This is a consequence of a very densely populated country with exposed low lying areas and also in being in the most tectonically active region of the planet. Indonesia has the fourth largest population, after China, India and USA.
I have seen a projection of the effects of the 1883 Krakatoa volcanic eruption if it happened today without warning. The estimated death toll today would have been nine million compared with the actual 36,000 in 1883.
''Give me a Ping and one Ping only'' - Sean Connery.
The Krakatoa history is quiet amazing, I came to it a few years ago reading the book by Simon Winchester. The vulcan was located in an unoccupied island, between Sumatra and Java. Some days before the explosion it started vomiting smoke, so thick it became at last that the vulcan was unseen from the nearby coasts. The day it exploded, nobody actually saw it, but the tsunami created devastated the villages located near the sea, killing 36000 people. Around 1920 a new vulcan emerged from the sea, called Anak Krakatoa ("the son of Krakatoa"), and is very active. In fact a tourist was killed in the island (where it is strictly forbidden to land) by a rock launched into the air by it.
I haven't seen the book by Simon Winchester, but the facts of the matter as I understand them are as follows:
In 1883 Krakatoa was an island of some 12 square miles (about 19 sq. km.) with three separate volcanic craters. It wasn't realised until the cataclysmic eruption that these three craters, each a mile or so from each other, were actually one giant volcano and not three separate volcanoes.
The 1883 eruption started in May and gradually increased in intensity. On 26 August there was the start of the final eruption, which triggered an initial tsunami in a NW direction, and featured several exceptionally loud explosions, now recognised as being sonic booms.
After continuing erupting overnight, by the middle of the next day, August 27, another violent discharge was sufficient to blow off the top of the mountain - as it did so the residue of the magma coming up from the regolith below reacted chemically with the atmosphere producing a sonic boom that was heard in Alice Springs, in the middle of Australia some 3,000 miles (4,800 km.) away, it was also heard in southern India and on the east coast of Africa.....
The regolith now being empty, so the island collapsed under its own weight. The collapse of the 13 mile high vortex of ash, pumice, steam etc. into a vast pyroclastic flow trigered the huge tsunami that did so much damage. Nothing was left of the island itself.
The quantity of sulphur and ash discharged into the upper trophosphere was such that it caused spectacular sunrises and sunsets for decades, and global insolation was reduced causing worldwide temperatures to drop below average until well into the twentieth century.
From local tribal accounts it appears that a similar eruption occured in 416 A.D. where again a whole island blew up and disappeared into the sea, from which it would seem that Krakatoa blows up every 1500 years or so.
Anak Krakatoa first appeared in 1927, and is growing at a rate of about five metres a year. Volcanologists have calculated that Anak Krakatoa poses no immediate substantial threat and given its structure it is likely that any future major discharge would be directed south west across the Indian Ocean and thus away from Indonesia itself.
''Give me a Ping and one Ping only'' - Sean Connery.
I live within sight of Mt. St. Helens. While I was growing up, it was this beautiful white capped mountain and now it is gone. I was here when it blew up. We were all fortunate that the ash plume drifted in the least damaging direction.
Krakatoa is an amazing story. I became aware of it when I was a kid and saw a movie called: "Krakatoa, east of Java." It won an Oscar for Special Effects.
I, myself, became involved in a "tsunami emergency" some weeks ago when an earthquake hit (August 15, 2007) Peru and the US tsunami warning system triggered an alert for the Pacific coast of Central America. I´m now working in the construction of the Sonata Resort over the coast in Costa Rica and the alarms were activated and we had an incredible civil movilization in order to reach 50+ meters highs in time for the tsunami to reach us. Luckily the alert was aborted an hour later because the tsunami "shadow" was lost in the ocean and nothing harmful reach us.
But again, regarding Krakatoa, I copy this from wikipedia:
"Origin and spelling of the name
The earliest mention of the island in the Western world was on a map by Lucas Janszoon Waghenaer, who labelled the island "Pulo Carcata". ("Pulo" is a form of pulau, the Indonesian word for "island".) There are two generally accepted spellings, Krakatoa and Krakatau. While Krakatoa is more common in the English-speaking world, Krakatau (or Krakatao in an older Portuguese based spelling) tends to be favored by Indonesians and geologists. The origin of the spelling Krakatoa is unclear, but may have been the result of a typographical error made in a British source reporting on the massive eruption of 1883.
