A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava, tephra, pumice and ash.Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and periodic intervals of explosive eruptions and effusive eruptions, although some have collapsed summit craters called calderas.
Stratovolcanoes form when a conduit grows out from a pocket of magma and eventually reaches the surface. Over millions of years and countless eruptions, the magma and ash cool and settle, forming the large, summit-like volcano. Stratovolcanoes grow larger than any of the other types of volcano and some reach more than a mile in height.
Stratovolcanoes form through explosive eruptions depositing material near a central vent. The most common eruption types at stratovolcanoes are Strombolian, Vulcanian, and Plinian eruptions.
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.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.
A cinder cone is a relatively small volcano that erupts mostly chunks of a variety of basaltic lava called scoria. Eruptions are somewhat explosive, but not very. Stratovolcanoes form tall mountains and can erupt a variety of materials ranging in composition from basalt to rhyolite.
Generally speaking, the volcanoes that cause the most trouble for humankind are of the kind known as stratovolcanoes or composite volcanoes. Like other types of volcanoes, stratovolcanoes form around vents from which molten rock, or magma, reaches the Earth’s surface as lava.
Viscous lavas tend to form stratovolcanoes or lava domes. Lassen Peak in California is an example of a volcano formed from felsic lava and is actually a large lava dome. Because siliceous magmas are so viscous, they tend to trap volatiles (gases) that are present, which cause the magma to erupt catastrophically, eventually forming stratovolcanoes.
These volcanoes generally take between tens of thousands and several hundred thousand years to form. Most of the stratovolcanoes in the world that are currently active are less than 100,000 years old but some are much older, possibly over a million, such as Mount Rainier. Eruptions
Although stratovolcanoes are sometimes called composite volcanoes, volcanologists prefer to use the term stratovolcano to distinguish among volcanoes because all volcanoes of any size have a composite (layered) structure — that is, are built up from sequential outpourings of eruptive materials.
Teachers Guide to Stratovolcanoes of the World : Introduction. What is a volcano? A volcano is simply a hole or vent in Earth's crust through which molten rock, steam and other gases come forth. Scientists group volcanoes into four main kinds--cinder cones, strato- or composite volcanoes, shield volcanoes, and lava domes.