Erosion in taffoni

Sandstones in the district of Bages often display holes like in the above picture that was obtained from Els Tres Salts (Sant Fruitós de Bages) cliff. The sculptural concavities over 10 cm diameter are named in Geology taffoni or tafoni (singular taffone or tafone) from Italian. Most of the concavities in the picture are tafoni, but much smaller holes on the left of the top layer are alveoli (singular alveolus).

Both, tafoni and alveoli may be caused by the impact of thrown by the wind particles in arid climates or in the coast. However, this is not the case of the climate neither the geographical location of the district of Bages where these concavities are caused by by dissolution of the lime that once was sticking the sandstone or by growth of salts crystals (haloclasty), differential disaggregation and further erosion by water.

[photo Florenci Vallès]

See also the alveolar erosion in the Tower of Breny, a memorial monument from Roman origin in the III century, in Castellgalí