A feeling for patterns in rivers:
understanding and reductionistic explanation
in earth science
Maarten G. Kleinhans
Faculty of Geosciences
Descartes Institute UU
The Young Academy (KNAW)
www.geog.uu.nl/fg/mkleinhans
This contribution
1. what’s this thing called earth science?
2. unification or reduction?
3. different understanding from unif. or reduct.?
2/26
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 planet
and that produce its distinctive objects.
3/26
Basic logic
abduction
causes /
minor premises /
initial and boundary conditions
(the world as it was)
laws /
generalisations
major premises
effects /
consequent
outcome
(the world as it is now)
4/26
Twisting the lion’s tail
5/26
Example: rivers
(NWO-Vidi)
• why different river patterns?
– explanation by reduction to physics
• how and why certain stacking of mud and sand
in valleys, terraces and deltas?
– explanation by unification: sequence stratigraphy
6/26
7/30
7/26
8/26
Experimentation
9/26
FOKKE & SUKKE
know what science is about...
...very impressive, dear collegue,
but does it also work in theory?
10/26
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
11/26
Bar theory
• Analogy: spring-damper system
12/26
12/30
Numerical physics-based modelling
13/26
Unification: sequence stratigraphy
• stratification = layering of sediment/rock layers
• sequence: order of stratification patterns
vertically and spatially
all explained by
– relative sea level movements
– climate change
 ‘long list of initial and boundary conditions’
14/26
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
15/26
sign for waves (sea floor)
sign for unidirectional current (river)
16/26
site observations and context
sandy delta with multiple channels
erosive by
contact
medium sand
formed
riverwith
Rhine
organic
material:
peat
sign for fluvial
sedimentation
covered
by
silt
(floodplain
deposits)
freshwater
following aplant
riverspecies
avulsion
sign
fortosedimentation
space
but (Biesbosch)
no sediment
clay
with
some
material
known
be St organic
Elisabeth
floods
interpreted plant
as distal
river Rhine floodplain
freshwater
species
sign for
lagoon of poorly sorted
rapid
alterations
interpreted
as transgressional
sand
and gravel
layers, no claylagoon
or peat
sign for braided river
interpreted as glacial Rhine
embodied skills
17/26
idealised schematics connecting and predicting local observations
18/26
Reductionistic components
• experiments on stratification processes
 local environmental reconstruction
based 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)
19/26
Unification or reduction?
• explanation with both approaches!
• ‘unification’ uses reductive components
• understanding?
20/26
Understanding in de Regt & Dieks
• phenomena understood if intelligible theory
• theory intelligible if qualitative characteristic
consequences are recognised
21/26
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 abstractions
predict observations in spatial and temporal context
– classical sites
– present-day analogues and (simplified experiments)
of basic sedimentary environments and sequences22/26
Obtaining understanding in Leonelli
• skillfull and consistent use
of theories, models, methods, experiments, tools,
instruments
 expertise
• skills: integrate
– theoretical
– performative (material, embodied)
– social
23/26
Skills in reduction approach
•
•
•
•
•
•
mathematical manipulation
numerical model operation
model building
measurements
instrument operation
experimentation
• repeatable and objective!
24/26
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 schools
comparable and translatable between schools
25/26
 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
26/26
Disciplines
•
•
•
•
•
•
•
•
•
geomorphology,
geoscience,
geology,
physical geography,
meteorology,
environmental sciences,
climatology,
paleontology,
geochemistry,
•
•
•
•
•
•
•
•
sequence stratigraphy
biogeology,
sedimentology,
geophysics,
physical oceanography,
civil engineering,
geological engineering,
...
27/26
28/26
idealised schematic for a sea level rise case
bounding surfaces for causally connected sequence of events
29/26
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?
30/26
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
31/26