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Evolution & Equilibrium (Grove Karl Gilbert (1871-74 Expedition to SW…
Evolution & Equilibrium
Introduction
G.K. Gilbert
Force & resistance to form equilibrium
Applied to slope processes & generating turbulence etc due to river banks/beds
William
Morris Davis
Ideas post Darwin
Landscape evolution i.e. progressive change
Functional vs evolutionary approaches
Contrasting equilibrium theories
American West Landscape
Exposed
- usefully not covered with thick soils or vegetated
Simple geology
- generally large swathes homogeneous rock units
e.g. Gooseneck State Park -
meanders incised from hard bedrock
Allowed analysis of large scale change
Powell's Grand Canyon Expedition 1869
John Wesley Powell
900 mile journey down Colorado River through Grand Canyon
Began understanding landscape formation processes
repeated
1871 & 1872
Studied geology, botany &
Native Americans culture/language
John Wesley Powell Findings
Classification of mountains & valleys
Base level theory
Aggradation
following rise in base level
Base Level
= level to which rivers erode down to
i.e. Glaciation
Drop in base level (mean sea level) due to glaciation
Rivers must erode down to ocean
Increased erosion
final stage of rivers
Aggradation
build up bed to compensate for rise in base level
streams build up their bed
via sediment accumulation
Grove Karl Gilbert
1871-74 Expedition to SW USA
1875-76 Studied Henry Mountains
Published 'Report of Henry Mountains'
Studied Lake Bonnevile, Utah
Studied effects 1906 San Fran equake
Published 'Transport of Debris by Running Water'
Hydraulic mining debris - using water to extract minerals
Grove Karl Gilbert Concepts
force & resistance
dynamic equilibrium
systems
interdependence
feedbacks btw components & input
/ propagating change
Landscape Sculpture
chapter Henry Mtns
Liquefaction wrt San Fran
solid ground behaves like liquid
William Morris Davis
1884 Cycle of Erosion presented
1889 Published Cyclic Concept in 'Rivers & Valleys of Penn'
1899 Published properly as 'The Geograhical Cyle' in Geographical Journal