10 of History’s Deadliest Volcanoes That Changed the World Forever

A Minor Eruption of Nevado del Ruiz Ended up Killing Tens of Thousands

Located about 75 miles northwest of Bogota, Colombia’s Nevado del Ruiz is a typical stratovolcano. Those are made of multiple layers, or strata, of hardened lava, pumice (volcanic debris), tephra (dust), and ash. What is atypical about it is that it is located by a river valley, which makes its eruptions produce flows known as “lahars”. Those are mudflows made of a slurry of volcanic debris, rocks, and water. The lahar flows are particularly powerful in Nevado del Rio’s case because it is located high up in the Andes, and its top is covered with a glacier. That is, a lot of frozen water just waiting to come down in an eruption as an avalanche and flow of snow, melted water, and debris.

On November 13th, 1985, after lying dormant for seven decades, Nevado del Ruiz awoke from its slumber and became active. It was a minor eruption, far as volcanic eruptions, but it produced a massive and massively devastating lahar. As lava erupted from the volcano, it melted the mountain’s glaciers, turning them into torrents of water. The result was four huge lahars of mudslides, landslides, and volcanic debris, racing down the mountainside at 30 miles an hour, and picking up speed as they reached and were channeled into mountain gullies.

The mud and debris flows struck nearby settlements, causing particular devastation in the town of Armero. There, about 20,000 of the town’s 29,000 population were killed in what came to be known as the Armero Tragedy. Thousands more died in nearby towns and villages. The haunting images of one victim in particular, 13 year old Omayara Sanchez and the fight to save her life, circulated around the world and was televised live. She was trapped in the mud and debris for days as rescuers frantically tried to free her, before dying of exposure on live TV.

The Nevado del Ruiz eruption killed about 25,000 people. That made it the 20th century’s second deadliest volcanic eruption, exceeded only by the Mount Pelee eruption. Sadly, the massive casualties could have easily been avoided, because volcanologists had detected clear signs of an impending eruption two months before it happened, and warned the authorities of impending disaster.

The location of Nevado del Ruiz by a river valley made the risk of lahars obvious. That, coupled with the glaciers atop the volcano which would supercharge such lahars in case of an eruption, made the dangers to Armero and its surroundings even clearer. Volcanologists and seismologists from multiple organizations warned the Colombian government to evacuate Armero, but were ignored.

The Krakatoa Eruption Produced the Loudest Sound in Human History, Bursting Eardrums 40 Miles Away

The Krakatoa eruption is one of the best known and well documented volcanic explosions of the modern era. It happened on Krakatoa Island, in the Sunda Strait between Java and Sumatra in the then Dutch East Indies (today’s Indonesia). Krakatoa, which had three volcanic peaks, started going off on the afternoon of August 26th, 1883, and reached a peak the next morning. By the time the eruptions stopped, most of Krakatoa Island and its surrounding archipelago had disappeared, having collapsed into a volcanic caldera. Tremors and other seismic activity then continued for a while, before silence fell months later.

The suddenness and intensity of the Krakatoa eruption might have been surprising, but the explosion itself was not, because there had been plenty of warnings. For years, Krakatoa had experienced intense seismic activity, with earthquakes whose tremors were felt as far away as Australia. Starting in May of 1883, three months before the dramatic explosion, Krakatoa began venting steam. Then it started hurtling columns of ash up to 20,000 feet into the air, and sounding off with pops that were loud enough to be heard in Jakarta, 100 miles away.

That initial activity went on for a week, then quieted down. It started again in mid June, with a thick black cloud that covered the area for a week. In the meantime, Krakatoa went off intermittently, spewing ash and throwing up volcanic debris that landed hundreds of miles away into the Indian Ocean. That activity did weird things to the tides in the surrounding region, and ships had to be moored with strong chains to resist the tide’s suddenly strong ebb and flow. By early August, Krakatoa was a desolate and abandoned island, covered in by nearly two feet of ash. All vegetation had died, leaving only tree stumps.

The final eruption began early in the afternoon of August 26. By 2PM, explosions were going off about every 10 minutes, and Krakatoa had spewed a 20 mile high ash cloud that was visible from far away. Ships up to 12 miles away reported a heavy ash fall, accompanied by bits of pumice up to 4 inches wide. By early evening, the volcanic activity had caused mini tsunamis, which hit the Sumatran and Javan coasts 25 miles away.

