Magma vs lava — WhatDiffers

Short answer

Magma is molten rock beneath Earth’s surface. Lava is that material after it erupts onto the surface as a fluid or viscous mass. The central distinction is where the material is in the volcanic process, rather than a fixed difference in chemical composition. 1 3

An erupting body of magma can become lava, but magma does not have to erupt. It may cool and solidify underground. Eruptions can also fragment magma into particles, for which terms such as tephra or ash are more informative than lava flow. 2 4

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At a glance

Question	Magma	Lava
Where is it in the basic distinction?	Beneath Earth’s surface.	Erupted onto Earth’s surface.
Is the term one chemical recipe?	No.	No.
Can it contain crystals and gas?	Yes; magma can include melt, crystals, and dissolved gas.	Erupted material can release gas and continue crystallizing as it cools.
Must it reach the atmosphere?	No; it may remain underground.	Eruption at Earth’s surface is the boundary, not merely exposure to air.
What can it become on cooling?	Intrusive igneous rock if it solidifies underground.	Extrusive igneous rock after eruption and solidification.
Does a roof change its name?	An underground reservoir contains magma.	Lava inside a crusted lava tube is still called lava.

Definitions and eruption: 1 2 3. Rock formation: 4.

What each thing is

Magma

Magma is often pictured as a completely liquid underground lake. In fact, USGS describes it as a mixture that can contain molten rock, crystals, and dissolved gas. The liquid portion and the whole mixture are not necessarily identical in composition or physical behavior. 2

The word also does not imply that an eruption is inevitable. Magma that remains at depth can cool slowly, allowing crystals to grow into an intrusive igneous rock such as granite. 4

Lava

Lava is erupted molten material that retains the character of a continuous fluid or viscous mass. It may flow readily or move so slowly that it accumulates near a vent as a dome. “Lava” therefore does not mean only a fast-moving, glowing stream. 2 3

A lava flow can develop a solid outer crust while molten material continues moving inside. USGS calls the resulting conduits lava tubes. They illustrate why a simple “visible above ground versus hidden underground” test is incomplete. 3

Key differences

Location and eruption history define the names

Temperature alone does not determine which word applies. Nor does color or the presence of bubbles. The practical question is whether the material is still beneath the surface before eruption, or is part of an erupted body of lava. 1 3

The change in name need not imply a sudden change into a completely different chemical substance. At the same time, eruption is not physically irrelevant: gas can escape, the material can cool, and crystals can form. The same volcanic system can therefore produce material with changing properties along its route. 2

Cooling environment helps shape the resulting rock

Molten material cooling at depth generally has more time to form large crystals. Material erupted at the surface generally cools more quickly. These tendencies help explain common textural differences between intrusive and extrusive rocks, but they are not a license to identify every unknown sample from one visible feature. 4

How to tell them apart

For an account of an active volcano, follow the material’s position and history. Material stored below a vent is magma; a flow emerging from the vent is lava. A photograph of hot material without context may not reveal that history. 1 3

For a cold specimen, a rock name is usually more informative. Granite records solidification at depth, while a mapped lava flow records eruption and cooling at the surface. Simply saying “it is solid now” does not tell you where it solidified. 4

Where they overlap

Both terms concern molten rock in volcanic systems, and the same material can pass from one category to the other. This is a distinction between stages and settings, rather than two unrelated substances. Their shared origin explains why composition alone is insufficient to separate them. 1 2

Edge cases

Lava in a tube: the flow remains lava after a solid roof forms over it. Eruption history explains the terminology. 3

An old lava flow: geologists can discuss a lava flow that has stopped, cooled, and solidified. Read the context before assuming every use of the phrase describes presently molten material. 3

Explosive fragmentation: not all erupting magma becomes a coherent flow. USGS distinguishes fragments called tephra, including fine ash, from flowing lava. 2

Why the distinction exists

The names mark a significant boundary in a volcanic system: storage and movement beneath the surface versus eruption. That boundary also connects to how igneous rocks are classified and how their textures develop. 2 4

Common misconceptions

“Magma is hotter; lava is cooler.” Temperature is not the defining criterion. 1
“All magma becomes lava.” Some solidifies underground. 4
“Lava must be runny.” Viscous lava can accumulate as a dome. 2
“Any molten material below a rock roof must be magma.” A lava tube is the practical counterexample. 3

Examples

A magma reservoir beneath a volcano, lava emerging through a vent, and a cooled lava flow are successive settings that may belong to one volcanic history. Granite provides the contrasting route: magma can solidify at depth without ever becoming an erupted flow. 2 3 4

Sources

Sources consulted October 3, 2026.

US Geological Survey — What is the difference between “magma” and “lava”?. Basic location distinction.
US Geological Survey — About Volcanoes. “How do volcanoes erupt?” and “Lava Dome.”
US Geological Survey — Volcano Hazards Program Glossary. Entries for magma, lava, lava flow, lava tube, and magma chamber.
British Geological Survey — Rocks and minerals. Intrusive and extrusive igneous rocks and cooling textures.