Krakatoa

Krakatoa is a small volcanic island in Indonesia, located about 100 miles west of Jakarta. In August 1883, the eruption of the main island of Krakatoa (or Krakatau) killed more than 36,000 people, making it one of the most devastating volcanic eruptions in human history.

WHERE IS KRAKATOA?

The volcanic island known as Krakatoa is located in the Sunda Strait, between the islands of Java and Sumatra. At the time of its famous eruption in 1883, the region was part of the Dutch East Indies; it’s now part of Indonesia.

A previous major eruption, likely in the fifth or sixth century A.D., is thought to have created Krakatoa and two nearby islands, Lang and Verlatan, as well as the undersea caldera (volcanic crater) between them.

By 1883, Krakatoa was made up of three peaks: Perboewatan, the northernmost and most active; Danan in the middle; and the largest, Rakata, which formed the southern end of the island.

Krakatoa was last thought to have erupted some two centuries earlier, in 1680, and most people believed it was extinct. But in May 1883, people reported feeling tremors and hearing explosions, first in western Java and then on the other side of the Sunda Strait in Sumatra.

Reports started coming in from ships sailing through the busy waterway, including the German warship Elizabeth, whose captain reported seeing a cloud of ash above Krakatoa stretching some 6 miles high. Things had quieted down by the end of the month, though smoke and ash continued to emerge from Perboewatan crater.

KRAKATOA ERUPTION

Around 1 p.m. on August 26, a volcanic blast sent a cloud of gas and debris some 15 miles into the air above Perboewatan.

It would be the first in a series of increasingly powerful explosions over the next 21 hours, culminating in a gigantic blast around 10 am on August 27 that propelled ash some 50 miles into the air and could be heard as far away as Perth, Australia (a distance of some 2,800 miles).

About 9 square miles of the island, including both Perboewatan and Danan, plunged underwater into the caldera to a depth of some 820 feet below sea level.

Krakatoa’s violent eruption killed more than 36,000 people. Relatively few of the victims were killed by the tephra (volcanic rock) and hot volcanic gases produced by the blasts themselves.

But tens of thousands more people drowned in the series of tsunamis caused by the volcano’s collapse into the caldera, including a 120-foot-high wall of water that formed just after the climactic blast and wiped out 165 coastal villages on Java and Sumatra.

As evidence of the tsunami’s devastating power, water deposited the steamship Berouw nearly a mile inland on Sumatra, killing all its crewmembers.

WHAT CAUSED THE ERUPTION?

Like all volcanic eruptions, Krakatoa’s can be traced to the movement of the tectonic plates that make up the Earth’s crust, which are constantly moving against each other over the thick liquid layer, or mantle, beneath.

Indonesia is located at the heart of a so-called subduction zone, where the Indo-Australian Plate collides with part of the Asian Plate (Sumatra) as it moves northward.

As a heavier oceanic plate, the Indo-Australian slides underneath the lighter, thicker continental plate (Sumatra), and the rock and other materials that slide with it heat up as it dives below the Earth’s surface. Molten rock (or magma) from below rushes upward through this channel, forming a volcano.

In 1883, each of the three distinct peaks of Krakatoa served as an exit route for the enormous magma chamber deep below it. Analysis suggests that during an earlier eruption, debris clogged the neck of Perboewatan, and pressure then built up below the blockage.

After the initial explosion split the magma chamber, and the volcano began to collapse, seawater came into contact with the hot lava, creating a cushion of explosively hot steam that carried the lava flows up to 25 miles at speeds of up to 62 mph.

GLOBAL IMPACT OF KRAKATOA

The 1883 Krakatoa eruption measured a 6 on the Volcanic Explosivity Index (VEI), with a force of 200 megatons of TNT. By comparison, the bomb that destroyed the Japanese city of Hiroshima in 1945 had a force of 20 kilotons, or nearly 10,000 times less power.

Krakatoa’s eruption sent six cubic miles of rock, ash, dust and debris into the atmosphere, darkening the skies and producing vividly colored sunsets and other spectacular effects around the world.

Writing from England, poet Gerard Manley Hopkins described skies of green, blue, gold and purple, “… more like inflamed flesh than the lucid reds of ordinary sunsets … the glow is intense; that is what strikes everyone; it has prolonged the daylight, and optically changed the season; it bathes the whole sky, it is mistaken for the reflection of a great fire.”

Dense clouds immediately lowered temperatures in the immediate area. As the dust spread, according to later studies, the eruption likely caused a drop in average global temperatures for several years.

Other climatic changes occurred thousands of miles from Indonesia: The amount of rainfall in Los Angeles – 38.18 inches – in the months following the Krakatoa eruption remains the city’s highest annual rainfall on record.

Though Krakatoa’s is far from the most powerful volcanic eruption in history (the eruption of nearby Tambora in 1815, for example, measured a 7 on the VEI), it’s arguably the most famous. Its 1883 eruption became the first truly global catastrophe, thanks to the recently installed worldwide telegraphic network, which instantly broadcast news of the eruption all over the world.

KRAKATOA TODAY

In late 1927, Krakatoa reawakened, producing steam and debris. In early 1928, the rim of a new cone appeared above sea level, and it grew into a small island within a year.

Called Anak Krakatoa (“child of Krakatoa”), the island has continued to grow to an elevation of some 1,000 feet, and erupts mildly at times. An eruption on March 31, 2014, measured a 1 on the VEI.

Sources

Mary Bagley, “Krakatoa Volcano: Facts About 1883 Eruption,” LiveScience (September 14, 2017).
Simon Winchester, Krakatoa – The Day the World Exploded: August 27, 1883 (New York: HarperCollins, 2003).
How Volcanoes Work: Krakatau, Indonesia (1883), Department of Geological Sciences – San Diego State University.
Jack Williams, “The epic volcano eruption that led to the ‘Year Without a Summer,’” Washington Post (June 10, 2016).

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