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in a few days and threaten the lives of many people.
A good example of an extinct volcano is Arthur’s Seat in Edinburgh, Scotland. All that is left are parts of the old cone and the vent.
A good example of a dormant volcano is Mount Ranier in the Cascade Mountains, Washington.
A good example of an active volcano is Mount St. Helens in the northwestern United States. When scientists surveyed the material of the cone before 1980, they felt that the volcano probably erupted once every hundred years or so. It had last erupted in the middle of the 19th century. Thus, although it was certainly inactive, the volcano was also certainly not extinct, and therefore must be dormant. In May 1980, with only a short period of warning, Mount St. Helens erupted in a spectacular way, devastating a wide area nearby with its glowing avalanche eruption.
Volcano
 Volcano—This satellite picture was taken in false-color to bring out the size, shape, and location of Mount Vesuvius, Italy, one of the world’s most famous volcanoes. It is in the center of the picture, appearing as an isolated circular mountain, well away from other mountain ranges.
Volcano
The name for a cone or other shape of mountain formed by volcanic eruptions.
The word volcano comes from the Italian mountain Vulcano. In ancient times this mountain was thought to be the entrance to
the underworld, which was looked after by Vulcan, the blacksmith god.
If you were asked to draw a picture of a volcano, you would probably draw one with sides that get steeper toward the top (the cone) and then draw a depression (crater) in the top. This type of volcano is the most common land volcano. Such volcanoes are called central vent volcanoes, meaning that the vent that allows the magma to reach the surface comes
from a single pipe (vent) in the center. It is also called a composite volcano because it contains both lava and ash, and a stratovolcano, because the cone contains layers, or strata, of lava and ash. The other main type of volcano erupts from long fissures. The lava from these fissure eruptions forms basalt and very broad cones. They are often called shield volcanoes.
Volcanic cones are not built in a single eruption, but are formed by hundreds of eruptions over many thousands of years. Each eruption produces ash or lava. Some of
the ash falls back down on the cone, adding a little more to the cone, while each flow of lava runs down over the sides of the cone and solidifies in tongues, like wax running from a candle.
The way that a volcano erupts affects the shape of the volcano
it produces. If the volcano always
produces runny lava, the volcanic cone will be broad and flat; but if the volcano usually explodes and produces ash and sticky lava, then a steep-sided cone will be formed.
A few volcanoes, like Mount Fuji in Japan, have a beautifully simple shape. Most volcanoes are not as elegant because, in their long histories, eruptions have blown away the tops of their cones, or eruptions have occurred out of their sides. These events make the cones less symmetrical.
The material that erupts at
the surface comes from deep underground, in a chamber filled with liquid rock under pressure.
It is called a magma chamber. The way the material comes to the surface depends on how runny the magma is and how much gas it contains. If the magma has little gas and is very runny, it will produce a fountain of runny lava
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