Theories as to the origin of the Indonesian name Krakatau include:
Onomatopoeia, imitating the noise made by white parrots which used to inhabit the island.
From Sanskrit karka or karkata or karkataka, meaning "lobster" or "crab".
From Malay kelakatu, meaning "white-winged ant".
There is a popular story that Krakatau was the result of a linguistic error. According to legend, "Krakatau" was adopted when a visiting ship's captain asked a local inhabitant the island's name, and the latter replied "Kaga tau" — a Jakartan/Betawinese slang phrase meaning "I don't know". This story is largely discounted; it closely resembles famous linguistic myths about the origin of the word kangaroo and the name of the Yucatán Peninsula.
The name is spelled Karata on a map drawn before 1708.
Pre 1883 history
Geography
The Sunda StraitBefore the 1883 eruption, Krakatoa consisted of three main islands: Lang ('Long', now called Rakata Kecil or Panjang) and Verlaten ('Forsaken' or 'Deserted', now Sertung), which were edge remnants of a previous very large caldera-forming eruption; and Krakatoa itself, an island 9 km long by 5 km wide. Also there was a tree-covered islet near Lang named Poolsche Hoed ('Polish Hat', apparently because it looked like one from the sea), and several small rocks or banks between Krakatoa and Verlaten. There were three volcanic cones on Krakatoa: running South to North they were: Rakata (823 m), Danan (445 m), and Perboewatan (also spelled Perbuatan) (122 m). (Danan may have been a twin volcano). Krakatoa is directly above the subduction zone of the Eurasian Plate and Indo-Australian Plate, where the plate boundaries undertake a sharp change of direction, possibly resulting in an unusually weak crust in the region.
416 AD event
The Javanese Book of Kings (Pustaka Raja) records that in the year 338 Saka (416 AD)
A thundering sound was heard from the mountain Batuwara ... a similar noise from Kapi ... The whole world was greatly shaken and violent thundering, accompanied by heavy rain and storms took place, but not only did not this heavy rain extinguish the eruption of the fire of the mountain Kapi, but augmented the fire; the noise was fearful, at last the mountain Kapi with a tremendous roar burst into pieces and sank into the deepest of the earth. The water of the sea rose and inundated the land, the country to the east of the mountain Batuwara, to the mountain Raja Basa, was inundated by the sea; the inhabitants of the northern part of the Sunda country to the mountain Raja Basa were drowned and swept away with all property [3] ... The water subsided but the land on which Kapi stood became sea, and Java and Sumatra were divided into two parts.
There is no geological evidence of a Krakatoa eruption of this size around that time; it may describe loss of land which previously joined Java to Sumatra across what is now the narrow east end of the Sunda Strait; or it may be a mistaken date, referring to an eruption in 535 AD, also referred to in the Javanese Book of Kings, and for which there is geological and some corroborating historical evidence.
535 AD event
David Keys and others have postulated that the violent eruption of Krakatoa in 535 may have been responsible for the global climate changes of 535-536. Keys explores what he believes to be the radical and far ranging global effects of just such a putative 6th century eruption in his book Catastrophe: An Investigation into the Origins of Modern Civilization. Additionally, in recent times, it has been argued that it was this eruption which created the islands of Verlaten and Lang (remnants of the original) and the beginnings of Rakata — all indicators of early Krakatoa's caldera's size. However, there seems to be little, if any, datable charcoal from that eruption, even if there is plenty of circumstantial evidence.
1600s
At least two Dutch travelers reported that Danan and Perboewatan were seen erupting in May 1680 and February 1681.
Visit by HMS Discovery
In February 1780, the crews of HMS Resolution and HMS Discovery, on the way home after Captain James Cook's death in Hawaii, stopped for a few days on Krakatoa. They found two springs on the island, one fresh water and the other hot. They described the natives who then lived on the island as "friendly" and made several sketches. (In his journal, John Ledyard calls the island 'Cocoterra'.)
