Home > Encyclopedia of Science > Volcano

• Words to Know
• How volcanoes form
• Hydrothermal Vents
• Volcanic eruptions
• Volcanic structures
• Volcanic catastrophes
• Volcanic benefits

A volcano is a hole in Earth's surface through which magma (called lava when it reaches Earth's surface), hot gases, ash, and rock fragments escape from deep inside the planet. The word volcano also is used to describe the cone of erupted material (lava and ash) that builds up around the opening.

Volcanic activity is the main process by which material from Earth's interior reaches its surface. Volcanoes played a large part in the formation of Earth's atmosphere, oceans, and continents. When Earth was new, the...