Below is the online edition of In the Beginning: Compelling Evidence for Creation and the Flood,
by Dr. Walt Brown. Copyright © Center for Scientific Creation. All rights reserved.
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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, on 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:
The values for g, m, and s are taken from page 531, and
Therefore, Slab A will move only if
In other words, if a slab of rock is longer than 12.6 km (8 miles), the compressive stress would exceed the rock’s maximum strength, so the right end would crush before movement could begin. This result holds regardless of the slab’s other dimensions.
Conclusion: A rock slab longer than 8 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 49 on page 113), something lubricated the movement.
Unlike the “applied force” above, gravity applies a “body force” that acts on every atom in the rock. If downhill gravity-sliding accelerated a lubricated slab, crushing and buckling could occur (1) where the slab was relatively weak or thin, (2) near the points where the lubricant was first depleted, or (3) where an obstacle is encountered. Therefore, mountains could form within a continental-size plate, and overthrusting could occur.