Intro to Geomorphology

Key Concepts

Geomorphology• Literally means the study of earth landforms

- Geo = Earth

- Morph=Form

- Logos= Study of

• Involves understanding ofInvolves understanding of

- Mineralogy- Structure- Tectonics- Stratigraphy- Chemistry- Physics- Meteorology & Climatology

Why Bother?• Critical toward understanding

- Climate change> systems respond differently to changes in rainfall, temperature changes, systems respond differently to changes in rainfall, temperature changes,

and changes in storm strengthand changes in storm strength

- Past tectonic activity> distinctive stratigraphic and landform features form in response to tectonicsdistinctive stratigraphic and landform features form in response to tectonics

- Engineering problems> Construction of bridges, highways, houses, etc depend on past, current andConstruction of bridges, highways, houses, etc depend on past, current and

future understanding of potentially destructive eventsfuture understanding of potentially destructive events

- Hazard assessment> map out locations that have good have high risk of potential changes map out locations that have good have high risk of potential changes

- Stratigraphy> all of the sedimentary stratigraphic record is the end product ofall of the sedimentary stratigraphic record is the end product of

geomorphic activity/ processesgeomorphic activity/ processes

Agents of Change...

GlaciersGlaciers

Rivers & OceansRivers & Oceans

WindWind

GravityGravity

And human beings...• • Significant agents of Geomorphic changeSignificant agents of Geomorphic change

- - causes changes themselvescauses changes themselves> > remove or oversteepening slopes causes mass wastingremove or oversteepening slopes causes mass wasting> > improperly operated dams and levee management cause

catastrophic failures improperly operated dams and levee management cause catastrophic failures

- - Accelerate processes already occurringAccelerate processes already occurring> > Build buildings along cliffs that are poised to failBuild buildings along cliffs that are poised to fail> > construct jettis along coastlines that are experiencing erosion

problemsconstruct jettis along coastlines that are experiencing erosion problems

Significant agents of change- > > Build buildings along cliffs that are poised to failBuild buildings along cliffs that are poised to fail> > > >

Why we are significant agents of change- - Accelerate processes already occurringAccelerate processes already occurring> > Build buildings along cliffs that are poised to failBuild buildings along cliffs that are poised to fail> > construct jettis along coastlines that are experiencing erosion problemsconstruct jettis along coastlines that are experiencing erosion problems

> > construct dams, often where they shouldn't beconstruct dams, often where they shouldn't be

Paradigms (1 of 2)

• Two end members

- 1. Evolutionary Geomorphology

> championed by William Morris Davischampioned by William Morris Davis

> part of trend toward seeing everything in light ofpart of trend toward seeing everything in light ofDarwinian Evolutionary TheoryDarwinian Evolutionary Theory> landscapes evolve throughout time, landscapes evolve throughout time,

> stage of evolution can be determined bystage of evolution can be determined byexamining the characteristics of the landscapeexamining the characteristics of the landscape

> implies that TIME is the critical factor in determining what the landscape looks likeimplies that TIME is the critical factor in determining what the landscape looks like

Davis' Landscape evolution model

(most notably identified for streams and mountains as in this example from an intro geology textbook)

(most notably identified for streams and mountains as in this example from an intro geology textbook)

Paradigms (2 of 2)

• Process Geomorphology

> > Originally proposed by G.K. GilbertOriginally proposed by G.K. Gilbert

> > Drew upon his Engineering backgroundDrew upon his Engineering background

> > landforms are a balance between resisting framework andlandforms are a balance between resisting framework andthe forces acting to alter the landscapethe forces acting to alter the landscape> > Implies that time is one component of many that affect theImplies that time is one component of many that affect theappearance of the Earthappearance of the Earth

> > Inferred that the landscape was in equilibrium Between driving forces and resisting forcesInferred that the landscape was in equilibrium Between driving forces and resisting forces

Time = 1Time = 1

Time = 0Time = 0

Time = 2Time = 2

Landscape in equilibrium- slope example from GilbertLandscape in equilibrium- slope example from Gilbert

Dynamic Equilibrium• Davisian Geomorphology & TIME as dominant factorDavisian Geomorphology & TIME as dominant factor

dominated the scientific literature until the 1960'sdominated the scientific literature until the 1960's

• John Hack proposed landscape development occurredJohn Hack proposed landscape development occurredsimilarly to the way Gilbert had espousedsimilarly to the way Gilbert had espoused

- Hack recognized, however, that there was considerableHack recognized, however, that there was considerablevariability in most geomorphic systemsvariability in most geomorphic systems

> most were in dynamic equilibriummost were in dynamic equilibrium

i.e., There is a balance between opposing forces that has considerable variation.

Once overcome, balance must be re-established under the new conditions

Equilibrium & Time

• Steady- no changes over short time

• Graded Time- small changes over longer

time- due to fluctuations in

boundary conditions• Cyclic time

- the same changes occur overtime

- as conditions dictate- Average conditions change

with time

Driving Forces in geomorphology• Climate

- - Originally recognized as an agent of change by Walther PenckOriginally recognized as an agent of change by Walther Penck

- - Ultimately driven by the Sun and incoming solar radiationUltimately driven by the Sun and incoming solar radiation(insolation) interacting with Earth’s major systems(insolation) interacting with Earth’s major systems

- - Variable at a number of temporal and spatial scalesVariable at a number of temporal and spatial scales

- - includes temperature, moisture, and pressure/wind systemsincludes temperature, moisture, and pressure/wind systems

• Gravity

- - acts in conjunction with other driving forcesacts in conjunction with other driving forces

- - determines how much work will operate on all systems determines how much work will operate on all systems

• Internal Heat

- drives plate motion and tectonic activity

- Ultimately controls potential energy for work

Work = Force (F) x distance (s)Fs = Potential Energy (PE)F=mass (m) x acceleration (a)

• on earth F=mg

Weight (W) = m x gravity (g)

In simplified terms work is related tothe amount of potential energy and themass of the stuff being transported

Resisting Framework• Rocks!

