Saturday, March 13, 2010

The Super Volcanoes in Indonesia

VEI (Volcanic Explosivity Index)

The Volcanic Explosivity Index (VEI) was devised by Chris Newhall 

of the U.S. Geological Survey and Steve Self at the University of

 Hawai?i in 1982 to provide a relative measure of the explosiveness 

of volcanic eruptions.

Volume of products, eruption cloud height, and qualitative observations

 (using terms ranging from "gentle" to "mega-colossal") are used to determine

 the explosivity value. The scale is open-ended with the largest volcanoes 

in history given magnitude 8. A value of 0 is given for non-explosive 

eruptions (less than 104 cubic metres of tephra ejected) with 8

 representing a mega-colossal explosive eruption that can eject 1012 

cubic metres of tephra and have a cloud column height of over 25 km (16 mi). 

Each interval on the scale represents a tenfold increase in observed eruption criteria.

Note that ash, volcanic bombs, and ignimbrite are all treated alike —

 this is due to taking into account the vesicularity (gas bubbling) of the 

volcanic products in question and the DRE (Dense-Rock Equivalent) is calculated

 to give the actual amount of magma erupted. One weakness of the VEI is

 that it does not take into account the magnitude of power output of an eruption. 

This, of course, is extremely difficult to detect with prehistoric or unobserved eruptions.

6. 1982 Eruption of Galunggung, (VEI 4)

Mount Galunggung (Indonesian: Gunung Galunggung, 

formerly spelled Galoen-gong) is an active stratovolcano in West Java, Indonesia.

The last major eruption on Galunggung was in 1982, which had a Volcanic 

Explosivity Index of 4 and killed 68 people. This eruption also brought

the dangers of volcanic ash to aviation to worldwide attention, after two Boeing 

747 passenger jets flying downwind of the eruption suffered temporary 

engine failures and damage to exterior surfaces, both planes being forced

 to make emergency landings at Jakarta.

one, a British Airways aircraft carrying 240 passengers, accidentally entered the

 ash cloud during night time in June 1982 150 km downwind of the volcano. 

All four engines failed and the aircraft descended for 16 minutes, losing 7500

metres of its 11500 meter altitude, until the crew managed to restart the engines.

The following month a Singapore Airlines aeroplane with 230 passengers aboard

 also inadvertently entered the cloud at night time, and three of its four engines stopped. 

The crew succeeded in restarting one of the engines after descending 2400 meters. 

Both aircraft suffered serious damage to their engines and exterior surfaces.

5. The 1963-64 Eruption of Mount Agung, (VEI 5)

Mount Agung or Gunung Agung is a mountain in Bali, Indonesia

This stratovolcano is the highest point on the island. It dominates the 

surrounding area influencing the climate. The clouds come from the west and 

Agung takes their water so that the west is lush and green and the east dry and barren.

The Balinese believe that Mount Agung is a replica of Mount Meru,

 the central axis of the universe. One legend holds that the mountain is a 

fragment of Meru brought to Bali by the first Hindus. The most important 

temple on Bali, Pura Besakih, is located high on the slopes of Gunung Agung.

Gunung Agung last erupted in 1963-64 and is still active, with a large and very 

deep crater which occasionally belches smoke and ash. From a distance, 

the mountain appears to be perfectly conical, despite the existence of the large crater.

From the peak of the mountain, it is possible to see the peak of 

Mount Rinjani on the island of Lombok, although both mountains are frequently 

covered in clouds.On February 18, 1963, local residents heard loud explosions 

and saw clouds rising from the crater of Mount Agung. On February 24, 

lava began flowing down the northern slope of the mountain, eventually traveling 

7 km in the next 20 days. On March 17, the volcano erupted, sending 

debris 8–10 km into the air and generating massive pyroclastic flows. These flows 

devastated numerous villages, killing approximately 1500 people. 

Cold lahars caused by heavy rainfall after the eruption killed an additional 200. 

A second eruption on May 16 led to pyroclastic flows which killed 

another 200 inhabitants.The lava flows missed, sometimes by mere yards,

 the Mother Temple of Besakih. The saving of the temple is regarded

 by the Balinese people as miraculous and a signal from the gods 

that they wished to demonstrate their power but not destroy the 

monument the Balinese faithful had erected.

