Lava

Lava is molten rock erupted onto the surface during volcanic activity. It originates as magma stored in the crust or mantle, and becomes lava when it erupts or reaches the surface. The temperature of lava commonly ranges from about 700 to 1,200 degrees Celsius, depending on chemical composition. Lava is classified by composition into felsic (rhyolitic and andesitic) and mafic (basaltic) types, with ultramafic varieties being rare on Earth's surface. The melt can also release gases such as water vapor, carbon dioxide, and sulfur dioxide as it decompressed and ascended.

The viscosity of lava, controlled by silica content and temperature, strongly influences eruption style. Mafic, low-viscosity lava flows easily to form extensive lava flows and shield volcanoes, while higher-viscosity felsic lava tends to pile up and form lava domes and slower, blocky flows. Common surface textures for basaltic lava include pahoehoe (smooth, ropey) and aa (rough, jagged). Underwater eruptions can produce pillow lava, while highly viscous lavas may trap gases and contribute to explosive activity elsewhere in the volcanic system.

Lava can create a range of geological features, including lava tubes, caves formed by cooled crust enclosing flowing melt, and vast lava plains. It is distinct from magma, which resides underground. Hazards from lava flows include property damage and disruption of activity, though lava typically travels slower than several other volcanic hazards, such as ash plumes or pyroclastic flows. Notable examples of lava-producing volcanism occur at shield volcanoes like Kilauea and in basaltic regions such as the East African Rift.