A volcano is an opening in Earth's crust where lava, ash, and gases escape from below. Magma rises from the mantle through cracks and chambers. When pressure builds, it erupts. Some eruptions are gentle flows. Others are explosive, sending ash plumes into the stratosphere.

Volcanoes form in several settings. Most ring the Pacific Ocean in the Ring of Fire, where tectonic plates collide. Others form over hotspots, like Hawaii and Yellowstone, where mantle plumes rise through the crust. Underwater volcanoes create new seafloor and sometimes new islands. Iceland sits astride the Mid-Atlantic Ridge, where plates pull apart.

Volcanoes are destructive and creative. They destroy homes, farmland, and entire cities. Pompeii and Herculaneum were buried in 79 CE. Mount St. Helens flattened forests in 1980. They also enrich soil with minerals, create geothermal energy, and attract tourism. Monitoring saves lives. Seismographs, gas sensors, and satellite imagery detect unrest before eruptions. Evacuation plans depend on accurate forecasts, which remain difficult.

Common types

• Stratovolcanoes
• Shield volcanoes
• Cinder cones
• Calderas
• Submarine volcanoes