Mount Pinatubo
Ash plume of Pinatubo during 1991 eruption
Elevation	1,486 meters (4,875 ft) 1745 meters before 1991 eruption
Location	Zambales, Luzon, Philippines Tarlac, Luzon, Philippines Pampanga, Luzon, Philippines
Range	Zambales Mountains
Coordinates	15°7.8′N 120°21.0′E / 15.13, 120.35Coordinates: 15°7.8′N 120°21.0′E / 15.13, 120.35
Type	Stratovolcano
Age of rock	1. In topography a summit is a point on a surface which is higher in Elevation than all points immediately adjacent to For the mountain chain see Zambales Mountains. For the ethnic group see Sambal people. Luzon is the largest and most economically and politically important Island in the Philippines and one of the three island groups in the country with Visayas The Philippines ( Filipino: Pilipinas, officially known as the Republic of the Philippines (fil ''Republika ng Pilipinas'' RP For the city see Tarlac City. For the river see Tarlac River. Luzon is the largest and most economically and politically important Island in the Philippines and one of the three island groups in the country with Visayas The Philippines ( Filipino: Pilipinas, officially known as the Republic of the Philippines (fil ''Republika ng Pilipinas'' RP Pampanga is a province of the Philippines located in the Central Luzon region. Luzon is the largest and most economically and politically important Island in the Philippines and one of the three island groups in the country with Visayas The Philippines ( Filipino: Pilipinas, officially known as the Republic of the Philippines (fil ''Republika ng Pilipinas'' RP A mountain range is a chain of Mountains bordered by highlands or separated from other mountains by passes or valleys The Zambales Mountains are a Mountain range located on the western side of Luzon, in the Philippines. A geographic coordinate system enables every location on the Earth to be specified in three coordinates using mainly a spherical coordinate system. A geographic coordinate system enables every location on the Earth to be specified in three coordinates using mainly a spherical coordinate system. Mountains can be characterized in several ways Some mountains are Volcanoes and can be characterized by the type of lava and eruptive history A stratovolcano, also called a composite volcano is a tall conical Volcano composed of many layers of hardened Lava, Tephra, and Volcanic The geologic time scale is a chronologic schema (or idealized Model) relating Stratigraphy to time that is used by Geologists and other 1 million years
Last eruption	1993[1]

Mount Pinatubo is an active stratovolcano located on the island of Luzon in the Philippines, at the intersection of the borders of the provinces of Zambales, Tarlac, and Pampanga. Plate tectonics and hotspots Divergent plate boundaries At the A stratovolcano, also called a composite volcano is a tall conical Volcano composed of many layers of hardened Lava, Tephra, and Volcanic Luzon is the largest and most economically and politically important Island in the Philippines and one of the three island groups in the country with Visayas The Philippines ( Filipino: Pilipinas, officially known as the Republic of the Philippines (fil ''Republika ng Pilipinas'' RP For the mountain chain see Zambales Mountains. For the ethnic group see Sambal people. For the city see Tarlac City. For the river see Tarlac River. Pampanga is a province of the Philippines located in the Central Luzon region. Ancestral Pinatubo was a stratovolcano made of andesite and dacite. For the extinct cephalopod genus see Andesites. Andesite (ˈændəsaɪt is an igneous, Volcanic rock, of intermediate Dacite ( deɪsaɪt) is an igneous, volcanic rock with a high iron content Before 1991, the mountain was inconspicuous and heavily eroded. Erosion is the carrying away or displacement of solids ( Sediment, Soil, rock and other particles usually by the agents of currents such as wind It was covered in dense forest which supported a population of several thousand indigenous people, the Aeta, who had fled to the mountains from the lowlands when the Spanish conquered the Philippines in 1565. A forest is an area with a high density of Trees There are many definitions of a forest based on various criteria The Aeta (pronounced as “eye-ta” Agta or Ayta are an Indigenous people who live in scattered isolated mountainous parts of Luzon, The Spanish Empire (Imperio Español was one of the largest Empires in history and one of the first Global empires In the 15th and 16th centuries

The volcano's eruption in June 1991 produced the second largest terrestrial eruption of the 20th century. ^[2] The 1991 eruption had a Volcanic Explosivity Index (VEI) of 6, and came some 450-500 years after the volcano's last known eruptive activity (estimated as VEI 5, the level of the 1980 eruption of Mount St. Helens), and some 500-1000 years after previous VEI 6 eruptive activity. The Volcanic Explosivity Index (VEI was devised by Chris Newhall of the U The 1980 eruption of Mount St Helens, a volcano located in Washington state in the United States was a major volcanic eruption. ^[3] Successful predictions of the onset of the climactic eruption led to the evacuation of tens of thousands of people from the surrounding areas, saving many lives, but surrounding areas were severely damaged by pyroclastic flows, ash deposits, and later by lahars caused by rainwater remobilizing earlier volcanic deposits: thousands of houses and other buildings were destroyed. A pyroclastic flow (also known as a pyroclastic density current) is a common and devastating result of some volcanic eruptions. A lahar is a type of Mudflow / Landslide composed of Pyroclastic material and Water that flows down from a Volcano, typically ^[2]

The effects of the eruption were felt worldwide. It ejected roughly 10 billion metric tons of magma, and 20 million tons of SO₂, bringing vast quantities of minerals and metals to the surface environment. It injected large amounts of aerosols into the stratosphere—more than any eruption since that of Krakatoa in 1883. Particulates, alternatively referred to as particulate matter (PM or fine particles, are tiny particles of solid or liquid suspended in a gas The stratosphere is the second major layer of Earth's atmosphere, just above the Troposphere, and below the Mesosphere. Krakatoa ( Indonesian: Krakatau) also spelled Krakatao or Krakatowa, is a volcanic island in the Sunda Strait Over the following months, the aerosols formed a global layer of sulfuric acid haze. Sulfuric (or sulphuric acid, H 2 S[[oxygen O]]4 is a strong Mineral acid. Global temperatures dropped by about 0. 5 °C (0. The Celsius Temperature scale was previously known as the centigrade scale. 9 °F), and ozone depletion temporarily increased substantially. Fahrenheit is a temperature scale named after Daniel Gabriel Fahrenheit (1686–1736 a German Physicist who proposed it in 1724 OZONE is an object oriented Operating system written in the C programming language.

