Between May 20 and October 21, 1883, the volcanic island of Krakatoa, located in the Sunda Strait (then part of the Dutch Empire, now modern-day Indonesia), began erupting. The eruption lasted more than five months. On August 27, the island experienced its most powerful eruption, which destroyed more than 70 percent of the island and its surrounding archipelago. The island collapsed into a caldera during this event. The August 27 eruption had a volcanic explosivity index of 6, making it one of the deadliest and most destructive volcanic events in recorded history. The third explosion of that day, which occurred at 10:02 AM, was the loudest sound ever recorded.

The explosion was heard 3,110 kilometers (1,930 miles) away in Perth, Western Australia, and 4,800 kilometers (3,000 miles) away in Rodrigues near Mauritius. The sound wave traveled around the globe more than three times. At least 36,417 deaths were linked to the eruption and the tsunamis it caused. Effects from the eruption were felt worldwide in the days and weeks following the event. Additional seismic activity was reported until February 1884. However, reports of activity after October 1883 were disregarded in Rogier Verbeek’s later investigation into the eruption.

Eruption

Before the 1883 eruption, the Krakatau volcano showed strong signs of activity. Earthquakes were felt as far away as the Australian Northern Territory, and one earthquake in 1880 damaged a lighthouse. On May 20, 1883, Strombolian eruptions began, and steam started coming from Perboewatan, the northernmost cone of the island. Ash from eruptions reached about 6 km (20,000 feet) high, and explosions were heard 160 km (100 miles) away in Batavia (Jakarta), shaking windows and doors. Dust from the eruptions fell 480 km (300 miles) away. An expedition group visiting the island on May 26 reported that the islands were covered in fine white dust, with explosions from Perboewatan happening every 5 to 10 minutes. Although the eruptions were becoming less intense, some explosions were still very strong, sending pumice flying in the opposite direction of the wind. A large crater about 900 meters (3,000 feet) wide formed, with steam plumes coming from it. The eruptions then became quieter after the initial activity.

Around June 16, loud explosions occurred, and a thick black cloud covered the islands for five days. Eruptions grew stronger again on June 19. On June 24, an east wind cleared the cloud, and two ash columns were seen coming from Krakatau. It was noticed that the top of Perboewatan’s cone was gone, which a report from years later said was because it had been blown away. The main eruption site was thought to be new vents formed between Perboewatan and Danan. The force of the eruptions caused unusually high tides, and ships had to be tied with chains to stay anchored. Earthquakes were felt in Anyer, Banten, and ships reported large pumice rocks in the Indian Ocean. A third vent, and later many more, appeared. Eruptions continued through July, growing more violent until the explosions of August 27.

In early August, a Dutch engineer named Captain H. J. G. Ferzenaar examined the Krakatau islands. He saw three major ash columns (one from Danan) covering the western part of the island and steam plumes from at least eleven vents between Danan and Rakata. When he landed, he found an ash layer about 50 cm (1.6 feet) thick and no vegetation, only tree stumps. He warned others not to land there.

By August 25, eruptions grew stronger. At 1:00 p.m. on August 26, the eruption reached its most intense phase. By 2:00 p.m., a black ash cloud was 27 km (89,000 feet) high. Explosions were heard every ten minutes, and by 5:00 p.m., the sounds were heard across Java. Waves about a meter high, possibly from steam explosions, hit the coasts of Java and Sumatra at 5:30 p.m. and continued through the night. Ships within 20 km (12 miles) of the volcano reported heavy ash falling, with hot pumice pieces up to 10 cm (4 inches) in size landing on their decks. Between 7:00 and 8:00 p.m., a small tsunami hit Java and Sumatra, 40 km (25 miles) away.

On August 27, eleven huge explosions marked the eruption’s peak. The first, at 5:30 a.m. at Perboewatan, caused a tsunami heading toward Telok Betong (now Bandar Lampung). At 6:44 a.m., Krakatau erupted again at Danan, sending tsunamis east and west. The third and largest explosion, at 10:02 a.m. (some sources say 9:58 a.m.), was so loud it was heard 3,110 km (1,930 miles) away in Perth, Western Australia, and on Rodrigues Island near Mauritius, 4,800 km (3,000 miles) away. This explosion was the loudest ever recorded. The sound at 160 km (100 miles) from the volcano was measured at 180 dB.

Although the explosions were heard far away, they were less noticeable or not heard near the volcano. Scientists believe this might be because sound waves traveled upward into the stratosphere and reflected away from the area, possibly due to ash in the air. The explosions and tsunamis likely had different causes. Explosions may have come from gas-rich magma, while tsunamis followed later as material fell back into the sea. Some tsunamis reached over 30 meters (100 feet) high. Pyroclastic flows from the volcano affected parts of the Sunda Strait and Sumatra’s coast. Verbeek and others believe the final major eruption was a lateral blast, or pyroclastic surge, with material ejected at 2,575 km/h (1,600 mph). The energy released was estimated to be equal to 200 megatonnes of TNT, about four times the power of the Tsar Bomba, the most powerful nuclear weapon ever tested. At 10:41 a.m., a landslide removed half of Rakata’s cone and the northern part of the island. This event may have caused the loudest explosion, but the collapse of the island into the magma chamber marked the end of the most intense eruption phase.