Dutch activity
In 1809, the Dutch established a penal colony on the islands. (No information on exactly where.) It was in operation for about a decade.
In 1880, Rogier Verbeek made an official survey of the islands and published a comprehensive report in 1884/5. This proved helpful in judging the geological and biological impact of the 1883 eruption.
The 1883 eruption
Early eruptions
In the years before the 1883 eruption, seismic activity around the volcano was intense, with some earthquakes felt as far distant as Australia. Beginning 20 May 1883, three months before the final explosion, steam venting began to occur regularly from Perboewatan, the northernmost of the island's three cones. Eruptions of ash reached an altitude of 6 km (20,000 ft) and explosions could be heard in Batavia (Jakarta) 160 km (100 miles) away. Activity died down by the end of May. Also, to help the eruption along, water seeped into the magma chamber and created vast amounts of super-pressured steam. It had been thought Krakatoa was 3 different volcanoes, but it was actually just one with a huge magma chamber.
The volcano began erupting again around 20 July. The seat of the eruption is believed to have been a new vent or vents which formed between Perboewatan and Danan, more or less where the current volcanic cone of Anak Krakatau is. The violence of the eruption caused tides in the vicinity to be unusually high, and ships at anchor had to be moored with chains as a result. On 11 August larger eruptions began, with ashy plumes being emitted from at least eleven vents. On 24 August, eruptions further intensified. At about 1pm (local time) on 26 August, the volcano went into its paroxysmal phase, and by 2pm observers could see a black cloud of ash 27 km (17 miles) high. At this point, the eruption was virtually continuous and explosions could be heard every ten minutes or so. Ships within 20 km (11 nautical miles) of the volcano reported heavy ash fall, with pieces of hot pumice up to 10 cm in diameter landing on their decks. A small tsunami hit the shores of Java and Sumatra some 40 km (28 miles) away between 6pm and 7pm.
Cataclysmic stage
On August 27, the volcano entered the final cataclysmic stage of its eruption. Four enormous explosions took place at 5:30 a.m., 6:42 a.m., 8:20 a.m., and 10:02 a.m., the last of which was worst and loudest. Each was accompanied by very large tsunamis believed to have been over 30 meters (100 ft) high in places. A large area of the Sunda Strait and a number of places on the Sumatran coast were affected by pyroclastic flows from the volcano. The explosions were so violent that they were heard 2,200 statute miles (3,500 km) away in Australia and the island of Rodrigues near Mauritius, 4,800 km away; the sound of Krakatoa's destruction is believed to be the loudest sound in recorded history, reaching levels of 180 dBSPL 100 miles (160 km) away.[4] Ash was propelled to a height of 50 miles (80 km). The eruptions diminished rapidly after that point, and by the morning of August 28 Krakatoa was quiet.
"The Burning Ashes of Ketimbang"
Around noon on August 27, a rain of hot ash fell around Ketimbang in Sumatra. Around a thousand people were killed, the only large number of victims killed by Krakatoa itself, and not the waves or after-effects.[5] Verbeek and later writers believe this unique event was a lateral blast or pyroclastic flow (perhaps traveling over the floating pumice rafts), similar to what happened in 1980 at Mt. St. Helens. The region of the ashfall ended to the northwest of Ketimbang, where the bulk of Sebesi Island offered protection from any horizontal surges.
After eruptions
Small eruptions continued through October, and continued to be reported through February 1884 (although any after mid October were discounted by Verbeek). In the aftermath of the eruption, it was found that the island of Krakatoa had almost entirely disappeared, except for the southern half of Rakata cone cut off along a vertical cliff, leaving behind a 250-meter-deep caldera.
Effects
The combined effects of pyroclastic flows, volcanic ashes and tsunamis had disastrous results in the region. There were no survivors from 3,000 people located at the island of Sebesi, about 13 km from Krakatoa. Pyroclastic flows killed around 1,000 people at Ketimbang on the coast of Sumatra some 40 km north from Krakatoa. The official death toll recorded by the Dutch authorities was 36,417 and many settlements were destroyed, including Teluk Betung and Ketimbang in Sumatra, and Sirik and Semarang in Java. The areas of Banten on Java and the Lampong on Sumatra were devastated. There are numerous documented reports of groups of human skeletons floating across the Indian Ocean on rafts of volcanic pumice and washing up on the east coast of Africa, up to a year after the eruption. Some land on Java was never repopulated; it reverted to jungle and is now the Ujung Kulon National Park.
