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GEOL 333 Principles of Geomorphology

GEOL 333 Principles of Geomorphology. Dr. Matthew Lachniet Spring 2013 Chapter 1 – Process Geomorphology. Goals of this class. Identify landforms from Topographic Maps and aerial stereopairs (photographs) Identify and describe landforms

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GEOL 333 Principles of Geomorphology

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  1. GEOL 333 Principles of Geomorphology Dr. Matthew Lachniet Spring 2013 Chapter 1 – Process Geomorphology

  2. Goals of this class • Identify landforms from Topographic Maps and aerial stereopairs (photographs) • Identify and describe landforms • Understand and discourse upon the origin(s) of the landform

  3. What do you need to know for exams? • Textbook chapters are the information source of reference for exams • Lecture is only a guide • Plan at 2-4 hours of reading time per chapter

  4. Chemical Weathering and Soils

  5. Physical Weathering and mass movement

  6. Drainage Basins and Fluvial Processes

  7. Fluvial Landforms

  8. EolianProcesses and Arid land geomorphology

  9. Glaciers and glacial mechanics Aletsch Glacier, Switzerland (Lachniet, 2011)

  10. Glacial erosion and landforms

  11. Karst Processes and Landforms

  12. Coastal Geomorphology

  13. What is Geomorphology? • The study of LANDFORMS • 1) Form • 2) Process • Theoretical • Experimental • Descriptive • 3) Geology and Climate (Physical) • 4) Geography (Spatial) • 5) History (Temporal)

  14. Basic Principles of Process Geomorphology • An equilibrium (“delicate balance”) exists between landforms and processes • Balance between form and process created by interaction of force and resistance • Driving Forces and Resisting Forces • A coastal bluff in California is stable only if the driving forces (gravity, weight of sediments) is less than the resisting force (friction between particles and cohesion) • Heavy rainfall on coastal bluff increases water table (adding weight), and decreases the cohesion of the sediment, and becomes a landslide (temporary disequilibrium) • The new slope has adjusted to be closer to equilibrium

  15. Example of Coastal Bluff

  16. La Conchita, California Ca. 1995 Ca. 2005

  17. Endogenic and Exogenic processes • Endogenic processes – energy source is internal, i.e. within the Earth • Volcanism • Orogeny and Tectonics • Exogenic processes – energy source is external to the system • Gravity • Sun • Solar constant of 2.0 cal/cm2/min • Climate • The average of weather over 30+ yr • Both may combine to produce landforms

  18. Volcan Popocatéptl Volcanism – composite volcano Angle of repose Gravity Age

  19. Volcan Iztaccíhuatl, Mexico Volcanism – composite volcano Temperature Precipitation Glaciation Gravity

  20. Thresholds and Equilibrium • Thresholds represent the limits of equilibrium • Can be measured • E.g. increasing slope angle, water content, and landsliding • An extrinsic threshold is where the threshold is crossed by exogenic processes • increased rainfall on a slope already near failure • An intrinsic threshold is crossed when endogenic processes result in a decrease in resisting forces • weathering of cements that bind grains together

  21. Example of threshold response Figure 1-9 Gullying in the Scottish highlands; Lachniet, 2001

  22. Driving Forces • Solar Radiation • Insolation – amount of energy absorbed by the system • The sun drives the climate system • Main energy source for exogenic processes

  23. Global Circulation

  24. Precipitation vs. latitude Figure 1-5

  25. Driving Forces • Gravity • Equal over surface of earth • Controls processes such as fluvial action, glacial flow, tides

  26. Driving Forces • Internal Heat • Radioactive decay • Less than solar radiation heat • Causes uplift and deformation

  27. Resisting Framework • Lithology and Structure • Silicic and mafic • Igneous, metamorphic, sedimentary (consolidated and unconsolidated) • Variations in weathering due to climate and mineralogy • Faults, folds, mountains, basins • Stratigraphic variations in rock density

  28. Complex Response and Process Linkage • Threshold-crossing events initiate sequence of changes • Process Linkage • “Cascading” effects in geomorphic system • Hydraulic mining in Sierra Nevada • Increased sediment loads • Bed aggradation • Slope steepening • Increased flooding • Gradual relaxation to original state (unfinished) • “Recovery time”: time to revert to original state

  29. Feedbacks • Positive • Reinforcing • “Snowball” effect • Not judgmental! • Uplift erosion  overburden removal  uplift • Negative • Dampening • Thermostat • Flood scouring of stream channel  wider x-sectional area  slower stream velocity  more sediment aggradation  smallerx-sectional area

  30. Next Topic: Internal Forces and Climate • Read Chapter 2.

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