Magma Becomes Lava Only When It Reaches the Surface
Magma is molten rock beneath the earth's crust. The same material is called lava once it emerges from a volcano.
Magma is molten rock beneath the earth's surface. The distinction from lava is purely one of location: the same material is magma underground and lava the moment it erupts. Nothing about its composition changes at the boundary, though dissolved gases escape once the pressure drops, which is what makes eruptions explosive. Rock that cools underground from magma is *intrusive*, and granite is the familiar example.
- Molten rock underground. *A magma chamber.*
- Lava — the same material above ground. *Flowing lava.*
- Magma chamber — where it collects. *The magma chamber.*
- Intrusive rock — cooled underground. *Granite is intrusive.*
- Greek — *magma*, a thick ointment. *The source.*
Word forms
| Form | Word | Example |
|---|---|---|
| Noun | magma | Rising magma. |
| Plural | magmas | Two magmas. |
| Adjective | magmatic | Magmatic activity. |
| Related | lava | Lava. |
| Greek | magma | A thick paste. |
- Magma rose through the crust.Underground.
- It becomes lava on eruption.The distinction.
- Granite cooled slowly from magma.Rock formation.
Intrusive and extrusive rock
- Intrusive — cooled slowly underground, with large crystals
- Granite — the classic intrusive rock
- Extrusive — cooled quickly on the surface, with fine crystals
- Basalt — the classic extrusive rock
- Obsidian — cooled so fast it formed glass with no crystals at all
Greek *magma*, a thick unguent or kneaded mass, from *massein*, to knead. The geological sense dates from the 1800s.
What is the difference between magma and lava?
Location only. Molten rock is magma underground and lava once it reaches the surface.
Why do some volcanoes explode and others flow?
It depends on how much gas and silica the magma contains. Thick, gas-rich magma traps pressure until it bursts.