The figure shows a chimney falling over by its own weight. That is, there are no cables, etc., helping it down, so it tries to fall as a rotation of a rigid body. This requires the end (top) to accelerate greater than the free-fall value of g. This in turn implies there are other forces at work on it besides weight: the binding force of the mortar between the bricks. For a long enough object the force required to do this can be much larger than the mortar can produce, and you see the result.
Photo from "Fundamentals of Physics", 2nd ed., by Halliday and Resnick, Wiley.