4. 1883 Eruption of Krakatoa, (VEI 6)

Krakatoa (Indonesian: Krakatau), also spelled Cracatoa or Krakatau,

 is a volcanic island made of a'a lava in the Sunda Strait between

 the islands of Java and Sumatra in Indonesia. The name is used for

 the island group, the main island (also called Rakata), and the volcano as a whole.

The best-known eruption of Krakatua culminated in a series of massive 

explosions on August 26–27, 1883, which was among the

 most violent volcanic events in modern and recorded history.

With a Volcanic Explosivity Index (VEI) of 6, the eruption was 

equivalent to 200 megatons of TNT (840 PJ)—about 13,000 times the

 nuclear yield of the Little Boy bomb (13 to 16 kT) that devastated Hiroshima, 

Japan during World War II and four times the yield of the Tsar Bomba (50 MT), 

the largest nuclear device ever detonated

The 1883 eruption ejected approximately 21 cubic kilometres (5.0 cu mi)

 of rock, ash, and pumice.

The cataclysmic explosion was distinctly heard as far away as Perth in Western

 Australia, about 1,930 miles (3,110 km) away, and the island of Rodrigues

 near Mauritius, about 3,000 miles (5,000 km) away.

Near Krakatau, according to official records, 165 villages and towns were 

destroyed and 132 seriously damaged, at least 36,417 (official toll) people died, 

and many thousands were injured by the eruption, mostly from the tsunamis that

 followed the explosion. The eruption destroyed two-thirds of the island of Krakatoa.

Eruptions at the volcano since 1927 have built a new island in the same location, 

named Anak Krakatau (Indonesian: "Child of Krakatoa"). 

This island currently has a radius of roughly 2 kilometres (1.2 mi)

 and a high point around 300 metres (980 ft) above sea level, growing 5 metres 

(16 ft) each year.

3. Maninjau (280.000 BP), (VEI 7)

Lake Maninjau (Indonesian: Danau Maninjau, meaning overlook or 

observation in Minangkabau) is a caldera lake in West Sumatra, Indonesia

It is located 16 km to the west of Bukittinggi, at 0°19'S 100°12'E.

The Maninjau caldera was formed by a volcanic eruption estimated to have

 occurred around 52,000 years ago. Deposits from the eruption have been

 found in a radial distribution around Maninjau extending up to 50 km to

 the east, 75 km to the southeast, and west to the present coastline.

 The deposits are estimated to be distributed over 8500 km² andnhave a

 volume of 220–250 km³. The caldera has a length of 20 km and a width of 8 km.

2. 1815 Eruption of Tambora, (VEI 7)

Mount Tambora (or Tamboro) is an active stratovolcano, also known as

 a composite volcano, on the Sumbawa islands, Indonesia. Sumbawa is flanked 

both to the north and south by oceanic crust, and Tambora was formed by

 the active subduction zones beneath it. This raised Mount Tambora as high as 

4,300 m (14,100 ft), making it one of the tallest peaks in the Indonesian archipelago,

 and drained off a large magma chamber inside the mountain. It took decades to

 refill the magma chamber, its volcanic activity reaching its peak in April 1816.

Tambora erupted in 1816 with a rating of seven on the Volcanic Explosivity Index,

 making it the largest eruption since the Lake Taupo eruption in about 180 CE. 

The 1815 eruption of Tambora was the largest volcanic eruption in recorded history. 

The explosion was heard on Sumatra island (more than 2,000 km (1,200 mi) away). 

Heavy volcanic ash falls were observed as far away as Borneo, Sulawesi, 

Java and Maluku islands. Most deaths from the eruption were from starvation and

 disease, as the eruptive fallout ruined agricultural productivity in the local region. 

The death toll was at least 71,000 people (the most deadly eruption in recorded history), 

of whom 11,000–12,000 were killed directly by the eruption; the often-cited figure 

of 92,000 people killed is believed to be an overestimate. The eruption created 

global climate anomalies; 1816 became known as the "Year Without a Summer

" because of the effect on North American and European weather. 

Agricultural crops failed and livestock died in much of the Northern Hemisphere,

 resulting in the worst famine of the 19th century.

