dec2_11
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Dec2_11TRANSCRIPT
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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?”
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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)
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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
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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
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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
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an approach to landform and landscape interpretation
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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
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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
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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
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Vertical accretion: short time-scale
Lateral migration: longer time-scale
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Has the frequency of small debris flows increased since 1870?
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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
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difficult to extrapolate from small to large
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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
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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
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Causes:Fan deposition and coalescenceLateral stream planation
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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
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Fluvial DivergenceFluvial Divergencese
mi-a
rid
subhumid
humid
sem
i-ar
id
sub-humid
humid
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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
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Effective Discharge: transports the Effective Discharge: transports the most sedimentmost sediment
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Maximum sed yield not at max precipitation
Low
pre
cip/
low
run
off
Transport-limited
High precip/low runoffSupply-limited
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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
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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
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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
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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)
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Problems of systems response: Problems of systems response: ComplexityComplexity
Multiple responses to a perturbationMultiple responses to a perturbation
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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
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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)
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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
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““Always ask yourself Always ask yourself important questions”important questions”
- Luna Leopold- Luna Leopold