A volcano is a vent in Earth's crust through which molten rock, ash, and gases escape from below the surface. The word volcano comes from Vulcano, the name of an island off the coast of Italy. The ancient Romans believed that Vulcano was the home of Vulcan, their god of fire. Volcanoes are found on every continent and even on the ocean floor. There are about 1,500 potentially active volcanoes worldwide, not counting the ones that lie under the sea.
Molten rock beneath Earth's surface is called magma. When magma erupts onto the surface, it is called lava. The temperature of lava can range from about 700 degrees Celsius to 1,250 degrees Celsius. That is hot enough to melt many common metals. As lava cools and hardens, it becomes solid rock. Over time, repeated eruptions build up layers of rock, creating the familiar cone-shaped mountain that many people picture when they think of a volcano.
What is the difference between magma and lava?
The word erupts appears in the chunk above. The text says 'When magma erupts onto the surface, it is called lava.' What does 'erupts' mean in this context?
Volcanoes are named after the Roman god of fire. Can you think of other natural features named after gods or mythological figures?
Not all volcanoes look like the classic cone shape. Shield volcanoes, like those in Hawaii, are built up from many thin, flowing layers of lava. They have gentle, sloping sides. Cinder cone volcanoes are smaller and steeper, formed from ash and cinders that pile up around the vent. Stratovolcanoes, also called composite volcanoes, are built from alternating layers of lava and ash. They are the most common type and include famous volcanoes like Mount Fuji in Japan and Mount St. Helens in the United States.
Volcanoes can be active, dormant, or extinct. An active volcano is one that has erupted recently and is likely to erupt again. A dormant volcano has not erupted in a long time but could still erupt in the future. An extinct volcano is one that scientists do not expect to erupt again because it no longer has a magma supply. However, sometimes what scientists thought was an extinct volcano can surprise them. Mount St. Helens in Washington State was dormant for over 100 years before it erupted violently in 1980.
What is one difference between a shield volcano and a stratovolcano?
Why might scientists be careful about calling a volcano 'extinct'?
Mount St. Helens erupted in 1980 after being dormant for over 100 years. How do communities prepare for events that might not happen for a very long time?