Tsunamis
Ships as far away as South Africa rocked as tsunamis hit them, and the bodies of victims were found floating in the ocean for weeks after the event. The tsunamis which accompanied the eruption are believed to have been caused by gigantic pyroclastic flows entering the sea; each of the five great explosions was accompanied by a massive pyroclastic flow resulting from the gravitational collapse of the eruption column. This caused several cubic kilometers of material to enter the sea, displacing an equally huge volume of seawater. Some of the pyroclastic flows reached the Sumatran coast as much as 25 miles (40 km) away, having apparently moved across the water on a "cushion" of superheated steam. There are also indications of submarine pyroclastic flows reaching 10 miles (15 km) from the volcano.
On a recent film and documentary, a research team at Kiel University of Germany conducted tests of pyroclastic flows moving over water. The tests revealed that hot ash traveled over the water on a cloud of superheated steam with the heavy matter precipitating out of the flow, shortly after initial contact with the water, to create a tsunami due to the precipitate mass.
Geographic effects
As a result of the huge amount of material deposited by the volcano, the surrounding ocean floor was drastically altered. It is estimated that as much as 18-21 km³ of ignimbrite was deposited over an area of 1.1 million km², largely filling the 30-40 m deep basin around Krakatoa. The land masses of Verlaten and Lang were increased, and volcanic ash continues to be a significant part of the geological composition of these islands. Poolsche Hoed ("Polish Hat") disappeared. A new rock islet called Bootsmansrots ('Bosun's Rock', a fragment of Danan) was left.
Two nearby sandbanks (called Steers and Calmeyer after the two naval officers who investigated them) were built up into islands by ashfall, but the sea later washed them away. Seawater on hot volcanic deposits on Steers and Calmeyer caused steam which some people mistook for continued eruption.
The fate of Krakatoa itself has been the subject of some dispute among geologists. It was originally proposed that the island had been blown apart by the force of the eruption. However, most of the material deposited by the volcano is clearly magmatic in origin and the caldera formed by the eruption is not extensively filled with deposits from the 1883 eruption. This indicates that the island subsided into an empty magma chamber at the end of the eruption sequence, rather than having been destroyed during the eruptions.
Global climate
In the year following the eruption, average global temperatures fell by as much as 1.2 degrees Celsius. Weather patterns continued to be chaotic for years, and temperatures did not return to normal until 1888. The eruption injected an unusually large amount of sulfur dioxide (SO2) gas high into the stratosphere which was subsequently transported by high-level winds all over the planet. This led to a global increase in sulfuric acid (H2SO4) concentration in high-level cirrus clouds. The resulting increase in cloud reflectivity (or albedo) would reflect more incoming light from the sun than usual, and cool the entire planet until the suspended sulfur fell to the ground as acid precipitation.
Global optical effects
The dramatic skyline in Edvard Munch's The Scream (1893) is thought to be based on the global optical effects caused by the eruption and seen over Oslofjord, Norway.[7]The eruption produced spectacular sunsets throughout the world for many months afterwards. British artist William Ashcroft made thousands of colour sketches of the red sunsets half-way around the world from Krakatoa in the years after the eruption. In 2004, researchers proposed the idea that the blood-red sky shown in Edvard Munch's famous 1893 painting The Scream is also an accurate depiction of the sky over Norway after the eruption. Munch said: "suddenly the sky turned blood red ... I stood there shaking with fear and felt an endless scream passing through nature." Also, a so called blue moon had been seen for two years as a result of the eruption.
Legacy of the 1883 eruption
The 1883 eruption of Krakatoa is among the most violent volcanic events in modern times (a VEI of 6, equivalent to 200 megatonnes of TNT — about 13,000 times the yield of the Little Boy bomb which devastated Hiroshima, Japan). Concussive air waves from the explosions travelled seven times around the world.[8] The sky was darkened for days afterwards. Sea waves caused by the eruption were recorded as far away as the English Channel.[9] The explosion is considered to be the loudest noise ever recorded to be heard by humans.[citation needed]
Cause of the explosion
The violence of the final explosions has also attracted debate. Four theories are:
Contemporary investigators believed that the volcano's vents had sunk below sea level on the morning of 27 August, letting seawater flood into it and causing a massive series of phreatic (interaction of ground water and magma) explosions.
