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Can Overthrusts Occur? Can Mountains Buckle?
Slab A has a length, height, width, and density of L, h, w, and r, respectively. It rests on horizontal surface B and is pushed from the right. The pressure or force trying to move slab A over surface B exerts the maximum compressive stress, s, throughout the right end of slab A.
Let us make the very generous assumption that slab A is not bonded to slab B. Resisting the movement is the static friction at their interface having a coefficient of m. For motion to occur, the pushing force must exceed the resisting force, that is:
Using the density of granite 
and the values for g, m, and s from page 420, Slab A will move only if
In other words, if a slab of rock is longer than 8.2 km (about 5 miles), the compressive stress would exceed the rock’s maximum strength, so before movement could begin, crushing would occur, but only near the end being pushed. This result holds regardless of the slab’s other dimensions.
Conclusion: A rock slab longer than 5 miles cannot be pushed over unlubricated rock, so overthrusts would not occur in this fashion, and mountains would not buckle. Because both happened (for example, see Figure 48 on page 108), something lubricated the movement.
Unlike the “applied force” above, gravity applies a “body force” that acts on every atom in the rock. If gravity sliding accelerated a lubricated slab, crushing and buckling could occur (1) where the slab was relatively weak or thin or (2) near the points where the lubricant was first depleted, such as near subterranean pillars. Therefore, mountains could form within a continental-size plate.