Geology Reference
In-Depth Information
(a)
(b)
Figure 8.19.
Gutters and flutings following and diverging from fractures, Wudinna Hill, Eyre Peninsula,
South Australia: (a) general view, showing runnels draining a soil patch on upper slope
(decantation runnels), (b) detail of part of Fig. 8.19a.
Most workers have steered a middle course and attributed runnels to both mechanical and
chemical agencies. The weight of evidence favours chemical processes and especially solution.
Flows of water cause the rock to be wetted in linear zones extending downslope; chemical reac-
tions take place; subsequent flows of water remove the particles loosened by weathering and so a
linear depression or channel develops. Once formed, the channel tends to gather water, and hence
the wetting and erosional processes are augmented.
As for biotic effects, several agents and processes have been noted. Alexander (1959), for instance,
considered lichens to be all-important. She argued that lichens colonise moist linear zones and that, by
