Origins of Mountains - Mountain Geography: Physical and Human Dimensions - page 48

FIGURE 2.17 Schematic and simplified representation of several major types of faulting associated
with mountain building. The history of erosion of many of these scarp types is important in un-
derstanding their characteristics and history. (After Price 1981, adapted from California Geology
1971.)
FAULTED MOUNTAINS
Faulted mountains result from displacement of the Earth's surface along fracture zones
(Fig. 2.17). This movement is generally very slow, taking place in short jerks over thou-
sands to millions of years. Displacements may be in any direction whatsoever, but com-
monly one block is raised past another. Features associated with faulting include juxta-
position of different types of material, raised escarpments, local alteration or crushing
of rocks, and various sorts of surface disturbances, such as the damming or rearrange-
ment of stream flow. The forces that stretch (tension) the crust and forces that squeeze
(compress) it each produce their own characteristic forms of faulting. Tension tends to
create abrupt and spectacular fault scarps, dropping or raising crustal blocks with re-
spect to one another; this is normal faulting (Fig. 2.18). If a central block drops in rela-
tion to the land on both sides of it, a fault trough or graben (German for “grave”) res-
ults. Normal faults and grabens are characteristic of rift valleys associated with plate-
tectonic spreading centers. Fault-scarp mountains along such rift valleys that have been
invaded by the sea can rise in a spectacular array of steep slopes to over 3,000 m
(∼10,000 ft asl) high, as along the coast of the Red Sea. A block that is raised with
normal faults on both sides, such as between two grabens, is called a horst (German
for “eagle's nest”). The Rhine Valley in Germany is a graben; the Ruwenzori Mountain
Range or “Mountains of the Moon” in East Africa is an example of a horst rising from
the grabens of the African Rift system. Down-faulted grabens in rift valleys are among
the lowest places on Earth outside of ocean basins, with the Dead Sea between Israel
and Jordan being the world's deepest place on land below sea level. Death Valley in