How Do Plateaus Really Form?

Question

Any time I hear the word "plateau", I usually associate it with the tallest in the world, Tibet. Anyone who looks closely at a map will see that the southern line of the plateau parallels the location and length of the Himalayas, leading to the assumption that the collision between India and mainland Asia, which resulted in the formation of the Himalayas, also forced Tibet upwards, creating the highest great plain on Earth.

But as the link here shows, it's not so simple.

The Altiplano is classified as a plateau, yet it does not span the entire length of the entire Andes, the longest mountain range in the world. Nor does the Colorado parallel the whole length of the Rockies.

So if a plateau is not formed as originally lowlands forced upwards by nearby mountain-building, then how does it REALLY form?

Answer 1

First of all, a plateau as an area of flat topography which stands at higher elevation than the surrounding region; it does not need to be at high elevation in absolute terms. Indeed, there are plateaux below sea level.

There are several different processes at the origin of the plateaux in the map you link.

Some, such as the Deccan and the Columbia plateau, are the results of infill of volcanic rocks in an accomodation space during voluminous volcanic eruptions, called "flood basalts". These flood basalts effectively flow into topographic depressions, thus flattening the topography and resulting in a plateau. Note that there are also oceanic plateaux which are formed by large magma outpours- they are usually below sea level. Examples of this are the Caribbean Oceanic Plateau and the Ontong-Java plateau.

Other plateaux such as the Altiplano and Loess plateau appear to be a result of basin infill by mainly sedimentary processes, either by water or wind transport. Past erosion removed material from topographic highs and dumped it in topographic lows, thus flattening out the relief. This is effectively a peneplenation process operating locally.

Although the high elevation of the Tibetan plateau is undoubtedly due to tectonic uplift, the cause of flat topography appears is likely to reflect relief reduction by combined erosion and deposition as above. It is unclear whether this was an ancient peneplain which was pushed upwards, or a more recent feature.