In August 26-27, 1883, a small island in the Indian Ocean obliterated itself in one the most notorious volcanic eruptions in history. Krakatau (often spelled Krakatoa) erupted with such violence that two-thirds of the island, about 23 square kilometers, sank into the Sunda Strait. The explosions heard in the 1883 eruption remain the loudest noise on human record. The sound was heard across the Indian Ocean, as far away as Rodriguez Island, 4,653 kilometers (2,890 miles) to the west, and Australia, 3,450 kilometers (2,144 miles) to the east. The massive eruption also generated a series of tsunamis, which produced waves as high as 30 meters tall.
The world’s loudest sound
At the time of the explosion, the British ship Norham Castle was 40 miles (64 km) from Krakatoa. The ship’s captain wrote in his log, “So violent are the explosions that the ear-drums of over half my crew have been shattered. My last thoughts are with my dear wife. I am convinced that the Day of Judgement has come.”
It was heard 1,300 miles (2,092 kilometers) away in the Andaman and Nicobar islands and described as “extraordinary sounds, as of guns firing”. The people of New Guinea and Western Australia (2,144 miles miles / 3,450 kilometers away) said that they have heard “a series of loud noises, resembling those of artillery in a north-westerly direction”. Even 2,890 miles (4,653 kilometers) away in the Indian Ocean island of Rodriguez, near Mauritius, people reported sounds “coming from the eastward, like the distant roar of heavy guns”.
A deadly tsunami
During its final cataclysmic eruption Krakatoa (Krakatau), which had been an island of about 30 square kilometers (12 square miles), nearly vanished. A total of 25 cubic kilometers (6 cubic miles) of material, including both new magma and bits of the old island, were blown into the stratosphere, the eruption column reaching more than 30 kilometers (20 miles) high.
The huge waves created when Krakatoa erupted were responsible for most of the 36,000 deaths associated with the event (some estimates exceed 120,000). While satellite imagery of Krakatau’s 1883 eruption is obviously not available, we do have images of Anak Krakatau, from the surface of Earth and from the space.
Child of Krakatoa
On 1927, About 50 years after the volcano destroyed itself, a new island appeared from the sea in about the same place. Called Anak Krakatau, meaning “Child of Krakatau (Krakatoa)” this young volcano now stands about 500 meters (1,500 feet) above the waves. Since then, Anak Krakatoa has been the site of frequent eruptions. This image of Anak Krakatau was taken by the Ikonos satellite on June 11, 2005. The volcano has been the site of frequent eruptions since 1927.
Like most of the approximately 130 active volcanoes in Indonesia, Krakatoa was formed along the Sunda Arc, a 3,000-kilometer-long curve where the Australia Plate sinks beneath the Eurasia Plate. Where these two sections of the Earth’s crust meet, earthquakes and volcanic eruptions are common. Krakatoa and the Sunda Strait sit at the hinge of the curve between Sumatra and Java, making this a region particularly prone to geologic activity.