Steps in Geomorphic Analysis and Steps in Geomorphic Analysis and PredictionPrediction

ObservationObservation DescriptionDescription ExplanationExplanation Extrapolation aka PredictionExtrapolation aka Prediction

• E.g. “What will be the response of E.g. “What will be the response of the river to this restoration the river to this restoration action?”action?”

• Specific e.g. “If I build these log Specific e.g. “If I build these log jams at these locations, will it jams at these locations, will it result in good salmon habitat?”result in good salmon habitat?”

GK Gilbert’s Method of ResearchGK Gilbert’s Method of Research

Concentrated ObservationConcentrated Observation Classification and Grouping of FactsClassification and Grouping of Facts Development of Multiple Hypotheses Development of Multiple Hypotheses

by Induction to Explain Observationsby Induction to Explain Observations• ““there is indeed an advantage to there is indeed an advantage to

entertaining several at once”, Gilbert, entertaining several at once”, Gilbert, 18861886

Hypothesis Testing (and Revising)Hypothesis Testing (and Revising)

Lake Bonneville by GK Gilbert, 1890

An example from GilbertAn example from Gilbert

Variable height of Variable height of Bonneville shorelineBonneville shoreline

Measured elevation at 2 Measured elevation at 2 locationslocations• not the samenot the same

Shoreline not horizontalShoreline not horizontal Explanation?Explanation?

• Crustal undulationCrustal undulation• Structural: FoldingStructural: Folding• FaultingFaulting

More msmtsMore msmts• max displacement near lake max displacement near lake

centercenter Isostatic reboundIsostatic rebound

Another take on multiple hypothesesAnother take on multiple hypotheses ““The studies of the geologist are peculiarly The studies of the geologist are peculiarly

complex. It is rare that his problem is a simple complex. It is rare that his problem is a simple unitary phenomenon unitary phenomenon explicable by a simple explicable by a simple single causesingle cause..

Even when it happens to be so in a given Even when it happens to be so in a given instance, or at a given stage of work, the instance, or at a given stage of work, the subject is quite sure, if pursued broadly to subject is quite sure, if pursued broadly to grade into some complication or undergo some grade into some complication or undergo some transition.transition.

If there any advantages in any field in being If there any advantages in any field in being armed with a full panoply of working armed with a full panoply of working hypotheses and in habitually employing them, hypotheses and in habitually employing them, it is doubtless the field of the geologist”it is doubtless the field of the geologist”

Chamberlin, 1897

Problem with PredictionsProblem with Predictions

Using modern (today) conditions as the Using modern (today) conditions as the basis for predictionbasis for prediction• uniformitarianismuniformitarianism

““the present is the key to the past” Geikie, the present is the key to the past” Geikie, 19051905

The assumption that natural laws are The assumption that natural laws are permanent, i.e.; under the same permanent, i.e.; under the same conditions a given cause will always conditions a given cause will always produce the same resultsproduce the same results• this assumption is required to extrapolate from this assumption is required to extrapolate from

the present to the past, and to the futurethe present to the past, and to the future

an approach to landform and landscape interpretation

10 Problems Associated with Using Modern 10 Problems Associated with Using Modern Conditions as a Basis for ExtrapolationConditions as a Basis for Extrapolation

1.1. Time: absolute duration and relativeTime: absolute duration and relative2.2. Space: scale and sizeSpace: scale and size3.3. LocationLocation4.4. Convergence (equifinality): production of similar Convergence (equifinality): production of similar

results from different processes/causesresults from different processes/causes5.5. Divergence: production of different results from Divergence: production of different results from

similar processes/causessimilar processes/causes6.6. Efficiency: variable efficacy/work done by a Efficiency: variable efficacy/work done by a

processprocess7.7. Multiplicity: multiple explanationsMultiplicity: multiple explanations8.8. Singularity: natural variability among like thingsSingularity: natural variability among like things9.9. Sensitivity: susceptibility to changeSensitivity: susceptibility to change10.10. Complexity: complex response to altered Complexity: complex response to altered

conditionsconditions

Three classes of problems:1. Scale and place2. Cause and effect3. System response