Overview of the Mount Pinatubo area

Location of Mt. Pinatubo, showing area over which ash from the 1991 eruption fell

Pinatubo is part of a chain of volcanoes which lie along the western edge of the island of Luzon. Luzon is the largest and most economically and politically important Island in the Philippines and one of the three island groups in the country with Visayas They are subduction volcanoes, formed by the Philippine Plate sliding under the Eurasian Plate along the Manila Trench to the west. In Geology, a subduction zone is an area on Earth where two tectonic plates meet and move towards one another with one sliding underneath the other Plate tectonics and hotspots Divergent plate boundaries At the The Philippine Plate is a Tectonic plate beneath the Pacific Ocean to the east of the Philippines. The Eurasian Plate is a Tectonic plate which includes most of the continent of Eurasia (a landmass consisting of the traditional Continents of Europe The Manila Trench is an Ocean trench in the South China Sea, west of the Philippines. Mount Pinatubo lies on a destructive plate boundary. The word 'pinatubo' means 'to have made grow' in Tagalog and Sambal {²}, which may suggest a knowledge of its previous eruption in about AD 1500, although there is no oral tradition among local people of earlier large eruptions. Tagalog is one of the major languages used in the Philippines. The Sambalic languages are part of the Central Luzon language family Kapampangan is one of the major Languages of the Philippines. Pinatubo might instead mean a fertile place where crops can be made to grow.

Before the catastrophic eruption of 1991, Pinatubo was an inconspicuous volcano, unknown to most people in the surrounding areas. Its summit was 1,745 m (5,725 ft) above sea level, but only about 600 m above nearby plains, and about 200 m higher than surrounding peaks, which largely obscured it from view. In Geography, a plain is an area of land with relatively low relief — meaning that it is flat Philippine President Ramon Magsaysay, a native of Zambales, named his C-47 presidential plane "Mt. The President of the Philippines is the head of state and government of the Republic of the Philippines. Ramon del Fierro Magsaysay ( August 31, 1907 - March 17, 1957) was the third President of the Third Republic of the Philippines WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout Pinatubo". The plane crashed in 1957, killing the President and 24 others onboard. The 1957 crash of a Douglas C-47 plane named "Mt Pinatubo" on the slopes of Mount Manunggal Cebu, Philippines, killed the 7th President of the ^[4]

An indigenous people, the Aeta (also spelt Ayta), had lived on the slopes of the volcano and in surrounding areas for several centuries, having fled the lowlands to escape persecution by the Spanish. The Aeta (pronounced as “eye-ta” Agta or Ayta are an Indigenous people who live in scattered isolated mountainous parts of Luzon, Spain () or the Kingdom of Spain (Reino de España is a country located mostly in southwestern Europe on the Iberian Peninsula. They were a hunter-gatherer people who were extremely successful in surviving in the dense jungles of the area. A hunter-gatherer society is one whose primary subsistence method involves the direct procurement of edible plants and animals from the wild Foraging and Hunting These people also grew some staple crops such as wheat, barley and rice.

In total, about 30,000 people lived on the flanks of the volcano in barangays (villages) and other small settlements. This article refers to a political administrative division See Barangay Ginebra Kings for other uses The dense jungle covering most of the mountain and surrounding peaks supported the hunter-gathering Aeta, while on the surrounding flatter areas, the abundant rainfall (almost 4 m annually) provided by the monsoon climate and the fertile volcanic soils provided excellent conditions for agriculture, and many people grew rice and other staple foods. A monsoon is a seasonal prevailing wind which lasts for several months Agriculture refers to the production of goods through the growing of plants and fungi and the raising of domesticated Animals The study of agriculture Rice is a Cereal foodstuff which forms an important part of the diet of many people worldwide and as such it is a staple food for many About 500,000 people continue to live within 40 km of the mountain, with population centres including the 150,000 in Angeles City, and 20,000 at Clark Air Base. Angeles City (Lungsod ng Angeles Kapampangan: Ciudad ning Angeles) geographically located within the province of Pampanga in the Philippines Clark Air Base is a former United States Air Force base on Luzon Island in the Philippines, located 3 miles west of Angeles City, about 40 miles

Several important river systems have their sources on Pinatubo, with the major rivers being the Bucao, Santo Tomas, Maloma, Tanguay and Kileng rivers. Before the eruption, these river systems were important ecosystems, but the eruption filled many valleys with deep pyroclastic deposits. An ecosystem is a natural unit consisting of all plants animals and micro-organisms( Biotic factors in an area functioning together with all of the non-living physical ( Since 1991, the rivers have been clogged with sediment, and the valleys have seen frequent lahars. Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of A lahar is a type of Mudflow / Landslide composed of Pyroclastic material and Water that flows down from a Volcano, typically Studies show that the river systems will take many years yet to recover from the 1991 eruption.

Geological history

Although there seems to be no local knowledge of the previous large eruptions in the Pinatubo area, several Aeta residents reported in 1991 that their elders recalled small explosions in the past. Pinatubo was a known geothermal area before the 1991 eruption, and small steam explosions are quite common in such areas. In Geology, geothermal refers to heat sources within the planet It was only after volcanic activity began in 1991 that geologists studied the eruptive history of the region in any detail. Eruptions at the site can be divided into two major eras.

