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1 Your web browser (Safari 7) is out of date. For more security, comfort and the best experience on this site: Update your browser Ignore VO L CANIC CO NE For the complete encyclopedic entry with media resources, visit: A volcanic cone is a triangle-shaped hill formed as material from volcanic eruptions piles up around the volcanic vent, or opening in Earth s crust. Most volcanic cones have one volcanic crater, or central depression, at the top. They are probably the most familiar type of volcanic mountain. Major Types of Volcanic Cones Composite cones Composite cones are some of the most easily recognizable and imposing volcanic mountains, with sloping peaks rising several thousand meters above the landscape. Also known as stratocones, composite cones are made up of layers of lava, volcanic ash, and fragmented rocks. These layers are built up over time as the volcano erupts through a vent or group of vents at the summit s crater. The eruptions that form these cones, called Plinian eruptions, are violently explosive and often dangerous. One of the most famous stratocones in the world is Mount Fuji, Japan. The tallest mountain in Japan, Mount Fuji towers 3,776 meters (12,380 feet) above the surrounding landscape. Mount Fuji last erupted in 1707, but is still considered an active volcano. Mount Rainier, Washington, is another stratocone. Mount Rainier rises 4,392 meters (14,410 feet) above sea level. Over the past half million years, Mt. 1 of 7

2 Rainier has produced a series of alternating lava eruptions and debris eruptions. These eruptions have given Mt. Rainier the classic layered structure and sloping shape of a composite cone. Unlike Mount Fuji, Mount Rainier s composite cone has been carved down by a series of glaciers, giving it a craggy and rugged shape. Cinder cones Cinder cones, sometimes called scoria cones or pyroclastic cones, are the most common types of volcanic cones. They form after violent eruptions blow lava fragments into the air, which then solidify and fall as cinders around the volcanic vent. Usually the size of gravel, these cinders are filled with many tiny bubbles trapped in the lava as it solidifies. Cinder cones stand at heights of tens of meters to hundreds of meters. Cinder cones may form by themselves or when new vents open on larger, existing volcanoes. Mauna Kea, a volcano on the American island of Hawaii, and Mount Etna, a volcano on the Italian island of Sicily, are both covered with hundreds of cinder cones. Other Types of Volcanic Cones Spatter Cones Volcanoes often eject small amounts of gaseous lava blobs into the air. These lava blobs, called spatter, are heavy and viscous. Viscosity refers to a substance s resistance to flow. In this case, it refers to the spatter s thickness. The viscosity of spatter means it often does not have time to cool before hitting the ground. The lava blobs in spatter stick together as they land, piling up to form steepsided spatter cones. Most spatter cones are very small, ranging between 1 and 5 meters (3 to 16 feet) in height, because they result from minor volcanic activity. They often form in linear groups along an eruptive fissure, or long crack, on the flank of an active volcano. A small spatter cone is called a hornito. 2 of 7

3 Spatter cones can be found in and around the Puʻu ʻŌʻō region of Mount Kilauea in Hawaii. Continuously erupting since 1983, Kilauea s volcanic activity is characterized by the fountaining of hot lava, making it the perfect incubator for spatter cones. Tuff Cones Unlike spatter cones that form from lava fountaining, tuff cones form from the interaction between rising magma and bodies of water. Tuff cones are sometimes called ash cones. When heated rapidly by lava, water flashes to steam and expands violently, fragmenting huge amounts of lava into plumes of very fine grains of ash. This ash falls around the volcanic vent, creating an ash cone. Over time, the ash weathers into a rock known as tuff. Tuff cones have steep sides and often stand between 100 and 300 meters (328 to 984 feet) high. They are much wider and have broader craters than spatter cones because they result from shallow explosions that eject materials sideways rather than upwards. Diamond Head, the famous volcano near Honolulu, Hawaii, is an enormous tuff cone. The mountain is the result of a brief volcanic eruption about 200,000 years ago. During Diamond Head s eruption period, the mountain rose from the ocean, and lava interacted with water and even a nearby coral reef. Today, Diamond Head s rim is about a kilometer (.62 mile) from the coast, and rises about 232 meters (760 feet) above sea level. Vocabulary Term 3 of 7

4 active Term volcano volcano that has had a recorded eruption since the last glacial period, about 10,000 years ago. carve verb to cut or slice through. characterize verb to describe the characteristics of something. cinder tiny bits of coarse lava. hill created by tiny bits of lava blown out of a volcano and cinder cone fallen down around the volcanic vent. Also called a scoria cone. coast edge of land along the sea or other large body of water. composite hill created by layers of volcanic lava, ash, and broken cone rock. coral reef rocky ocean features made up of millions of coral skeletons. craggy adjectiverugged or rocky. crater bowl-shaped depression formed by a volcanic eruption or impact of a meteorite. crust rocky outermost layer of Earth or other planet. debris remains of something broken or destroyed; waste, or garbage. depression indentation or dip in the landscape. eject verb to get rid of or throw out. enormous adjectivevery large. erupt verb to explode or suddenly eject material. expand verb to grow or get larger. fine adjectivevery thin. fissure narrow opening or crack. flank side of something. fragment piece or part. glacier mass of ice that moves slowly over land. gravel small stones or pebbles. 4 of 7

5 hill Term hornito land that rises above its surroundings and has a rounded summit, usually less than 300 meters (1,000 feet). small spatter cone, or mound of material ejected by a volcano. imposing adjectivelarge or very impressive. incubator location that supports the development of something. landscape the geographic features of a region. lava molten rock, or magma, that erupts from volcanoes or fissures in the Earth's surface. magma molten, or partially melted, rock beneath the Earth's surface. mountain landmass that forms as tectonic plates interact with each other. powerful, violent volcanic explosion characterized by Plinian pyroclastic flows and ejection of material high into the eruption atmosphere. hill created by tiny bits of lava blown out of a volcano and pyroclastic fallen down around the volcanic vent. Also called a cinder cone cone. recognizableadjectiveable to be identified. rock natural substance composed of solid mineral matter. rugged adjectivehaving an irregular or jagged surface. hill created by tiny bits of lava blown out of a volcano and scoria cone fallen down around the volcanic vent. Also called a cinder cone. sea level base level for measuring elevations. Sea level is determined by measurements taken over a 19-year cycle. solidify verb to make solid. spatter cone hill formed by partially liquid lava dripping and falling from a volcanic eruption. 5 of 7

6 Term steam water vapor. Strombolian mildly violent explosion of a volcano. eruption tuff type of rock formed from hardened volcanic ash. tuff cone hill formed by ash falling from a volcanic eruption. Also known as an ash cone. viscosity measure of the resistance of a fluid to a force or disturbance. volcanic ash fragments of lava less than 2 millimeters across. volcanic cone hill created by a volcanic eruption. volcanic activity that includes a discharge of gas, ash, or lava from eruption a volcano. volcanic opening in the Earth's crust where lava and gases escape vent to the Earth's surface or atmosphere. volcano an opening in the Earth's crust, through which lava, ash, and gases erupt, and also the cone built by eruptions. weather verb to change as a result of exposure to wind, rain, or other atmospheric conditions. Articles & Profiles National Geographic Magazine: On Assignment Hawai i Volcanoes National Geographic Forces of Nature: Krakatau, Indonesia Video National Geographic Video: Volcanoes 101 Websites National Geographic Environment: Volcanoes USGS: Principal Types of Volcanoes 6 of 7

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