The climax happened the next morning, with two big eruptions, at 5:30 and 6:44AM on August 27th, that caused tsunamis. That was followed at 10:02AM by the loudest sound ever heard until then in recorded history: a cataclysmic explosion of about 180 decibels. That was equivalent to 15,000 Hiroshima bombs, and made the earlier eruptions seem like firecrackers by comparison. It was heard almost 2000 miles away in Perth, Australia, and 3000 miles away on the island of Rodrigues in the Indian Ocean. It also produced a tsunami about 100 feet high in places.

But the worst was yet to come. A fourth, and even more powerful eruption, occurred at 10:41AM. It was almost twice as loud as the earlier one, at 310 decibels. That was so loud that it ruptured eardrums 40 miles distant, and was clearly heard from 3100 miles away. A tsunami with a wall of water up to 120 feet high raced out. Ash was tossed 50 miles up into the sky by an explosion that produced a pressure wave that was recorded in barometers all over the world.

Recorded on global barometers not once, but seven times, as Krakatoa’s pressure wave raced around the planet for five days. It circled the earth and came back to the volcano, then continued on, again and again and again, still powerful enough to register on barometers everywhere on the planet as it circled the globe multiple times. The eruptions and resultant tsunamis killed at least 36,000 according to official Dutch estimates. Modern estimates put the casualty figures at up to 120,000.

Tambora’s Eruption Led to the “Year Without Summer”

The biggest volcanic eruption in recorded human history happened in Mount Tambora, on Sumbawa Island in the Dutch East Indies (today’s Indonesia). It was preceded by five days of rumblings, starting on April 5th, 1815, when a loud eruption occurred, with a thunderous clap that was heard almost a thousand miles away. When Tambora finally blew up in a grand finale on April 10th, 1815, it was the strongest volcanic explosion of the past ten thousand years.

After the initial pop on April 5th, Mount Tambora had smoldered for the next few days, giving off faint detonation sounds from time to time. Then, on April 10th, people in Sumatra, 1600 miles away, were shocked by what sounded like the boom of big guns opening up nearby. It was the sound of Tambora going off. The eruption instantly killed about 12,000 inhabitants of Sumbawa Island in a cataclysmic explosion. 80,000 more died in the surrounding region from famine and starvation, after falling ash and pumice ruined their crops and fields.

As investigators subsequently pieced the chain of events, Tambora’s eruptions had grown more energetic early in the morning of April 10th. Flames shot up into the sky, and lava and glowing ash began pouring down the mountainside. By 8AM, bits of pumice up to 8 inches wide were falling down. Ash spewed into the air so thickly that it was pitch dark for two days, up to 400 miles away. The volcano gushed rivers of glowing ash down its sides to scorch Sumbawa island, while its tremors sent tsunamis racing across the Java Sea.

Tambora hurled ash and 12 cubic miles of gasses far up into the skies, causing extreme weather conditions around the planet. The fine ash dispersed throughout the atmosphere created odd optical phenomena throughout the world. The results included prolonged and brilliantly colored sunsets and twilights that were red or orange near the horizon, and pink or purple above.

However, the ashes spewed by Tambora into the atmosphere had other impacts that were less lovely and pleasing. The ash caused a volcanic winter, which lowered global temperatures and turned 1816 into what came to be known as The Year Without Summer. That led to an agricultural disaster of crop failures and food shortages in the northern hemisphere. The weird weather phenomena reached thousands of miles away from Tambora, all the way to the eastern United States. There, the spring and summer of 1816 were marked by a persistent dry fog that reddened and dimmed the sunlight. That May, a frost killed off most crops in upstate New York, as well as Massachusetts, Vermont, and New Hampshire, and snow fell as late as June 6 in Albany, NY. Similar examples of unusual weather were recorded around the world.

Mount Unzen’s 1792 Eruption Was Japan’s Deadliest Volcanic Disaster

Mount Unzen is a volcanic group in the island of Kyushu, Japan. It is situated on the Shimabara Peninsula, about 25 miles east of Nagasaki. Unzen has several lava domes – mounds atop volcanoes, resulting from the accumulation of slow seeping lava, which cools and solidifies before flowing very far. On May 21st, 1792, a volcanic eruption caused one of those lava domes to fall into the sea, resulting in a tsunami and earthquake that caused considerable devastation and loss of life.

It began months earlier, in late 1791, with tremors and earthquakes on the western side of Mount Unzen, which gradually made their up to one of its volcanic peaks. In February of 1792, one of those began erupting, causing lava to flow for the next two months. In the meantime, the earthquakes and tremors continued, until the night of May 21st, 1792, when two big quakes hit. They were powerful enough to shake one of the lava domes loose, causing it to collapse down the eastern side of the mountain. That triggered a landslide, which swept through the city of Shimabara down below, and continued on to Ariake Bay.

