Pinatubo
| Pinatubo | ||
|---|---|---|
 Pinatubo eruption, June 12, 1991 |
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| height | 1486 m | |
| location | Philippines ( Luzon ) | |
| Mountain range | Zambales mountains | |
| Coordinates | 15 ° 8 ′ 0 ″ N , 120 ° 21 ′ 0 ″ E | |
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| Type | Stratovolcano | |
| Age of the rock | 1.1 million years | |
| Last eruption | 1991 | |
The Pinatubo is an active volcano in the Philippines in the west of the island of Luzon . Today's 1486 m high mountain (before the 1991 eruption it was 1745 m high) is 93 km northwest of Manila and 26 km west of Angeles City . It is located in the border triangle of the provinces of Zambales , Bataan and Pampanga , in the Zambales Mountains . Until 1991 the volcano was considered extinct.
The last eruption of the Pinatubo occurred on June 15, 1991 after around 550 years of rest and was one of the most violent of the 20th century. The prediction of the impending eruption led to the evacuation of the surrounding areas, affecting tens of thousands of people. Even so, at least 875 people died as a result of the outbreak and its aftermath. In addition, the surrounding land was destroyed by pyroclastic currents , layers of ash and later also by lahars .
The effects of this Plinian eruption were felt worldwide. It caused a greater release of aerosols into the stratosphere than any other volcanic eruption since the Krakatau eruption in 1883. This resulted in a global layer of sulfuric acid fog in the months that followed . Furthermore, a temperature drop of 0.5 ° C and an increased reduction in ozone were recorded.
The Pinatubo and the surrounding area
The Pinatubo is part of a volcanic chain that extends along the western tip of the island of Luzon. These are volcanoes of a subduction zone , which are fed by the sinking of the Philippine plate under the Eurasian plate along the Manila Trench and the magma that rises in the process.
population
The word "pinatubo" means "let it grow " in the language of the Sambal and Tagalog , which could be related to the knowledge of an eruption around 1500, although reports of the earlier eruptions have not been passed down. Instead, “Pinatubo” could also be understood as a place where grain thrives particularly well. Before the 1991 disaster , the mountain was an inconspicuous volcano, the existence of which was unknown to most people in the surrounding areas. Its highest point was 1745 m above sea level, but only 600 m higher than the surrounding plains and only 200 m higher than the surrounding peaks, which rather obscured it. For millennia, also before and after previous eruptions, hunters and gatherers of the indigenous people of the Aeta have lived on the slope of the volcano . After the outbreak in 1991, the government relocated many to areas that were unaffected or less affected by the outbreak. In total, about 30,000 people lived on the slopes in villages and smaller settlements.
vegetation
The dense jungle that covered most of the many surrounding mountains gave the hunters an advantage. In contrast, the flatter areas were more suitable for agriculture due to the heavy rainfall of around 4000 mm per year due to the monsoon and the fertile volcanic soil . Half a million people live within a 40 km radius of the volcano, including the large population centers of Angeles (150,000) and Clark Air Base (20,000).
Waters
Many important rivers have their origin on the Pinatubo. Among others the Bucao , Santo Tomas , Maloma , Tanguay and the Kileng River . Before the 1991 eruption, these rivers were a significant ecosystem , but the eruption covered many valleys with pyroclastic layers . Today the rivers are blocked with sediment and lahars often occur in the valleys . Studies have shown that around 15 years after the eruption , the river system will take many years to recover.
The last remnants of the formerly up to 200 m high lahar deposits will soon disappear or be hidden from the human eye due to the heavy rainfall of the rainy season and the overgrowth caused by the lush vegetation.
Geological history
Although there was no knowledge of previous major eruptions in the Pinatubo area, some aeta report that their elders can recall a few small explosions in the past. Pinatubo was known as a geothermal area even before the 1991 eruption and minor explosions are nothing special in such areas. It was only after 1991 that geologists began to study the history of the eruption in detail. It can be divided into two ages, old and modern Pinatubo.
