What's the difference between magma and lava?

How it works

Deep underground, where it is very hot and the pressure is huge, some rock melts into a glowing, sticky liquid called magma, full of dissolved gas. When it flows out of a volcano onto the surface, we call it lava, and much of its gas escapes into the air.

Some lava is runny and some is thick. Runny lava flows fast and far like hot syrup and can cool into smooth, rope-like rock. Thick lava oozes slowly like toothpaste. It traps gas more easily, so it tends to cause more explosive eruptions.

As soon as lava reaches the surface it starts to cool. A crust forms on top, and the colour changes from bright orange to dark red to black rock. Sometimes the crust hardens while hot lava keeps flowing underneath, leaving behind a long tunnel called a lava tube.

Where to see it in New Zealand

On Rangitoto Island in Auckland, you can walk across fields of rough black rock: lava that flowed out a few hundred years ago and cooled. The island also has lava caves you can explore with an adult and a torch. Many of Auckland's other volcanic cones were built from old lava and scoria, a bubbly volcanic rock.

Try it together

Put a spoonful of honey straight from the fridge and a spoonful of room-temperature honey on a plate, then tilt it. Which runs faster? Cold honey is thicker and slower, just like lava stiffening as it cools, until it stops and becomes rock.