Last modified on 11 March 2017, at 00:01

Krakatoa

Krakatoa (Indonesian: Krakatau) is a volcanic island within the Sunda Strait between Sumatra and Java in the Dutch East Indies - now Indonesia. One of several known geologically catastrophic events that were felt or seen worldwide, the 1883 explosion and eruption destroyed most of the island and killed thousands of people. It was the first of these mega-events news of which was relayed daily to the rest of the world via the telegraph, which had reached nearby Java on its route to Australia not much more than a decade before.

Description

Krakatoa is a small island group, clustered together about 27 miles west of Java; administratively they are part of the South Lampung Regency of Sumatra. The largest island is Pulau Krakatau (or Pulau Rupat) to the south; the others are Pulau Sertung (or Verlaten, northwest), Pulau Lang (northeast), and Pulau Anak Krakatau in the center, a relatively new island which emerged from the sea in 1930 after a series of eruptions.

Prior to 1883 Krakatau was more than twice its present size, filling in an area to the northwest where Anak Krakatau is now, and boasting a volcanic cone the locals named Rakata at 2,667 feet above sea level; two more cones (Perboewatan and Danan) were also present. The island group may have once been a single island in the past, destroyed during an eruption in 416 A.D., with subsequent eruptions slowly increasing the size of Krakatau Island.

1883 explosion

On May 23, 1883 volcanic activity from one of the smaller cones occurred; the clouds of ash generated by this eruption reached a height of six miles (estimated by the captain of a nearby German warship), with the sounds of the explosions reaching Batavia (modern-day Jakarta), approximately 100 miles to the east. This period of activity lasted until the end of May, becoming relatively quiet until June 19 when eruptions resumed, continuing without letup for over a month.

On August 26, 1883, at about 1:00 PM local time, massive explosions occurred in the Perboewatan cone, culminating in a black ash cloud which rose to a height of some 17 miles an hour later. At 10:00 AM the following morning tremendous explosions believed to be the equivalent of 200 megatons of TNT were followed by ash clouds reaching 50 miles in height and causing atmospheric pressure waves which were recorded on barographs around the world. The explosions were also loud enough to have been heard as far away as Perth, Australia and the island of Madagascar. The sound wave was picked up several times by instruments in New York each time it passed on its trips around the world.

This major series of explosions also fractured the magma chamber within the volcano, opening the magma to sea water and creating what is called a "phreatomagmatic event"; the steam created allowed superheated gasses and ash to travel in a pyroclastic flow, killing inhabitants in western Java. The force of the explosions weakened the island so severely that much of it collapsed into a newly created caldera in the sea; the tsunamis generated by the force of the collapse were estimated to have been 120 feet high in shallow water in nearby coastal areas, and overwhelmed smaller, nearby islands and the coastal areas of Java and Sumatra, killing well over 36,000 people. Some 11 cubic miles of debris was ejected from the volcano, resulting in blood-red sunsets for up to a year around the world.

Aftermath

The island of Krakatau was reduced in size considerably; its greatest height today is 2,560 feet at the cliff on the northern side of the island, once part of the Rakata cone. Volcanic debris covered all three islands completely, snuffing out all trace of life and leaving the islands completely sterile; scientists would discover an opportunity to observe how life can reestablish itself there some five years later. Anak Krakatau ("Child of Krakatoa") would appear as an island in the center of the caldera following a series of eruptions in the 1920s.