What is lava?

Lava is molten rock that reaches Earth’s surface during a volcanic eruption. It originates from magma — molten rock stored beneath the crust — that rises through cracks or volcanic vents. When magma emerges above ground, it is called lava.

Key facts:

• Composition: Lava is mainly silicate minerals (silicon and oxygen combined with metals like iron, magnesium, calcium, sodium and potassium). Composition ranges from basaltic (low silica, more fluid) to andesitic and rhyolitic (higher silica, more viscous).
• Temperature: Typical lava temperatures range from about 700 °C to 1,200 °C (1,300–2,200 °F), depending on composition.
• Viscosity and flow: Low-silica (basaltic) lava is runny and can travel long distances; high-silica (rhyolitic) lava is thick and moves slowly, often piling up to form domes.
• Surface types: Two common Hawaiian-stage surface textures are pahoehoe (smooth, ropy) and a'a (rough, jagged). Other lavas form blocky or glassy surfaces (obsidian is volcanic glass formed when lava cools very quickly).
• Cooling and solidification: As lava cools it crystallizes into igneous rock — basalt from basaltic lava, andesite from intermediate lava, rhyolite from high-silica lava. Cooling rate affects crystal size (fast cooling → small or glassy crystals).
• Hazards and effects: Lava flows can destroy buildings, roads and vegetation but typically move slowly enough for people to evacuate. They reshape landscapes, build volcanic landforms (shield volcanoes, lava plateaus, lava domes), and create new rock and soil that can be fertile over time.
• Subaqueous and submarine lava: When lava erupts under water it cools rapidly, forming pillow lavas and volcanic glass.

In short: lava is molten rock on the surface; its chemistry and temperature determine how it behaves and what kind of volcanic rock it becomes when it cools.