Krakatoa Eruption (1883)

Leading up to the Eruption

After 200 years of inactivity, Krakatoa became active in early 1883 with a large earthquake. Seismic activity strengthened until May 20, 1883, when the first explosive eruption occurred.

In the early afternoon of August 26, 1883, explosions increased in frequency to about every 10 minutes. The crater rim was about 0.6 miles in diameter, and 0.3 miles deep. The central vent was plugged by lava, and pressure was rapidly building. Between August 26 and 27, there were four gigantic explosions. The first occurred at 5:07 p.m. on the afternoon of August 26. A black cloud of ash rose 17 miles above Krakatoa. On August 27, three more explosions occurred at 5:30 A.M., 6:44 A.M., and 10:02 A.M. The last, sudden eruption blew away the northern two-thirds of the island, and was the most severe volcanic explosion in modern times. The collapse of the volcanic chambers formed a huge underwater caldera, generating tsunami waves as high as 120 feet. The abruptness of Krakatoa's explosion was caused by ocean water entering the magmatic chambers and creating superheated steam that built up tremendous pressure.

This Parker & Coward lithograph of Krakatoa in Indonesia, 1883, shows the early stages of the devastating eruption

[Page 375]The eruption has been assigned a Volcanic Explosivity Index (VEI) of 6, which rates as “colossal”; the plume height was over 15 miles, and the eruption had a displacement between 6 and 62 cubic miles. The total energy released by the main eruptions was equivalent to 200 megatons of TNT. Most of the energy, released by the third explosion, was estimated to be 150 megatons. About 11 cubic miles of material was ejected into the atmosphere. What remained were a few small islands, including Anak Krakatoa (Krakatoa's Child), which is an extremely active young volcano.

The Effects

Blast waves cracked walls and broke windows up to 100 miles away. Atmospheric shock waves circled the Earth seven times and were recorded throughout the world. Massive amounts of hot gases, rocks, and ash ejected by the eruptions (pyroclastic flows) traveled over the water at hundreds of miles per hour, hitting islands 25 miles away. About 4,500 deaths (10 percent of the total) were attributed to falling tephra (ash, cinders, and rocks) in the pyroclastic flows, and about 2,000 people died from severe burns. The flows were also recorded by several ships. The Louden, 30 miles north-northeast of Krakatoa, was struck by severe winds and tephra; and the W.H. Besse, 50 miles east-northeast of Krakatoa, was hit by hurricane-force winds, heavy tephra, and the strong smell of sulfur.

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