A plateau is a large, elevated landform with a relatively flat top and often steep sides. Plateaus are shaped by powerful natural forces acting over vast geological timescales, involving complex interactions within the Earth’s crust and surface processes.
Uplift and Crustal Movement
Plateaus can originate from forces deep within the Earth’s crust, causing large blocks of land to rise. One primary mechanism involves crustal shortening, where continental plates collide, leading to one block of crust thrusting over another or the folding of rock layers. This process thickens the Earth’s crust, resulting in high-altitude plateaus, such as the Tibetan Plateau, formed by the collision between the Indian and Eurasian continental plates.
Another way uplift occurs is through thermal expansion of the lithosphere. This happens when hot material, such as a mantle plume or upwelling from the asthenosphere, heats the underlying crust. The warming causes the rock to expand and the overlying surface to uniformly uplift. The high plateaus of East Africa and the Ethiopian Plateau are examples of landforms created by this thermal process.
Magma rising from the mantle can also cause the ground above to swell, leading to plateau formation. This upwelling mechanism can gradually lift large, flat areas of rock. The Colorado Plateau in the western United States has been rising steadily for over 10 million years due to such underlying mantle processes. These tectonic processes involve gradual lifting of the Earth’s crust, often over millions of years, creating elevated regions.
Volcanic Processes
Volcanic activity is another significant contributor to plateau formation, creating lava or basalt plateaus. This occurs when highly fluid basaltic lava erupts from long fissures or multiple vents. These eruptions are typically quiet due to the low viscosity of the lava, allowing it to spread widely rather than build tall volcanic cones.
Successive flows of this fluid lava accumulate over vast areas, burying pre-existing terrain. These layers solidify into thick, extensive sheets of rock, building up flat-topped, elevated landforms. Examples include the Columbia Plateau in the northwestern United States and the Deccan Traps in India, which are massive formations of solidified lava. Some lava plateaus are associated with geological hotspots, where magma continually rises from deep within the mantle.
Erosional and Dissectional Shaping
Erosion plays a dual role in shaping plateaus, both by forming them and by modifying their appearance. Erosional plateaus are created through differential erosion, where softer surrounding rock layers are worn away over geological time. This leaves behind more resistant rock, often capped by a hard, durable layer like sandstone or basalt, which protects the underlying material. This resistant caprock allows the elevated, flat-topped landform to stand prominently above the lower, eroded landscape.
Once plateaus are formed, whether by tectonic uplift or volcanic processes, they are subject to dissection by rivers and streams. These waterways cut deep valleys, gorges, and canyons into the plateau surface. This downward cutting, known as river incision, creates a rugged and incised landscape.
The Colorado Plateau, for instance, has been sculpted by the Colorado River, which carved the Grand Canyon into its elevated surface. While the initial uplift or volcanic activity creates the broad elevated area, ongoing dissection evolves the plateau’s appearance, often characterized by steep-sided features and deep river channels.