geol 333 principles of geomorphology

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 PDFs are only guides• Plan for 2-4 hours of reading time per

chapter• Make your own study guides from

lectures and text

Chemical Weathering and Soils

Physical Weathering and mass movement

Drainage Basins and Fluvial Processes

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

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– Gravity– Sun

• Solar constant of 2.0 cal/cm2/min– Climate

• The average of weather over 30+ yr• Both combine to produce landforms

Volcan Popocatéptl

Volcanism – composite volcanoAngle of reposeGravityAge

Volcan Iztaccíhuatl, Mexico

Volcanism – composite volcano

TemperaturePrecipitation

GlaciationGravity

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

Example of threshold response

Gullying in the Scottish highlands; Lachniet, 2001

Driving Forces

• Incoming Solar Radiation• Insolation – amount of energy absorbed by

the system• The sun drives the climate system• Main energy source for exogenic processes

Global Circulation

Figure 1-5

Precipitation vs. latitude

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

– 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.