Lava of basaltic composition which is erupted from a laterally continuous fissure to form a widely dispersed, low aspect-ratio, flow sheet. The Roza Member of the mid-Miocene Columbia River Plateau in the USA is the largest flood basalt unit in the geologic record, comprising basalt flows with a total volume of more than 1500 km3 which have travelled up to 300 km from their source fissure. The largest individual lava flows in this member have volumes up to 700 km3.