Summary
Highlights
A volcano is defined as a mountain or hill, typically conical, with an opening through which lava, rock fragments, hot vapor, and gas are or have been erupted from the Earth's crust. Countries like the United States, Indonesia, Japan, New Zealand, and the Philippines, located along the Pacific Ring of Fire, are home to many volcanoes. The Pacific Ring of Fire is a region around the Pacific Ocean where numerous volcanic eruptions and earthquakes occur, named for the many volcanoes along its belt.
The external parts of a volcano consist of the summit, slopes, and base. The summit is the highest point or apex, featuring either a crater (a funnel-shaped opening) or a caldera (formed when part of the wall collapses after an explosive eruption). Slopes are the sides or flanks radiating from the main vent, and the base is the lower, outer part of the volcano.
Key internal features include magma, which is molten rock beneath the Earth's surface, and the magma chamber, a region where molten rock is stored before eruption. The conduit is an underground tube-like structure connecting the magma chamber to the crater. A secondary vent is an alternate pathway for magma to reach the surface. Other features are sills (hardened magma in cracks), the throat (entrance and part of the conduit ejecting lava and ash), the main vent (primary outlet for volcanic materials), parasitical cones (small cones formed by volcanic debris), lava (molten rock on the surface), and ash and gas clouds (mixtures of rock, minerals, glass particles, and gases expelled during eruption).