Ancestral Pinatubo

Pinatubo before the major eruption of 1991

Much of the rugged land surrounding the present volcano consists of remnants of 'ancestral' Pinatubo. This volcano was located roughly in the same place as the present mountain, and activity seems to have begun about 1. 1 million years ago. Ancestral Pinatubo may have reached a height of up to 2,300 m (7,550 ft) above sea level, based on profile fitting to the remaining lower slopes. M is the thirteenth letter of the modern Latin alphabet. Its name in English is spelled em (ɛm A foot (plural feet or foot; symbol or abbreviation ft or sometimes &prime – the prime symbol) is a non-SI unit Mean sea level (MSL is the average (mean height of the Sea, with reference to a suitable reference surface

Several mountains near modern Pinatubo are old satellite vents of ancestral Pinatubo, formed from volcanic plugs and lava domes. A volcanic plug, also called a volcanic neck or lava neck, is a volcanic landform created when Lava hardens within a Vent on In Volcanology, a lava dome or plug dome is a roughly circular Mound -shaped protrusion resulting from the slow eruption of Felsic Lava Some nearby peaks are also remnants of ancestral Pinatubo, formed from erosion-resistant parts of the old mountain slopes left behind when the less resistant parts were eroded away by weathering. Erosion is the carrying away or displacement of solids ( Sediment, Soil, rock and other particles usually by the agents of currents such as wind Weathering is the decomposition of earth rocks, Soils and their Minerals through direct contact with the planet's Atmosphere.

The eruptive activity of ancestral Pinatubo was much less explosive than modern Pinatubo, and probably ended about 45,000 years ago. After a long period of dormancy, modern Pinatubo was born in eruptions beginning about 35,000 years ago.

Modern Pinatubo

The birth of modern Pinatubo occurred in the most explosive eruption in its history, which deposited pyroclastic flow material up to 100 meters thick on all sides of the mountain. A pyroclastic flow (also known as a pyroclastic density current) is a common and devastating result of some volcanic eruptions. The total volume of material erupted may have been up to 25 cubic kilometers (6 mile³), and the removal of this amount of material from the underlying magma chamber led to the formation of a large caldera. A magma chamber is a large underground pool of molten rock lying under the surface of the earth's crust A caldera is a cauldron-like volcanic feature formed by the collapse of land following a volcanic eruption

Later large eruptions occurred 17,000, 9000, 6000–5000 and 3900–2300 years ago. Each of these eruptions seems to have been very large, ejecting more than 10 km³ of material and covering large parts of the surrounding areas with pyroclastic flow deposits. Scientists estimate that the most recent eruption before 1991 happened about 500 years ago, and after that, the volcano lay dormant. Its slopes became completely covered in dense rainforest, and eroded into gullies and ravines. Rainforests are Forests characterized by high Rainfall with definitions setting minimum normal annual rainfall between 1750–2000 mm (68-78 inches

1991 awakening

One of the early explosive eruptions at Pinatubo after the April 1991 onset of ash eruptions

On July 16, 1990, an earthquake of magnitude 7. Events 622 - The beginning of the Islamic calendar. 1054 - Three Roman legates fractured relations between the Western and Year 1990 ( MCMXC) was a Common year starting on Monday (link displays the 1990 Gregorian calendar) The 1990 Luzon earthquake occurred on Monday July 16, 1990, at 426 PM local time in the Philippines. The Richter magnitude scale, or more correctly local magnitude M L scale assigns a single number to quantify the amount of seismic energy released 8 (comparable in size to the 1906 San Francisco earthquake and the 2008 Sichuan earthquake) struck central Luzon. The 2008 Sichuan earthquake ( or " Great Sichuan Earthquake " which measured at 8 Its epicenter was at Cabanatuan City, about 100 km northeast of Pinatubo, leading some volcanologists to speculate that it might ultimately have triggered the 1991 eruption, although this is impossible to prove conclusively. The City of Cabanatuan ( Ilokano: Ciudad ti Cabanatuan; Kapampangan: Lakanbalen ning Cabanatuan/Siudad ning Cabanatuan; Two weeks after the earthquake, local residents reported steam coming from the volcano, but scientists visiting the mountain found that small landslides rather than any eruptive activity were responsible. Uses A Steam engine uses the expansion of steam in order to drive a Piston or Turbine to perform Mechanical work. A landslide is a geological phenomenon which includes a wide range of ground movement such as rock falls deep failure of slopes and shallow debris flows which can occur

On March 15, 1991, a succession of earthquakes was felt by villagers on the north-western side of the volcano. Events 44 BC - Julius Caesar, Dictator of the Roman Republic, is stabbed to death by Marcus Junius Brutus, Year 1991 ( MCMXCI) was a Common year starting on Tuesday (link will display full calendar of the Gregorian Calendar. Further earthquakes of increasing intensity were felt over the next two weeks, and it became clear some kind of volcanic activity was imminent. On April 2, the volcano awoke, with phreatic eruptions occurring near the summit along a 1. Events 68 - Galba, Governor of Hispania, names himself legatus senatus populique Romani, breaking the line of A Phreatic eruption, also called an ultravulcanian eruption, occurs when rising Magma makes contact with ground or surface water 5 km long fissure. In Anatomy, fissure ( Latin fissura, Plural fissurae) is a groove natural division deep furrow cleft or tear in various parts of Over the next few weeks, small eruptions continued, dusting the surrounding areas with ash. Volcanic ash consists of small Tephra, which are bits of pulverized rock and glass created by volcanic eruptions less than in diameter Seismographs recorded hundreds of small earthquakes every day. Seismometers (from Greek Seism - "the shakes" - and Metro - "I measure" are instruments that measure and record motions of the ground including

Scientists immediately installed monitoring equipment and analyzed the volcano for clues as to its previous eruptive history. Radiocarbon dating of charcoal found in old volcanic deposits revealed the three major explosive eruptions in recent millennia, about 5500, 3500 and 500 years ago. Radiocarbon dating is a Radiometric dating method that uses the naturally occurring Radioisotope Carbon-14 (14C to determine the age of Geological mapping showed that much of the surrounding plains were formed by lahar deposits from previous eruptions. A lahar is a type of Mudflow / Landslide composed of Pyroclastic material and Water that flows down from a Volcano, typically

