Minor forms developed on steep slopes - Landforms and Geology of Granite Terrains - page 177

(c)

(d)

Figure 8.7. (c) Cassia City of Rocks, Idaho - the Kaiser's Helmet (Mueller and Twidale, 1988). (d) Flared

side of cleft on Pearson Islands, Great Australian Bight.

action, considered together with the likely age of the forms, cannot account for their spatial distri-
bution (for example, their occurrence at elevations of some 2,500 m above sealevel in the Sierra
Nevada, California, or in Pic Boby, Andringitra Massif, Madagascar (Vidal Romaní, Ramanohison
and Rabenandrasana, 1997), and several hundreds of metres above sealevel in the piedmonts of
residuals in central Australia (e.g. some 530 m at the base of Ayers Rock). Wind action does not
offer a satisfactory explanation for either the local preferred orientation of the steepened slopes or,
indeed, for their location in the scarp-foot zone; the latter, being moist, is commonly better vege-
tated than the surrounding plain and is for that reason protected against any possible sand blast
action. Running water fails to account for either the preferred orientation or their development on
the points of spurs (where flow diverges). The only explanation that takes account of all the evi-
dence is that the flares are a particular form of etch surface or weathering front developed in the
scarp-foot zone as a result of moisture attack on massive rocks and subsequently exposed ( Fig. 8.8).
The crucial evidence is seen at such sites as Yarwondutta Rock, Calca Quarry, Quarry Hill, and
Chilpuddie Hill, all on northwestern Eyre Peninsula, South Australia, and at Veyrières in southern
France, where incipient flared slopes, in the shape of concave sectors of the weathering front, are
present beneath the natural land surface (Figs 6.20 and 8.5b), and at various sites on Eyre
Peninsula and in the southern Yilgarn of Western Australia where a moat of weathered detritus
located around the base of residuals has been demonstrated by augering (Clarke, 1936).
The material with which the concave or flared forms are covered is not transported, introduced
detritus but grus, or granite weathered in situ . The bedrock surfaces were not formed by epigene