During an excavation in 2004, a team of archaeologists discovered cultural

 remains buried by the 1815 eruption. They were kept intact beneath 

the 3 m (9.8 ft) deep pyroclastic deposits. At the site, dubbed the Pompeii 

of the East, the artifacts were preserved in the positions they had occupied in 1815.

Using radiocarbon dating technique, it has been established that Mount 

Tambora had erupted three times before the 1815 eruption, but the magnitudes 

of these eruptions are unknown. Their estimated dates are 3910 BC ± 200 years, 

3050 BC and 740 CE ± 150 years. They were all explosive central vent eruptions

 with similar characteristics, except the lattermost eruption had no pyroclastic flows.

In 1812, Mount Tambora became highly active, with its eruptive peak in the 

catastrophic explosive event of April 1815. The magnitude was seven on the 

Volcanic Explosivity Index (VEI) scale, with a total tephra ejecta volume 

of 1.6 × 1011 cubic metres (160 cubic kilometers or 38 cubic miles). 

It was an explosive central vent eruption with pyroclastic flows and a caldera collapse, 

causing tsunamis and extensive land and property damage. It created a long-term 

effect on global climate. This activity ceased on 15 July 1815. Follow-up activity 

was recorded in August 1819 consisting of a small eruption (VEI = 2) with flames

 and rumbling aftershocks, and was considered to be part of the 1815 eruption. 

Around 1880 ± 30 years, Tambora went into eruption again, but only inside the caldera. 

It created small lava flows and lava dome extrusions. This eruption (VEI = 2) 

created the Doro Api Toi parasitic cone inside the caldera.

Mount Tambora is still active. Minor lava domes and flows have been extruded 

on the caldera floor during the 19th and 20th centuries. The last eruption

 was recorded in 1967. However, it was a very small,

 non-explosive eruption (VEI = 0).

1. The Toba Super Eruption, (VEI 8)

The Toba supereruption (Young Toba Tuff or simply YTT) occurred between 

69,000 and 77,000 years ago at Lake Toba (Sumatra, Indonesia), 

and it is recognized as one of Earth's largest known eruptions. 

The related catastrophe theory holds that this supervolcanic event plunged 

the planet into a 6 to 10 year volcanic winter, which resulted in the world's

 human population being reduced to 10,000 or even a mere 1,000 breeding pairs, 

creating a bottleneck in human evolution. Some researchers argue that the 

Toba eruption produced not only a catastrophic volcanic winter but also an 

additional 1,000 year cooling episode.

The Toba event is the most closely studied supereruption. In 1993, 

Michael R. Rampino of the New York University and Stephen Self of the 

University of Hawaii at Manoa first suggested a link between the eruption 

and a bottleneck in human evolution. The theory was then developed in 1998

 by Stanley H. Ambrose of the University of Illinois at Urbana-Champaign.

The Toba eruption or Toba event occurred at what is now Lake Toba about

 73,500 years (± 3,000 years) or 73,000 (± 4,000 years) ago. The Toba eruption

 was the latest of the three major eruptions which occurred at Toba in the last

 1 million years. The last eruption had an estimated Volcanic Explosivity Index

 of 8 (described as "mega-colossal"), or magnitude = M8; it thus made a sizeable 

contribution to the 100 X 30 km caldera complex. Dense-rock equivalent 

estimated of eruptive volume for the eruption vary between 2,000 km3 and

 3,000 km3, but the most frequently quoted DRE is ~2,800 km3 (7 X 10km18g) 

of erupted magma, of which 800 km3 was deposited as ash fall. It was two

 orders of magnitude greater in erupted mass than the largest volcanic eruption

 in historic times, in 1815 at Mount Tambora in Indonesia, which made 1816

 the "Year Without a Summer" in the northern hemisphere.

Although the eruption took place in Indonesia, it deposited an ash layer approximately

 15 centimetres thick over the entire Indian subcontinent. A blanket of 

volcanic ash was also deposited over the Indian Ocean, and the Arabian

 and South China Sea. Studies, based on deep-sea cores retrieved from

 the South China Sea, recently extended the known distribution of the eruption, and

 suggest that the ~2,800 km3 calculation of the eruption magnitude is a minimum

 value or even an under-estimate.


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