High alpine pyramidal peaks formed by cirque-carving glaciers very commonly (not always) have three nearly symmetrical faces and corresponding ridges spaced roughly 120 deg. apart. This is easily visible in a random search of alpine topo maps, Google Earth etc. Without conducting an exhaustive statistical study, it in fact seems to be the most common alpine shape.

Is there some principle of physics or geology that causes the erosion of the cirques to form in this regular pattern?

  • $\begingroup$ can you think of a shape with fewer facets that still makes a three dimensional shape. $\endgroup$
    – John
    Commented Mar 4, 2022 at 0:16
  • $\begingroup$ @John 1) why facets at all? 2) why not more? $\endgroup$
    – uhoh
    Commented Mar 4, 2022 at 22:02
  • $\begingroup$ @Uhoh because the shape of mountains are created by erosion which is often glacial in nature, and glaciers are movement which means a plane of movement. $\endgroup$
    – John
    Commented Mar 4, 2022 at 22:36
  • $\begingroup$ @John perhaps that can develop into an answer? $\endgroup$
    – uhoh
    Commented Mar 4, 2022 at 22:39

1 Answer 1


It's an expression of what my lecturers used to call the rule of six, they seemed to consider it something of a natural constant. The peaks look triangular from a distance but they're actually hexagonal with three long sides and three very short sides at the apparent vertices. Why 6 sided forms are so common in nature, is a matter that has been debated for time immemorial without, to my knowledge, any answer that can be broadly applied but the phenomenon demonstrably exists; columnar jointing whether caused by cooling or physio-chemical bonding forms six sided prisms, minerals with two and three fold symmetry form six sided crystals, the cirques are effectively V shaped erosion features three of them gives you another 6 sided formation at the base of the peak as well.

  • $\begingroup$ The hexagonal-form idea is debatable, but regardless doesn't address drivers of formation. Similarly, columnar jointing and crystal formation may be results of original rock formation but does not address subsequent erosional processes. $\endgroup$ Commented Mar 10, 2022 at 22:05

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