Part of Hall of Planet Earth.
Effusive volcanism and plate tectonics
People associate volcanoes with spectacular explosive eruptions, yet most volcanoes erupt basalt, a fluid lava from the mantle that erupts effusively and forms flows. Most basaltic lava erupts on the ocean floor, along an undersea mountain chain called the mid-ocean ridge system. Basaltic lava also erupts at “hot spots,” where molten rock, or magma, forms in plumes of hot rock that rise from deep in the Earth to penetrate a moving plate above. Over time, a chain of volcanoes forms, such as the Hawaiian Islands, aligned along the direction of the plate’s movement.