Volcanic activity increased throughout April and May. Measurements of sulfur dioxide emission showed a rapid increase from 500 tons per day by May 13 to 5,000 tons/day by May 28. Units of mass There are three similar units of Mass called the ton: Long ton (simply ton in countries such as the United Events 1497 - Pope Alexander VI excommunicates Girolamo Savonarola. Events 585 BC - A Solar eclipse occurs as predicted by Greek philosopher and scientist Thales, while Alyattes is battling This implied that there was a rising column of fresh magma beneath the volcano. Magma (Plurals magmas and magmata) is molten rock that sometimes forms beneath the surface of the Earth (or any other Terrestrial planet After May 28, the amount of SO₂ being emitted decreased substantially, raising fears that the degassing of the magma had been blocked somehow, leading to a pressure build-up in the magma chamber and a high likelihood of explosive eruptions. Events 585 BC - A Solar eclipse occurs as predicted by Greek philosopher and scientist Thales, while Alyattes is battling Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface A magma chamber is a large underground pool of molten rock lying under the surface of the earth's crust

The first magmatic eruptions occurred on June 3, and the first large explosion on June 7 generated an ash column 7 km (4. Magma (Plurals magmas and magmata) is molten rock that sometimes forms beneath the surface of the Earth (or any other Terrestrial planet Events 350 - Roman usurper Nepotianus, of the Constantinian dynasty, proclaims himself Roman Emperor, entering Events 1099 - The First Crusade: The Siege of Jerusalem begins 5 miles) high. The Philippine Institute of Volcanology and Seismology (PHIVOLCS) led by Raymundo Punongbayan issued a warning indicating the possibility of a major eruption within two weeks. Volcanology (also spelled vulcanology) is the study of Volcanoes, Lava, Magma, and related geological and Geophysical phenomena Seismology (from Greek grc σεισμός seismos, "earthquake" and grc -λογία -logia) is the scientific study of Earthquakes Dr Raymundo Santiago Punongbayan (1937 &ndash 2005 was the former director of the Philippine Institute of Volcanology and Seismology (PHIVOLCS.

Evacuation

Pinatubo evacuation zones

Given all the signs that a very large eruption was imminent, PHIVOLCS worked in cooperation with the US Geological Survey to convince people in the local area of the severity of the threat. The United States Geological Survey ( USGS) is a scientific agency of the United States government. A false warning might have led to cynicism about any later warnings but delaying a warning until an eruption began might lead to thousands of deaths, so the volcanologists were under some pressure to deliver a timely and accurate assessment of the volcanic risk. Volcanology (also spelled vulcanology) is the study of Volcanoes, Lava, Magma, and related geological and Geophysical phenomena

Three successive evacuation zones were defined, the innermost containing everything within 10 km of the volcano's summit, the second extending from 10 to 20 km from the summit, and the third extending from 20 to 40 km from the summit (Clark Air Base and Angeles City were in this zone). Clark Air Base is a former United States Air Force base on Luzon Island in the Philippines, located 3 miles west of Angeles City, about 40 miles Angeles City (Lungsod ng Angeles Kapampangan: Ciudad ning Angeles) geographically located within the province of Pampanga in the Philippines The 10 km and 10–20 km zones had a total population of about 40,000, while some 331,000 people lived in the 20–40 km zone. Five stages of volcanic alert were defined, from level 1 (low level seismic disturbances) up to level 5 (major eruption in progress). Daily alerts were issued stating the alert level and associated danger area, and the information was announced in major national and local newspapers, radio and television stations, nongovernmental organizations (NGOs), and directly to the endangered inhabitants. A newspaper is a written Publication containing News, information and Advertising, usually printed on low-cost paper called Newsprint. Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. Television ( TV) is a widely used Telecommunication medium for sending ( Broadcasting) and receiving moving Images, either monochromatic

Many of the Aeta who lived on the slopes of the volcano left their villages of their own volition when the first explosions began in April, gathering in a village about 12 km from the summit. They moved to increasingly distant villages as the eruptions escalated, with some Aeta moving up to nine times in the two months preceding the cataclysmic eruption.

The first formal evacuations were ordered from the 10 km zone on 7 April. Events 529 - First draft of Corpus Juris Civilis (a fundamental work in Jurisprudence) is issued by Eastern Roman Emperor Evacuation of the 10–20 km zone was ordered when a level 4 alert was issued on 7 June. Events 1099 - The First Crusade: The Siege of Jerusalem begins A level 5 alert triggered evacuation of the 20–40 km zone on 14 June, and in all some 60,000 people had left the area within 30 km of the volcano before 15 June. Events 1276 - While taking exile in Fuzhou in southern China, away from the advancing Mongol invaders, the remnants of the Events 763 BC - Assyrians record a Solar eclipse that will be used to fix the Chronology of Mesopotamian history Most people temporarily relocated to Manila and Quezon City, with some 30,000 using the Amoranto Sports Stadium in Quezon City as an evacuee camp. The City of Manila Quezon City ( Filipino: Lungsod Quezon) is the former capital ( 1948 - 1976) and the most populous

Eruptions build to a climax

Explosive eruption, early June 1991

In early June, tiltmeter measurements had shown that the volcano was inflating, evidently due to growing amounts of magma filling the reservoir beneath the summit. A tiltmeter is an instrument designed to measure very small changes from the horizontal level either on the ground or in structures At the same time, seismic activity, previously concentrated at a depth of a few kilometers below a point about 5 km northwest of the summit, shifted to shallow depths just below the summit. On June 7, the first magmatic eruptions took place with the formation of a lava dome at the summit of the volcano. Events 1099 - The First Crusade: The Siege of Jerusalem begins In Volcanology, a lava dome or plug dome is a roughly circular Mound -shaped protrusion resulting from the slow eruption of Felsic Lava The dome grew substantially over the next five days, reaching a maximum diameter of about 200 m and a height of 40 m.

