Prerequisites for the formation of earth pyramids are certain properties of the material (relative fine-grainedness, low but not too low consolidation), the climate (regular rainfall), a wind-protected location and the occurrence of larger stones or boulders made of erosion-resistant solid rock (e.g. magmatic rock). or gneiss) in the fine-grained material. In many cases, the source rock is therefore Pleistocene boulder clay or boulder clay.
The formation proceeds as follows:
The starting point for the formation of earth pyramids is the exposure of a body of sediment with corresponding properties on a relatively steep slope.
Rainwater running off the surface cuts deep furrows (flushing grooves that widen into gullies) in the slope or the sediment body. Individual blocks of solid rock, naturally occurring in the eroding body of sediment, protect the underlying fine-grained material. As a result, this erodes significantly more slowly than unprotected material. More or less high columns of fine-grained sediment remain below such a stone, partly because the wind-protected location ensures that rain can only attack directly from above.
If a pillar loses its capstone, it then erodes relatively quickly. She takes on the form of Sugar Loaf and gets smaller and smaller until she finally disappears altogether. Meanwhile, further up the slope, new cones of earth are forming (retrogressive erosion).
Source: Wikipedia