Geology Reference
In-Depth Information
(a)
(b)
Figure 9.12.
(a) Mushroom rock in dolomite, with massive cap and flared sidewall, and (b) cleft in dolomite
pavement showing flared sidewall, at Ciudad Encantada, near Cuenca, central Spain.
(see Fig. 8.13b), and to river erosion. The presence of an abundance of moisture and resultant
weathering near (but above) ground level has also been invoked in explanation of pedestal rocks.
In that case, pedestal rocks ought to be consistently asymmetrical because of insolational drying,
but they are not. Also, if moisture were responsible, more is retained in the regolith than on bare
rock surfaces. Shallow subsurface alteration can be expected to exceed that on outcrops. In addi-
tion, biota live in the soils and organic acids are formed there. The most probable explanation for
pedestal rocks is that the cap, structurally more resistant or not, is exposed, and is on that account
weathered less rapidly than the shaft which is in continuous contact with moisture retained in the
regolith. This suggestion finds support in the development of pedestals with flared sidewalls in
dolomite at the Ciudad Encantada, near Cuenca in central Spain, and also by the development of
such features in clefts weathered below the plateau, the level of the pedestal caprock, in the same
area (Fig. 9.12b).
