Lava plateaus are formed when a landscape is covered by lava and volcanic ash. The huge volume of volcanic materials needed to produce a lava plateau comes from an event known as a flood basalt eruption, an eruption extreme in both extent and duration.
A flood basalt eruption may last tens of thousands or even millions of years. The ash and lava produced by these large-scale eruptions is typically carried a great distance and may eventually come to cover landscapes and areas that are far from the actual eruption. Volcanic rock produced by a flood basalt eruption can be hundreds of meters thick and typically features a top surface that is very flat.
The formation of lava plateaus may also be influenced by other forces. The distinction between a plateau formed by a flood basalt eruption and one formed by the expansion of the lithosphere or crustal shorting is not always clear, as many plateaus are formed by multiple forces that may be operating simultaneously. The most well-known example of a lava plateau in the United States is the Columbia Plateau, which covers large parts of Washington State and extends all the way to the Pacific Ocean and into parts of Oregon.