Honestly, the words “lava” and “magma” probably only come up when you’re discussing how unevenly your microwave heats your food. You know, when like half of your food is basically lava and then the other half might as well still be an ice cube? When you sit down and really give it a good think, though, people do seem to use the words “lava” and “magma” pretty interchangeably. So what’s the difference between lava and magma?
How Do Volcanoes Erupt Anyway?
You might have thought volcanoes were the coolest thing as a kid–what’s cooler than a giant mountain that also shoots fire? There’s a reason they’re almost always used as evil lairs or places where great fantasy artifacts are forged or whatever.
Anyway, you probably thought they were cool until you read about what would happen if, like, Yellowstone erupted or something. Hint: it’s bad and obliterates a lot of stuff. The ash would also block out the Sun and cool the Earth. When Pinatubo erupted in 1991 Earth was cooled by a full 1 degree Celsius. No, volcanoes will not solve global warming.
For a handful of reasons, it gets hot the closer to the center of the Earth you get. A good chunk of that is actually heat from all the way back when Earth formed like 4.5 billion years ago.
Further Reading: How Hot Is the Center of the Earth? Why Is It So Hot?
So when you get deeper into the Earth the hotter it gets–and eventually the very ground you walk on starts to melt. Here’s the thing about the melting of the crust (by the way it makes magma), magma has a greater volume than the solid rock it was before. The thing is, it has the same mass because things don’t get heavier or lighter just because they changed states of matter.
Anyway, depending on its composition the density of magma may differ–and less dense magma rises. If the magma reaches the surface because the density between where it was formed and the ground we walk on is less than the rock around it–the magma comes out and we get an eruption.
Other Ways Volcanoes Erupt
Different compositions in magma leads to andesitic magma and rhyolitic magma. The latter is really high in potassium and sodium, and occurs at a lower temperature range than andesitic magma. This changes how the magma ends up flowing both underground and above ground–but these mineral compositions also have an effect on the dissolved gas inside the magma. This can raise pressures under the crust that also causes volcanic eruptions.
Magma is also stored in magma chambers. They are filled by influxes of new magma, called magma injections. Sometimes when magma is injected into a magma chamber you also get a volcanic eruption. “Injection” makes it sound like we go and take a giant syringe and shove it into the Earth, which while definitely the plot of some Bond villain, isn’t something scientists do.
But What’s Up with Lava?
You might have picked up on our use of “magma” but not “lava.” That’s because lava is just magma–but on the surface of the Earth. That’s literally it. Outside of where you find it, there is no difference. The composition doesn’t change all that much when it leaks out of the Earth, it’s still going to kill you if you sit in it.
See if you know your volcanoes here.