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Bahasa Indonesia Krakatau, volcano on Pulau (island) Rakata in the Sunda Strait between Java and Sumatra, Indonesia. Its eruption in 1883 was one of the most catastrophic in history. Sometime within the past 1,000,000 years, the volcano built a cone-shaped mountain composed of flows of volcanic rock alternating with layers of cinder and ash. From its base, 1,000 ft (300 m) below sea level, the cone projected about 6,000 ft above sea level. Later, the mountain's top was destroyed, forming a caldera, or bowl-shaped depression, 4 mi (6 km) across. Portions of the caldera projected above the water as four small islands: Pulau Sertung (Verlaten) on the northwest, Lang and Polish Hat on the northeast, and Rakata on the south-southwest. Over the years, three new cones were formed, merging into a single island. The highest of the three cones rose to 2,667 ft above sea level.

The only known eruption prior to 1883 occurred in 1680; it was only moderate. On May 20, 1883, one of the cones again became active; ash-laden clouds reached a height of 6 mi, and explosions were heard in Batavia, (Jakarta), 100 mi away, but by the end of May the activity had died down. It resumed on June 19 and became paroxysmal by August 26. 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 mi above Krakatoa. The climax was reached at 10:00 Am on August 27, with tremendous explosions that were heard 2,200 mi away in Australia and propelled ash to a height of 50 mi. 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 discharge of Krakatoa threw into the air nearly 5 cu mi (21 cu km) of rock fragments, and large quantities of ash fell over 300,000 sq mi (800,000 sq km). Near the volcano, masses of floating pumice were so thick as to halt ships. The surrounding region was plunged into darkness for two and a half days because of ash in the air. The fine dust drifted several times around the Earth, causing spectacular red sunsets throughout the following year.

After the explosion, only a 2,667-ft-high islet remained in a basin covered by 900 ft of ocean water. As much as 200 ft of ash and pumice fragments had accumulated on Verlaten and Lang islands and on the remaining southern part of Rakata. Analysis of this material revealed that very little of it consisted of debris from the former central cones: the fragments of old rock in it represented less than 10 percent of the volume of the missing part of the island. Most of the material was new magma brought up from the depths of the Earth, most of it distended into pumice by expansion of the gas it contained or completely blown apart to form ash. Thus, the former volcanic cones were not blown into the air, as was first believed, but instead, sank out of sight as the top of the volcano collapsed because of the removal of a large volume of magma from the underlying reservoir.

The volcano's collapse triggered a series of tsunamis, or tidal waves, recorded as far away as South America and Hawaii. The greatest wave, which reached a height of 120 ft and took 36,000 lives in nearby coastal towns of Java and Sumatra, occurred just after the climactic explosion. All life on the Krakatoa island group was buried under a thick layer of sterile ash, and reestablishment of plant and animal life did not begin for five years.

Krakatoa was quiet until Dec. 29, 1927, when a new eruption began on the seafloor along the same line as the previous cones. By Jan. 26, 1928, a growing cone had reached sea level and formed a small island called Anak Krakatoa (Child of Krakatoa). Sporadic activity continued until, by 1973, the island had reached a height of 622 ft above sea level. It was still in eruption in the early 1980s.

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