Some islands in the western Indian Ocean, 4,800 km (3,000 miles) away, still heard the explosion as clearly as a gun blast. Due to the speed of sound, people on these distant islands likely heard the eruption nearly four hours after it happened. The pressure wave from the third explosion traveled at 1,086 km/h (675 mph). The eruption reached 180 dB, loud enough to be heard 5,000 km (3,100 miles) away. The sound ruptured the eardrums of sailors on the RMS Norham Castle, 64 km (40 miles) away, and caused a pressure spike of over 8.5 kilopascals (2.5 inHg) in Batavia (Jakarta), breaking the scale

Aftermath

The eruptions of Krakatoa caused severe damage in the region. In Banten, about 80 km south, some land was never repopulated and became a jungle now known as Ujung Kulon National Park. Volcanic ash traveled as far as 2,500 km (1,600 mi) away. Large areas of floating pumice were seen in the ocean for months after the eruption. Reports describe human remains floating on pumice rafts across the Indian Ocean and washing up on Africa’s east coast up to a year later.

Two weeks after the eruption, the village of Tjaringin was completely destroyed. The official death toll was 36,417. No survivors were found among the 3,000 people on the island of Sebesi.

After the eruption, Krakatoa had nearly disappeared, except for its southern third. The Rakata cone was mostly removed, leaving a 250-meter (820-foot) cliff. Only a small rocky islet called Bootsmansrots and a piece of Danan remained from the northern two-thirds of the island. Poolsche Hoed was gone.

The eruption changed the ocean floor by depositing large amounts of material. Volcanic rock filled a basin around the mountain, which was 30–40 meters (100–130 feet) deep before the eruption and became 200–300 meters (700–1,000 feet) deep afterward. The islands of Verlaten and Lang grew in size, as did part of the remaining Rakata. Much of this new material eroded quickly, but volcanic ash remains a key part of the islands’ geology.

Two nearby sandbanks, named Steers and Calmeyer, were covered in ash and turned into temporary islands. Later, seawater washed them away. Steam rising from hot volcanic material on these sandbanks was mistaken for ongoing eruptions.

The eruption caused a volcanic winter. In the year after the eruption, summer temperatures in the Northern Hemisphere dropped by 0.4°C (0.72°F). Heavy rainfall in Southern California during 1883–1884, including 970 mm (38.18 in) in Los Angeles and 660 mm (25.97 in) in San Diego, was linked to the eruption. This occurred without an El Niño event, though scientists are unsure if the eruption directly caused the rain.

The eruption released large amounts of sulfur dioxide (SO₂) gas into the stratosphere. This gas spread globally, increasing sulfuric acid (H₂SO₄) in high-level clouds. These clouds reflected more sunlight, cooling the planet until the sulfur fell as acid rain.

The 1883 eruption darkened the sky worldwide for years and created vivid sunsets for months. British artist William Ascroft sketched these red sunsets from far away. In some places, the sunsets were so bright that fire engines were called to “put out” the apparent fires. The eruption also caused a Bishop’s Ring around the sun and a purple glow at twilight. In 2004, scientists suggested that the red sky in Edvard Munch’s painting The Scream reflects the sky after the eruption.

At the time, people observed the sky and called the ash cloud movement the “equatorial smoke stream.” This was the first recorded identification of the jet stream. For years after the eruption, the moon sometimes appeared blue or green because ash particles scattered red light. People also saw lavender suns and recorded the first sightings of noctilucent clouds.

Although the main eruption ended by late afternoon on August 27, 1883, reports of ongoing eruptions continued for months. Investigations found these claims were false, except for small mud eruptions that lasted into October. By mid-October, experts concluded the activity was due to steam, landslides, and distant electrical effects, not renewed eruptions.

No further activity was seen until 1913, when an eruption was reported. Investigations found no signs of volcanic awakening, likely due to a major landslide. After 1930, maps from 1919 showed a bulge near the site of Anak Krakatoa, suggesting magma was close to the surface.

Possible causes

The way northern Krakatoa changed after the eruption has been a topic of debate among scientists. One idea was that the island was broken apart by the power of the eruption. Most of the material left behind by the volcano came from molten rock, and the large crater formed by the eruption is not filled with material from the 1883 event. This suggests that the island sank into an empty space filled with molten rock after the eruption ended, rather than being destroyed during the eruptions.

According to recent research, some scientists believe part of the island sank before the first explosions on August 27. This caused the volcano’s openings to be below sea level, leading to:

• Large amounts of seawater flooding the area, which created explosions from the interaction of water and hot magma.
• Seawater cooling the magma enough for it to harden, creating pressure that only released when the pressure became too great.

Evidence does not fully support the idea that sinking before the eruption was the only cause. For example, the layers of rock left behind, such as pumice and ignimbrite, do not match what would happen if seawater and magma mixed. This has led to other theories:

• A sudden slide of land underwater or partial sinking exposed a highly pressurized magma chamber, allowing seawater to enter and mix with the magma.
• The final explosions may have been caused by magma mixing: a quick addition of very hot basaltic magma into cooler magma below the volcano. This would have caused pressure to rise rapidly, leading to a powerful explosion. Evidence for this includes pumice with both light and dark parts, where the dark parts came from hotter magma. However, this type of material makes up less than 5% of the Krakatoa ignimbrite, and some scientists do not think this was the main cause of the August 27 explosions.

In 2006, Mader & Gittings described a model showing how a hydrovolcanic explosion at Krakatoa and the resulting tsunami might have happened. The model suggests a very high wall of water, more than 100 meters tall, was formed by the sudden disturbance of water, basalt rock, and air.

In popular culture

• The explosion is believed to have inspired Edvard Munch's 1893 painting The Scream. The red sky in the painting reflects the artist's memory of the volcanic eruption of Krakatoa in 1883. This eruption colored the sunset skies red in parts of the Western hemisphere for months, about a decade before Munch created The Scream.
• The explosion is an important part of Don Rosa's comic The Cowboy Captain of the Cutty Sark. In the story, Scrooge McDuck sees the explosion and uses it to his advantage.
• In The Dresden Files, the explosion is shown to have been caused by Ebenezar McCoy in his role as "the Blackstaff," the White Council's assassin. It is linked to other events, including the Tunguska event.