Volcano also refers to a vent in the Earth's crust from which molten rock, ash and gas emanate.
Lava is molten rock from a volcano that has reached the Earth's surface.
Molten rock below the Earth's surface is referred to as magma.
Volcanoes are generally classified into four main types:
- Cinder cones - the most common volcanoes, steep conical hills with a vent and a crater at the summit, usually no more than 1,000 feet high.
Examples: Sunset Crater Arizona, Lassen Peak in California, and San Quintin Volcanic Field in Baja, Mexico.
- Composite volcanoes or stratovolcanoes - symmetrical, cone-shaped, and have a conduit system through which magma flows to the surface through one or more vents, can reach 8,000 feet in height.
Examples: Mount St. Helens, Mount Fuji, Redoubt, Pinatubo, Soufriere Hills and Mount Pelée in Martinique.
- Lava domes - small masses of lava that accumulate around and over the volcano's vent, then cool to break apart flowing down the dome's side. They commonly occur inside the crater of large stratovolcanoes or composite volcanoes.
Example: Augustine Volcano in Alaska
- Shield volcanoes - form when fluid lava cools to form a gently sloping hill. The largest group of volcanoes on Earth is of this type.
Examples: Mauna Loa and Mauna Kea in Hawaii, Eyjafjallajokull and Grimsvotn in Iceland, and Novarupta in Alaska.
More than 50% of the world's active volcanoes above sea level encircle the Pacific Ocean, forming the "Ring of Fire." The ring starts at New Zealand, goes north around the eastern coast of Asia to the Aleutian Islands, and south down the western coasts of North, Central and South America.
Volcanic Explosivity Index (VEI):
Proposed in 1982, the Volcanic Explosivity Index measures the relative magnitude of an explosive volcanic eruption.
It is similar to the Richter Scale, which measures the magnitude of earthquakes.
On a scale of 0-to-8, each whole number represents a tenfold increase of explosivity.
Uses several factors to determine a number, including volume of erupted pyroclastic material (for example, ashfall, pyroclastic flows and other ejecta), height of eruption column, duration in hours and qualitative descriptive terms. (USGS)
Major and Notable Eruptions, most VEI 4 and above (1902 - current):
(Sources: CNN, National Geophysical Data Center / World Data Service & Smithsonian's Global Volcanism Program
May 7, 1902 - La Soufrière on St. Vincent island erupts, resulting in 1,680 deaths. (VEI 4)
May 8, 1902 - Mount Pelée on Martinique erupts, destroying the town of St. Pierre, and killing almost 30,000 people. (VEI 4)
August 30, 1902 - Mount Pelée on Martinique erupts again, killing more than 1,000 people. (VEI 4)
October 24, 1902 - Santa Maria in Guatemala erupts, resulting in more than 1,500 deaths. (VEI 6)
1907 - Ksudach in Russia erupts, one of the Kamchatka region's largest. (VEI 5)
January 30, 1911 - Taal volcano in the Philippines erupts, killing 1,335 people. (VEI 4)
1912 - Novarupta volcano erupts in Alaska. It is the largest volcanic eruption of the 20th century in the United States, producing 21 cubic kilometers of volcanic material. (VEI 6)
January 17, 1913 - Colima in Mexico erupts. (VEI 5)
1916 - Cerro Azul in Chile erupts. (VEI 5)
May 19, 1919 - Kelut in East Java, Indonesia, erupts, resulting in 5,110 deaths. (VEI 4)
January 8, 1933 - Kharimkotan in Russia erupts. (VEI 5)
January 15, 1951 - Mount Lamington, Papua New Guinea, erupts and kills 2,942 people. (VEI 4)
October 22, 1955 - Bezymianny in Russia erupts. (VEI 5)
February 18, 1963 - Agung in Indonesia erupts. (VEI 5)
May 18, 1980 -
Mount St. Helens in Washington erupts, killing 57 people and disrupting highways and railways. (VEI 5)
March 28, 1982 - El Chichon in Mexico erupts, resulting in 1,879 deaths. (VEI 5)
March 27, 1986 - Augustine Volcano in Alaska sends up an ash cloud, disrupting air traffic. (VEI 4)
April 2, 1991 - The eruption of Pinatubo Volcano in the Philippines results in the loss of 350 lives, mostly from collapsed buildings. (VEI 6)
August 8, 1991 - Cerro Hudson in Chile erupts. (VEI 5)
March 20, 2010 - The volcano Eyjafjallajokull erupts in Iceland for the first time since an eruption in the early 1820s. (VEI 4)
April 14-21, 2010 - A stronger eruption of Eyjafjallajokull expels an ash cloud 30,000 feet into the air, shutting down airports in northern and western Europe for a week. The International Air Transport Association (IATA) estimates that the work disruption due to volcanic ash cost the airline industry $1.7 billion in revenue. (VEI 4)
September 27, 2014 -
Mount Ontake in Japan
erupts suddenly, engulfing hikers in an ash cloud. At least 57 people are killed. (VEI3)
May 21, 2016 -
Mount Sinabung in Indonesia erupts, killing at least seven people.