Fissure eruptions occur when magma reaches the surface through long linear cracks rather than a single pipe. This is the dominant form of volcanism at mid-oceanic ridges, where tectonic plates diverge. Geographically, these eruptions are responsible for the seafloor spreading process that constantly renews the ocean floor. On land, fissure eruptions create “flood basalts” that form extensive volcanic plateaus. Because the basaltic lava is highly fluid, it floods the landscape in thin, horizontal layers. This type of volcanic activity is less explosive but geographically significant for building the Earth’s most extensive igneous rock provinces.