The geologic history of volcanic activity on Earth tells us that large eruptions are less frequent than smaller ones. Volcanic eruptions are rated according to how much magma they produce. A colossal eruption would involve more than 1,000 cu km (240 cu mi) of magma, enough to cover the state of Kansas—an area of 213,109 sq km (82,282 sq mi)—in a layer of magma 4.7 m (15.4 ft) thick. An eruption of this size occurs on Earth approximately every 100,000 years, and the last one occurred about 74,000 years ago. By comparison, great eruptions produce about 100 cu km (24 cu mi) of magma, or enough to cover the area of Kansas in a layer of magma 0.47 m (1.54 ft) thick. An eruption of this size occurs about every 500 years. The explosion of Tambora in 1815 was the last one of this magnitude to be recorded. Large eruptions, such as the eruption of Krakatau in 1883, produce about 10 cu km (2 cu mi) of magma, or enough to cover Kansas in a layer of magma 0.047 m (0.154 ft) thick. An eruption of this size occurs about every 100 years. In comparison, the famous 1980 eruption of Mount Saint Helens produced barely 1.0 cu km (0.24 cu mi) of magma, or enough to cover Kansas in a layer only 0.5 mm (0.02 in) thick.

Volcanic eruptions are remembered, however, not for the amount of magma they produce, but for the impact they have on human civilization. The following eruptions are the worst in recorded history in terms of the devastation they wreaked on local populations.


In about 1640 BC a colossal explosive volcanic eruption occurred on the island of Thíra (Thera) in the Aegean Sea, an arm of the Mediterranean Sea. The disaster may have been the basis for Greek philosopher Plato’s writings on the lost continent of Atlantis.


Mount Vesuvius exploded on August 24 in AD 79, generating deadly pyroclastic flows (a mixture of hot ash, rock debris, and volcanic gases) that destroyed the Roman cities of Pompeii, Herculaneum, and Stabiae in a matter of minutes.


In June 1783 a fissure 25 km (16 mi) long opened up in the southern highlands of Iceland and spewed out enormous quantities of basalt lava for two months. It was the largest lava-flow eruption on Earth since the beginning of recorded history.


On April 10, 1815, the Tambora volcano burst to life on the island of Sumbawa in what is now Indonesia. It was the largest explosive eruption since the beginning of recorded history. The eruption ejected more than 100 cu km (24 cu mi) of magma along with a huge quantity of volcanic gases. The eruption immediately killed at least 10,000 people.


On August 27, 1883, the island volcano of Krakatau in present-day Indonesia violently exploded. The eruption created tsunamis (tidal waves) that reached a height of 30 m (100 ft) and struck the neighboring islands of Sumatra and Java. The tsunamis swept people out to sea, and more than 34,000 people drowned.


On May 8, 1902, the volcano Montagne Pelée on the Caribbean island of Martinique set off a relatively small explosion that sent pyroclastic flows and surges down its western flank. These hot and swift-moving flows went directly into the city of Saint-Pierre, then the capital of Martinique. The flows completely devastated the city, killing all but one of its estimated 30,000 inhabitants.


On May 18, 1980, the Cascade Range volcano of Mount Saint Helens in Washington state burst to life when an earthquake caused a landslide on the mountain’s north face, taking off the top of the mountain. This “uncorked” the column of magma that had been building up, unleashing a major explosive eruption. Mount Saint Helens had been dormant since 1857. The 1980 eruption occurred in a largely unpopulated region, killing 57 people.


On November 13, 1985, the glacier-covered volcano Nevado del Ruiz in the Colombian Andes Mountains burst to life. The small explosive eruption sent hot surges and pyroclastic flows across the glacier and snowfields, generating a great flood. The resulting lahar (mudflow) swept down the valleys to the east and discharged onto the lowlands. The town of Armero was in its path and was struck at about 11 o’clock at night, when most of the town’s inhabitants were sleeping. The acidic lahar buried the town, killing an estimated 23,000 people. It was a catastrophe that could have been averted had measures been taken to evacuate Armero. Volcanologists had warned Colombian authorities that an eruption was imminent and Armero was in danger.


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