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Two Landscape Evolution Theories (Davisian Cycle of Erosion (Low relief…
Two Landscape Evolution Theories
Henry Mountains
Surrounded by peneplains either side
Pluton laccolith intrusion
less dense than surrounding rock
granite solidifiesin crust & either
doming overlying crust results
surface erodes down to expose
Peneplain
low relief, non-constructional plain
implies near final stage of fluvial erosion
during times of extended tectonic stability
Erosion
theory
Steeper slope
greater erosion rate - water moves faster
Interdependence
Changing one component affects others
Change propagates to other channels & basins
Q change causes erosion rate above increase & below decrease
Dynamic Equilibrium
Downward wear ceases
when load = transportation capacity
Lateral erosion predominates as slope decreases
(as vertical erosion decreases)
Landscapes become planated (flat)
Gilbert argued this mechanism formed flat landscapes in Utah - Monument Valley etc
Dynamic equilibrium reached over time across landscape
River in perfect equilibrium simply transports load --> no dep/erosion
Idealised - equilibrium can be upset by small changes in the system i.e. by deposition
Knickpoints
Relict features
Record change in base level
propagating backward through system
Davis' Approach
Landforms = f (structure, process & stage)
Evolutionary thinking
in sense of life cycle / embryo
Darwinian
Time = important factor
wrt stage of development
youthful period, older mature period
Davisian Cycle of Erosion
Low relief landsurface rapidly uplifted
(Hutton's cycle uplift-erosion-uplift)
Youthful landscape
--> initial incision by water running down hills
Maturity with maximum relief
--> steepening of sides, transport material away
Late maturity with lowered divides
--> slopes decrease as approach
base level & erosion ceases
Old age - flat peneplains develop
Rejuvenation
--> new phase of surface uplift & cycle restarts as surface once again in disequilibrium vs base level
Base level
limit of no further erosion