A small explosion at 03:41 on June 12 marked the beginning of a new, more violent phase of the eruption. Events 1381 - Peasants' Revolt: in England, rebels arrive at Blackheath. A few hours later, large explosions lasting about half an hour generated an eruption column which quickly reached heights of over 19 km, and which generated pyroclastic flows extending up to 4 km from the summit in some river valleys. An eruption column consists of hot Volcanic ash emitted during an explosive Volcanic eruption. A pyroclastic flow (also known as a pyroclastic density current) is a common and devastating result of some volcanic eruptions. In Geology, a valley (also called a vale, dale, glen or strath and near or in Appalachia, a draw) is Fourteen hours later, a 15 minute eruption hurled ash to heights of 24 km. Friction in the uprushing ash column generated abundant lightning. Lightning is an atmospheric discharge of Electricity, which typically occurs during Thunderstorms and sometimes during volcanic eruptions or

A third large eruption began at 08:41 on June 13, after an intense swarm of small earthquakes over the previous two hours. Events 1525 - Martin Luther marries Katharina von Bora, against the Celibacy rule decreed by the Roman Catholic Church for It lasted about five minutes, and the eruption column once again reached 24 km. After three hours of quiet, seismic activity began, growing more and more intense over the next 24 hours, until a three-minute eruption generated a 21 km-high eruption column at 13:09 on June 14. Events 1276 - While taking exile in Fuzhou in southern China, away from the advancing Mongol invaders, the remnants of the

Tephra fall from these four large eruptions was extensive to the southwest of the volcano. Two hours after the last of these four explosions, a series of eruptions began which lasted for the next 24 hours, and which saw the production of much larger pyroclastic flows and surges which travelled several kilometres down river valleys on the flanks of the volcano.

Dacite was the igneous rock making up the tephra in these eruptions and in the following climactic event. Dacite ( deɪsaɪt) is an igneous, volcanic rock with a high iron content Igneous rocks (etymology from Latin ignis, fire are rocks formed by solidification of cooled Magma (molten rock The most abundant phenocryst minerals were hornblende and plagioclase, but an unusual phenocryst mineral was also present—the calcium sulfate, anhydrite. A phenocryst is a relatively large and usually conspicuous Crystal distinctly larger than the grains of the rock groundmass of a Porphyritic Igneous Hornblende is a complex inosilicate series of Minerals Hornblende is not a recognized mineral in its own right but the name is used as a general or field term to Plagioclase is a very important series of tectosilicate Minerals within the Feldspar family Anhydrite is a mineral - anhydrous Calcium Sulfate, CaSO4 It is in the Orthorhombic crystal system with three directions of perfect cleavage The dacite magma was more oxidized than most magmas, and sulfur-rich nature of the eruption probably was causally related to the redox state. Magma (Plurals magmas and magmata) is molten rock that sometimes forms beneath the surface of the Earth (or any other Terrestrial planet In geology a redox buffer is an assemblage of minerals or compounds that constrains oxygen Fugacity as a function of temperature

The climactic eruption

The eruption cloud shortly before the climactic eruption

June 15 saw the onset of the climactic eruption. Events 763 BC - Assyrians record a Solar eclipse that will be used to fix the Chronology of Mesopotamian history Large tremors starting at 13:42 saturated all the seismographs at Clark Air Base, and by 14:30 all had been rendered inoperative, mostly by pyroclastic density currents. Clark Air Base is a former United States Air Force base on Luzon Island in the Philippines, located 3 miles west of Angeles City, about 40 miles Intense atmospheric pressure variation was also recorded. Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five

On the same day, Typhoon Yunya struck the island, passing about 75 km (50 miles) north of the volcano. The 1991 Pacific typhoon season has no official bounds it ran year-round in 1991 but most Tropical cyclones tend to form in the northwestern Pacific Ocean between This is about the direction for other uses see North (disambiguation. The typhoon rains made direct visual observations of the eruption impossible, but measurements showed that ash was ejected to heights of 34 km by the most violent phase of the eruption, which lasted about three hours. Pyroclastic flows poured from the summit, reaching as far as 16 km away from it. A pyroclastic flow (also known as a pyroclastic density current) is a common and devastating result of some volcanic eruptions. Typhoon rains mixed with the ash deposits caused massive lahars. A lahar is a type of Mudflow / Landslide composed of Pyroclastic material and Water that flows down from a Volcano, typically

The ash cloud from the volcano covered an area of some 125,000 km² (50,000 mi²), bringing total darkness to much of central Luzon. Almost all of the island received some ashfall, which formed a heavy, rain-saturated snow-like blanket. Tephra fell over most of the South China Sea and ashfall was recorded as far away as Vietnam, Cambodia and Malaysia. Tephra is air-fall material produced by a volcanic eruption regardless of composition or fragment size The South China Sea is a Marginal sea south of China. It is a part of the Pacific Ocean, encompassing an area from Singapore to the Vietnam (ˌviːɛtˈnɑːm Việt Nam) officially The Kingdom of Cambodia ( formerly known as Kampuchea (, transliterated: Preăh Réachéanachâkr Kâmpŭchea) is a country in South East For the biogeographical region see Malesia Malaysia (məˈleɪʒə or /məˈleɪziə/ is a country that consists of thirteen states and

By about 22:30, nine hours after the onset of the climactic phase, atmospheric pressure waves had decreased to the pre-eruption levels. No seismic records were available at this time, but volcanologists believe 22:30 marked the end of the climactic eruption.

