Lava domes are built up when the lava is too viscous to flow, according to the U.S. It is also one of the Earth's most active volcanoes and is carefully monitored with regular updates posted by the National Park Service (opens in new tab). Mauna Loa is about 55,770 feet (17,000 m) from its base beneath the ocean to the summit, which is 13,681 feet (4,170 m) above sea level. The world's largest volcano, Mauna Loa in Hawaii, is a shield volcano, according to the U.S. Eruptions of these volcanoes are not generally explosive, but are more like liquid overflowing around the edges of a container. The gentle convex slopes give them an outline like a medieval knight’s shield. They have wide bases several miles in diameter with steeper middle slopes and a flatter summit. Shield volcanoes are huge, gently sloping volcanoes built of very thin lava spreading out in all directions from a central vent. Over the course of the day, winds blew 520 million tons of ash eastward across the United States and caused complete darkness in Spokane, Washington, 250 miles (402 km) from the volcano, according to the U.S. Approximately 230 square miles (596 square km) of forest was completely obliterated and 57 people were killed. Helens, in Washington state, is a stratovolcano that erupted on May 18, 1980. Stratovolcanoes are considered the most violent. Because they form in a system of underground conduits, stratovolcanoes may blow out the sides of the cone as well as the summit crater. When the magma reaches the conduits the pressure is released and the gases explode, according to San Diego State University. Pressure builds in the magma chamber as gases, under immense heat and pressure, are dissolved in the liquid rock. Stratovolcanoes can erupt with great violence. These more viscous lavas allow gas pressures to build up to high levels (they are effective "plugs" in the plumbing), therefore these volcanoes often suffer explosive eruptions," according to Oregon State University (opens in new tab). "Strato Volcanoes comprise the largest percentage (~60%) of the Earth's individual volcanoes and most are characterized by eruptions of andesite and dacite - lavas that are cooler and more viscous than basalt. When dormant, they typically have steep concave sides that sweep together at the top around a relatively small crater. Stratovolcanoes result from a conduit system of vents leading from a magma reservoir beneath the surface. They are larger than cinder cones, rising up to 8,000 feet (2,438 m). Stratovolcanoes are also called composite volcanoes because they are built of layers of alternating lava flow, ash and blocks of unmelted stone, according to the U.S. They can build up over short periods of a few months or years. Cinder cone volcanoes are fairly small, generally only about 300 feet (91 meters) tall and not rising more than 1,200 feet (366 m). The lava cools rapidly and fall as cinders that build up around the vent, forming a crater at the summit, according to the U.S. Airborne fragments of lava, called tephra, are ejected from a single vent. They may occur as single volcanoes or as secondary volcanoes known as "parasitic cones" on the sides of stratovolcanoes or shield volcanoes. Mount Etna Types of volcanoesĬinder cone volcanoes (also called scoria cones) are the most common type of volcano, according to San Diego State University (opens in new tab), and are the symmetrical cone-shaped volcanoes we typically think of. Magma can explode from the vent, or it can flow out of the volcano like an overflowing cup. At the boundaries of these plates - where they move past, are pushed under, or move away from each other - magma, which is lighter than the surrounding solid rock, is often able to force its way up through cracks and fissures. These plates float on a layer of magma - semi-liquid rock and dissolved gases.
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