Magma & Lava

See how composition and temperature change the movement of magma and lava.

About Magma & Lava

Magma is molten rock underground, while lava is molten rock that reaches the surface. Composition, temperature, crystal content, and dissolved gases strongly influence whether lava flows easily or magma traps pressure.

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Kilauea Lava — Kilauea LavaLava at Kilauea shows molten rock reaching Earth's surface.

Mount St. Helens — Mount St. HelensMount St. Helens is a famous Cascade volcano shaped by explosive eruptions.

Mauna Loa — Mauna LoaMauna Loa is one of the largest active volcanoes on Earth.

Volcanic Crater — Volcanic CraterVolcanic craters form around vents where material reaches the surface.

Basaltic Magma

Basaltic magma is relatively low in silica and often quite fluid.

Andesitic Magma

Andesitic magma has intermediate composition and viscosity.

Rhyolitic Magma

Rhyolitic magma is rich in silica and can be extremely viscous.

Viscosity

Viscosity measures resistance to flow.

Dissolved Gas

Gas can remain dissolved under high pressure underground.

Crystals

Magma often contains crystals.

Lava Textures

Basaltic lava can form smooth ropy surfaces or rough broken surfaces.

Cooling

Lava solidifies into igneous rock.

Basaltic Magma

It commonly erupts at ocean ridges, hot spots, and some rift zones.

Andesitic Magma

It is common in volcanic arcs above subduction zones.

Rhyolitic Magma

Its resistance to flow can help trap gases and contribute to explosive eruptions.

Viscosity

Hotter, lower-silica melts generally flow more easily than cooler, silica-rich melts.

Dissolved Gas

As magma rises and pressure drops, gas bubbles grow, much like bubbles appearing when a carbonated drink is opened.

Crystals

Cooling history and composition determine which minerals form and how large crystals become.

Lava Textures

Hawaiian terms such as pahoehoe and aa are widely used in volcanology.

Cooling

Cooling speed, gas bubbles, chemistry, and environment produce different textures.