Vast quantities of minerals and metals were brought to the surface. Overall, introduced to the surface environment, was an estimated 800,000 tons of zinc, 600,000 tons of copper, 550,000 tons of chromium, 300,000 tons of nickel, 100,000 tons of lead, 10,000 tons of arsenic, 1000 tons of cadmium, & 800 tons of mercury. Zinc (ˈzɪŋk from Zink is a Metallic Chemical element with the symbol Zn and Atomic number 30 Copper (ˈkɒpɚ is a Chemical element with the symbol Cu (cuprum and Atomic number 29 Chromium (ˈkroʊmiəm is a Chemical element which has the symbol Cr and Atomic number 24 Nickel (ˈnɪkəl is a metallic Chemical element with the symbol Ni and Atomic number 28 Characteristics Lead has a dull luster and is a dense, Ductile, very soft highly Arsenic (ˈɑrsənɪk is a Chemical element that has the symbol As and Atomic number of 33 Cadmium (ˈkædmiəm is a Chemical element with the symbol Cd and Atomic number 48 Mercury (ˈmɜrkjʊri also called quicksilver or hydrargyrum, is a Chemical element with the symbol Hg ( Latinized hydrargyrum ^[5]

Aftermath

Snow-like ashfall caused by heavy rain mixing with ash columns

In all, the eruption ejected about ten cubic kilometres (2. 5 mile³) of material, making it the largest eruption since that of Novarupta in 1912 and some ten times larger than the 1980 eruption of Mount St. Helens. Novarupta, meaning "new eruption" is a Volcano located on the Alaska Peninsula in the Katmai, about southwest of Anchorage. The 1980 eruption of Mount St Helens, a volcano located in Washington state in the United States was a major volcanic eruption. Ejected material such as tephra fallout and pyroclastic flow deposits are much less dense than magma, and the volume of ejected material was equivalent to about four cubic kilometres (1 mile³) of unerupted material. Tephra is air-fall material produced by a volcanic eruption regardless of composition or fragment size This colossal eruption had a Volcanic Explosivity Index of 6. The Volcanic Explosivity Index (VEI was devised by Chris Newhall of the U ^[6] The former summit of the volcano was replaced by a caldera 2. A caldera is a cauldron-like volcanic feature formed by the collapse of land following a volcanic eruption 5 km wide. The highest point on the caldera rim now stood 1,485 m above sea level, some 260 m lower than the pre-eruption summit.

About 300 people were killed by the eruption, mostly by roofs collapsing under the weight of accumulated wet ash, a hazard that was greatly exacerbated by the simultaneous arrival of Typhoon Yunya. The evacuation in the days preceding the eruption certainly saved tens of thousands of lives, and has been hailed as a great success for volcanology and eruption prediction.

Before and after the eruption: a river valley filled in by pyroclastic flow deposits

However, since the eruption, each rainy season has brought further lahars, which have caused the displacement of thousands of people. A pyroclastic flow (also known as a pyroclastic density current) is a common and devastating result of some volcanic eruptions. A wet season or rainy season is a Season in which the average Rainfall in a region is significantly increased A lahar is a type of Mudflow / Landslide composed of Pyroclastic material and Water that flows down from a Volcano, typically Hundreds have died from poor sanitation in relocation camps. Sanitation is the hygienic means of preventing human contact from the hazards of wastes to promote health Agriculture in the region also suffered badly from the effects of the eruption, with hundreds of square kilometres of formerly arable land being rendered infertile, destroying the livelihoods of thousands of farmers. Agriculture refers to the production of goods through the growing of plants and fungi and the raising of domesticated Animals The study of agriculture In Geography, arable land (from Latin arare, to Plough) is an agricultural term meaning land that can be used for

The United States maintained two large military bases in the region; U.S. Naval Base Subic Bay was 75 km (50 mi. The United States of America —commonly referred to as the US Naval Base Subic Bay was a major ship-repair supply and rest and recreation facility of the United States Navy located in Zambales, Philippines ) to the southwest, while Clark Air Base was less than 25 km (16 mi. Clark Air Base is a former United States Air Force base on Luzon Island in the Philippines, located 3 miles west of Angeles City, about 40 miles ) to the east of the volcano's summit. Both were abandoned after being severely damaged by the eruption.

Although the 1991 eruption was one of the largest and most violent of the 20th century, it was weaker than any of the historical eruptions uncovered by geologists. There is some evidence that eruptions at Pinatubo are getting weaker over time, but this is by no means conclusively established.

Local economic and social effects

Aircraft hangars at Clark Air Base destroyed by ashfall

The eruption of Pinatubo severely hampered the economic development of the surrounding areas. Clark Air Base is a former United States Air Force base on Luzon Island in the Philippines, located 3 miles west of Angeles City, about 40 miles Economic development is the development of economic wealth of countries or regions for the well-being of their inhabitants Extensive damage to buildings and infrastructure cost billions of pesos to repair, and further costs were incurred in constructing dikes and dams to control the post-eruption lahars. Infrastructure typically refers to the technical structures that support a society such as Roads Water supply, Wastewater, Power grids The peso ( Filipino: piso) ( sign: ₱; code: PHP) is the currency of the Philippines. LeveeEmbankmentDitch A dike (or dyke) levee, levée, embankment, floodbank or stopbank is a natural or artificial A dam is a barrier that divides waters. Dams generally serve the primary purpose of retaining water while other structures such as Floodgates, Levees

In total, 364 communities and 2. 1 million people were affected by the eruption, with livelihoods and houses being damaged or destroyed. More than 8,000 houses were completely destroyed, and a further 73,000 were damaged. In addition to the severe damage sustained by these communities, roads and communications were damaged or destroyed by pyroclastic flows and lahars throughout the areas surrounding the volcanoes. The estimated cost of repairing the damage to infrastructure was 3. 8 billion pesos.