When the landslide struck the water, it caused a mega tsunami, with waves nearly 70 feet high, rising up to 187 feet high in some places because of the seabed’s topography. The tsunami travelled across Ariake Bay, until it hit the city of Higo on the other side, where it caused widespread devastation. It then bounced back across the bay, and hit the city of Shimabara, where the dust had still not settled from the landslide that had swept through it and triggered the tsunami in the first place. About 15,000 people were killed in the disaster, making it Japan’s deadliest volcanic eruption.

Of the roughly 15,000 dead, about 5000 were estimated to have been killed in the landslide that swept through Shimabara city. Another 5000 were estimated to have been killed by the ensuing tsunami when it reached Higo, across the bay from Shimabara. And another 5000 were estimated to have been killed when the tsunami bounced back from Higo, recrossed the bay, and struck Shimabara. Because the eruption happened on Mount Unzen, in the Shimabara Peninsula, but many deaths from the ensuing tsunami occurred in Higo, about 15 miles away across the Ariake Bay, the Japanese coined a phrase: Shimabara erupted, Higo affected.

Laki Was History’s Deadliest Volcano

The Laki eruption in 1783 was not one of history’s most powerful volcanic events. It was not a violent and massive explosion like Krakatoa or Tambora or Vesuvius. It did not go off with a thunderous bang, blowing its top and releasing a massive amount of energy in a dramatic explosion, with fires reaching to the heavens and rivers of lava rushing down the volcano’s sides. Indeed, the Laki eruption was not even a single explosion. Instead, it was 8 months of rumblings. There were some small eruptions every now and then, with lava slowly seeping out, while the volcano steadily spewed sulfuric dioxide gasses. In short, Laki was not a vigorous and energetic volcano, but a tired and lazy one, farting gasses for 8 months before it finally subsided. Nonetheless, Laki was the deadliest volcanic eruption in human history.

Its deadliness was a result of its steady release, during its 8 months of activity, of massive amounts of gasses. They included flourine, and over 120 million tons of sulfuric dioxides, which produced fog and haze as far away as Syria. The flourine settled on Iceland’s grass, which gave grazing animals flouride poisoning and killed most of the island’s livestock. Because of the loss of livestock, about a quarter of Iceland’s human population starved to death.

However, Iceland was thinly populated, so the death of a quarter of its inhabitants did not make Laki history’s deadliest eruption. The greatest impact lay beyond Iceland, where Laki’s eruption led to a decline in temperatures throughout the northern hemisphere. Winter temperatures in the US, for example, dropped 10 degrees Fahrenheit in 1783, and remained below normal for several years afterwards. Still, Laki’s deadliest impact was not in the US or North America.

The worst effects were felt in Europe and those parts of the northern hemisphere, southeast of Iceland. The summer of 1783 had been a particularly hot one, and a rare high pressure zone formed over Iceland, which caused winds to blow to the southeast. So when Laki started spewing prodigious amounts of sulfuric dioxide gasses into the sky, they were carried by the winds from Iceland in a southeasterly direction. There, they caused crop failures in Europe, draught in North Africa and India, Japan’s worst famine, as well as a historic famine in Egypt, where a sixth of the population starved to death in 1784. The Laki eruption and its aftermath caused the deaths of an estimated six million people. That made it the deadliest eruption in human history. It also illustrated that low energy but large volume eruptions over an extended period can have a greater impact than huge explosive eruptions.

A Volcanic Eruption in Peru Killed a Third of Russia’s Population

Huayanaputina is a volcano located in Andean Mountains, in the uplands of southern Peru, about 50 miles from the city of Arequipa. The cliche of natives making human sacrifices to volcanoes is not so cliche or mythical when it comes to Huayanaputina: such sacrifices actually were made to this volcano. The Spanish put a halt to such practices after they conquered Peru and introduced Catholicism.

However, considering what happened not long after the sacrifices stopped, maybe the natives had been on to something. On February 19th, 1600, Huayanaputina went off in the biggest volcanic eruption ever experienced in South America during recorded history. The consequences were catastrophic locally, and produced negative impacts worldwide. Naturally, the natives drew a link between the end of the sacrifices, which angered Supay, their god of death, and the massive eruption.

Rumbling and booming noises were heard in the days before Huayanuptina exploded, and witnesses reported seeing fog and gasses spewing from the volcano’s crater. A local priest reported frightened natives, recently converted to Christianity, falling back on their old religious beliefs and traditions. Shamans, not seen for years, scrambled to appease the volcano, preparing plants, flowers, pets, and virgin girls for sacrifice. During the sacrifice ceremony, the volcano spewed hot ash. The natives took it as a sign that the gods were too angry by then to be appeased by belated sacrifices, after having being ignored for so long.

