Wednesday 16 March 2011

MOunt Pinatubo

Mount Pinatubo

Mount Pinatubo

The eruption column of Mount Pinatubo on June 12, 1991, three days before the climactic eruption.
Elevation1,485 m (4,872 ft) (current)1,745 m (5,725 ft) (before 1991 eruption)
Pronunciation[English: /ˌpiːnəˈtuːboʊ/]
Location
LocationZambales, Luzon, Philippines
Tarlac, Luzon, Philippines
Pampanga, Luzon, Philippines
RangeZambales Mountains
Coordinates15°08′30″N 120°21′00″E / 15.14167°N 120.35°E / 15.14167; 120.35Coordinates: 15°08′30″N 120°21′00″E / 15.14167°N 120.35°E / 15.14167; 120.35
Geology
TypeStratovolcano
Age of rockBetween 635,000 ± 80,000
and 1.1 ±; 0.09 million years[1]
Last eruption1991[2] (deaths reached to 847)[3]
Mount Pinatubo is an active stratovolcano located on the island of Luzon, at the intersection of the borders of the Philippine provinces of Zambales, Tarlac, and Pampanga. It is located in the Tri-Cabusilan Mountain range separating the west coast of Luzon from the central plains, and is 42 km (26 mi) west of the dormant and more prominent Mount Arayat,[4] occasionally mistaken for Pinatubo. Ancestral Pinatubo was a stratovolcano made of andesite and dacite. Before 1991, the mountain was inconspicuous and heavily eroded. 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 during the protracted Spanish conquest of the Philippines which began in 1565.
The volcano's Plinian/ Ultra-Plinian eruption (~VEI 6) in June 1991 produced the second largest terrestrial eruption of the 20th century (after the 1912 eruption of Novarupta) and the largest eruption in living memory.[5] The colossal 1991 eruption had a Volcanic Explosivity Index (VEI) of 5 or 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 1000 years after previous VEI 6 eruptive activity.[2] A VEI of 6 corresponds to 10 to 100 cubic km of released material (Pinatubo released an estimated 6 to 16 cubic km of ash). 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.[5]
The effects of the eruption were felt worldwide. It ejected roughly 10 billion metric tonnes (10 cubic kilometres) 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. Over the following months, the aerosols formed a global layer of sulfuric acid haze. Global temperatures dropped by about 0.5 °C (0.9 °F), and ozone depletion temporarily increased substantially.

