Lava
Lava is molten rock that reaches Earth's surface and flows or accumulates there. It cools and solidifies into volcanic rock.
Viscosity: Viscosity is a fluid’s resistance to flowing. Lava viscosity governs whether it spreads readily or piles up near its vent.
Magma: Magma is molten or partially molten rock beneath Earth's surface, often containing crystals and dissolved gases. Lava is magma that has erupted onto the surface.
Hawaiian eruption: A Hawaiian eruption is a volcanic eruption dominated by relatively fluid basaltic lava and gentle fire fountains. It commonly produces extensive, readily flowing lava.
Lava hazard: A lava hazard is the threat posed by molten rock and associated heat, gases, and volcanic activity. Lava can destroy structures and sever roads, even when it moves slowly.
Pyroclastic flow: A pyroclastic flow is a fast, ground-hugging current of hot gas, ash, and volcanic fragments. Unlike lava, it is a turbulent mixture of gas and particles rather than a coherent molten flow.
Silica: Silica is the compound silicon dioxide, a major component of many rocks and minerals. Higher silica content generally increases lava’s viscosity.
Basalt: Basalt is a dark, fine-grained volcanic rock low in silica and rich in iron and magnesium. Basaltic lava is typically fluid enough to travel far from its vent.
Pāhoehoe: Pāhoehoe is basaltic lava with a smooth, billowy, or ropy surface. Its distinctive skin forms while fluid lava continues moving beneath it.
Lava diversion: Lava diversion is the use of barriers or other measures to redirect a lava flow. Attempts to protect settlements depend on the flow’s behavior and local terrain.
Lahar: A lahar is a destructive flow of water-saturated volcanic debris moving down a volcano's slopes or river valleys. It can resemble a lava flow from a distance but contains water and loose sediment.