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TOPIC: Anak Krakatau


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RE: Anak Krakatau
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The largest `normal` volcanic eruption in recorded history happened in August 1883, on the island of Krakatau situated in the narrow channel that separates the Indonesian islands of Sumatra to the northwest and Java to the southeast.
The sound of the explosion was so loud that people heard it thousands of kilometres away in Madagascar and Australia.
Krakatau originally consisted of three islands that were themselves the remnants of an even older volcanic eruption and collapse: Venlaten to the northwest, Lang to the east, and Krakatau Island, which was a coalescence of three volcanoes running in a north-to-south line.
As the eruption emptied the island’s magma chamber, the northern two-thirds of Krakatau Island collapsed beneath the sea surface into the emptying caldera. The tsunamis produced as the island collapsed into the sea were as high as 40 meters ; the monster waves radiated out from the explosion across the Indonesia islands, killing tens of thousands of people, and stripping some islands of all vegetation and animal life.
Only a small remnant of the southernmost volcano on the island, known as Rakata, remained. Today, that remnant has grown.


Latitude: 6.102°S, 6°6'6"S. Longitude: 105.423°E, 105°25'22"E

In 1927, a small island had broken the surface of the Sunda Strait. Eruptions have continued to occur nearly every year since. Krakatau was reborn as Anak Krakatau or `Child of Krakatau` . The numerous lava flows have given the new island an alien and lifeless look.

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Krakatoa
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When the Krakatoa volcano erupted at 6am on August 26 in 1883, it unleashed one of the most violent explosions mankind had ever seen.
This Sunday, the BBC re-examines the impact of one of the world's largest volcanoes in a factual drama, Krakatoa - The Last Days*, and in an accompanying documentary, Krakatoa Revealed. Human tragedy aside, Krakatoa was important because it was declared a "modern" disaster and became one of the first global media events.

The force of the eruption created the loudest noise ever recorded: it was heard 4,653km away on Rodriguez Island in the Indian Ocean and some 4,800km away in Alice Springs; shock waves travelled around the world seven times; and the force of the blast was some 10,000 times greater than that of the hydrogen bomb dropped on Hiroshima. The volcano left 36,000 people dead and the survivors battled to cope with tsunamis, further eruptions and superheated ash clouds.

Krakatoa has been erupting irregularly since 250 AD; the last previous explosion was even more powerful and had happened only 200 years before the one in 1883, yet few have heard of that catastrophe.

*Krakatoa - The Last Days, a factual drama, BBC1, Sunday 7 May, 8-9.30pm; Krakatoa Revealed, BBC1, Sunday 7 May, 10-10.50pm

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If the Krakatoa volcano in Indonesia had not erupted in 1883, Sea levels would have risen higher and ocean temperatures would have been warmer in the 20th century.

The impact of the eruption that spewed molten rock and sulphate aerosols into the atmosphere was felt for decades -- much longer than previously thought.

"It appears as though with a very large eruption the effect can last for many decades and possibly as long as a century. As we looked at the first picture of all these models together, we saw that just at the time of Krakatoa there was this very clean separation of those that included the eruption and those that did not. Volcanoes have a big impact. The ocean warming and sea level would have risen much more if it weren't for volcanoes" - Peter Gleckler, climatologist at the Lawrence Livermore National Laboratory in California.

Sea levels rise when ocean temperatures are warmer and recede when they cool. Volcanoes release aerosols and dust that block sunlight and cause the ocean surface to cool which can offset, at least temporarily, sea level rises caused by increased greenhouse gases in the atmosphere.

Krakatoa (Indonesian name: Krakatau) has erupted repeatedly, massively and with disastrous consequences throughout recorded history. The best known of these events occurred in late August, 1883.

The 1883 eruption ejected more than 25 cubic kilometres of rock, ash, and pumice, and generated the loudest sound ever historically recorded by human beings — the cataclysmic explosion was distinctly heard as far away as Perth in Australia, and the island of Rodrigues near Mauritius. Atmospheric shock waves reverberated around the world. Near Krakatoa, according to official records, 165 villages and towns were destroyed and 132 seriously damaged, 36,417 people died, and many thousands were injured by the eruption, mostly in the tsunami which followed the biggest explosion.
The eruption destroyed two-thirds of the pre-existing island of Krakatoa.
New eruptions at the volcano since 1927 have built a new island, called Anak Krakatau (child of Krakatoa).

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Anak Krakatau
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Brown and almost barren, Anak Krakatau rises out of the Sunda Strait, the narrow band of the Indian Ocean that separates the Indonesian islands of Sumatra and Java.


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This detailed image of the young volcano was taken by the Ikonos satellite on June 11, 2005. The volcano’s circular crater sits southwest of the centre of the island and is surrounded by fresh lava flows and ash.
The black shores of the island are scalloped where the flows have solidified in the ocean.
Anak Krakatau emerged from the sea less than 80 years ago, and is a natural laboratory to watch the development of an ecosystem.
Since the soil is new, it was uncontaminated with seeds. All of the plants seen growing on the island came from seeds that drifted in on the sea or blew across the ocean on the wind.
As a result, the plants are clumped on the shallowly sloped eastern shores of the volcano where loose ash and volcanic sand cover the ground. In contrast to the solid rock seen elsewhere on the island, these loose soils allow plants to take root easily.

Most of the plants seen here are grasses, ferns, and herbs that blew in on the wind or coastal trees like coconut, shrubs, and ground vines that floated ashore. Inland, clumps of plants are probably Australian Pine trees and a wild plant related to the sugar cane, both of which disperse seeds on the wind.

This strip of ocean was not empty before the island pushed its way up.
Phoenix-like, Anak Krakatau rose from the crater left when its parent, Krakatau, disappeared in one of the most notorious volcanic eruptions in history. Over a two-day period, August 26-27, 1883, Krakatau erupted with such violence that two-thirds of the island, about 23 square kilometres, sank into the Sunda Strait.
Prior to that date, the Krakatau volcano peaked 450 meters above sea level; after the eruption, the top of the volcano sat 250 meters below sea level.
Anak Krakatau, which means “child of Kratatau,” replaced the craters destroyed in the 1883 eruption.

The explosions heard in the 1883 eruption remain the loudest noise on human record. The sound was heard across the Indian Ocean, as far away as Rodriguez Island, 4,653 kilometres to the west, and Australia, 3,450 kilometres to the east.
The massive eruption also generated a series of tsunamis, which produced waves as much as 30 meters tall.
In contrast, the December 26 tsunami that devastated the region in 2004 reached up to 20 meters in height in a few locations. The huge waves created when Krakatau erupted were responsible for most of the 36,000 deaths associated with the eruption.

Like most of the approximately 130 active volcanoes in Indonesia, Krakatau was formed along the Sunda Arc, a 3,000-kilometer-long curve where the Australia Plate sinks beneath the Eurasia Plate. Where these two sections of the Earth’s crust meet, earthquakes and volcanic eruptions are common. Krakatau and the Sunda Strait sit at the hinge of the curve between Sumatra and Java, making this a region particularly prone to geologic activity.

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