In May 1883, the captain of the German warship Elisabeth observed a column of smoke and ash that he estimated be 6.8 miles (1.97 kilometers) tall, rising into the sky over an uninhabited mountainous island in the Sunda Strait between Java and Sumatra in Indonesia. "Ash fell so thickly as to obscure the sun," according to a report later compiled by Great Britain's Royal Society. Over the next few months, according to the report, other ships noticed ominous rumblings from the island, whose Indonesian name was Krakatau, though it would later become famous — possibly due to a typographical error by someone transmitting a news dispatch — as Krakatoa.
Finally, on Aug. 27, 1883, all hell broke loose, as a colossal volcanic eruption demolished Krakatoa, causing two-thirds of it to collapse and fall into the sea, and generated massive lava, pumice and ash flows. The explosion also triggered immense tsunamis that inundated hundreds of coastal towns and villages, causing the deaths of an estimated 36,000 people, according to the National Oceanic and Atmospheric Administration (NOAA). Krakatoa, which scored a 6 on the Volcano Explosivity Index, was one of the biggest documented volcanic eruptions in the last 760,000 years of natural history.
Krakatoa became one of the most famous volcanoes ever, not just because of its fearsome power and effects, but because it was the first really gigantic volcano to blow in the era when humans had communications technology — telegraph lines and printed newspapers — to transmit accounts of what was happening, as well as scientific instruments to measure its effects. The legend gradually grew, and Krakatoa eventually became the veritable King Kong of volcanoes, even serving as the subject of a 1968 cinematic historical thriller, "Krakatoa, East of Java," starring Maximilian Schell, Diane Baker and Brian Keith, and the subject of a 2003 bestseller, "Krakatoa: The Day the World Exploded: August 27, 1883," by author Simon Winchester.
Just How Powerful Was It?
The Krakatoa eruption produced the loudest sound in modern history, one that was heard across more than 10 percent of Earth's surface, according to NOAA. On the island of Mauritius in the Indian Ocean, more than 2,800 miles (4,600 kilometers) away, people heard what sounded like distant gunfire.
It generated intense pressure waves that traveled several times around the planet, causing spikes on scientific instruments in Great Britain and the U.S.
As Krakatoa blew up, it sent something in the magnitude of 5 cubic miles (21 cubic kilometers) of shattered rock into the air. Ash from the explosion soared 50 miles (80 kilometers) up, almost to the edge of Earth's mesosphere, and blanketed an area covering 300,000 square miles (776,996 square kilometers).
"The volcano of Krakatoa vomited forth an ink-black cloud which spread over the clear tropical sky with inconceivable blackness, involving the land in complete darkness," according to a breathless account in the Los Angeles Herald two weeks afterward.
The ash drifted and gradually enshrouded the planet in a haze that caused halos to form around the moon and sun, and filtered out enough solar radiation to lower global temperatures as much as 0.9 degrees Fahrenheit (0.5 degrees Celsius) for an entire year after it happened, according to NOAA.
"It is of a type of eruption in which the magma reservoir underlying the volcano discharges enough lava that the structure collapses in on itself," Thomas explains. "The current thinking is that these eruptions may be the result of a process of magma — hot, semi-liquid rock located beneath the Earth's surface — mixing in the magma chamber. The magma reservoir may be active for many years, discharging modest amounts of lava periodically, but, if an injection of magma from much deeper in the crust rises up under the magma reservoir, the system may become unstable: hotter, less dense basaltic magma from depth is sitting below cooler and denser magma above."
"If sufficient basaltic magma accumulates," continues Thomas, "an overturn can occur which will bring that hot magma to a shallow depth very quickly and allow it to begin degassing (exploding) through the existing magmatic conduit to the surface. As the top of the volcano is blown away, the explosive front will move downward into the older magma due to depressurization — kind of like blowing the lid off a pressure cooker — and discharge a massive volume of lava."
"As the pressure within the deeper reservoir bleeds off, the surface of the volcano will collapse in on itself — and, along with the collapse, comes massive quantities of seawater which leads to further explosive activity," Thomas continues.
