KRAKATAU, INDONESIA (1883)

Early in the morning of May 20, 1883, the captain of the German warship Elizabeth reported seeing an ~11-km-high cloud of ash and dust rising above the uninhabited island of Krakatau, thus documenting the first eruption from this Indonesian island in at least two centures. Over the ensuing two months, crews on commercial vessels and sightseers on charted ships would experience similar spectacles, all of which were associated with explosive noises and churning clouds of black to incandescent ash and pumice. From a distance, the largest of these natural fanfares impressed the local inhabitants on the coastal plains of Java and Sumatra, creating a near-festive environment. Little did they realize, however, that these awe-inspiring displays were only a prelude to one of the largest eruptions in historic times. A series of cataclysmic explosions began at mid-day on August 26, and ended on August 27 with a stupendous paroxysmal eruption. On this day, the northern two-thirds of the island collapsed beneath the sea, generating a series of devasting pyroclastic flows and immense tsunamis that ravaged adjacent coastlines. The events that began on August 26 would mark the last 24 hours on earth for over 36,000 people, and the destruction of hundreds of coastal villages and towns.

 

LOCATION AND PLATE-TECTONIC SETTING

Indonesia contains over 130 active volcanoes, more than any other country on earth. They comprise the axis of the Indonesian island arc system, which is generated by northeastward subduction of the Indo-Australian plate. The great majority of these volcanoes lie along the topographic crest of the arc's two largest islands - Java and Sumatra. The islands are separated by the Sunda Straits, which is located at a distinct bend in axis of the island arc volcanoes, from a nearly east-west orientation in Java to a northwest-southeast orientation in Sumatra. Krakatau is one of a several volcanic islands in the Sunda Straits located above an active north-northeast trending fault zone, an orientation quite distinct from the main island-arc trend. Although relatively small when compared to the largest volcanoes along the island arc, Krakatau and its associated volcanoes have shown the capacity to generate highly explosive eruptions

 

PHYSIOGRAPHY BEFORE AND AFTER THE 1883 ERUPTION

The pre-eruption island of Kratatau was composed of three coalsced volcanoes aligned along a north-northwest direction, parallel to the volcanoes on Sumatra. From north to south, these were Perboewatan, Danan, and Rakata.

During the eruption, Perboewatan, Danan, and the northern half of Rakata appear to have collapsed into the vacating magma chamber, thus forming a submarine caldera and destroying the northern two-thirds of the island. Some workers, however, have argued for an alternative to the caldron-collapse model, and instead have suggested that the caldera formed by explosive destruction of the island, and the reaming out of the pre-eruption edifice. Eruptions since 1927 have built a new cone called Anak Krakatau ("child of Krakatau") in the center of the 1883 caldera.