1. Concepts in Geomorphology

2. Geomorphology
Study of landforms

3. Includes study of current processes at work to create landforms and
the evolution of landscapes

4. Geomorphology Combo of: physical geography = landforms
surficial geology = processes

5. Landscapes or Land forms
Bedrock structure
Material properties
Tectonics
Geologic history
Landscapes or
Land forms ~
(geology, surficial processes, time) ~
Climate
Biology
Weathering
Transport
Hydrology
Controls others
erosion

6. Themes in Geomorphology
Landforms Processes
Equilibrium between landforms and processes
that create the landform as long as the processes
and their climatic and tectonic controls do not change
Equilibrium between process and form, cause and effect
Time dependent
Study deposits to
understand processes
controlling landform

7. Types of Equilibrium: Static Steady State Dynamic
Time, major factor in equilibrium

9. Dynamic Equilibrium
JT Hack – recognized there was considerable variability in driving forces over time,
leads to a dynamic equilibrium, whereby following a change in forcings
(internal or external), the system tends to re-establish a new equilibrium

10. Themes in Geomorphology
2. Driving Forces Resisting Forces
Lithology, structure
Climate, Gravity, internal heat

11. Controlling Factors
Tectonic Setting: Determines what materials are exposed at the Earth’s
surface, the manner in which they are distributed, and rate of change in
geometries within the landsurface
Climate: Determines what geological ‘agents’ are available to interact with the
exposed rocks/sediment and influences the rate of physical and chemical reactions
Geomorphic Agents and Processes: Affect how rocks and seds are eroded
Also includes biologic factors

12. Themes in Geomorphology
3. Climate Tectonics
Dominant driving forces
Control processes and landforms
Studies in “ “ Geomorphology

13. Themes in Geomorphology
4. Thresholds – limits to equilibrium conditions
Once crossed, system tends towards a new equilibrium condition
(part of the concept of Dynamic Equilibrium)
During period of adjustment process and form in disequilibrium
Extrinsic thresholds – caused by external factors (driving forces)
Intrinsic thresholds – caused by instability in a system
(due to deterioration of resisting forces
rather than driving forces)

14. separating gullied and non-gullied catchments
Relationship between valley slope and drainage area, suggesting a threshold
separating gullied and non-gullied catchments
threshold
Schumm and Hadley 1957
Patton and Schumm, 1975

15. Concept of a Geomorphic Threshold - Schumm

16. Response Time and shift to a new dynamic Equilibrium State (Bull)

17. Evolution of geomorphic thought
(foundation)
James Hutton ( ) – concept of an ancient Earth
sculpted by water
John Playfair ( ) – Law of accordant
stream junctions
Charles Lyell ( ) – Law of Uniformitarianism
Uniformity of Law, Process, Rate and State
“Present is the Key to the Past”
Louis Agassiz ( ) – Glacial geology
– erratic boulders from ice, not great flood

18. JW Powell (1834 – 1902)
– concept of base level
1869 – Exploration of the Green and Colorado River
Second Director of the USGS

19. GK Gilbert (1843 – 1918)
- interaction of driving forces of erosion and resisting forces of rocks (Equilibrium)
- relationship between present form and processes
USGS Monograph 1 – Lake Bonneville

20. WM Davis ( ) - Harvard
“cycle of erosion”
Davis 1889 The Rivers and Valleys of Pennsylvania
The father of American geography
‘time’ dependant cycles of erosion – ‘Davisian’ concept
of landscape evolution

21. JT Hack ( ) – USGS
Proposed alternative model to Davis
equilibrium as a fundamental, time-independent geomorphic model
Processes of uplift and erosion eventually reach equilibrium
“Dynamic Equilibrium”

23. Stanley A. Schumm (1927-2011) – Colorado State Univ
- Concept of Thresholds in geomorphology
- Quantitative approach