Geology Reference
In-Depth Information
(a)
(b)
Figure 9.11.
(a) Tolmer Rocks, South East district, South Australia, showing part of large residual boulder,
moat and plinth. (b) Section showing suggested mode of development of moat and plinth.
9.3
PEDESTAL ROCKS
9.3.1
Terminology
Pedestal rocks have been reported developed in granite, sandstone, dolomite, rhyolite and basalt
(Twidale and Campbell, 1992). They are widely distributed and occur in most if not all climatic
contexts. Pedestal rocks are mushroom-shaped pillars, consisting of a cap or table supported by a
stem or shaft (Figs 8.13 and
9.12)
.
They are also known as mushroom rocks, hoodoo rocks,
Pilzfelsen, Tischfelsen, roches champignons and rocas fungiformes. They differ from the plinth
and boulder assemblage described earlier in that pedestal rocks are essentially a coherent whole,
whereas a plinth is separated from the block or boulder by an open, frequently gaping, fracture.
The boulder may be unstable (a balancing rock, balanced rock or logging stone - Fig. 5.11d), a
condition not found in pedestals.
9.3.2
Origin
The cap may be structurally resistant but this is not a necessary condition. Pedestal rocks have
been variously attributed to sandblasting by ice crystals which may be correct in hyper-arid warm
and cold deserts, though the wind almost certainly exploits bedrock weaknesses due to weathering