Old Pinatubo
Much of the rocky area around today's volcano comes from the remains of ancient Pinatubo. This volcano was roughly where today's Pinatubo is. The activity seems to have started 1.1 million years ago. The old Pinatubo could have reached a size of around 2300 m above sea level , this is evident from the profile of the remaining lower slope.
Many mountains near modern Pinatubo are old satellite chimneys of ancient Pinatubo. They were created by chimneys and lava domes . Some mountains are also remnants of the ancient Pinatubo. They were preserved because they were erosion-resistant parts of the old mountain slope, while the less resistant parts were eroded by the influence of weather .
Today's Pinatubo
The formation of today's Pinatubo began 35,000 years ago with the strongest eruption in its history. Up to 100 m thick layers of pyroclastic material were thrown in all directions of the mountain. The total amount of material ejected was 25 km³. The disappearance of this enormous amount of material from the magma chamber below led to the formation of a large caldera .
1991 eruption
Signs of an outbreak
On July 16, 1990, there was an earthquake measuring 7.8 on the Richter scale in central Luzon . The epicenter was 100 km northeast of the Pinatubo. According to leading volcanologists, this could be the cause of the eruption in 1991, although this can no longer be clearly proven today. Two weeks later the volcano began to steam . Scientists who then examined the volcano, however, were more of the opinion that smaller landslides, and not eruption activities, were responsible.
In early 1991, villagers could sense a small earthquake on the northwest side of the volcano. More earthquakes of increasing intensity followed over the next two weeks, making it clear that volcanic activity was imminent. The outbreak occurred on April 2nd. First phreatic eruptions occurred near the summit along a 1.5 km long crevice. For the next two weeks, the smaller eruptions that covered the surrounding areas with ash continued . Seismographs registered hundreds of earthquakes every day.
Scientists immediately began doing analysis to find clues about previous eruptions. The radiocarbon method on charcoal, found in ancient volcanic layers, revealed three major eruptions in earlier millennia. They took place 5500, 3500 and 500 years ago. Geological maps show that many of the surrounding plains were formed by layers of lahars during previous eruptions. Volcanic activity increased during April and May. Measurements of sulfur dioxide emissions showed an increase in values from 500 tons on May 13th to 5000 tons per day on May 28th. The amount of sulfur dioxide emitted then suddenly decreased. It was feared that the outgassing of the magma had been blocked, which would lead to an increase in pressure in the magma chamber and make an explosive eruption likely.
The first magma eruption occurred on June 3rd and the first large explosion with a 7 km high ash column on June 7th. The Philippine Institute of Volcanology and Seismology ( PHIVOLCS ) issued a warning of a major eruption in the next two weeks.
evacuation
With all the indications that a major explosion was imminent, PHIVOLCS worked with the US Geological Survey to convince locals of the seriousness. One false warning would have rendered subsequent warnings ineffective, while waiting would have killed thousands. The volcanologists were therefore under pressure to work out a timely and accurate assessment of the eruption risk.
Three evacuation zones have been defined. The innermost had a radius of 10 km around the volcano, the second a distance of 10 to 20 km from the center, and the last 20 to 40 km. Approximately 40,000 people lived in the first and second zones, while the third zone was 331,000. Five warning levels of volcanic activity have been set, from level 1 (minor seismic unrest) to level 5 (main eruption is taking place). Daily warnings were issued. They each contained the step for the zones that were in danger. The information was disseminated through national newspapers , radio , television and non-governmental organizations , as well as being passed on directly to those affected.
Many of the aeta who lived on the slopes of the volcano left their villages voluntarily when the first explosions began in April. They gathered in a village 12 km from the summit. As the eruptions escalated, they moved further and further away from the volcano. Some Aeta moved up to nine times in the two months.
