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Krakatoa or (Indonesian:Krakatau), volcano on Rakata Island in the Sunda Strait between Java and Sumatra, Indonesia. Krakatoa mountain is situated in the rendezvous of the Indian-Australian and Eurasian tectonic plates, a zone of high volcanic and seismic activity. After its formation on earth, the volcano transformed into cone-shaped mountain composed of flows of volcanic rock alternating with layers of cinder and ash. Krakatau is directly above the subduction zone where the plate boundaries make a sharp change of direction, possibly resulting in an unusually weak crust in the region. Krakatoa is currently one of the Most dangerous volcano in the world. It is currently an Active volcano, one of the few active volcanoes in the world.

Topology
From its base, 1,000 feet (300 metres) below sea level, the cone projected about 6,000 feet (1,800 metres) above the sea. Later (possibly in AD 416), the mountain’s top was destroyed, forming a Caldera, or bowl-shaped depression, 4 miles (6 km) across. Portions of the caldera projected above the water as four small islands: Sertung (Verlaten) on the northwest, Lang and Polish Hat on the northeast, and Rakata on the south. Over the years, three new cones were formed, merging into a single island. The highest of the three cones rose to 2,667 feet (813 metres) above sea level.

1883 Eruption
Krakatoa is widely famous one of the distinguished series of eruptions on 26-27 August 1883. Its explosive eruption in 1883 was one of the most catastrophic in history of volcanic eruptions. Eruptions at Krakatoa started around 16 June, with loud explosions and a thick black cloud covered the islands surrounding the volcano for five days.

On May 20, 1883, one of the cones again became active; ash-laden clouds reached a height of 6 miles (10 km), and explosions were heard in all of the Jakarta region stretching 100 miles (160 km) away, but by the end of May the activity had died down. It resumed on June 19 and became paroxysmal by August 26.

climatic activity
At 1:00 PM of that day the first of a series of increasingly violent explosions occurred, and at 2:00 PM a black cloud of ash rose 17 miles (27 km) above Krakatoa. The climax was reached at 10:00 AM on August 27, with tremendous explosions that were heard 2,200 miles (3,500 km) away in Australia and propelled ash to a height of 50 miles (80 km). Pressure waves in the atmosphere were recorded around the Earth. Explosions diminished throughout the day, and by the morning of August 28, the volcano was quiet. Small eruptions continued in the following months and in February 1884.

The pressure wave generated by the colossal third explosion radiated out from Krakatoa at 1,086 km/h (675 mph). The eruption is estimated to have reached 310 dB, loud enough to be heard clearly 5,000 kilometres (3,100 mi) away. It was so powerful that it ruptured the eardrums of sailors 64 km (40 miles) away on ships in the Sunda Strait' and caused a spike of more than 8.5 kilopascals (2.5 inHg) in pressure gauges 160 km (100 miles) away, attached to gasometers in the Batavia gasworks, sending them off the scale.

The pressure wave was recorded on barographs all over the world. Several barographs recorded the wave seven times over the course of five days: four times with the wave travelling away from the volcano to its antipodal point, and three times travelling back to the volcano. Hence, the wave rounded the globe three and a half times. Ash was propelled to an estimated height of 80 km (50 mi).

Effects
The initial explosion ruptured the magma chamber and hot lava was flowing out of the volcano getting into contact with the sea water. The result is known as a phreatomagmatic event. Due to the contact with extreme temperatures, The water flash-boiled, creating a cushion of superheated steam that carried the pyroclastic flows up to 25 miles (40 km) at speeds in excess of 62 mph (100 kph). The eruption has been assigned a rating of 6 on the Volcanic Explosion Index and is estimated to have had the explosive force of 200 megatons of TNT, which is ten thousand times more explosive than the bomb that is devastated in hiroshima.

The Burning Ashes of Ketimbang
The final major Krakatoa eruption was a lateral blast, or pyroclastic surge. Around noon on 27 August 1883, a rain of hot ash fell around Ketimbang (now Katibung in Lampung Province) in Sumatra. Approximately 1,000 people were killed in Sumatra; there were no survivors from the 3,000 people located on the island of Sebesi. There are numerous documented reports of a bunch of human skeletons floating across the Indian Ocean on volcanic pumices as a carrier and washing up on the east coast countries of African continent, up to an year after the eruption.hello.....

Tsunamis and distant effects
Tsunamis hit almost ever place in Indian ocean even reaching the bottom most country of Africa. The tsunamis which accompanied the eruption were believed to have been caused by gigantic pyroclastic flows entering the sea; each of the four great explosions was accompanied by massive pyroclastic flows resulting from the gravitational collapse of the eruption columns.The ruptured volcano has deposited several tons of magma and ash into the sea which displaced the ocean water causing the sea levels to rise. The town of Merak was destroyed by a tsunami which was 46 meters high. Some of the pyroclastic flows reached the Sumatran coast as much as 40 km away, having apparently moved across the water on a cushion of superheated steam. There are also indications of submarine pyroclastic flows reaching 15 km from the volcano.

Ackowledgment

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