is possible in part because of the rapid rate of extrusion (over a cubic km per day per km of fissure length) and the relatively low viscosity of basaltic lava. However, the lateral extent of individual flood basalt flows is astonishing even for so fluid a lava in such quantities. It is likely that the lava spreads by a process of inflation in which the lava moves beneath a solid insulating crust, which keeps it hot and mobile. Studies of the Ginkgo flow of the Columbia River Plateau, which is thick, show that the temperature of the lava dropped by just over a distance of . This demonstrates that the lava must have been insulated by a surface crust and that the flow was laminar, reducing heat exchange with the upper crust and base of the flow. It has been estimated that the Ginkgo flow advanced 500 km in six days (a rate of advance of about 3.5 km per hour). The lateral extent of a flood basalt flow is roughly proportional to the cube of the thickness of the flow near its source. Thus, a flow that is double in thickness at its source can travel roughly eight times as far. Flood basalt flows are predominantly pāhoehoe flows, with ʻaʻā flows much less common. Eruption in flood basalt provinces is episodic, and each episode has its own chemical signature. There is some tendency for lava within a single eruptive episode to become more silica-rich with time, but there is no consistent trend across episodes. Large igneous provinces Large Igneous Provinces (LIPs) were originally defined as voluminous outpourings, predominantly of basalt, over geologically very short durations. This definition did not specify minimum size, duration, petrogenesis, or setting. A new attempt to refine classification focuses on size and setting. LIPs characteristically cover large areas, and the great bulk of the magmatism occurs in less than 1 Ma. Principal LIPs in the ocean basins include Oceanic Volcanic Plateaus (OPs) and Volcanic Passive Continental Margins. Oceanic flood basalts are LIPs distinguished from oceanic plateaus by some investigators because they do not form morphologic plateaus, being neither flat-topped nor elevated more than 200 m above the seafloor. Examples include the Caribbean, Nauru, East Mariana, and Pigafetta provinces. Continental flood basalts (CFBs) or plateau basalts are the continental expressions of large igneous provinces. Impact Flood basalts contribute significantly to the growth of continental crust. They