A volcano is a crack or opening in Earth’s outermost crust where molten rock called magma and gases can escape, spilling or falling to the surface. Geologists generally group volcanoes onto a spectrum of behavior that can be summed up by four principal types: cinder cones, stratovolcanoes, shield volcanoes and lava domes. Let's take a peek at each one.
Cinder cone volcano - Amboy Crater, Mojave Desert, California
Cinder cones are the simplest type and are formed from a single vent, which may live on another existing volcano itself. During an eruption, lava is blown into the air, cools and then falls as cinders. Gradually through time, cinders build up to form the shape we all recognize as a volcano. Generally, cinder cone volcanoes are not exceptionally tall, rarely reaching more than 1,000 feet in elevation. This type of volcano is very common, and numerous examples can be found in western North America and throughout the world.
Stratovolcano - Mt. Fuji, Japan
Stratovolcanoes, also called composite volcanoes, are symmetrical and steep-sided, often rising to over 8,000 feet in elevation. Some of the most beautiful mountains in the world are stratovolcanoes, including Mt. Shasta in California, Mt. Rainier outside of Seattle, and Mt. Fuji in Japan. The essential characteristic of a stratovolcano is a conduit system that taps into magma deep inside the Earth. Layer upon layer of lava flows, volcanic ash and cinders that have built up from repeated eruptions form the structure of this type of volcano. Stratovolcanoes generally have a central vent or a cluster of vents, with fissures on the flanks of the cone. As erupted lava cools and solidifies within side vents and fissures, it can form dikes that act as ribs to strengthen the cone, allowing it to grow to greater heights.
Shield volcano - Piton de la Fournaise, Reunion Island, Indian Ocean
Shield volcanoes are built almost entirely of lava flows and are some of the largest volcanoes on Earth. Lava flows from a central vent accumulate gradually, often for thousands of years, to create a broad gently sloping cone. Mauna Loa, the largest active shield volcano in the world, has an elevation of 13,677 feet above sea level, but counting its rise from the ocean floor, its actual height is over 28,000 feet.
Lava dome volcano - Lassen Peak, California
Lava domes, the fourth volcano type, are formed by lava that is too viscous to flow far, so it piles up at the vent. Lava domes usually form in the craters or on the flanks of stratovolcanoes, although sometimes they stand alone. Lassen Peak in California is classified as a lava dome.
According to the US Geological Survey, the United States is one of Earth’s most volcanically active countries in the world, home to 161 potentially hazardous volcanoes. Since 1980, there have been 120 eruptions and 52 episodes of notable volcanic unrest at 44 U.S. volcanoes. The USGS Volcanic Threat Assessment combines 24 criteria (15 hazard factors and 9 exposure factors) that describe an individual volcano’s hazard potential and the exposure of people and property to those hazards. In 2018, Kilauea ranked as the U.S. volcano with the highest threat score. More on Kilauea in an upcoming blog...
Love volcanoes? Learn more about volcanoes' awesome power of creation in Volcanoes: The Fires of Creation now showing in the Dome.
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