The Tsunamis Were Even Worse Than the Explosion
As scary as the volcanic eruption itself was, the gigantic tsunamis generated by Krakatoa were even deadlier, according to NOAA. Some of the waves reached Hawaii and even South America, on the other side of the Pacific. But the destruction mostly happened in the Indonesian archipelago itself. Waves as tall as 135 feet (41 meters) crashed into coastal cities, towns and villages on the islands of Java and Sumatra. In Batavia — now Jakarta – 2,000 Chinese immigrants who lived on low-lying areas around the harbor were drowned, according to this wire service account published in the Vancouver, Wash. Independent. The city of Serang reportedly was entirely submerged under the waves, with nearly its entire population killed.
In an earlier time, these horrors might have remained strictly local tragedies. But thanks to newspaper coverage, people in the U.S. were shocked by front-page stories on them as well.
"Some prior events were certainly much larger than the 1883 event, but the level of communication and technology at those times was such that there are no, or very few, human records of those events," Thomas says. "We are only in modern times able to determine when these events occurred through our advanced technology — ice cores have recorded these events (as changes in compounds associated with eruptive products) over many centuries. Certainly, any populations living in proximity to those larger events would have been impacted and possibly wiped out."
Though the eruption destroyed most of the original volcano, it didn't completely vanish. Instead, 43 years later, a portion emerged from the sea as a new island, Anak Krakatoa. Eighty-nine years later, in December 2018, Anak Krakatoa erupted, sending out a wave of water that caused the deaths of more than 400 people and displaced 47,000 from their homes, according to the BBC. And Anak Krakatoa will erupt again someday, causing more deadly tsunamis, according to University of East London coastal engineering expert Ravindra Jayaratne. He advocated a number of measures to prepare, including installation of an early warning system that would detect a sudden increase in water levels, and an effort to raise awareness among vulnerable local residents and help them prepare.
Though the risk of Anak Krakatoa is scary enough, it's probably never going to explode in an event on the scale of the eruption in 1883.
"I don't think anyone would say that an event of similar magnitude won't occur at Anak Krakatoa, but the likelihood is extremely small," Thomas says. "The original magma reservoir that was there is, for all intents and purposes, gone. A new magma reservoir would have to regenerate there (over who knows how many millennia) before we could expect a repeat of the 1883 event. These are, fortunately, fairly rare events and require fairly unusual conditions to occur."
Though a lot of things have changed in the nearly century-and-a-half since the Krakatoa eruption, there's no guarantee that our modern, technologically advanced civilization necessarily would be any better prepared for a similar catastrophe.
"That is a difficult question to answer with any certainty since the answer would depend on the magnitude of the event, the type of eruption that occurred, its duration, and it's location on the planet," Thomas explains.
In a worst-case scenario, "a large eruption that was explosive and rich in sulfur dioxide could bring about a sudden climate change — similar to the 'Little Ice Age' — that could have catastrophic impacts on the planet's ability to feed its population," Thomas says. "The 1783 eruption of Skaftafell in Iceland caused a significant climate cooling in the northern hemisphere (it wasn't as explosive as Krakatau, but it lasted for many months and pumped out huge quantities of sulfur dioxide). It resulted in a famine in Iceland that killed, I believe, about 25 percent of their human population, and a large fraction of their livestock due to the sulfur dioxide and fluoride that was produced. Some argue that one of the after effects of the eruption was significant cooling and increased summer rainfall that produced widespread wheat crop failure in Europe which triggered the French Revolution. The global population today is about 10 times what it was in 1783. I'll let you do the math."
While it might be possible to better protect the population in the vicinity of a volcano, it would be far tougher to deal with the potential for global impacts. Fortunately, Thomas says, "these events are very rare and infrequent."
Now That's Scary
Krakatoa was only the second biggest eruption in the 1800s in Indonesia. The 1816 eruption of Mount Tambora was so ferocious that it almost instantly killed 10,000 people on the island of Sumbawa and ultimately took about 90,000 lives.
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