Along hot spots, vast amounts of basaltic lava can flow from fissures, forming:

The answer would be flood basalt. This is the outcome of a huge volcanic eruption or sequence of eruptions that covers large expanses of land or the ocean floor with basalt lava. The development and effects of a flood basalt hinge on a variety of factors, like latitude, continental configuration, rate, volume, period of eruption, the preexisting climate state, style and location, and the biota flexibility to alteration.