Other granitic residuals and uplands - Landforms and Geology of Granite Terrains - page 159

(a)

(b)

Figure 7.11. (a) Suggested evolution of conical residuals. (b) Tower tending to acute cone-shape in granite

surrounded by periglacial scree from Pit ~ es das Junhas, Serra do Geres, northern Portugal/
southern Galicia, Spain.

inclined fracture sets. The borrageiros or koppies, with which they are spatially associated, are found
in coarse-grained granites. Both conical and castellated forms are of two-stage origin.

7.1.4 Towers and acuminate forms
Towers due to the exploitation, most commonly by frost action, of prominent steeply inclined frac-
tures are found in the eastern Sierra Nevada, California (Bateman and Wahrhaftig, 1966), around
Mt Whitney, in southern Greenland, in the Tassili of the central Sahara, in the Organ Mountains of
southern New Mexico, in Os Pitões das Junhas, northern Portugal/southern Galicia, Spain, in the
Patagonian Andes (with the Cerro Torre prominent) in Argentina and in Sabah, East Malaysia ( Fig.
7.12) . The Organ Mountains stand in a midlatitude desert landscape, but are high enough to attract
snow and ice in winter. The Tassili examples stand at high elevations and may have been cold
enough in glacial periods of the Pleistocene to induce nival action. Though close to the Equator,
northeastern Sabah, standing more than 4000 m above sealevel was sufficiently cold in glacial
times of the later Cainozoic for nival processes to produce prominent acuminate peaks ( Fig. 7.12c).
Elsewhere, towers of rock rather than domes or koppies protrude above the general level of the
massif or slope. Cathedral Rocks, in the Yosemite of California, are a good example (Huber, 1987 and
see Fig. 7.13 ). Again, well-developed vertical or near vertical fractures have been exploited.