A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic explosive eruptions and quiet eruptions, although there are some with collapsed craters calledcalderas. The lava that flows from stratovolcanoes typically cools and hardens before spreading far due to high viscosity. The magma forming this lava is often felsic, having high-to-intermediate levels of silica (as in rhyolite, dacite, or andesite), with lesser amounts of less-viscous mafic magma.
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Lassen Peak is an example of what is called a "volcanic dome".The most recent eruptive activity occurred at Lassen Peak in 1914-1917. The eruption began on May 30, 1914, with a small vent near the summit of the peak. More than 150 explosions of various sizes occurred during the following year. By mid-May 1915, the eruption changed in character, and lava began to flow over the east crater walls. Lava on the upper east side of Lassen Peak on May 19 resulted in an avalanche of hot rock onto a snowfield. A lahar was generated that reached more than 18 miles down Lost Creek.
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Mount Etna is an active stratovolcano on the east coast of Sicily, Italy, close to Messina and Catania. It lies above the convergent plate margin between the African Plate and the Eurasian Plate. It is the tallest active volcano on the European continent, currently 3,329 m (10,922 ft) high, though this varies with summit eruptions. It is the highest mountain in Italy south of the Alps.Mt. Etna is Europe's largest active volcano. The last major eruption of Mt. Etna occurred in 1992.
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Mount St. Helens is an active stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States. It is 96 miles (154 km) south of Seattle, Washington, and 50 miles (80 km) northeast of Portland, Oregon. Mount St. Helens takes its English name from the British diplomat Lord St Helens, a friend of explorer George Vancouver who made a survey of the area in the late 18th century. The volcano is located in the Cascade Range and is part of the Cascade Volcanic Arc, a segment of the Pacific Ring of Fire that includes over 160 active volcanoes. This volcano is well known for its ash explosions and pyroclastic flows.