Volcanoes: Earth's Fiery Giants
A volcano is a mountain with an opening at the top that leads all the way down to melted rock. Sometimes that rock comes out.
Magma and lava: the same rock, two names
Deep inside the Earth it is hot enough to melt rock. That melted rock is called magma while it is still underground.
Sometimes magma pushes up through cracks in the Earth's crust. The moment it reaches the surface, we stop calling it magma and call it lava instead.
Same rock. The name changes when it comes out.
What an eruption throws out
A volcano erupts when the pressure from the magma below gets too strong. What comes out is not only lava:
- Lava — melted rock, flowing down the sides.
- Ash — tiny pieces of rock, like a gritty dust.
- Gas — invisible gases bubbling out.
- Rocks — sometimes large ones, blasted into the air.
Two shapes of volcano
Volcanoes do not all look alike, and the shape tells you how the volcano erupts.
- Shield volcanoes are wide with gentle slopes, built up by runny lava that spreads out a long way before it cools.
- Composite volcanoes are tall and cone-shaped with steep sides, built from alternating layers of lava and ash from explosive eruptions.
A geologist points at melted rock still deep underground. What should she call it?
- Lava, because it is melted
- Magma, because it has not reached the surface yet
- Ash, because it is still under the volcano
Volcanoes are one of the few places where you can actually watch the inside of the Earth arrive at the surface.