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Tuesday, August 26, 2014


BIG BANG—On Aug. 26, 1883, one of the most catastrophic volcanic eruptions in recorded history occurred on the Indonesian island of Krakatoa.  Explosions were heard 2,000 miles away.  Tidal waves 120 ft high killed 36,000 persons on nearby islands, while five cubic miles of earth were blasted into the air up to a height of 50 miles.  Image above is the Krakatoa volcano in recent times.  The most recent eruption occurred in Feb. 2014.
KRAKATOA UNLEASHED—The 1883 eruption of Krakatoa in the Dutch East Indies (now Indonesia) began on August 26, 1883 (with origins as early as May of that year). The final out of many explosive eruptions that day was heard 3,000 miles away; caused at least 36,417 deaths; 20 million tons of sulfur released into the atmosphere; produced a volcanic winter (reducing worldwide temperatures by an average of 1.2°C for 5 years); and was the loudest explosion in recorded history.

On August 27, two thirds of Krakatoa collapsed in a chain of titanic explosions, destroying most of the island and its surrounding archipelago. Additional seismic activity continued to be reported until October 1883. It was one of the deadliest and most destructive volcanic events in recorded history, with at least 36,417 deaths being attributed to the eruption itself and the tsunamis it created. Significant additional effects were also felt around the world.

Early phase
In the years before the 1883 eruption, seismic activity around the volcanoes was intense, with earthquakes felt as far away as Australia. Beginning 20 May 1883, steam venting began to occur regularly from Perboewatan, the northernmost of the island's three cones.  Danan and Rakata being the other cones.  Eruptions of ash reached an estimated altitude of 20,000 ft and explosions could be heard in New Batavia (now
Jakarta) 99 mi away. Activity died down by the end of May, and there was no further recorded activity for several weeks.

Eruptions started again around June 16, featuring loud explosions and covering the islands with a thick black cloud for five days. On June 24, a prevailing east wind cleared the cloud, and two ash columns were seen issuing from Krakatoa. The violence of the ongoing eruptions caused tides in the vicinity to be unusually high, and ships at anchor had to be moored with chains as a result. Earthquake shocks began to be felt at Anyer, West Java, and ships began to report large pumice masses appearing in the Indian Ocean to the west

On 11 August, a Dutch topographical engineer, Captain H. J. G. Ferzenaar, investigated the islands. He noted three major ash columns (the newer from Danan), which obscured the western part of the island, and steam plumes from at least 11 other vents, mostly between Danan and Rakata. When he landed, he noted an ash layer about 1 ft 8 in thick, and the destruction of all vegetation, leaving only tree stumps. He advised against any further landings. The next day, a ship passing to the north reported a new vent "only a few meters above sea level."

Present day Anak Krakatau island a.k.a. Krakatoa Volcano
Climactic phase
By August 25, eruptions further intensified. At about 1 pm (local time) on August 26, the volcano went into its paroxysmal phase. By 2 pm observers could see a black cloud of ash 17 mi high. At this point, the eruption was virtually continuous and explosions could be heard every ten minutes or so. Ships within 12 mi of the volcano reported heavy ash fall, with pieces of hot pumice up to 3.9 in diameter landing on their decks. A small tsunami hit the shores of Java and Sumatra, some 25 mi away, between the time of 6 pm and 7 pm.

On August 27 four enormous explosions took place in the morning at 05:30, 06:44, 10:02, and 10:41 local time. At 5:30 am, the first explosion was at Perboewatan volcano, triggering a tsunami heading straight to Telok Betong. At 6:44 am, Krakatoa exploded again on Danan volcano, with the resulting tsunami stretching eastward and westward.

The largest explosion, at 10:02 am, was so violent that it was heard 1,930 mi away in Perth, Western Australia, and the Indian Ocean island of Rodrigues near Mauritius 3,000 mi away), where they were thought to be cannon fire from a nearby ship.

