Geology Reference
In-Depth Information
(c)
Figure 3.2.
(c) Spalling in granodiorite in the Snowy Mountains, New South Wales.
(a)
Figure 3.3.
(a) Scree slopes of granite blocks and fragments, Panticosa, Pyrenees, northeastern Spain.
especially susceptible, and the clitter and screes, consisting of angular blocks and plates (Fig. 3.3),
found in granitic terrains in cold regions are widely attributed to freeze-thaw alternations. Flaggy
granite (pseudobedding) is especially well-developed in cold regions and may also be an expression
of freeze-thaw activity, though the water and ice may exploit strain zones in the country rock. Various
aspects of the freeze-thaw mechanism have been questioned from time to time (White, 1973) (for
instance, pressures in adjacent partings are opposed, and only oscillations around freezing point are
effective) but the field evidence pointing to the reality of frost shattering is compelling.
Crystallisation of salts such as halite and gypsum (Bradley, Hutton and Twidale, 1972) has been
shown experimentally to exert enough force to disrupt even fresh granite. The mechanism, known
