An active volcano is an opening in the earth's crust through which molten lava, ash and steam are periodically expelled. The largest eruption in recent history was the 1815 Tambora eruption in Indonesia. Ejecting 100 cubic kilometers of material, Tambora killed 92,000 people and changed the global climate. Measured on the Volcanic Explosivity Index, or VEI, Tambora rated a 7. Although one of the biggest volcanic events during the past 10,000 years, Tambora is dwarfed by several ancient eruptions.
The biggest eruptions in geological history occurred in the Paraná and Etendeka traps in present-day Brazil. Between 128 and 132 million years ago, five separate eruptions expelled over 5,600 cubic kilometers of material each, with the largest measuring 8,600 cubic kilometers. Approximately 28 million years ago, the La Garita Caldera erupted in present-day Colorado with 5,000 cubic kilometers of outflow. Three separate additional Paraná eruptions were over 3,000 cubic kilometers in size, or 300 times larger than the largest historical volcanic eruption. The largest eruption of the Yellowstone caldera occurred 2.5 million years ago. Yellowstone has seen at least 12 supereruptions in the course of geological history. 6,850 years ago, Crater Lake was formed by a 40 cubic kilometer eruption in modern-day Oregon.
Tambora was the deadliest volcano eruption in history; the second deadliest was the Krakatau eruption, also in Indonesia. In 1883 Krakatau caused a tsunami killing approximately 36,400 people. In 1902, Mount Pelee in Martinique killed 29,000 people in resulting ash flows. More recently, mudflows from Ruiz in Colombia killed approximately 25,000 people in 1985. The Unzen volcano in Japan killed 14,300 people in 1792, with a combination of volcano debris and the resultant tsunami.
Santorini and Vesuvius
Two culturally notable eruptions occurred around the area of the Mediterranean Sea. In the middle of the second millennium B.C., a massive volcanic explosion destroyed much of the island of Thera, also known as Santorini. The Thera eruption may have caused the decline of the Minoan civilization on nearby Crete, and is also the possible inspiration for the legend of Atlantis. In 79 A.D., Mount Vesuvius erupted, burying the cities of Pompeii and Herculaneum. The cities remained buried until excavations started during the 18th century; these excavations revealed many well-preserved details of Roman life during the first century.
In 1980, Mt. St. Helens erupted in Washington state; it was the most destructive volcanic event to have occurred in the history of the United States. 57 people were killed and the area suffered extensive property damage. On the big island of Hawai'i, the Kilauea volcano has been erupting continuously since 1983, the most recent of 52 eruptions since 1952. Currently Kilauea is a non-explosive eruption, although explosive eruptions have occurred in the past.