Each explosion was accompanied by large tsunamis, which are believed to have been over 98 feet 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 energy released from the explosion has been estimated to be equal to about 200 megatons of TNT roughly four times as powerful as the Tsar Bomba (the most powerful thermonuclear weapon ever detonated). At 10:41 am, a landslide tore off half of Rakata volcano, causing the final explosion.

Final explosive eruption
The pressure wave generated by the colossal fourth and final explosion radiated out from Krakatoa at 675 mph. It was so powerful that it ruptured the eardrums of sailors on ships in the Sunda Strait and caused a spike of more than 2½ inches of mercury in pressure gauges attached to gasometers in the New Batavia gasworks, sending them off the scale.

The pressure wave radiated across the globe and was recorded on barographs all over the world, which continued to register it up to five days after the explosion. Barographic recordings show that the shock wave from the final explosion reverberated around the globe seven times in total. Ash was propelled to an estimated height of 50 mi.

The eruptions diminished rapidly after that point, and by the morning of August 28 Krakatoa was silent. Small eruptions, mostly of mud, continued into October 1883.

Global climate
In the year following the eruption, average Northern Hemisphere summer temperatures fell by as much as 2.2 °F. Weather patterns continued to be chaotic for years, and temperatures did not return to normal until 1888. The record rainfall that hit Southern California during the “water year” from July 1883 to June 1884 – Los Angeles received 38.18 inches and San Diego 25.97 inches has been attributed to the Krakatoa eruption.

The eruption also darkened the sky worldwide for years afterward, and produced spectacular sunsets throughout the world for many months. British artist William Ashcroft made thousands of color sketches of the red sunsets half way around the world from Krakatoa in the years after the eruption.

The ash caused "such vivid red sunsets that fire engines were called out in New York, Poughkeepsie, and New Haven to quench the apparent local fires. This eruption also produced a Bishop's Ring around the sun by day, and a volcanic purple light at twilight.

Weather watchers of the time tracked and mapped the effects on the sky. They labeled the phenomenon the "equatorial smoke stream.” This was the first identification of what is known today as the jet stream.

For several years following the eruption it was reported that the moon appeared to be blue and sometimes green. Blue moons resulted because some of the ash clouds were filled with particles about 1 µm wide—the right size to strongly scatter red light, while allowing other colors to pass. White moonbeams shining through the clouds emerged blue, and sometimes green. People also saw lavender suns and, for the first time, noctilucent clouds.

NATURE’S SCREAM--In 2004, an astronomer 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 of Krakatoa in 1883.
Description of Indonesia from old source
The archipelago of Indonesia consists of more than 13,000 islands, spread over an area that is similar in size to that of the continental United States. It is the country with the greatest number and density of active volcanoes.

Most volcanoes in Indonesia belong to the Sunda Volcanic Arc, streching over 3,000 kilometers from NW Sumatra to the Banda Sea. This volcanic arc results from the subduction of Indian Ocean crust beneath the Asian Plate and includes 76% of the region's volcanoes. To the NNW, the basaltic volcanism of the Andaman Islands results from short spreading centers, and to the east the Banda Arc reflects Pacific Ocean crust subducted westward. North of this arc, the tectonic setting is much more complex: several fragments of plates are converging  to form multiple subduction zones, mainly oriented N-S. These produce the Sulawesi-Sangihe volcanoes on the west and Haimahera on the east of the collision zone.

Indonesia leads the world in many volcano statistics. It has the largest number of historically active volcanoes (76), its total of 1,171 dated eruptions is only narrowly exceeded by Japan's 1,274, although not much is know about the volcanic activity in the time before European colonialists arrived from the 15th century on. Indonesia has suffered the highest numbers of eruptions producing fatalities, damage to arable land, mudflows, tsunamis, domes, and pyroclastic flows. Four-fifths of Indonesian volcanoes with dated eruptions have erupted in this century.

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