Problems of scale and place: TimeProblems of scale and place: Time

““A means of measuring change” SchummA means of measuring change” Schumm Not enough of it (for data collection)Not enough of it (for data collection)

• Records are short; life too shortRecords are short; life too short Short historyShort history

• Short-term records less variable than long-term recordsShort-term records less variable than long-term records Present physical systems (e.g. landforms, Present physical systems (e.g. landforms,

structures) are influenced by historystructures) are influenced by history Short time-span studies applied to long time span Short time-span studies applied to long time span

problems is trickyproblems is tricky ExamplesExamples

• Colorado River compactColorado River compact• Floodplain formationFloodplain formation

Law of the River, 1922Allocated 7.5M acre-feetTo the upper and lower basins

Hurst phenomenon:Persistence within a recordIe closely spaced events havea high degree of autocorrelation

Vertical accretion: short time-scale

Lateral migration: longer time-scale

Has the frequency of small debris flows increased since 1870?

Problems of scale and place: Problems of scale and place: SpaceSpace

““Three dimensional field in which Three dimensional field in which natural phenomena function and natural phenomena function and occur”, Schummoccur”, Schumm

Complexity increases as resolution Complexity increases as resolution increasesincreases• Observations made at poor resolution Observations made at poor resolution

may yield predictions of low accuracymay yield predictions of low accuracy

difficult to extrapolate from small to large

Problems of scale and place: Problems of scale and place: LocationLocation

““the site or place at which observations of natural the site or place at which observations of natural system are made” Schummsystem are made” Schumm

Can we extrapolate from one location to another?Can we extrapolate from one location to another? Response to the same event could be different Response to the same event could be different

from one location to another: e.g deglaciationfrom one location to another: e.g deglaciation• E.g., (Knox, 1983) Eastern US: rivers respond to E.g., (Knox, 1983) Eastern US: rivers respond to

deglaciation by lateral shiftdeglaciation by lateral shift• Western US: rivers respond to deglaciation by vertical Western US: rivers respond to deglaciation by vertical

change (erosion or deposition)change (erosion or deposition) Climate during glacial periodsClimate during glacial periods

• Here: cooler/wetterHere: cooler/wetter• Other places: cooler/drier; cooler/no change in precipOther places: cooler/drier; cooler/no change in precip

Problems of cause and effect: Problems of cause and effect: Convergence (Equifinality)Convergence (Equifinality)

““different processes and different different processes and different causes produce similar effect” Schummcauses produce similar effect” Schumm

Different processes produce similar Different processes produce similar looking landformslooking landforms

E.g., terrace formation (channel E.g., terrace formation (channel incision)incision)• Caused byCaused by

Change in base level: sea level rise (marine Change in base level: sea level rise (marine terraces)terraces)

Tectonics: faultingTectonics: faulting Climate change: change in sed supply/precipClimate change: change in sed supply/precip

Causes:Fan deposition and coalescenceLateral stream planation

Problems of cause and effect: Problems of cause and effect: DivergenceDivergence

““the opposite of the opposite of convergence; similar convergence; similar causes and causes and processes produce processes produce different effects” different effects” SchummSchumm

Effect of melting ice Effect of melting ice sheets on sea levelsheets on sea level• Generically, SL risesGenerically, SL rises• Actually, results are Actually, results are

variablevariable

isostatic uplift: raised shoreline

submergence

partial submergence

submergence

submergence/emergence

Fluvial DivergenceFluvial Divergencese

mi-a

rid

subhumid

humid

sem

i-ar

id

sub-humid

humid

Problems of cause and effect: Problems of cause and effect: EfficiencyEfficiency

““ratio of the work done to the energy ratio of the work done to the energy expended” Schummexpended” Schumm

““More” energy expended doesn’t More” energy expended doesn’t necessarily result in the most work necessarily result in the most work donedone

