Skip to content
Know.itKnow.it
Create an animated lesson
On request

This article is free to read. Creating a lesson uses your daily or stored credits; review the language and settings before starting.

What is a volcano?

ScienceLesson on requestFree to read

Quick answer

A volcano is an opening in Earth's surface where molten rock, ash, and gases escape from deep underground. When the pressure of magma below builds up enough, it erupts — sometimes as gentle flows of lava, sometimes as violent explosions.

Key things to understand

  1. Beneath the surface, intense heat melts rock into magma; once it reaches the surface it's called lava.
  2. Most volcanoes form at tectonic plate boundaries, where plates pull apart or one dives beneath another.
  3. Eruptions range from slow oozing lava to explosive blasts of ash and rock, depending on the magma's thickness and gas content.
  4. Over many eruptions, volcanoes build landforms — mountains, islands, and plateaus.
  5. The 'Ring of Fire' around the Pacific Ocean holds most of the world's active volcanoes.

People also ask

What causes a volcano to erupt?
Pressure. Magma is less dense than the surrounding rock and rises; dissolved gases expand as it nears the surface, and when the pressure exceeds what the rock above can hold, it erupts.
What's the difference between magma and lava?
It's the same molten rock — 'magma' while it's still underground, and 'lava' once it has erupted onto the surface.
Are volcanoes always dangerous?
Not always. Some erupt gently and predictably, and volcanic soil is very fertile. But explosive eruptions can be deadly, releasing ash, gas, and fast-moving flows.