Lava repeatedly flowing out of the earth's surface from cracks in the ground spreads over hundreds of square miles to build lava plateaus. The lava spillage occurs over long periods of time to slowly build up a massive plateau. In the United States, the Columbia Plateau was formed over millions of years by lava flows spreading over the land. The formation of a lava plateau is the result of basaltic lava -- dark, dense volcanic rock pouring out of cracks in the earth's surface -- rather than from the central vents of the volcano. The basalt flow is of low viscosity and does not cool quickly; these characteristics enable the lava to travel a great distance from the fissure. The repeated accumulation of lava flows causes the formation of a broad plateau.
A lava plateau has certain specific characteristics that include relatively flat land with gentle slopes. Layered structures are caused by repeated lava layer formations from volcanic eruptions over a long period of time. Land is flat, featureless, mostly devoid of soil and vegetation cover. Because of the slow cooling nature of the lava that forms the plateau, the formation of columnar jointing may take place, as in the example of the Columbia Plateau. Lava plateaus often have rivers running across the plateau. This includes the Columbia River that cuts across the Columbia Plateau. Lava plateaus also have river valleys worn into the plateau; for example, the Wardha river valley in the Deccan Plateau.
The Columbia Plateau or Columbia Basalt Plain was formed by successive basalt flows over millions of years. The earth's crust is believed to have sunk into the molten lava, leaving a depressed plain that is called the Columbia Plateau. The plateau is a wide area of flat land, gently sloping hills and steep river canyons, gorged into the plateau by the Columbia River and its tributaries. The plateau covers approximately 63,000 square miles and is bordered by the Columbia River in the north, the state of Oregon's Deschutes River in the south, the Idaho Camas Prairie in the east and the Cascade Mountains in the west.
The Deccan Plateau lies in the west-central-south region of India. It is one of the oldest land areas in the country. The plateau was formed by lava flows over a period of more than one million years. The word Deccan comes from the ancient Sanskrit language and means "south." The plateau covers an approximate land area of 300,000 square miles, is roughly triangular in shape and encompasses the states of Andhra Pradesh, Kerala, Karnataka and Tamil Nadu. On the eastern and western sides of the plateau are the Ghats, and almost all the rivers that bisect the plateau flow into the Bay of Bengal.
