tianchi volcano in Changbai Mountain into four eruption cycles from old to new and identified it as a large multi-origin central volcano with a history of multiple eruptions.
(B) Monitoring of Volcanic Activity
The earliest volcanic earthquake observations began in 1888 at the summit of Bandai Volcano, with systematic volcanic monitoring commencing in the early 20th century. In 1911, Japan established a volcanic observatory on Honshu, and by now, they have 15 monitoring stations equipped with instruments for long-term observation of 17 out of the country’s 67 volcanoes, forming one of the world’s most advanced volcanic monitoring systems.
In the early 1950s, the Earthquake Research Institute of Tokyo University conducted detailed studies of the Izu-Oshima volcanic eruption, monitoring aspects such as geochemistry, geomagnetism, geoelectricity, deformation, and seismic activity. In October 1986, the Volcanic Prediction Liaison meeting concluded that an eruption at Miharayama’s summit was imminent, and indeed, the Izu-Oshima volcano erupted on November 15, 1986.
In 1997, the Chinese Academy of Sciences and the China Earthquake Administration launched the “Monitoring and Research of Several Recently Active Volcanoes in China” project. Research on the deep structure of the Changbai Mountain, Tengchong, and Wudalianchi volcanoes revealed magma chambers beneath Tianchi and Tengchong. Seismic monitoring, deformation measurements, subterranean fluid monitoring, and geochemical analyses indicated volcanic seismic activity, abnormal deformations, and deep mantle fluid anomalies, providing qualitative conclusions on the eruption risks of these three major volcanoes.
Currently, China is accumulating data on volcanic monitoring, with volcanic hazard mapping in the field investigation and identification stages, while the assessment of volcanic activity risks is still in the qualitative research phase.
How to Reduce Volcanic Risks
(A) Identification, Prediction, and Assessment of Volcanic Hazards
- Identification and Prediction of Hazardous Volcanoes
Only a small fraction of the world’s known active volcanoes have been or are being studied. Many explosive volcanoes are located in densely populated developing countries, where limited human, material, and financial resources necessitate prioritizing certain volcanoes for attention. Based on historical eruption frequency, location, characteristics, geological maps, isotope dating, known deformation, and seismic events, as well as eruptive product features and demographic factors, UNESCO organized three working meetings to identify 89 high-risk volcanoes globally. These include 42 in Southeast Asia and the Western Pacific, 40 in the Americas and the Caribbean, and 7 in Europe and Africa. Detailed research, monitoring, prediction, and disaster mitigation measures should be undertaken for these high-risk volcanoes. In China, volcanic research started relatively late, focusing on the geology and geochemistry of volcanoes and volcanic rocks until the “Ninth Five-Year Plan”. In 1997, the Chinese Academy of Sciences and the China Earthquake Administration launched the “Monitoring and Research of Several Recently Active Volcanoes in China” project, which provided qualitative conclusions on the eruption risks of the Changbai Mountain, Tengchong, and Wudalianchi volcanoes. Volcanic eruptions, though seemingly sudden, follow certain patterns and often present more evident precursors than earthquakes. Volcanic hazard prediction is highly valued in countries with many volcanoes, such as Japan, the United States, Italy, Indonesia, the Philippines, New Zealand, and Russia. Since the 1950s, most monitored volcanoes have shown detectable signs weeks or months before eruptions. Successful International Volcanic Predictions
There have been many successful international predictions of volcanic eruptions, such as the 1980 eruption of Mount St. Helens in the United States, the 1986 eruption of Izu-Oshima in Japan, and the 1991 eruption of Mount Pinatubo in the Philippines. Predicting the timing of volcanic eruptions is generally not very difficult, but convincing governments to take appropriate actions can be challenging. For example, a hazard zoning map was provided one month before the 1985 eruption of Ruiz Volcano, accurately predicting the areas affected by volcanic mudflows and debris, but the warnings were not heeded, resulting in a disaster. - Volcanic Hazard Zoning
By using historical records of similar volcanic events, the frequency, type, severity, and range of future volcanic disasters in a given area can be predicted, and volcanic hazard zones can be mapped accordingly. During periods of volcanic calm, these maps can guide resource development, economic growth, and tourism planning. In times of volcanic crisis, they can help determine evacuation routes and shelters, mitigating disaster impacts. For instance, before the April 2, 1991 eruption of Mount Pinatubo in the Philippines, a series of phreatic explosions prompted the formation of a joint observation team of Filipino and American scientists. They mapped the volcanic hazard zones, developed a five-level alert system, and informed relevant departments, ensuring the safe evacuation of at least 58,000 people. Despite being the largest eruption in the Philippines since 1912, timely countermeasures significantly reduced casualties.
(B) Collaboration Between Volcanologists and Medical Professionals
Collaboration between scientists and medical professionals is crucial in responding to volcanic emergencies. Scientists, by studying past eruptions, can create hazard distribution maps and predict potential eruption times and associated health impacts. Medical professionals need to identify high-risk populations and prepare for potential disasters.
Medical personnel should work with volcanologists to train local residents on the health impacts of various volcanic hazards, especially those in low-lying areas and valleys. Providing safety advice to workers and tourists near volcanoes is also essential.
For example, individuals should be informed about the history of the volcano, current alert levels, and safety instructions; they should engage in activities under the guidance of experienced locals and inform reliable contacts of their plans; wear helmets and masks; be aware of volcanic hazards such as falling rocks, avalanches, and toxic gases; and recognize warning signs of imminent eruptions, evacuating immediately if necessary.
Emergency medical assistance is less critical during severe volcanic eruptions, as the number of survivors who can benefit from treatment is significantly lower than those who perish within minutes of the disaster. Therefore, prevention is key. Early evacuation is crucial to reduce morbidity and mortality. Medical professionals should be trained to handle various types of injuries among survivors and be aware that severe ash conditions and debris burial might limit access to victims.
Volcanic disasters can cause various injuries, including:
- Blunt trauma from volcanic debris, mudflows, avalanches, and tsunamis
- Burns, trauma, and complications like gangrene
- Asphyxiation and acute respiratory injuries from ash inhalation, exacerbation of existing respiratory conditions, and burns from inhaling hot steam
- Conjunctivitis and corneal damage
- Toxic effects from gases like carbon dioxide, hydrogen sulfide, sulfur dioxide, hydrogen fluoride, and carbon monoxide
- Gastroenteritis
- Skin damage from acid rain
- Drowning from volcanic mudflows or tsunamis
- Mental health issues like depression, anxiety, psychosis, insomnia, neurasthenia, and obsessive-compulsive disorder
Medical professionals should provide targeted treatments based on these conditions.