A feeling for patterns in rivers:understanding and reductionistic explanation

in earth science

Maarten G. KleinhansFaculty of GeosciencesDescartes Institute UU

The Young Academy (KNAW)www.geog.uu.nl/fg/mkleinhans

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This contribution1. what’s this thing called earth science?

2. unification or reduction?

3. different understanding from unif. or reduct.?

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A definition of geoscience• study the planet: phenomena, processes and their

history on and in terrestrial planets.

• historical aim: development of the planet from its earliest beginnings to its present form.

• causal aim: causes that shape the planetand that produce its distinctive objects.

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Basic logic

deductioninductionab

duct

ion

laws /generalisationsmajor premises

causes /minor premises /

initial and boundary conditions(the world as it was)

effects /consequent

outcome(the world as it is now)

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Twisting the lion’s tail

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Example: rivers (NWO-Vidi)

• why different river patterns?– explanation by reduction to physics

• how and why certain stacking of mud and sandin valleys, terraces and deltas?– explanation by unification: sequence stratigraphy

7/267/30

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Experimentation

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FOKKE & SUKKEknow what science is about...

...very impressive, dear collegue,

but does it also work in theory?

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Explanation by reduction to physics• Various channel patterns explained by:

– bar theories (Navier-Stokes + mass conservation)– numerical model for flow & morphodynamics

• physical phenomena identified in field and experiments

• theory and models supported by experiments

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Bar theory

• Analogy: spring-damper system

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Numerical physics-based modelling

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Unification: sequence stratigraphy• stratification = layering of sediment/rock layers

• sequence: order of stratification patternsvertically and spatiallyall explained by – relative sea level movements– climate change

‘long list of initial and boundary conditions’

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Seq Strat: explanation by unification• site observations (outcrop, core)

– sedimentology local environmental conditions– fossils, radiometric dating, ... rough dating

• + general regional setting– continental margin

initial morphology, relative sea level change– physical or biogenical sediment:

• drainage basin, valley, river, delta and sea floor fan• mud flat / karst, coral reef, pelagic sea floor

combine– predict for unvisited locations (oil!)– infer past climate, tectonics, relative sea level change

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sign for unidirectional current (river)

sign for waves (sea floor)

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site observations and context

rapid alterations of poorly sortedsand and gravel layers, no clay or peatsign for braided riverinterpreted as glacial Rhine

clay with some organic materialfreshwater plant speciessign for lagooninterpreted as transgressional lagoon

organic material: peatfreshwater plant speciessign for sedimentation space but no sedimentinterpreted as distal river Rhine floodplain

erosive contact with medium sandsign for fluvial sedimentationfollowing a river avulsionknown to be St Elisabeth floods (Biesbosch)

sandy delta with multiple channelsformed by river Rhinecovered by silt (floodplain deposits)

embodied skills

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idealised schematics connecting and predicting local observations

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Reductionistic components• experiments on stratification processes

local environmental reconstructionbased on patterns / signs, OK

• simplified seq strat experiments idealised cases, OK

• sedimentation / erosion laws: f (gradient) yep, gravity, OK(fluid flow, drag forces on granular materials)

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Unification or reduction?• explanation with both approaches!• ‘unification’ uses reductive components

• understanding?

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Understanding in de Regt & Dieks• phenomena understood if intelligible theory

• theory intelligible if qualitative characteristic consequences are recognised

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Qualitative characteristic consequences• reduction approach: refer to

– exemplar cases (recorded in graphs and pictures)– classical manipulative experiments and modelling– simple technical analogues (spring-damper, thermostat,

balance)• unification approach: refer to

– exemplar cases idealised in drawn abstractionspredict observations in spatial and temporal context

– classical sites– present-day analogues and (simplified experiments)

of basic sedimentary environments and sequences

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Obtaining understanding in Leonelli• skillfull and consistent use

of theories, models, methods, experiments, tools, instruments expertise

• skills: integrate– theoretical– performative (material, embodied)– social

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Skills in reduction approach• mathematical manipulation• numerical model operation• model building• measurements• instrument operation• experimentation

• repeatable and objective!

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Skills in unification approach• taste, feel, hear, hammer, drill (embodiment)• pattern recognition• draw a log at one site• connect logs into profile• identify sequences• ‘think spatially and temporally’

– just mapping? 3D mental movie of the past!

• repeatable and objective within schoolscomparable and translatable between schools

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Understanding in two approaches?for both unification and reduction approaches:

• phenomena and theories intelligible:qualitative characteristic consequences understood

• understanding obtained by training and consistent use of integrated theoretical and performative skills

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Disciplines• geomorphology,• geoscience, • geology, • physical geography, • meteorology, • environmental sciences, • climatology, • paleontology, • geochemistry,

• sequence stratigraphy• biogeology, • sedimentology, • geophysics, • physical oceanography, • civil engineering, • geological engineering, • ...

ALLALL

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idealised schematic for a sea level rise casebounding surfaces for causally connected sequence of events

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Problems of reduction• theory or model ‘simplified representation’ etc.:

– which laws from physics?– numerical issues?– how verify?

multiple auxiliarly hypotheses

• underdetermination of initial conditions:– initial and boundary conditions from data? far past?– sensitive! one-to-one comparison not sensible!– how compare patterns? how choose between models?

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But:• skills require long training• leads to specialisation and entrenchment

no understanding of other approach• same phenomena + different approaches

different answers?• unity of earth sciences in danger?

explicitly teach:– reduction and unification approaches

on one phenomenon– integration of theoretical and performative skills