Honeycomb weathering

Honeycomb weathering, also known as fretting, cavernous weathering, alveoli weathering, or tafoni weathering, is a type of salt weathering common on coastal and semi-arid sandstones and limestones.

Cause

Salt is deposited on the surface of the rock by saltwater spray or by wind. As the salt solution evaporates the salt begins to crystallize within the pore-spaces of the rock. These salt crystals pry apart the mineral grains, leaving them vulnerable to other forms of weathering.

The cause of the characteristic honeycomb pattern is still under debate. Some geologists believe that the side walls of the alveoli may be protected from salt weathering by microscopic algae (Mustoe 1982), while others believe that case-hardening, wind and sun exposure, wetting and drying cycles or mineralogical variations within the stone may be responsible. Most likely, a combination of these factors are to blame.

Research

Honeycomb weathering has been studied using Scanning Electron Microscope (SEM) imaging, laboratory reconstruction of weathering conditions, Mass Spectroscopy, Electron Diffraction Spectroscopy (EDS) and other techniques. It has been studied extensively as it is responsible for the slow destruction of many historical sites worldwide including, the ruined city of Petra, Jordan and the sea walls of Weston-super-Mare, UK.

References

* Mustoe, G. E., 1982, The Origin of Honeycomb Weathering, "Geology Society of America Bulletin", v. 93, p. 108-115.