- Strength of the rocks/sediments affects the potentialprocesses that might act upon the materials

- e.g., some lithologies behave as a brittle solid, somebehave as a plastic solid

- controls processes at a variety of temporal and spatialscales

• Structure (Tectonics)

- causes zones of weakness

- causes redistribution of lithologies

- causes climatic variability

Basin and Range- Structure and geomorphology

Ridge and Valley - structure and geomorphology

San Andreas Fault on the Carrizo Plain in California

Structure, climate and geomorphology

Thresholds of Change• Implied within dynamic equilibrium

- - some variability is absorbed by the systems withoutsome variability is absorbed by the systems withoutdiscernable changesdiscernable changes

• two kinds of thresholds

- - Extrinsic= external thresholdsExtrinsic= external thresholds> > e.g., climate changese.g., climate changes

- - Intrinsic=internal to the systemIntrinsic=internal to the system> > e.g., gullying of streams? Difficult to identifye.g., gullying of streams? Difficult to identify

when and what controls thewhen and what controls the

- - some variability forces the system to changesome variability forces the system to changecreating permanent changescreating permanent changes

intrinsic thresholds.intrinsic thresholds.

Complex response• can occur at a variety of scales

- common in larger systems

• different areas in the systems respond

differently depending on a variety of factors

• some may respond in exactly the opposite way to

the same event

Stream gradient profiles adjusting to climatically driven change

Process Linkage•Operates on domino principle

•one part of a system changes, which triggers changes in another part

•Complicates what is known as “complex response”

•Example the Post Creek Cut-off of the Cache River in Southern Illinois

Process Linkage•Operates on domino principle

•one part of a system changes, which triggers changes in another part

•Complicates what is known as “complex response”

•Example the Post Creek Cut-off of the Cache River in Southern Illinois

Internal Influences• • Endogenic changesEndogenic changes

- - keep the world from progressing to a featureless ballkeep the world from progressing to a featureless ball

- - In theory this could occurIn theory this could occur

- - idea proposed by William Morris Davis called idea proposed by William Morris Davis called peneplanation peneplanation

- - doesn't happen on earth (in most areas) becausedoesn't happen on earth (in most areas) becauseinternal forces cause upliftinternal forces cause uplift

> > increases potential energyincreases potential energy

> > usually initiates changeusually initiates change

Categories of Endogenic influence• Epeirogeny

- regional uplift with minimal deformation of strata> Geomorphic responses are less than with other categories

- influenced by GEOID> equipotential surface of the Oceans

> has considerable distortions that appear as topography

> hypothetical equipotential surface called the SPHEROID

> all the minor perturbations in the surface due to interaction of allthe gravitational forces are removed

- Isostasy> adjustment of crust due to mass of rocks, sediments, & water

> elevation of continents and other crust is a function of density ofcrustal materials and the forces acting inside the earth

Geoid / Spheroid

Why worry about this?Why worry about this?• • Motion dictates geomorphic reactionMotion dictates geomorphic reaction

- - Upward vertical motionUpward vertical motion> > increases potential energy- can be used by exogenic processes to actincreases potential energy- can be used by exogenic processes to act

on the surface- see slide 13 of this seton the surface- see slide 13 of this set

- - Downward vertical motionDownward vertical motion> > decreases potential energydecreases potential energy

Isostatic equilibriumIsostatic equilibrium• • continents are in some balance with the internalcontinents are in some balance with the internalmaterialsmaterials

Exogenic Forces- Climate change

Primary influence on surface processes

Has its own subcategory called climatic geomorphology

relates climate to why certain landforms form under a given set of climate conditions

•Glacial and periglacial landforms

•Aeolian and arid region landforms

•Mass wasting landforms

•River response and form

•Coastal processes

Exogenic Forces- Climate change

Primary influence on surface processes

Has its own subcategory called climatic geomorphology

relates climate to why certain landforms form under a given set of climate conditions

•Glacial and periglacial landforms

•Aeolian and arid region landforms

•Mass wasting landforms

•River response and form

•Coastal processes

Major climatic zones influencing Earth’s surface processes

What are the dominant agents and processes likely to influence surface processes in each zone?

What are the dominant agents and processes likely to influence surface processes in each zone?

Langbein and Schumm, 1958

Climatic implications…?

Moisture distribution- where are worlds largest rivers?Moisture distribution- where are worlds largest rivers?

Maximum precipitation

August 2004 Flood Event in Death Valley, CA

Remnant debris flow deposit(s), indicating significant aggradation and then in later stages degradation during the event. Note the high water scour line above the deposit.

Remnant debris flow deposit(s), indicating significant aggradation and then in later stages degradation during the event. Note the high water scour line above the deposit.

aggradationaggradation

scour linescour line

degradationdegradation

aggradationaggradation

Climate-related geomorphologyClimate-related geomorphology

Eustasy- Changes in the volume of water in ocean basins relative to the size of the basins

Strong influence on climate AND geomorphic processes in coastal and fluvial settings

Eustasy- Changes in the volume of water in ocean basins relative to the size of the basins

Strong influence on climate AND geomorphic processes in coastal and fluvial settings