The first official evacuation took place in the ten-kilometer zone on April 7th. The evacuation of the second zone was ordered when warning level 4 was issued on June 7th. When they went to warning level 5 on June 14th, the third zone was also evacuated. By June 15, 60,000 people had left an area 30 km from the volcano. Most of the people were temporarily housed in Manila or Quezon City . 30,000 of them used the Amoranto Stadium in Quezon City as a refugee camp .
Build up the eruption to its climax
At the beginning of June 1991, inclination measurements showed that the volcano was expanding. It was clear that the cause was the increasing amount of magma that was accumulating in the reservoir under the volcano. At the same time, seismic activity was measured 5 km northwest of the summit, not deep below the rock surface. On June 7th, the first magma eruption occurred in the form of a lava dome at the top of the volcano. The lava dome grew significantly over the next five days. It reached a diameter of 200 m and a height of 40 m.
A small explosion on June 12th at 3:41 am marked the beginning of a new, more violent phase of the eruptions. A few hours later, large explosions lasted for half an hour. They created an eruption column that quickly reached heights of over 19 km, causing pyroclastic flows in some river valleys to expand up to 4 km from the summit. 14 hours later, an eruption hurled ash up to 15 miles into the air. The eruption caused many eruptive thunderstorms .
The third major eruption began at 8:41 am on June 13th after several smaller earthquakes in the previous two hours. These became stronger in the next five minutes and the eruption column reached a height of 24 km again. After three hours of rest, seismic activity started again. It became more and more intense over the next 24 hours, until on June 14th at 1:09 pm a three-minute eruption created a 21 km high eruption cloud. The volcanic material tephra fell from the ash cloud through the four large eruptions, especially in the southwest of the volcano. Two hours after the last of the four explosions, there was a series of eruptions that lasted for the next 24 hours and led to much larger pyroclastic currents that reached many kilometers down the river on the sides of the volcano.
Main eruption
The beginning of the great eruption could be seen on June 15th. Large earthquakes started at 1:42 pm. They disrupted the Clark Air Base seismographs, so they had to be shut down at 2:30 p.m. A large variation in atmospheric pressure was also sensed.
On the same day, Typhoon Yunya moved across the island about 75 km north of the volcano. This made direct observation of the eruption impossible. Measurements have shown, however, that ashes were thrown up to 34 km into the air during the gigantic three-hour phase. Pyroclastic currents flowed up to 16 km from the summit.
The ash cloud covered an area of 125,000 km² and resulted in total darkness over central Luzon. The ash rain reached almost all the islands and formed a massive snow-like layer that was increasingly saturated with rainwater and became unstable. The large amounts of water from the typhoon rains mixed with layers of ash, resulting in massive lahars. Tephra fell as far as the South China Sea and there was ash rain even in Vietnam , Cambodia and Malaysia . Around 10:30 p.m., nine hours after the peak of the main eruption, the pressure waves fell back to the strength that had prevailed before the main eruption. Although there were no longer any seismographs in the vicinity of the Pinatubo, volcanologists assume that the main phase of the eruption ended around 10:30 p.m.
Effects
In total, the eruption ejected approximately 10 km³ of tephra. It is the largest eruption since Novarupta in 1912 and it is about 10 times bigger than the eruption of Mount St. Helens in 1980. This huge explosion had the volcanic explosion index 6. The former summit of the volcano was now a 2.5 km wide crater . The highest point of the crater is now 1486 m above sea level. That is 259 m less than the summit before the eruption.
At least 875 people died in the eruption, most of them because the roofs of their houses collapsed from the heavy ash-water mixture. That was a danger that was compounded by the typhoon. The evacuation of large areas before the eruption probably saved the lives of tens of thousands of people here and can be seen as a great success for the volcanologists and the eruption forecast.
Since the eruption, more lahars have appeared during each rainy season , which is why thousands of people have had to move. Hundreds died because of the poor sanitary conditions in the refugee camps . The agriculture also had to suffer the effects of the eruption. Hundreds of square kilometers of arable land became sterile and the livelihoods of thousands of farmers were destroyed.