Mount Pinatubo Eruption

The Volcanic Mount Pinatubo Eruption of 1991 that Cooled the Planet

Mount Pinatubo Eruption
Mt. Pinatubo eruption plume, July 1991, from Clark Air Base control tower
J.N. Marso, courtesy of USGS/Cascades Volcano Observatory
Mar 2 2011
In June 1991, the second largest volcanic eruption of the twentieth century* took place on the island of Luzon in the Philippines, a mere 90 kilometers (55 miles) northwest of the capital city Manila. Up to 800 people were killed and 100,000 became homeless following the Mount Pinatubo eruption, which climaxed with nine hours of eruption on June 15, 1991. On June 15, millions of tons of sulfur dioxide were discharged into the atmosphere, resulting in a decrease in the temperature worldwide over the next few years. Mount Pinatubo is part of a chain of composite volcanoes along the Luzon arc on the west coast of the island (area map). The arc of volcanoes is due to the subduction of the Manila trench to the west. The volcano experienced major eruptions approximately 500, 3000, and 5500 years ago.
The events of the 1991 Mount Pinatubo eruption began in July 1990, when a magnitude 7.8 earthquake occurred 100 kilometers (62 miles) northeast of the Pinatubo region, determined to be a result of the reawakening of Mount Pinatubo.
In mid-March 1991, villagers around Mount Pinatubo began feeling earthquakes and vulcanologists began to study the mountain. (Approximately 30,000 people lived on the flanks of the volcano prior to the disaster.) On April 2, small explosions from vents dusted local villages with ash. The first evacuations of 5,000 people were ordered later that month.
Earthquakes and explosions continued. On June 5, a Level 3 alert was issued for two weeks due to the possibility of a major eruption. The extrusion of a lava dome on June 7 led to the issuance of a Level 5 alert on June 9, indicating an eruption in progress. An evacuation area 20 kilometers (12.4 miles) away from the volcano was established and 25,000 people were evacuated.
The following day (June 10), Clark Air Base, a U.S. military installation near the volcano, was evacuated. The 18,000 personnel and their families were transported to Subic Bay Naval Station and most were returned to the United States. On June 12, the danger radius was extended to 30 kilometers (18.6 miles) from the volcano resulting in the total evacuation of 58,000 people.
On June 15, the eruption of Mount Pinatubo began at 1:42 p.m. local time. The eruption lasted for nine hours and caused numerous large earthquakes due to the collapse of the summit of Mount Pinatubo and the creation of a caldera. The caldera reduced the peak from 1745 meters (5725 feet) to 1485 meters (4872 feet) high is 2.5 kilometers (1.5 miles) in diameter.
Unfortunately, at the time of the eruption Tropical Storm Yunya was passing 75 km (47 miles) to the northeast of Mount Pinatubo, causing a large amount of rainfall in the region. The ash that was ejected from the volcano mixed with the water vapor in the air to cause a rainfall of tephra that fell across almost the entire island of Luzon. The greatest thickness of ash deposited 33 centimeters (13 inches) approximately 10.5 km (6.5 mi) southwest of the volcano. There was 10 cm of ash covering an area of 2000 square kilometers (772 square miles). Most of the 200 to 800 people (accounts vary) who died during the eruption died due to the weight of the ash collapsing roofs and killing to occupants. Had Tropical Storm Yunya not been nearby, the death toll from the volcano would have been much lower.
In addition to the ash, Mount Pinatubo ejected between 15 and 30 million tons of sulfur dioxide gas. Sulfur dioxide in the atmosphere mixes with water and oxygen in the atmosphere to become sulfuric acid, which in turn triggers ozone depletion. Over 90% of the material released from the volcano was ejected during the nine hour eruption of June 15.
The eruption plume of Mount Pinatubo's various gases and ash reached high into the atmosphere within two hours of the eruption, attaining an altitude of 34 km (21 miles) high and over 400 km (250 miles) wide. This eruption was the largest disturbance of the stratosphere since the eruption of Krakatau in 1883 (but ten times larger than Mount St. Helens in 1980). The aerosol cloud spread around the earth in two weeks and covered the planet within a year. During 1992 and 1993, the Ozone hole over Antarctica reached an unprecedented size.
The cloud over the earth reduced global temperatures. In 1992 and 1993, the average temperature in the Northern Hemisphere was reduced 0.5 to 0.6°C and the entire planet was cooled 0.4 to 0.5°C. The maximum reduction in global temperature occurred in August 1992 with a reduction of 0.73°C. The eruption is believed to have influenced such events as 1993 floods along the Mississippi river and the drought in the Sahel region of Africa. The United States experienced its third coldest and third wettest summer in 77 years during 1992.
Overall, the cooling effects of the Mount Pinatubo eruption were greater than those of the El Niño that was taking place at the time or of the greenhouse gas warming of the planet. Remarkable sunrises and sunsets were visible around the globe in the years following the Mount Pinatubo eruption.
The human impacts of the disaster are staggering. In addition to the up to 800 people who lost their lives, there was almost one half of a billion dollars in property and economic damage. The economy of central Luzon was horribly disrupted. In 1991, the volcano destroyed 4,979 homes and damaged another 70,257. The following year 3,281 homes were destroyed and 3,137 were damaged. Damage following the Mount Pinatubo eruption was usually caused by lahars - rain-induced torrents of volcanic debris that killed people and animals and buried homes in the months after the eruption. Additionally, another Mount Pinatubo eruption in August 1992 killed 72 people.
The United States military never returned to Clark Air Base, turning over the damaged base to the Philippine government on November 26, 1991. Today, the region continues to rebuild and recover from the disaster.


Mount Pinatubo

Mount Pinatubo , active volcano, 5,840 ft (1,780 m), central Luzon island, the Philippines, c.55 mi (90 km) NW of Manila. Dormant for 600 years, it began erupting on Apr. 2, 1991. Most residents had evacuated surrounding areas when Pinatubo erupted catastrophically (June 15, 1991), killing over 500 people and burying over 310 sq mi (800 sq km) under volcanic ash. As much as 2 cu mi (8 cu km) of ash was ejected in the eruption. The nearby U.S. Clark Air Force Base was devastated by the ash fall, which resulted in the base's closure. Landslides of rain-soaked volcanic ash caused further destruction in 1991 and subsequent years.
Resoureces:  http://en.wikipedia.org/wiki/Mount_Pinatubo
http://geography.about.com/od/globalproblemsandissues/a/pinatubo.htm

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