Krakatoa will break out next year

Information sheet on the volcanic island of Krakatau

The eruption of Krakatoa - one of the most devastating natural disasters in history

The stratovolcanic island of Krakatau is located between the islands of Java and Sumatra in the Sunda Strait. It belongs to the Indonesian volcanoes, which formed in the collision area of ​​three continental plates. In this area the Indo-Australian plate dips under the Eurasian plate. This is why one speaks of subduction volcanism.
Due to the eastward movement of the Eurasian plate and the drifting of the Indo-Australian plate to the northeast, the island of Sumatra rotates clockwise. This causes the earth's crust to expand and break open between the islands. Magma can rise to the surface and activate the Krakatau fault.

The eruption of August 23, 1883

The island of Krakatau consisted of three interconnected volcanoes until the great eruption in 1883. These ran in a north-northwest direction and were called Perbuwatan, Danan (450 m) and Rakata (800m). The name of the volcanic island comes from the latter. Its area was 34 km², making it the largest of an archipelago of four islands. Located at the intersection of two major fault zones, there was no clear evidence of volcanic activity in this area until 1883, apart from reports of eruptions in 1680 and 1681.
Several earthquakes were registered between 1877 and 1880, heralding one of the most destructive natural disasters in history, which was to occur in 1883.
On August 23, 1883, the Krakatau eruption occurred. As sea water flowed into the magma chamber, hot water vapor expanded and provided a large part of the explosion energy, which corresponded to about 100 million tons of TNT. This largest ever human-witnessed explosion of a volcano blasted the island apart in the middle and could still be heard within a radius of 4,000 km. Her shock waves circled the earth seven times.
With an area of ​​23 km², two thirds of the island sank into the emptying magma chamber and formed a caldera six kilometers in diameter and a basin 300 m deep. The eruption also resulted in tsunamis with wave heights of 15 to 30 m. A total of 36,400 people were killed. 18 km³ of rock in the form of pumice and ash were deposited in the surrounding sea. Floating pumice blocks blocked the sea routes and bays for a long time.
Fine dust rose, lingered in the stratosphere, and orbited the earth for nearly three years. As a result, the average solar radiation in Europe decreased by 10% over the next three years and global temperatures fell below the normal mean. In addition, spectacular sunrises and sunsets, circles of haze around the sun and bluish-green discoloration of the sun and moon could be observed.
It was almost impossible to continue agriculture on the coasts of Java and Sumatra. Agricultural areas therefore remained fallow for decades.

The development of the volcanic island until today

The effects on Krakatau's flora and fauna were particularly severe. At the same time, the island is a classic example of the ability of living things to regenerate. After the outbreak had destroyed the entire fauna and flora of the archipelago around Krakatau, resettlement took place relatively quickly. Plant seeds were dispersed by winds, ocean currents and birds, smaller animals were washed up on debris and larger ones swam over the sea. In 1886, 26 plant species were found in isolated places, in 1906 more than 108 species were counted and in 1934 271 species could be identified.
It is estimated that 60% of the animal population has been able to regenerate, but precise statements cannot be made because the fauna from before 1883 was not recorded in detail.
One can only speculate about the emergence of new species in the course of restoring the ecological balance.

After the Krakatau eruption described, volcanic activity continued in the fault zone. Due to eruptions, material was piled up in the area of ​​the collapsed caldera. After initial, repeated erosion, a cone appeared permanently above the water surface in August 1930, which continues to grow up to the present day. The first volcanic opening reached the surface of the water in 1960 as an ash cone in the crater. The newly emerging volcanic island was named "Anak Krakatau", meaning the child of Krakatau. In 2004 it had an area of ​​10 km² and the rim of the crater was about 200 m above sea level. The last outbreaks were recorded in 1994 and 2001.
On November 8, 2007, a major eruption of Anak Krakatau took place without endangering people; in June 2009 the Anak Krakatau erupted again and has shown sustained strombolian activity since then. This makes it one of the most active volcanoes on earth. The newly created mountain called Anak Krakatau, child of Krakatau, grows around five meters a year and is now 400 meters high. In 2011, the Indonesian authorities asked tourists and fishermen to keep a distance of at least two kilometers from Anak Krakatau. After the number of quakes on the volcano had risen to 7,200 per day, the second highest warning level was declared.


F. Press; R. Siever (1995): General Geology. An introduction. Heidelberg.
I. J. Demhardt (2004): Islands: Great catastrophes of the mountains of fire. - In: Petermanns Geographische Mittteilungen; 148 (2004) 1; Pp. 74-75. Gotha.
H. Hess (2003): Haack Pocket Atlas Volcanoes and Earthquakes. Gotha.
J. Zeilinga de Boer; D. T. Sanders (2004): The year without a summer. The great volcanic eruptions in human history and their consequences. Eat.
R. Decker; B. Decker (1992): Vulkane. Image of the earth dynamics. Heidelberg; Berlin; New York.

Source: Geography Information Center
Author: Katrin Eilert
Publisher: Klett
Location: Leipzig
Source date: 2007
Processing date: 03/31/2012

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