Geology Reference
In-Depth Information
Models of Landscape Evolution
uplift
youth
rock-uplift rate: short-lived, constant
maturity
old age
maximum
relief
Davis
altitude of
highest divides
altitude of main
valley floors
waning
waxing
rock-uplift rate: variable
altitude of
highest divides
altitude of main
valley floors
Penck
dynamic equilibrium
rock-uplift rate: long-lived, constant
Hack
altitude of
highest divides
altitude of main
valley floors
li
constant relief
Time
Fig. 1.2 Classical models of tectonic forcing and landscape responses.
Based on the landscape response theories of (top) Davis (1899), (middle) Penck (1953), and (bottom) Hack (1975),
each panel is characterized by differences in the duration and rate of tectonic forcing (rock uplift) and by the
topographic response engendered by these different styles of rock uplift. Modified after Summerfield (1991).
Charles Darwin, it was perhaps natural to con-
ceive of landscapes as evolving from one stage
to the next. In Davis's models, tectonic forcing
is an impulsive phenomenon that occurs at the
beginning of the “geomorphic cycle.” All of the
building of topography occurs at the start of
the cycle (Fig. 1.2). Subsequently, geomorphic
processes attack and degrade the topography,
with the end-result predicted to be a peneplain.
This view of landscape evolution prevailed
through much of the 1900s and is still widely
cited by introductory geology textbooks.
A new theory of landscape development that
opposed Davis's models was promoted by
Walther Penck in the 1950s (Penck, 1953). Rather
than having all of the tectonic deformation at
the beginning of a cycle, Penck suggested a
more wave-like pattern of tectonic forcing
through time. In this scheme, the magnitude of
deformation gradually increases toward a climax
and then slowly wanes away. Instead of calling
upon an impulsive building of topography
followed by long intervals of erosion, Penck's
model invoked steadily increasing rates of defor-
mation that would accelerate rock uplift and
gradually build the topography toward a maxi-
mum state of topographic relief. Geomorphic
processes were conceived as attacking the
uplifting region throughout the period of moun-
tain building, so that the resulting landscape
could be interpreted as a product of this compe-
tition between deformation and erosion. As the
Search WWH ::




Custom Search