What happened when Krakatoa erupted in 1883?

On August 26 and 27, 1883, the volcano Krakatau in the Sunda Strait between Java and Sumatra erupted in a series of increasingly powerful explosions. The USGS describes more than 4 cubic miles of debris thrown upward over about 23 hours, with more than 36,000 deaths. Most victims died in tsunamis rather than from the blasts. The eruption also produced worldwide effects, including pressure waves, vivid sunsets and a temporary cooling of global temperatures. [1] [2]

According to HISTORY, a blast around 1 p.m. on August 26 sent gas and debris about 15 miles into the air. Explosions grew stronger over roughly 21 hours and culminated in a huge blast around 10 a.m. on August 27 that sent ash about 50 miles up. About 9 square miles of the island collapsed into the caldera. NCEI reports that the northern two-thirds of the island fell beneath the sea, and that pyroclastic flows and ash flows accompanied the collapse. [3] [2]

The final explosion produced what NCEI calls the loudest sound ever recorded in modern history. It was heard in Australia and Mauritius, more than 2,800 miles away. Ash fell on Singapore and on ships thousands of kilometres away, and darkness covered the Sunda Strait for much of a day or longer, depending on the source. [2] [4]

The death toll is given as more than 36,000, with Oregon State's Volcano World citing at least 36,417. NCEI attributes more than 34,000 of these deaths to tsunamis. Tsunami waves destroyed 165 coastal settlements on Java and Sumatra. HISTORY notes the steamship Berouw was carried nearly a mile inland on Sumatra. Wave height estimates differ by source: about 41 meters (135 feet) for the largest wave in Banten per NCEI, 40 meters per Volcano World, and 120 feet per HISTORY. [2] [4] [3]

Every recording barograph in the world registered the atmospheric pressure wave, some several times as it travelled back and forth around the planet over five days. Tide gauges far away recorded the sea wave. Fine ash and aerosols reached the stratosphere and circled the equator in about 13 days, producing blue and green suns and, months later, red sunsets so vivid that fire engines were reportedly called out in New York and nearby towns. The Natural History Museum explains that particles slightly wider than the wavelength of red light absorbed red and let other colours through, producing blue Moons. [4] [5]

Floating pumice rafts crossed the Indian Ocean in about ten months. The telegraph network also meant news of the disaster spread quickly, which HISTORY says made it the first truly global catastrophe. [4] [3]

Sources agree on cooling but not on its size. NCEI says up to 0.5°C in the following year, the Natural History Museum gives an average of 0.6°C, and Volcano World's FAQ says as much as 1.2°C, with temperatures returning to normal by 1888. A separate Oregon State page cites Rampino and Self (1982), who estimated a Northern Hemisphere drop of 0.3°C. That page adds that Krakatau's magma was relatively poor in sulfur, so its climate impact was smaller than some lower-volume, sulfur-rich eruptions such as Agung. The sources do not reconcile these figures. [2] [5] [4] [6]