The seawater could have chilled the magma, causing it to crust over and producing a "pressure cooker" effect relieved only when explosive pressures were reached.
Both these ideas assumed that the island subsided before the explosions; however, the evidence does not support that conclusion and the pumice and ignimbrite deposits are not of a kind consistent with a magma-seawater interaction.
A massive underwater land slump or partial subsidence suddenly left the highly pressurized magma chamber wide open.
The final explosions may have been caused by magma mixing caused by a sudden infusion of hot basaltic magma into the cooler and lighter magma in the chamber below the volcano. This would have resulted in a rapid and unsustainable increase in pressure, leading to a cataclysmic explosion. Evidence for this theory is the existence of pumice consisting of light and dark material, the dark material being of much hotter origin. However, such material reportedly is less than 5% of the content of the Krakatoa ignimbrite and some investigators have rejected this as a prime cause of the 27 August explosions. "
Kind regards
An appeaser is one who feeds a crocodile, hoping it will eat him last. Sir Winston Churchill
I found the above very interesting. It makes you wonder what will happen when the regolith or magms chamber below Yellowstone National Park in Wyoming finally blows - these supervolcanic eruptions seem to take place every 600,000 years or so, and the last was 640,000 years ago.....
''Give me a Ping and one Ping only'' - Sean Connery.
I believe Discovery Channel has been covering this in the last months. I saw a documentary about it lately but don´t remember if it was on Discovery or History Channel.
The fact is that this "super volcanoes" can really harm the planet in a way that could make global warming a desired joke. Yellowstone is one but not the only: there is another one below a lake in Indonesia (it´s like every geologic phenomena decided not to spare Indonesia) and at least five others, including one in asiatic Russia. Any one of them could give us a surprise. But Yellowstone, I believe, is the one that presents some kind of activity that the others lacks.
I expect that neither I nor my children have the "opportunity" to see such a thing.
Kind regards...
An appeaser is one who feeds a crocodile, hoping it will eat him last. Sir Winston Churchill
"A supervolcano is a volcano that produces the largest and most voluminous kinds of eruption on Earth. The explosivity of such eruptions varies, but the volume of ejected tephra is enough to radically alter the landscape and severely affect global climate for years, with cataclysmic consequences for life (see also volcanic winter).
Word origin
The term was originally coined by the producers of the BBC popular science program, Horizon, in 2000 to refer to these types of eruption.[1] [2] That investigation brought the subject more into the public eye, leading to further studies of the possible effects.
At first, supervolcano was not a technical term used in volcanology, but more recently, in 2003 and 2004, the term has been used in articles.
Though there is no well-defined minimum explosive size for a "supervolcano", there are at least two types of volcanic eruption that have been identified as supervolcanoes: massive eruptions and large igneous provinces.
Large igneous provinces
Main article: Large igneous province
A large igneous province (LIP) is an extensive region of basalts on a continental scale, resulting from flood basalt eruptions. When created, these regions often occupy several million km² and have volumes on the order of 1 million km³. In most cases, the majority of this is laid down over an extended but geologically sudden period of about several million years.
Massive eruptions
Eruptions with a Volcanic Explosivity Index of 8 (VEI-8) are mega-colossal events that eject at least 1,000 km³ of pyroclastic material.
VEI-8 eruptions are so powerful that they form circular calderas rather than mountains because the downward collapse of land at the eruption site fills emptied space in the magma chamber beneath. The caldera can remain for millions of years after all volcanic activity at the site has ceased.
Known eruptions
Satellite image of Lake Toba.VEI-8 volcanic events have included eruptions at the following locations. Estimates of the volume of erupted material are given in parentheses.
