Volcano by James Hamilton

Author:James Hamilton
Language: eng
Format: epub
Publisher: Reaktion Books

6 Krakatoa Shakes the World

On 27 August 1883, the island of Krakatoa (Krakatau) in the Sunda Strait, midway between Java and Sumatra, exploded with a noise that woke the planet.1

The Krakatoa ‘event’, as volcanologists disarmingly put it, profoundly disrupting and disturbing though it was for the immediate area, was just one of many cataclysmic eruptions within historic memory that were of the scale Volcanic Explosivity Index (VEI) of 6.5. This was larger than Vesuvius in AD 79 (VEI 5.8), but smaller than Tambora in 1815 (VEI 7.3). It was still smaller than some prehistoric eruptions, and yet larger ones had taken place in the millions of years when the earth was still forming, but after animal life began. This is a well-shaken planet.

The volcanic Krakatoa island, which before 1883 had been known as the ‘island with a pointed mountain’, straddled the area of sea where the Indo-Australian tectonic plate, colliding into the Eurasian plate, is diverted downwards towards the earth’s core. As a consequence, there is a line of active volcanoes along its leading edge. To say that the island was destroyed by the volcano would be misleading, as it and the sea basin around it had also been formed as a result of eruptions, and this was just one step in a continuous process. Volcanoes explode at points where pressure from simple mechanical shifts beneath the earth’s crust is too strong for the crust to hold in place.

Until mid-summer 1883, the Sunda Strait was the highway for vessels trading east and west from Sumatra and Java. There had been preliminary events beginning around 10 May, when rumblings were heard and a lighthouse was seen to move. Ships’ captains filed anxious reports. Ten days later a thick white column of smoke and ash rose from the volcano to a height of about 11,000 metres.2The Times reported these events on 3 July, but they turned out merely to be polite preliminaries.

The sound of the main cataclysm of late August radiated many thousands of miles around the Pacific, being heard on the west coast of Australia to the southeast, and Rodriguez Island and Diego Garcia to the west. A tsunami followed this huge breaking wave of sound, falling eventually on Ceylon and the east coast of India, and making tide-gauges flicker as far away as Port Elizabeth in South Africa, Grytviken in South Georgia and Biarritz in France. Even in Birmingham, England, the calm rustle of the trees at Edgbaston were disturbed as the local observatory registered changes in air pressure as the shock-waves ran around the globe.3 Noise and tides pass very quickly, and leave no trace. What did remain, however, and for months, was a cloud of ash dust and gas that encircled the planet in the upper atmosphere: ‘where mountain Krakatua once stood, the sea now plays’, wrote The Times.4 The dust was the pulverised mountain floating silently around the earth, creating lurid and intense sunsets and sunrises. The particles scattered the sun’s light, dispersing the shorter blue/violet end of the spectrum and allowing the longer red wavelengths to dominate.

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