Many reforestation projects were destroyed in the eruption, with a total area of 150 square kilometres (37,000 acres) valued at 125 million pesos destroyed. Reforestation is the restocking of existing forests and woodlands which have been depleted with native tree stock The acre is a unit of Area in a number of different systems including the imperial and U Agriculture was heavily disrupted, with 800 square kilometres (200,000 acres) of rice-growing farmland destroyed, and almost 800,000 head of livestock and poultry killed. Agriculture refers to the production of goods through the growing of plants and fungi and the raising of domesticated Animals The study of agriculture Rice is a Cereal foodstuff which forms an important part of the diet of many people worldwide and as such it is a staple food for many Poultry is the category of Domesticated Birds which some humans keep for the purpose of collecting their eggs, or kill for their Meat and/or The cost to agriculture of eruption effects was estimated to be 1. 5 billion pesos.

Damage to healthcare facilities, and the spread of illnesses in relocation facilities, led to soaring death rates in the months following the eruption. Health care is the prevention treatment and management of illness and the preservation of mental health through the services offered by the medical, Nursing Education for thousands of children was seriously disrupted by the destruction of schools in the eruption. Education encompasses both the Teaching and Learning of Knowledge, proper conduct, and technical competency A school (from Greek σχολεῖον - scholeion) is an Institution designed to allow and encourage Students (or "pupils" The gross regional domestic product of the Pinatubo area accounted for about 10% of the total Philippine gross domestic product. The GRDP had been growing at 5% annually before the eruption, but fell by more than 3% from 1990 to 1991.

Global environmental effects

Space Shuttle (Mission STS-43) photograph of the Earth over South America taken on August 8, 1991, showing double layer of Pinatubo aerosol cloud (dark streaks) above high cumulonimbus tops

The powerful eruption of such an enormous volume of lava and ash injected significant quantities of aerosols and dust into the stratosphere. STS-43, the ninth mission for Space Shuttle ''Atlantis'', was a nine-day mission whose primary goal was launching the fourth Tracking and Data Relay Satellite South America is a Continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a Events 1220 - Sweden is defeated by Estonian tribes in the Battle of Lihula. Year 1991 ( MCMXCI) was a Common year starting on Tuesday (link will display full calendar of the Gregorian Calendar. Particulates, alternatively referred to as particulate matter (PM or fine particles, are tiny particles of solid or liquid suspended in a gas Dust is a general name for minute Solid particles with Diameters less than 500 micrometers. The stratosphere is the second major layer of Earth's atmosphere, just above the Troposphere, and below the Mesosphere. Sulfur dioxide oxidised in the atmosphere to produce a haze of sulfuric acid droplets, which gradually spread throughout the stratosphere over the year following the eruption. Sulfuric (or sulphuric acid, H 2 S[[oxygen O]]4 is a strong Mineral acid. The injection of aerosols into the stratosphere is thought to have been the largest since the eruption of Krakatoa in 1883, with a total mass of SO₂ of about 17 million tons being injected—the largest volume ever recorded by modern instruments (see chart and figure). Krakatoa ( Indonesian: Krakatau) also spelled Krakatao or Krakatowa, is a volcanic island in the Sunda Strait

This very large stratospheric injection resulted in a reduction in the normal amount of sunlight reaching the earth's surface by roughly 10% (see figure). Sunlight, in the broad sense is the total spectrum of the Electromagnetic radiation given off by the Sun. This led to a decrease in northern hemisphere average temperatures of 0. Northern Hemisphere is the half of a Planet that is North of the Equator —the word hemisphere literally means 'half ball' 5–0. 6 °C (0. The Celsius Temperature scale was previously known as the centigrade scale. 9–1. 1 °F), and a global fall of about 0. 4 °C (0. 7 °F). At the same time, the temperature in the stratosphere rose to several degrees higher than normal, due to absorption of radiation by the aerosols. The stratospheric cloud from the eruption persisted in the atmosphere for three years after the eruption.

Satellite measurements of ash and aerosol emissions from Mount Pinatubo. Particulates, alternatively referred to as particulate matter (PM or fine particles, are tiny particles of solid or liquid suspended in a gas

The eruption had a significant effect on ozone levels in the atmosphere, causing a large increase in the destruction rate of ozone. OZONE is an object oriented Operating system written in the C programming language. Ozone levels at mid-latitudes reached their lowest recorded levels, while in the southern hemisphere winter of 1992, the ozone hole over Antarctica reached its largest ever size until then, with the fastest recorded ozone depletion rates. Southern Hemisphere is the half of a Planet that is South of the Equator —the word hemisphere literally means 'half ball' Ozone depletion describes two distinct but related observations a slow steady decline of about 4 percent per decade in the total amount of Ozone in Earth's The eruption of Mount Hudson in Chile in August 1991 also contributed to southern hemisphere ozone destruction, with measurements showing a sharp decrease in ozone levels at the tropopause when the aerosol clouds from Pinatubo and Hudson arrived. Mount Hudson (locally known as Cerro Hudson) is a Stratovolcano in southern Chile, and the site of one of the largest eruptions in the twentieth century Chile, officially the Republic of Chile ( Spanish:) is a country in South America occupying a long and narrow Coastal strip wedged between the The tropopause is in the atmosphere between the Troposphere and the Stratosphere.

Another noticeable effect of the dust in the atmosphere was the appearance of lunar eclipses. A lunar eclipse occurs whenever the Moon passes through some portion of the Earth's shadow Normally even at mid-eclipse, the moon is still visible although much dimmed, but in the year following the Pinatubo eruption, the moon was hardly visible at all during eclipses, due to much greater absorption of sunlight by dust in the atmosphere.