The seismic and volcanic activity continued and increased, and by February 15th, 1600, earthquakes started. By the 18th, tremors were being felt every four or five minutes, some of them powerful enough to shake those who’d managed to sleep into wakefulness. Finally, around 5PM on February 19th, Huayanaputina erupted, sending a column of steam and ash high into the skies. Witnesses described the sound as that of giant cannons going off. Streams of lava began flowing down the mountainside, and when they reached the nearby Rio Tambo river, they created lahars – mudflows of volcanic slurry, debris, and water. Volcanic ash began falling down, and within a day, the city of Arequipa, 50 miles away, was covered by ash nearly a foot deep. Falling ash was recorded over 300 miles away, in Chile and Bolivia. Smaller eruptions continued for the next couple of weeks, until the volcano finally went quiet on March 5th.

In the eruption, lava flowed about ten miles from the volcano, while lahars, or mud slides, made it all the way to the Pacific Ocean, 75 miles away. Several villages were destroyed, while the earthquakes stemming from the eruption caused significant damage in Arequipa and nearby towns. About 15,000 people were killed in the immediate region.

The ashes from Huayanaputina spread into the atmosphere, and had a significant impact in the northern hemisphere, where temperatures cooled considerably. In Russia, for example, 1601 was the coldest year in six centuries, resulting in crop failures and producing the Russian Famine of 1601 – 1603, in which two million people, or a third of Russia’s population at the time, died.

Mount Kelud Erupted Over 30 Times in the Past Millennium

Mount Kelud is one of the most active volcanoes on the island of Java, in today’s Indonesia. In the past millennium, it erupted more than 30 times. In just the 20th century, it went off four times, and its latest eruption occurred as recently as 2014. Throughout most of its history, Kelud had a massive crater, which filled with rainwater to form a beautiful lake. The lake was an attractive vacation destination, but during eruptions, the lake’s waters frequently led to devastating mud flows, or lahars. In 2007, seeping lava piled into a big mound at the center of the crater, which displaced most of the lake’s water.

Kelud’s volcano is one of the most dangerous, not only in Java, but in the entire world. Not because of massive eruptions – Kelud’s explosions are not as energetic as some historically powerful eruptions, such as Tambora or Krakatoa – but because of how often it goes off. The danger of Kelud’s frequent eruptions is made even worse by its tendency to produce deadly mud flows, because of the presence of massive amounts of water in the volcano’s crater. In 1586, an eruption emptied Kelud’s crater lake, resulting in devastating lahars, or mud flows. By the time things quieted down, about 10,000 people had been killed by the eruption and the ensuing lahars.

Mount Kelud behaved itself without major eruptions and significant devastation for over three centuries, during which the volcano’s crater refilled with water and turned into a crater lake. That period of relative peace ended on May 19th, 1919, when Kelud exploded yet once again, in another devastating eruption. An estimated 38 million cubic meters of boiling water and steam blew up from Kelud’s crater lake, and caused massive flows of hot mud, or lahars. The mud flow travelled for about 30 miles, destroying about 100 villages in its path. By the time it stopped, an estimated 5100 people had been killed.

The colonial government of the Dutch East Indies responded by creating a volcanological authorities to study and warn about future eruptions. It also launched an ambitious engineering project to avert future devastation. The authorities created a drainage system for Mount Kelud’s crater lake, to manage the hazards and potential future mud flows, in case of another eruption. Drainage tunnels were dug, which reduced the crater lake’s water level by about 150 feet, and they proved highly effective. The next time Mount Kelud erupted, which happened in 1951, there was too little water in the crater lake to form massive flood flows, and thus another major Mount Kelud disaster was averted.

The drainage tunnels were destroyed in that 1951 eruption, however, and were not immediately rebuilt. When Kelud erupted again, in 1966, the crater lake had refilled, and contained over 50 million cubic meters of water. In the resultant lahars, over 200 people were killed by the mud flows. The Indonesian authorities responded by digging a new, and deeper tunnel, which reduced the crater lake’s volume to only 1 million cubic meters of water.

