A feeling for patterns in rivers: understanding and reductionistic explanation in earth science

1. A feeling for patterns in rivers:understanding and reductionistic explanationin earth science Maarten G. Kleinhans Faculty of Geosciences Descartes Institute UU The Young Academy (KNAW) www.geog.uu.nl/fg/mkleinhans

2. This contribution • what’s this thing called earth science? • unification or reduction? • different understanding from unif. or reduct.?

3. 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.

4. abduction induction deduction Basic logic causes / minor premises / initial and boundary conditions (the world as it was) effects / consequent outcome (the world as it is now) laws / generalisations major premises

5. Twisting the lion’s tail

6. 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. 7/30

9. Experimentation

10. FOKKE & SUKKE know what science is about... ...very impressive, dear collegue, but does it also work in theory?

11. 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

12. Bar theory Analogy: spring-damper system 12/30

13. Numerical physics-based modelling

14. 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’

15. Seq Strat: explanation by unification • site observations (outcrop, core) • sedimentology  localenvironmental 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

16. sign for waves (sea floor) sign for unidirectional current (river)

17. site observations and context sandy delta with multiple channels formed by river Rhine covered by silt (floodplain deposits) erosive contact with medium sand sign for fluvial sedimentation following a river avulsion known to be St Elisabeth floods (Biesbosch) organic material: peat freshwater plant species sign for sedimentation space but no sediment interpreted as distal river Rhine floodplain clay with some organic material freshwater plant species sign for lagoon interpreted as transgressional lagoon rapid alterations of poorly sorted sand and gravel layers, no clay or peat sign for braided river interpreted as glacial Rhine embodied skills

18. idealised schematics connecting and predicting local observations

19. 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)

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

21. Understanding in de Regt & Dieks • phenomena understood if intelligible theory • theory intelligible if qualitative characteristic consequences are recognised

22. 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

23. Obtaining understanding in Leonelli • skillfull and consistent use of theories, models, methods, experiments, tools, instruments expertise • skills: integrate • theoretical • performative (material, embodied) • social

24. Skills in reduction approach • mathematical manipulation • numerical model operation • model building • measurements • instrument operation • experimentation • repeatable and objective!

25. 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

26.  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

27. geomorphology, geoscience, geology, physical geography, meteorology, environmental sciences, climatology, paleontology, geochemistry, sequence stratigraphy biogeology, sedimentology, geophysics, physical oceanography, civil engineering, geological engineering, ... Disciplines ALL

29. idealised schematic for a sea level rise case bounding surfaces for causally connected sequence of events

30. 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?

31. 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