Lifted, not built
Why Are Some Mountains Flat on Top?
A plateau is not a mountain that lost its peak. It is a whole flat region that was pushed up as one piece.
-
Step 1 of 5
Height and shape are separate questions.
How high land is depends on how much it was lifted. What shape it is depends on how. Lift it evenly and it stays flat, however high it goes.
-
Step 2 of 5
Some are pushed up from below.
Hot rock rising underneath swells the crust upward like a blister. The surface is carried up without being crumpled, so it arrives at the top still flat.
-
Step 3 of 5
Some are built by floods of lava.
Very runny lava can pour out and spread for hundreds of kilometres before it cools. Enough of those, layer on layer, and the whole region ends up high and level.
-
Step 4 of 5
Rivers cut them to pieces from the edge.
A plateau's flat top is only safe until water gets a grip. Rivers cut back from the edges, leaving steep-sided valleys and flat-topped remnants standing between them.
-
Step 5 of 5
Living high up changes everything.
A plateau is cold, dry and thin-aired for its latitude. Crops, animals and the people who live there are all shaped by the height rather than the map position.
The largest plateau on Earth is high enough to change the weather for a continent, by steering the winds that bring the monsoon.
The short version
A plateau is flat land lifted high as one block, so it keeps its flat surface — until rivers cut it apart from the edges.
Try it yourself
Push a book up flat with one hand, then squeeze it from both ends. Flat top, or folded ridges.