The US maintained two large military bases in the region. The Subic Bay Naval Base was 40 km south and the Clark Air Base 20 km east of the volcanic summit. After being seriously damaged by the eruption, both were returned to the Philippines as planned.
Although the 1991 eruption was one of the most violent in the 20th century, geologists believe that it was weaker than others in the history of Pinatubo.
Social and Economic Impact
The eruption hampered the economic development of the surrounding areas. Heavy damage was caused to buildings and infrastructure , which cost billions of pesos to repair . Additional costs were incurred in building canals and dams to control the post-eruptive lahars.
A total of 364 communities and 2.1 million people were affected by the eruption . More than 8000 houses were completely destroyed. Another 73,000 homes were damaged. In addition to this serious damage, roads and communications facilities all around the volcano have been damaged or destroyed by pyroclastic currents or lahars. The total cost of the repair was 3.8 billion pesos. Many reforestation projects were ruined by the eruption. A total area of 150 km² worth 125 million pesos was destroyed. The agriculture has been greatly disturbed. 8,000 km² of rice land was devastated and 800,000 head of livestock and poultry died. The agricultural damage amounted to 1.5 billion pesos.
The damage to medical facilities and the rapid spread of diseases in the refugee camps led to a steep rise in the death rate in the months after the eruption. Schooling could no longer be continued because of the destroyed schools . The area around Pinatubo contributed ten percent to the gross national product . It previously grew by five percent annually in this region, but fell by three percent after the eruption from 1990 to 1991.
Global impact
The massive eruption brought an enormous amount of aerosols and dust into the stratosphere . Sulfur dioxide (SO 2 ) oxidized in the earth's atmosphere , creating fog of sulfuric acid droplets that spread into the stratosphere, orbiting the earth for three weeks. A total of 17 million tons of SO 2 were injected into the stratosphere, the largest volume since the Krakatau eruption in 1883.
The result of this huge injection was a 5 percent reduction in sunlight . This in turn led to an average temperature drop of 0.5 to 0.6 ° C in the northern hemisphere and 0.4 ° C worldwide. At the same time, the temperature in the stratosphere rose by several degrees. According to Jason Wolfe (2000) the temperature rose by four degrees, F. Arfeuille et al. (2013) consider the model calculations for the temperature increase in the stratosphere to be too high. The following two warmer winters are attributed to the reactions of volcanic aerosols in the lower stratosphere. The clouds in the stratosphere created by the eruption persisted for three years.
The eruption also had a significant effect on the ozone layer in the earth's atmosphere . The mid- latitude ozone layer was the lowest level ever measured, and over Antarctica the ozone hole reached a new record. The Hudson's eruption in Chile in August 1991 also contributed to the destruction of the ozone layer. During the tropopause , when the aerosol clouds from Pinatubo and Hudson arrived, a steep drop in ozone levels was observed.
Another effect of the dust in the atmosphere was the appearance of the lunar eclipse . Usually the moon is also visible in the umbra . In the year after the Pinatubo eruption, however, it was almost invisible during the eclipse because too much sunlight was absorbed by the dust in the atmosphere.
The Pinatubos eruption provided important data for the study of geoengineering , i. H. Procedures to counteract the climate crisis . It could be concluded that a sulfur input that is large enough to compensate for the overheating of the earth's surface caused by the doubling of atmospheric CO 2 would have major consequences for the ozone layer . The atmospheric scientist Simone Tilmes used these results to warn of the risks of geoengineering through the introduction of sulfur into the atmosphere: "Our results show that this approach of an artificial reduction in global warming would entail major risks." She later commented as follows: "In order to keep the global rise in temperature in check, the annual sulfur input into the stratosphere would have to correspond to that of the eruption of Pinatubo on June 12, 1991."
The area since 1991
After the main eruption on June 15, 1991, the activity of the volcano decreased more and more. In August 1991 the ash eruptions stopped. Other sporadic eruptions continued for another month. The activity then continued to decline until a new lava dome formed in the crater in July 1992 .
