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The Deadliest Volcanic Eruptions in Human History

Written by Kevin Jennings

Volcanoes, the silent killer…is a sentence that no one has ever said before. Volcanoes are loud, with eruptions often being reported as being heard thousands of kilometers away. There are also numerous warning signs that a volcano may be ready to erupt. The two most noticeable are increased seismic activity and steaming coming from the mouth of the volcano. There are either signs as well, such as subtle swelling of the ground’s surface and new and enlarged areas of hot ground surrounding the volcano, but these are much less obvious.

When most people think of a volcanic eruption, they think of lava. Lava is molten rock that spews down the side of a volcano. It is generally very slow, moving on average less than one mile per hour. Speeds can reach as high as 6 miles per hour, or in extremely rare circumstances requiring very specific terrain, as fast as 30 miles per hour. With all of these warning signs, and with lava being easily outrun by a human on foot, except in the absolute rarest of circumstances, at first glance it seems like deaths from volcanic eruptions would be extremely rare. In fact, on average only 540 people die each year from volcanic eruptions.

However, those are only averages, and while lava itself may not be a large concern, the deadly part of the eruption is the pyroclastic flow. A pyroclastic flow is a dense, destructive mass of very hot ash, lava fragments, and gasses ejected from the volcano at high speeds. The average speed of a pyroclastic flow is 100 km/h (about 62 mph), but speeds can reach as much as 700 km/h (435 mph). Most pyroclastic flows are 1-10 cubic kilometers in volume (0.25-2.5 cubic miles) and travel for several kilometers, though larger ones will travel further. There is also both anecdotal and experimental evidence that suggests these flows can sail across bodies of water without losing their destructive properties.

Today we’ll be looking at the deadliest volcanic eruptions across all of recorded history.

Mount Vesuvius


              This is the most famous volcanic eruption in history, despite only being the 6th most deadly. Its fame stems from a combination of being the first eruption of this magnitude in recorded history, and because it would be another 1,500 years before another event of this scale.

              It began in 62 AD with the first major earthquake the region had seen in over 150 years. While this was nearly two decades before Mount Vesuvius would erupt, it was the first warning the mountain gave. The next came two years later, in the form of a smaller earthquake. There were more earthquakes as the years went on, though the frequency is unknown. We know that starting one autumn day in 79 AD, several small earthquakes occurred over the course of four days. This was the final warning Vesuvius would give, but the residents didn’t understand the message.

              The only surviving witness to leave a record of the event, Pliny the Younger, wrote that the earthquakes weren’t a cause for concern among the citizens as those of the region were no strangers to small tremors. He said they “were not particularly alarming because they are frequent in Campania”.

              It was at around 1:00 pm that the eruption began. Vesuvius spewed a column of ash and pumice into the stratosphere, as high as 30 km (19 miles) that rained down on the surrounding cities. The sky was black, thicker and darker than any night. The only light that could be seen was the fires of Mount Vesuvius. This phase, also known as the Plinian eruption, lasted for 18-20 hours. The accumulation of ash and pumice was as high as 2.8 meters (9 ft).

              The second stage, called the Pelean eruption, was a series of six pyroclastic flows. These flows killed anything that remained. Two of these pyroclastic flows went in the direction of Pompeii, leaving behind another 1.8 meters (6 ft) of volcanic debris. The eruption finally completed on the second night after it had begun, though over the course of those two days the words “day” and “night” would have held no meaning.

              Despite evacuation efforts, including those led by Pliny the Elder, commander of the Roman fleet, thousands of lives were lost, most notably Pliny the Elder himself, Princess Drusilla, and her son Agrippa. The most remarkable thing about this disaster maybe not have been the damage itself, but how well the site was preserved as a result.

              Nearly 1700 years later in 1748, a group of explorers discovered the lost ruins of Pompeii. Underneath the thick layers of volcanic debris, the buildings were intact and the skeletons were preserved in whatever pose they were in at the time of their deaths. The most famous of these were the “two maidens”, a couple preserved sharing one last embrace before death. Of course, in 2017 it was discovered that the two were in fact not maidens, but rather were both men.

