Flood basalts form when low-viscosity basaltic magma flows from a volcano repeatedly for a long distance, forming a lava tableland and lava plateau, from which it gets the name flood basalt. The coverage can reach 100,000 km2 with a very gentle slope gradient in the range of 2°–3°. The basalt on the Colombian Plateau in Oregon and Idaho, United States, is a typical flood basalt. It covers approximately 220,000 km2 and has an estimated volume of 195,000 km3. It formed during the Middle Miocene with an eruption period of two to three million years. The Permian Emei basalt in the border areas of Sichuan, Yunnan and Guangxi Provinces is also a type of flood basalt.