The formation of a plateau requires one of the same three types of tectonic processes that create mountain ranges—volcanism, crustal shortening (by the thrusting of one block or slice of crust over another or by the folding of layers of rock), and thermal expansion. The simplest of these is thermal expansion of the lithosphere (or the replacement of cold mantle lithosphere by hot asthenosphere).
This type of plateau can form where extensive lava flows (called flood basalts or traps) and volcanic ash bury preexisting terrain, as exemplified by the Columbia Plateau in the northwestern United States, Deccan Traps of peninsular India, Laurentian plateau or The Canadian Shield and the Siberian Traps of Russia.
Volcanic plateaus are commonly associated with eruptions that occurred during the Cenozoic or Mesozoic.
Eruptions on the scale needed to produce volcanic plateaus are rare, and none seems to have taken place in recent time.
The volcanism involved in such situations is commonly associated with hot spots. The lavas and ash are generally carried long distances from their sources, so that the topography is not dominated by volcanoes or volcanic centers.
For example, the basalts of the Deccan Traps, which cover the Deccan plateau in India, were erupted 60–65 million years ago when India lay in the Southern Hemisphere, probably over the same hot spot that presently underlies the volcanic island of Reunion.
The thickness of the volcanic rock can be tens to even hundreds of metres, and the top surface of flood basalts is typically very flat but often with sharply incised canyons and valleys.
In North America the Columbia River basalts may have been ejected over the same hot spot that underlies the Yellowstone area today. Lava plateaus of the scale of those three are not common features on Earth.
Crustal shortening is the process of plateau formation by the thrusting of one block or slice of crust over another or by the folding of layers of rock.
The great heights of some plateaus, such as the Plateau of Tibet is due to crustal shortening.
Crustal shortening, which thickens the crust as described above, has created high mountains along what are now the margins of such plateaus.
Plateaus that were formed by crustal shortening and internal drainage lie within major mountain belts and generally in arid climates. They can be found in North Africa, Turkey, Iran, and Tibet, where the African, Arabian, and Indian continental masses have collided with the Eurasian continent.
When the lithosphere underlying a broad area is heated rapidly—e.g., by an upwelling of hot material in the underlying asthenosphere—the consequent warming and thermal expansion of the uppermost mantle causes an uplift of the overlying surface.
If the uplifted surface had originally been low and without prominent relief, it is likely to remain relatively flat when uplifted to a relatively uniform elevation.
The high plateaus of East Africa and Ethiopia were formed due to thermal expansion. As in parts of Africa, plateaus of that sort can be associated with volcanism and with rift valleys, but those features are not universal.