GEOL 333 Principles of Geomorphology

Goals of this class Read landforms from topographic maps and aerial stereophotos Identify and describe landforms Discourse upon landform origin

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

Chemical Weathering and Soils

Physical Weathering and mass movement

Drainage Basins and Fluvial Processes GA18_01.pct portion of from Gabler cd; Grand Canyon, North is to the right of Kaibab Plateau, coconino plateau is left to south.

Fluvial Landforms

Eolian and Arid land geomorphology

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

Glacial erosion and landforms

Karst Processes and Landforms

Coastal Geomorphology

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)

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

Example of Coastal Bluff

La Conchita, California http://geohazards.cr.usgs.gov/html_files/gsaslide/geohaz_38.html Ca. 1995 Ca. 2005

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

Volcan Popocatéptl Volcanism – composite volcano Angle of repose Gravity Age

Volcan Iztaccíhuatl, Mexico Volcanism – composite volcano Temperature Precipitation Glaciation Gravity Basic form related to endogenic energy – volcanic activity and eruption of Lavas. Scalloping and slopes on the volcano are a result of atmospheric processes such as snowfall, low temperatures, and the formation of glaciers which are driven by gravity.

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

Gullying in the Scottish highlands; Lachniet, 2001 Example of threshold response Gullying in the Scottish highlands; Lachniet, 2001

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

Global Circulation

Precipitation vs. latitude Figure 1-5

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

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

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

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

Feedbacks Positive Negative 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  smaller x-sectional area

Next Topic: Internal Forces and Climate Read Chapter 2.