              It is likely impossible to ever know for sure the complete death count from this disaster. The remains of over 1,500 people have been found between Pompeii and Herculaneum, but the actual total is estimated to be in the range of 13,000-16,000. Were the world as densely populated 2000 years ago as it is today, that number undoubtedly would have been much higher.

Nevado del Ruiz


             The Nevado del Ruiz is a stratovolcano, or composite volcano, located in Tolima, Columbia. The main physical characteristic of a stratovolcano is its tall, steep incline, the type of incline that might facilitate much faster flows of lava. Though the Nevado del Ruiz had remained dormant for 69 years, in September of 1985 the government of Columbia received warnings from volcanological organizations to evacuate the area. These organizations had detected volcanic activity, and understood the threat a major eruption could cause.

              The government did little with this information. Though they produced a hazard map that was finalized in October, the map was poorly distributed. Of the copies that were distributed in popular newspapers, most were confusing or filled with glaring errors. The maps were not drawn to scale, making it difficult to interpret how far the danger went. The maps also appeared to be topographical in nature, and with no proper scale the public used these topographic indicators to relate the map to their surrounding landscape. Unfortunately it turned out that these drawings were of an artistic nature and not a scientific one, and it was not meant to be an accurate topographical map of the area.

Further confusing the situation, the map seemed to indicate that the main threat from this eruption would be the pyroclastic flows, as is normally the case, but Nevado del Ruiz is a different beast entirely. Finally, there were coloured zones to indicate levels of risk, but there was no key to decipher what the colours actually meant. The city of Armero was located in the green zone, logically interpreted as the safest zone on the map. It was anything but, and this eruption has since been known as the Armero tragedy.

              On November 13, 1985, two months after the warnings began, the eruption would commence. It began at approximately 3:00 pm, with columns of black ash spewing into the sky. The ash rained down on surrounding areas for a few hours before stopping. Once it had stopped, local officials told citizens to stay calm and go inside, and that the falling ash was nothing to worry about. There was a large storm that night, and it is believed that the heavy rain and constant thunder may have drowned out the sounds of the volcano, leaving the citizens of Armero to believe that the eruption was completed and there really was nothing to worry about.

              Then, at 9:09 pm, Nevado del Ruiz began the main event. Reaching heights of 30 km (20 miles), the volcano erupted a total mass of 35 million metric tons. But the biggest danger was not the ash or the pyroclastic flows, it was lahars, a type of volcanically induced mudslide. The high altitude summit of the volcano was covered in glaciers, and the intense heat of the pyroclastic flows caused the glaciers to melt, creating four lahars that ran down the sides of the mountains. These lahars reached an average speed of 60 km/h (40 mph), and they were headed straight towards Armero, 48 km (30 miles) away.

              The storm had knocked out power and most radio communications. Though radio reports had previously said for residents to simply remain calm, they were now calling for an evacuation, but Armero couldn’t hear them. Just before 11:30 pm, a huge stream of water swept through the city, flipping over cars and tossing people around like dolls. Thinking it was a flood, residents panicked and took cover indoors. Minutes later, the first lahar would crash through the city, followed shortly by the others.

              The front of these mud flows carried boulders that would tear down buildings and crush any humans in their path. The remainder was filled with smaller, sharp rocks that would cause lacerations. For those not instantly crushed, the sharp rocks were not as big a hazard as the mud itself, which could cause a person to suffocate in under two minutes. Those not killed directly by the lahar itself risked being injured by collapsing buildings.

              The Mayor of Armero, Ramon Rodriguez was one of the local officials that had been unsuccessfully trying to bring the potential threat the volcano posed to the attention of the Columbian government. Despite being aware of the damage an eruption of Nevado del Ruiz could cause, Ramon was ironically heard speaking over a ham radio saying that he did not think Armero was in much danger at the precise moment he was overtaken by one of the lahars.

