Weathering processes and resulting forms
257
Figure 11.15. Gnammas in or pits, of unequal development, elaborated on Miocenes sandstones. These
small closed depressions are filled up with silt-clay material. Region of Alcafiiz, Ebro Depression, Teruel
Province, Spain.
slopes, with a triangular cross section and constituting an intermediate step towards tafoni
morphologies. Their origin is due to differential weathering along joints or especially
along intersection of weakness planes, although in some cases no structural control can be
observed. They can also develop under a soil or below a mantle of alteration (Figure 11.15),
2
3
4a
4b
5
Figure 11.16. Gnammas cross sections of the Alcafiiz region, Ebro Depression, Teruel Province, Spain.
(1) Gnamma with smooth borders. (2) Gnamma in or pit. (3) Gnamma in or pan. (4a) Gnamma in with
overhanging sidewall. (4b) Asymmetrical gnamma. (5) Gnamma in armchair or armchair (Guti6rrez and
Ibafiez, 1979).