The area since 1991

Thick ash deposits from Pinatubo are evident in this 1992 photo from the Space Shuttle Atlantis

Following the climactic eruption of June 15, 1991, activity at the volcano continued at a much lower level, with continuous ash eruptions lasting until August 1991 and episodic eruptions continuing for another month. Space Shuttle Atlantis ( Orbiter Vehicle Designation: OV-104 is one of the three currently operational orbiters in the Space Shuttle fleet of Events 763 BC - Assyrians record a Solar eclipse that will be used to fix the Chronology of Mesopotamian history Year 1991 ( MCMXCI) was a Common year starting on Tuesday (link will display full calendar of the Gregorian Calendar. Activity then remained low until July 1992, when a new lava dome began to grow in the caldera. In Volcanology, a lava dome or plug dome is a roughly circular Mound -shaped protrusion resulting from the slow eruption of Felsic Lava A caldera is a cauldron-like volcanic feature formed by the collapse of land following a volcanic eruption

This dome appeared to be composed of fresh lava from the deep magma reservoir beneath the volcano, rather than material 'left over' in a shallow reservoir from the 1991 eruption. Magma (Plurals magmas and magmata) is molten rock that sometimes forms beneath the surface of the Earth (or any other Terrestrial planet Thus, volcanologists suspected that further violent eruptions could be possible, and some areas were once again evacuated. However, the eruption did not become violent, perhaps due to outgassing from the deep reservoir reducing the explosivity of the lava reaching the surface. Since 1992, the volcano has been dormant.

The Aeta people were the hardest hit by the eruption. The total destruction of many villages by pyroclasts and lahar deposits meant that many Aeta were unable to return to their former way of life. After the areas surrounding the volcano were declared safe to return to, those whose villages had not been destroyed moved back, but most people moved instead to government-organized resettlement areas. Conditions on these were poor, with each family receiving only small plots of land, which were not ideal for growing crops. Many Aeta found casual labor working for lowland farmers, and overall Aeta society became much more fragmented, and reliant on and integrated with lowland culture. A farmer is a person who raises living organisms for food or raw materials

After eruptions ended, a crater lake formed in the 1991 caldera, with the 1992 lava dome forming an island. Crater Lake is a Caldera Lake located in the US state of Oregon. An island (ˈaɪlənd or isle (/ˈaɪl/ is any piece of land that is completely surrounded by water in two dimensions above high tide and isolated from other significant At first, the lake was small, hot and highly acidic, with a minimum pH of 2 and a temperature of about 40 °C. In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are pH is the measure of the acidity or alkalinity of a Solution. Abundant rainfall cooled and diluted the lake, lowering the temperature to 26 °C and raising the pH to 5. 5 by 2003.

The lake increased in depth by about 1 metre per month on average, until September 2001, when fears that the walls of the crater might be unstable prompted the Philippine government to order a controlled draining of the lake. 9,000 people were once again evacuated from surrounding areas in case a large flood was accidentally triggered. A flood is an overflow of an expanse of water that submerges land a deluge Workers cut a 5 m notch in the crater rim, and successfully drained about a quarter of the lake's volume.

Ecotourism

As of 2007, Mt. Pinatubo is a popular tourist destination in Central Luzon. Tour operators offer a whole-day package which includes a 4x4 jeep ride that starts off at Capas, Tarlac, taking tourists across the barren plains. Capas is a 1st class municipality in the province of Tarlac, Philippines. A 2-3 hour trek then commences on a trail that leads to the crater lake. There, facilities include a viewdeck, cottages, and kayaks. Swimming in the lake is allowed although it is restricted to the proximal banks. ^[7]

Related images

Mount Pinatubo and crater lake, May 2005	Sulfur dioxide emissions.	Solar radiation reduction due to volcanic eruptions.	Sulfur dioxide emissions by volcanoes. Plate tectonics and hotspots Divergent plate boundaries At the
The Pinatubo crater lake in January 2006	Map showing major volcanoes of the Philippines

Notes

References

• Decker, R. and Decker, B. (1997) Volcanoes, 3rd edition, WH Freeman, New York.
• Hiromu Shimizu (2002), Struggling for Existence after the Pinatubo Eruption 1991: Catastrophe, Suffering and Rebirth of Ayta Communities. Paper presented inter-congress of the International Union of Anthropological and Ethnological Sciences, Tokyo, Japan.
• McCormick, M. Patrick et al. (1995). "Atmospheric effects of the Mt Pinatubo eruption". Nature 373: 399–404. Nature is a prominent Scientific journal, first published on 4 November 1869 doi:10.1038/373399a0. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
• Newhall, C. and Punongbayan, R. Dr Raymundo Santiago Punongbayan (1937 &ndash 2005 was the former director of the Philippine Institute of Volcanology and Seismology (PHIVOLCS. , eds. (1997) Fire and Mud: Eruptions and Lahars of Mount Pinatubo, Philippines. ISBN 0-295-97585-7.
• Scaillet, B. and Evans, B. W. (1999) The 15 June 1991 Eruption of Mount Pinatubo. I. Phase Equilibria and Pre-eruption P–T–fO2–fH2O Conditions of the Dacite Magma. Journal of Petrology, v. 40, 381–411.
• Stimac J. A. , Goff F. , Counce D. , Larocque A. C. L. , Hilton D. R. (2003), The crater lake and hydrothermal system of Mount Pinatubo, Philippines: evolution in the decade after eruption, Bulletin of Volcanology, v. 66, p. 149–167
• Wiesner, M. G. , Wetzel, A. Catane, S. G. , Listanco, E. L. and Mirabueno, H. T. (2004) Grain size, areal thickness distribution and controls on sedimentation of the 1991 Mount Pinatubo tephra layer in the South China Sea. Bulletin of Volcanology, v. 66, 226–242.
• Dhot, S. Mt Pinatubo Safety.

External links

• Philippine Institute of Volcanology and Seismology
• Mt. Pinatubo
• Weather effects of the 1991 eruption
• CVO Pinatubo photo archive
• News article about the draining of the crater lake
• The Cataclysmic 1991 Eruption of Mount Pinatubo, Philippines