              It took 12 hours for relief efforts to reach Armero, as the mud had made traveling extremely difficult. By the time help finally arrived, many of those that had only been injured by the lahars had now died from their untreated wounds. The city of Armero had a population of 28,700 in 1985. This tragedy claimed the lives of over 20,000 of those residents, and the deaths in neighbouring cities brought the total to over 23,000 killed by the eruption. It was the 4th deadliest volcanic eruption in recorded history, and it was completely preventable. Even once the ash began to fall from the sky, there were still over eight hours to evacuate had the government only taken the danger seriously.

Mount Pelée


            Volcanic activity operates on a grand scale. Signs that a particular volcanic is preparing to erupt are often seen not only days before the eruption, but years. Sometimes, even decades. In the case of Mount Pelée, there was over a century of warning that the volcano was active and potentially dangerous.

              While this may have been news to the newer inhabitants of the island of Martinique, a French territory that is home to Mount Pelée, the indigenous Carib people were well aware. To them, Mount Pelée was known as “fire mountain” a name it earned from eruptions in ancient times.

              But it is not only the warnings that operate on a grand scale, so too can the eruptions themselves, and the eruption of Mount Pelée that began in April of 1902 would not cease until October of 1905. The early eruptions were relatively minor, resulting in less than 200 deaths total. Volcanic activity was being monitored, but they saw no significant changes or developments. Then, seemingly out of nowhere, it was already too late.

              At 8:00 am, the side of Mount Pelée split open, firing a massive pyroclastic surge horizontally, directly at the city of Saint-Pierre. The remainder of the volcanic activity that day is largely irrelevant, as this death cloud was traveling with an initial speed in excess of 160 km/h (100 mph). At 8:02 am, the surge tore through Saint-Pierre. Of the 28,000 people in the city proper, there were only two survivors. One was a felon being held in an underground jail cell, and the other was a man who lived on the very outskirts of the city. There were tens of other survivors outside the city that were caught within the edges of the cloud, but all survivors had severe burns.

              Thinking the damage was done, relief attempts began. Rescuers, engineers, and mariners were bringing supplies to the island. The damage had extended beyond Saint-Pierre, but that city had taken the brunt of it. Still, there were other people in need of aid, and an entire city that needing rebuilding, so these people had come to help. On May 20, a second eruption nearly identical to the first took place. Little had remained of Saint-Pierre after the May 8 eruption, but the destruction of the city was now complete. The eruption claimed not only the tattered remnants of the city, but the lives of 2,000 people that had come to provide relief to the devastated island.

              Still, Mount Pelée wasn’t done yet. On August 30, there was another eruption. While not as powerful as the previous two, the pyroclastic flow extended much further this time, possibly because it was no longer impeded by that pesky city that used to be in its way, and struck four more cities, resulting in over another 1,000 deaths.

              In total, the eruption of Mount Pelée claimed over 30,000 lives. It was the most deadly volcanic eruption of the 20th century, and likely the most immediately destructive. While there are two volcanic eruptions that have claimed more lives than Pelée did, little can compare in terms of sheer terror to a volcano breaking open, erupting sideways, and wiping an entire city and its population of the map in a span of two minutes.

Mount Tambora


              On April 10, 1815, the eruption of Mount Tambora reached its violent climax. The volcano is located on the island of Sumbawa, part of modern day Indonesia, and this was the most powerful volcanic eruption humanity has ever witnessed. All plant life on the island was destroyed. The eruption caused the immediate deaths of over 71,000 people, but that was just the start of the story.

              Tambora spewed a staggering 200 cubic km (50 cubic miles) of material into the air, enough to block out the sun and trigger global climate change. The decreased temperatures resulted in harvest failures and famine around the world. At least another 90,000 deaths are attributed to the cold climate resulting from the eruption in what would be dubbed “The Year Without a Summer”.

              The effects of Mount Tambora are simply too epic to be contained within this episode, but if you’d like to see an in depth look at one of the world’s most incredible natural disasters, be sure to check out “Mount Tambora: The Year Without a Summer” over on the Geographics channel. 

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