During periods of drought, this loamy material solidifies and extremely hard surfaces are formed. A huge stone covering the mass protects the material below from rain, and over the course of several millennia a cone-shaped mound - an earth pyramid - is formed. At a certain point, the covering stone becomes unbalanced and falls to the ground. This event signals the gradual demise of the earth pyramid, which is now exposed to rain and over time becomes ever thinner and shorter, until it disappears entirely. Simultaneously, new earth pyramids are formed in the terrain to the rear.