The 79 AD Vesuvius Eruption Killed Tens of Thousands – and Contributed to Our Knowledge of Roman History

The Vesuvius eruption of August 24th, 79 AD, was one of antiquity’s most famous volcanic eruptions, and one of Europe’s most powerful volcanic explosions. Vesuvius went off with a force 100,000 times greater than that of the Hiroshima and Nagasaki atomic bombs. The eruption tossed deadly debris, mixed with a cloud of poisonous gasses, over 20 miles up into the sky. As it spewed gasses into the air, lava and hot pumice poured out of the volcano’s mouth at a rate of 1.5 million tons per second. The glowing hot material raced down Vesuvius’ side to devastate the surrounding region. Nearby towns were destroyed, of which Pompeii and Herculaneum are the best known.

Pliny the Younger, a Roman author and magistrate, was 15 miles away at Cape Misenum. He was visiting his uncle, Pliny the Elder – a Roman admiral who would lose his life during rescue efforts after the eruption. History is deeply indebted to Pliny’s detailed description of the events he saw, and those told him by first hand witnesses. His work is the best written and most thorough narrative of the disaster.

Vesuvius had been giving off tremors for days, but they were not unusual. Then, around noon on August 24th, a cloud appeared atop the volcano. About an hour later, Vesuvius erupted, and ash began to fall on Pompeii, 6 miles away. By 2PM, pumice started falling with the ash, and by 5PM sunlight had been completely blocked. Around that time, roofs in Pompeii began collapsing under the accumulating weight of ash and pumice. Panicked townspeople rushed to the harbor, seeking any ship that would take them away.

By midnight, Vesuvius was spewing a hot deadly column over 20 miles up into the air. Simultaneously, lava flowed down its side in six major surges, as the volcano vomited molten rock in a rapid flow that incinerated all that it encountered. The lava did not reach Pompeii or Herculaneum, but it sent heat waves of more than 550 degrees Fahrenheit into those towns. That turned them into ovens, and killed any who had not yet escaped or had not yet already suffocated from the fine ash. When Pompeii and Herculaneum were unearthed centuries later, about 1500 bodies were found in them. Those 1500 bodies were recovered from just one small area of the region impacted by the volcano’s eruption. Extrapolating to the surrounding regions, total casualties are estimated to have been in the tens of thousands.

Pompeii and Herculaneum, whose populations at the time numbered about 20,000, were buried under up to 20 feet of volcanic ash and pumice. While tragic and terrifying, the ash did a remarkably great job of preserving those towns. As a result, future historians got an unrivaled snapshot of 1st century AD Roman architecture, city planning, urban infrastructure, and town life in general.

The Thera Eruption Shaped History and Led to Today’s World

One of the most powerful eruptions in recorded history occurred in Thera, today’s Greek island of Santorini, sometime between 1642 and 1540 BC. It was four times as powerful as the gigantic Krakatoa explosion of 1883. It sundered the island of Thera, and wiped out the flourishing Minoan settlement of nearby Arkotiri and surrounding islands. That gave rise to the legend of the vanished civilization of Atlantis, which was doomed by a natural catastrophe and swallowed by the sea. Beyond legend, however, Thera’s eruption had the greatest impact of any volcanic eruption on human history. The consequences stretched far beyond its own era, with knock on effects and a chain of causation leading directly to the world in which we live today.

In addition to the immediate devastation of Thera and surrounding islands, the eruption produced powerful tsunamis that devastated Crete. That greatly weakened Crete’s Minoan civilization, led to its decline, and put it on the path to extinction. The Minoans were the Mediterranean’s greatest naval power, as well as the dominant power of the Aegean, including what became Greece and the Greek world. A trading power, the Minoans were oriented towards Egypt and the Eastern Mediterranean, and were strongly influenced by those civilizations. While the Minoans flourished, the Aegean world in their thrall was by necessity oriented in the same direction, and strongly influenced by the Egyptian and eastern civilizations as well.

Thera’s eruption weakened Crete and the Minoans, creating a power vacuum in the Aegean. It was filled by the emerging Mycenaeans, in mainland Greece. The Myceneans went on to conquer Crete and destroy the Minoans, and became the dominant power of the Aegean. However, unlike the Minoans, the Mycenaeans’ energies were not focused on trade with Egypt and the Levant. Instead, they focused on colonizing the Aegean, the western coast of Asia Minor, the Black Sea coast, and the western Mediterranean.

That change of orientation significantly reduced Egyptian and eastern influences upon the Greeks. Thus, when the Greek world flourished centuries later, long after the Mycenaeans had themselves disappeared, it would do so as a civilization and culture distinct from those of Egypt and the eastern Mediterranean, not an extension and outpost of those civilizations. And since western civilization is founded upon that of the ancient Greeks, an argument could be made that today’s western civilization and its impact on the modern world would not exist but for the Thera eruption.