E.g., Flood effectivenessE.g., Flood effectiveness• Varies with preceding floods (event Varies with preceding floods (event

ordering)ordering) Effectiveness is greater if preceded by a large Effectiveness is greater if preceded by a large

event rather than a small oneevent rather than a small one Antecedent precipitationAntecedent precipitation

Effective Discharge: transports the Effective Discharge: transports the most sedimentmost sediment

Maximum sed yield not at max precipitation

Low

pre

cip/

low

run

off

Transport-limited

High precip/low runoffSupply-limited

Problems of cause and effect: Problems of cause and effect: Multiplicity (many)Multiplicity (many)

““multiple causes acting simultaneously and in multiple causes acting simultaneously and in combination to produce a phenomenon” Schummcombination to produce a phenomenon” Schumm

Single explanations are not sufficient in most Single explanations are not sufficient in most casescases

Multiple explanations are neededMultiple explanations are needed• Ie multiple working hypothesesIe multiple working hypotheses• Each variable provides partial explanationEach variable provides partial explanation• Each variable deals with a different aspect of the Each variable deals with a different aspect of the

phenomenonphenomenon ExamplesExamples

• Hydraulic geometryHydraulic geometry• Discharge: Q=f(drainage area)Discharge: Q=f(drainage area)

baQw

Problems of systems response: Problems of systems response: SingularitySingularity

““the condition or characteristic that the condition or characteristic that makes one thing different from others” makes one thing different from others” SchummSchumm

Randomness or unexplained variation in a Randomness or unexplained variation in a data set (Mann, 1970)data set (Mann, 1970)

Easier to make predictions for a pop’n of Easier to make predictions for a pop’n of landforms but prediction for landforms but prediction for a single onea single one is very difficultis very difficult

Problems of systems response: Problems of systems response: SensitivitySensitivity

““propensity of a system to respond to a propensity of a system to respond to a minor external change” Schummminor external change” Schumm

The change occurs at a thresholdThe change occurs at a threshold If the system is near a threshold, it is If the system is near a threshold, it is

sensitivesensitive Proximity to the threshold drives Proximity to the threshold drives

responseresponse Example, incipient motionExample, incipient motion

Problems of systems response: Problems of systems response: SensitivitySensitivity

Schumm and Khan, 1973

External and internal thresholds: External e.g.: increase in external variable (slope below) Internal e.g.: long-term weathering to slope failure (Ennis L. dam)

Problems of systems response: Problems of systems response: ComplexityComplexity

Multiple responses to a perturbationMultiple responses to a perturbation

Deposition

Example of process linkage and complex response

1959 Hebgen Lake earthquake-inducedlandslide

t0, x0

Deposition t2, x3Incision t2, x2

Incision t3, x3Locke, 1998

Deposition t3, x4

TIME t1, x1Incision t1, x2

SPACE

Problems of systems response: Problems of systems response: ComplexityComplexity

Can lead to unintended Can lead to unintended consequencesconsequences• E.g., geo-engineeringE.g., geo-engineering

““if you can’t think of three if you can’t think of three things that can go wrong then things that can go wrong then you don’t understand the you don’t understand the system” (Weinburg and system” (Weinburg and Weinburg, 1979)Weinburg, 1979)

SolutionsSolutions

What happened?What happened?• Assemble Assemble historicalhistorical information and develop a information and develop a

history of past events that can help lead to history of past events that can help lead to predictionprediction

What controls it?What controls it?• Develop an understanding of the Develop an understanding of the processesprocesses that that

operate and determine the applicable physical operate and determine the applicable physical and chemical relationshipsand chemical relationships

Where does it fit into the spectrum of this Where does it fit into the spectrum of this phenomenon?phenomenon?• CompareCompare the results in space and determine the the results in space and determine the

characteristics that exist at different locationscharacteristics that exist at different locations

““Always ask yourself Always ask yourself important questions”important questions”

- Luna Leopold- Luna Leopold