Volcanic eruptions are among the most stunning phenomena in the natural world. Volcanoes erupt because of the way heat moves beneath Earth’s surface. Heat is conveyed from the planet’s interior to its surface largely by convection—the transfer of heat by movement of a heated fluid. In this case, the fluid is magma—molten or partially molten rock—which is formed by the partial melting of Earth’s mantle and crust. In the final stage of this heat-releasing process, the magma rises and erupts as volcanoes at the surface. The majority of volcanoes are connected to plate tectonic activity. On the edges of the enormous solid rocky plates that make up the surface of the Earth, for instance, you’ll find the volcanoes of Japan, Iceland, Indonesia, and many other places. When one plate slides under another, water that is trapped in the subducted, sinking plate is squeezed out by a lot of pressure. This generates enough heat to melt nearby rock, which results in the formation of magma. Magma rises because it is buoyanter than the surrounding rock and may accumulate in chambers closer to the surface. The pressure inside a chamber may rise as it gets fuller. Cracks frequently form above when the weight of the rock above the chamber exerts less downward pressure than the rock below the chamber exerts upward pressure. The magma may eventually become lava as a result of the upward pressure pushing it through the cracks and out of surface vents. Although it is possible to use the term “volcano” to refer to the landform formed by the accumulation of solidified lava and volcanic debris close to the vent, this is not the only instance where the term “volcano” is used.
stratovolcano, volcanic landform characterized by a conical shape formed by layers of volcanic material deposited during successive volcanic eruptions. Stratovolcanoes tend to slope gently at the base but rise quickly near the summit to form tall mountain peaks. They are typically found above subduction zones, and they are often part of large volcanically active regions, such as the Ring of Fire that frames much of the Pacific Ocean. There are more than 700 known volcanoes classified as stratovolcanoes, many more than any other volcanic formation. Several are among the best-known volcanoes because of their striking appearance and their notoriety for some of the most-spectacular eruptions in history.
Development and features
volcanic landforms The landforms on the left and right are vertically overexposed, and the ones on the right are out of proportion to the ones on the left. In reality a cinder cone would be approximately one-tenth the size of a stratovolcano.(more)
Stratovolcanoes are formed by repeated eruptions and other volcanic activity over many thousands of years. A single stratovolcano can be made up of mixed layers of ash, mud, solidified lava flows, volcanic domes (large, hill-like bulges of solidified magma), and pyroclastic material (fluidized mixtures of hot rock fragments and gases that move rapidly down slopes). They are one of the most complex volcanic formations. Many researchers prefer to refer to these layers as composite volcanoes because they are deposited in varying, overlapping concentrations rather than neat strata. Because of the uneven deposition, there are now a number of vents from which magma and gas can escape. Typically, a stratovolcano has one primary vent near its peak. A crater in which debris has been blasted away during one or more previous eruptions often contains this vent. The crater may be filled with water or ice, or it may contain a volcanic dome during a period of relative inactivity. Since the vent’s location changes over time, craters are frequently unstable features. Fumaroles are one of the volcano’s other vents, and they release gas and vapor.
The andesite and dacite rocks common to stratovolcanoes produce cooler and more-viscous lavas than the basalt rocks common to shield volcanoes, which produce faster-moving and less-viscous lavas. Around the stratovolcano’s vent, thick extrusions form on previous volcanic deposits. Over thousands of years, multiple eruptions produce tall cone-shaped peaks. As magma escapes from a mountain chamber during an eruption, a significant portion of the rock above may give way, and the chamber may collapse. A caldera, a large volcanic depression in the shape of a bowl, is the result. Calderas are many times larger than the vents that often appear near the top of a stratovolcano, and they are also larger than volcanic craters.
Due to its composite structure and steep slope, the flanks of a stratovolcano are particularly susceptible to lahars, which are mudflows of volcanic material, avalanches, and landslides brought on by the collapse of significant portions of the mountain. Lahars can be the result of a volcanic eruption, heavy rain on loose ash, or an unusually rapid ice melt. Communities far from the volcano can be impacted by the massive flow of water, ash, rock, and other volcanic debris that can travel great distances. Examples of explosions Several of the most-famous volcanic disasters in history resulted from the eruptions of stratovolcanoes. The eruptions of Mount Vesuvius in 79 CE, Mount Tambora in 1815, Krakatoa in 1883, Novarupta in 1911, and Mount Pinatubo in 1991 disrupted the climate and caused enormous damage. The 1985 eruption of Mount Ruiz, a stratovolcano in the Cordillera Central of Colombia, melted the snowcap of the volcano and sent huge mudflows downslope, destroying the city of Armero and killing over 25,000 people.