Lake Taupo, North Island, New Zealand - Oruanui eruption 26,500 years ago (1,170 km³)
Lake Toba, Sumatra, Indonesia - 75,000 years ago (2,800 km³)
Yellowstone Caldera, Wyoming, United States - 2.2 million years ago (2,500 km³) and 640,000 years ago (1,000 km³)
La Garita Caldera, Colorado, United States - Source of the truly enormous eruption of the Fish Canyon Tuff 27.8 million years ago (~5,000 km³)
The Lake Toba eruption plunged the Earth into a volcanic winter, eradicating an estimated 60%[3] [4] [5] [6] [7]of the human population (although humans managed to survive even in the vicinity of the volcano[8] ), and was responsible for the formation of sulfuric acid in the atmosphere.
Many other supermassive eruptions have also occurred in the geological past. Those listed below measured 7 on the VEI scale. Most of these were larger than Tambora's eruption in 1815 (160 km³), which was the largest eruption in recorded history.
Aira Caldera, Kyūshū, Japan - 22,000 years ago (110 km³)
Aso, Kyūshū, Japan - four large explosive eruptions between 300,000 to 80,000 years ago (Total volume 600 km³)
Kikai Caldera, Ryukyu Islands, Japan - 6,300 years ago (150 km³ (bulk volume))
Lake Taupo, North Island, New Zealand - 181 AD (100 km³)
Long Valley Caldera, California, United States - 760,000 years ago (600 km³)
Valle Grande, New Mexico, United States - 1.12 million years ago (~600 km³)
Yellowstone Caldera, Wyoming, United States - 1.3 million years ago (280 km³)
Bennett Lake Volcanic Complex, British Columbia/Yukon, Canada - 50 million years ago (850 km³)
Bruneau-Jarbidge, Idaho, United States - 10-12 million years ago (>250 km³) (responsible for the Ashfall Fossil Beds 1,600 km to the east[9])
Campi Flegrei, Naples, Italy - 12,000 years ago (Could be as much as 300 km³)
For large flood basalt eruptions, see large igneous province.
Media portrayal
A National Geographic documentary called Earth Shocks portrayed the destructive impact of the rapid eruption of Lake Toba some 75,000 years ago, which caused a phenomenon known as the Millennial Ice Age that lasted for 1000 years and wiped out more than 60%[10][11][12] [13][14] of the global population of the time.
An eruption of the Yellowstone supervolcano was originally one of the scenarios depicted in the docu-drama End Day, but was excluded from all airings to date for unknown reasons and is only presently mentioned at the show's BBC website (dead as of May 18, 2007; Internet Archive version).
In 2005, a two-part television docudrama entitled Supervolcano was shown on BBC, the Discovery Channel, and other television networks worldwide. It looked at the events that could take place if the Yellowstone supervolcano erupted. It featured footage of volcano eruptions from around the world and computer-generated imagery depicting the event. According to the program, such an eruption would have devastating effect across the globe and would cover virtually all of the United States with at least 1 cm of volcanic ash, causing mass destruction in the nearby vicinity and killing plants and wildlife across the continent. The dramatic elements in the program were followed by Supervolcano: The Truth About Yellowstone, a documentary about the evidence behind the movie. The program had originally been scheduled to be aired in early 2005, but it was felt that this would be insensitive so soon after the 2004 Indian Ocean earthquake. The program and its accompanying documentaries were released on DVD region 2 simultaneously with its broadcast.
In 2006, the Sci Fi Channel aired the documentary Countdown to Doomsday which featured a segment called "Supervolcano".
In the Stargate Atlantis episode Inferno, the main characters are caught in the eruption of a supervolcano and escape using an Ancient warship."
An appeaser is one who feeds a crocodile, hoping it will eat him last. Sir Winston Churchill
Karl, about Krakatoa the movie, be aware that the volcano was actually located to the WEST of Java. That is a movie blunder far worst that the Japaneses "nuclear" carriers attacking Pearl.
Other blunder of the movie is that it shows people as living on Krakatoa, which was untrue. Anyway, I loved the movie when I was a kid. It had all the elements of adventure: balloon, batisphere, diving girls, steam ship, volcano, tsunami.
A case of circumferential licence methinks - the World is round and if you go the odd 24.850 miles east of Java you will find Krakatoa, or at least Anak....
''Give me a Ping and one Ping only'' - Sean Connery.