This lava dome consisted mostly of material left behind from the 1991 eruption and less of the magma reservoir deep below the volcano. Volcanologists expected that more massive eruptions were imminent, so that some areas were evacuated again. However, the eruption did not become violent. This could be because the pressure was reduced by the escape of gas before the lava reached the surface. The volcano has been inactive since 1993.
After the eruption, a crater lake formed in 1991 .
The lava dome created in 1992 created an island in it. In the beginning the lake was small, hot (40 ° C) and very acidic ( pH value was 2). The rain lowered the temperature to 26 ° C by 2003 and increased the pH to 5.5.
The water level rose by an average of 1 m per month. In September 2001, the government feared that the crater walls would soon no longer be able to withstand the increasing pressure. The surrounding areas were evacuated again, because a drainage of the lake should be triggered artificially. A 5 m wide opening was cut into the rim of the crater, which made it possible to reduce the volume of the lake by a quarter. About 9,000 people were affected by this evacuation.
The Aeta of the Zambales Mountains suffered the most from the disaster. The almost complete destruction of their villages by pyroclastic currents or lahars prevented most of them from returning to their previous way of life. The few indigenous people whose villages were not destroyed returned. The others moved to the government-created resettlement areas. However, living conditions there were poor. Each family only got a small piece of land that was unsuitable for growing grain. Many Aeta became casual workers on lowland farmers. Overall, the aeta of the region became more and more fragmented and dependent and had to integrate into the lowland culture.
Lahar deposits from the volcano can be used to make high-quality stones for building houses. Some large mining sites for the building material have emerged around the Pinatubo.
The crater lake of the Pinatubo has meanwhile been developed for tourism on a small scale. Local guides offer hikes there. Usually, visitors are driven by four-wheel drive vehicles along the riverbed of the Tarlac River until the terrain becomes impassable and one has to continue on foot. The Philippine Air Force monitors access to the mountain from a small base.
See also
literature
- Alan Robock: Introduction: Mount Pinatubo as a Test of Climate Feedback Mechanisms . In: Alan Robock, Clive Oppenheimer (Eds.): Volcanism and the Earth's Atmosphere . American Geophysical Union, Washington, DC 2003, ISBN 0-87590-998-1 , pp. 1–8 , doi : 10.1029 / 139gm01 ( rutgers.edu [PDF]).
Web links
- Literature by and about Pinatubo in the catalog of the German National Library
- Nicole Engelbrecht: 9.6.1991: The Pinatubo breaks out. In: kalenderblatt.de. Deutsche Welle , June 9, 2018 .
- Pinatubo in the Global Volcanism Program of the Smithsonian Institution (English)
- Pinatubo at the Phivolcs (English)
Individual evidence
- ^ The Peoples of the World Foundation: Aeta
- ↑ Supervolcanoes. In: geolinde.musin.de. Archived from the original on March 13, 2014 ; accessed on March 13, 2014 .
- ↑ Jason Wolfe: Volcanoes Climate Change. earthobservatory.nasa.gov, September 5, 2000
- ↑ F. Arfeuille, BP Luo, P. Heckendorn, D. Weisenstein, JX Sheng, E. Rozanov, M. Schraner, S. Brönnimann, LW Thomason, T. Peter: Modeling the stratospheric warming following the Mt. Pinatubo eruption: Uncertainties in aerosol extinctions. In: Atmos. Chem. Phys., 13, 2013, pp. 11221-11234
- ↑ Tilmes, S., Muller, R., & Salawitch, R. (2008). The sensitivity of polar ozone depletion to proposed geoengineering schemes. Science, 320 (5880), 1201-1204. doi: 10.1126 / science.1153966
- ↑ Researchers warn against geoengineering. Heise Online, April 24, 2008, accessed December 14, 2019 .
- ↑ Climate manipulation: With technology against global warming. Berliner Zeitung, August 20, 2018, accessed on December 14, 2019 .