There are an estimated 1.5 thousand active volcanoes on the Earth. Fortunately, the word “active” doesn’t mean erupting. In order for us to consider a volcano active, it has to have erupted at least once in geological history. Active volcanoes can either be erupting or dormant. A dormant volcano is one that is resting (in Spanish, the word dormir means to sleep!) However, although this volcano is asleep, it’s expected to erupt again sometime in the future. An erupting volcano is in the process of… erupting!
Lava flows from Kilauea, June 2018.
The Life Cycle of a Volcano
There are actually three stages in the life of a volcano: erupting, dormant, and extinct. While erupting and dormant volcanoes are active, extinct volcanoes are not. An erupting volcano doesn’t always look like the ones we see in movies and on TV.
There are actually many types of eruptions, which produce things such as magma and ash. Different volcanoes erupt at different speeds and have different impacts. Sometimes, a volcano that appears to be dormant isn’t, because it is experiencing unrest. This might not always be visible because it may be happening within or around the volcano.
A dormant volcano was once an erupting volcano and may be one again. If a volcano remains dormant for more than 10,000 years, it’s considered extinct and will likely never erupt again.
Volcanoes Throughout History
Mount Vesuvius: The Most Notorious
The ruins of Pompeii in the shadow of Mount Vesuvius.
Mount Vesuvius is a volcano located in Campania, Italy. It has erupted more than fifty times since its most famous eruption in 79 C.E., which buried Pompeii and its neighboring cities in ash.
At the time, Pompeii was a popular vacation spot for the wealthy. It had a population of between ten and twenty thousand. This included vacationers, townspeople, and slaves.
On August 24th, Mount Vesuvius erupted, sending ash, pumice, and other debris into the sky, making it hard to breathe. When this debris, combined with toxic gas, flowed down the mountain, it buried the city. An estimated two thousand people died. Pompeii remained untouched until the 1780s. Excavators found the city surprisingly intact. The ash preserved the ancient city, including buildings, skeletons, and more. Today it is once again a popular tourist destination, and the excavation continues.
Mount Tambora: The Most Devastating
There is a volcano in Indonesia, Mount Tambora. On April 15, 1815, it erupted, leaving ten thousand islanders dead and tens of thousands more homeless. The eruption consisted of the initial blast, triggered tsunamis, and pyroclastic flows. Pyroclastic flows consist of ash, lava, and toxic gas (like the flow from Mount Vesuvius) and move at incredible speeds.
The eruption caused destruction for tens of miles, and the blast had an impact on Earth’s atmosphere! Weather around the world changed dramatically. The effects were felt even in the United States, where it snowed in June that year!
Mount St. Helens: The Most Destructive in the U.S.
Mount St Helens is a volcano located in Washington. On May 18, 1980, the volcano erupted, following nearly two months of increased activity such as earthquakes and minor eruptions. On that day, an earthquake triggered an eruption and a landslide that might be the largest ever recorded. 150 square miles of forest surrounding Mount St Helens were destroyed, and the volcano itself lost 1,300 feet of its summit. An estimated fifty-seven people died, some of whom were scientists eagerly awaiting the eruption. Today, the volcano is a national park, and more than half a million people visit it each year!
Mount St. Helens