time, space and landscape. do landscapes evolve or do they adjust to characteristic forms? w.m....
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Time, Space and Landscape
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Do Landscapes Evolve or do they adjust to Characteristic Forms?
W.M. Davies – the Cycle of ErosionEvolution of Landscape
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Characteristic Form
• Shift from constant degradation (reducing energy) to open system approach with balance between inputs and morphology
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Process studies: ruling paradigm or selective myopia
Massive shift in time (and space) scales of investigation
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Equilibrium
Continual adjustment toexternal stimuli at a range of time scales
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Magnitude and FrequencyPlots of frequency of occurrence against magnitude
Size of landslide
Fre
quen
cy o
f oc
curr
ence
Size of landslideF
requ
ency
of
occu
rren
ce
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Relaxation Time and Sensitivity
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Sensitivity
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Schumm and Lichty (1965) ‘Time, Space, and Causality in Geomorphology’
Status of Variables During DesignatedTime Spans
Drainage Basin Variables Cyclic Graded Steady
1 Time I2 Initial relief I3 Geology I I I4 Climate I I I5 Vegetation D I I6 Relief above base level D I I7 Runoff and sediment yield D I I8 Drainage network Morphology D D I9 Hillslope morphology D D I10 Water and sediment flux D D D
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Time and Methodology• Seconds - Automated monitoring e.g. streamflow
• Minutes/Hours Automated or manual sampling
• Days to Year Repeat visits/Photography
• 101 years repeat aerial photography/syrvey
• 102 years tree rings/historical records
• 102-4 years radiocarbon dating
• 105-6 years Other isotopic techniques e.g. U-Series
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Time and Methodology
• Increasing Timescale– Shift from observation/measurement to
inference– Loss of resolution– Shift fromlow tech/cost to high tech/cost
• Loss of spatial resolution
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• Drainage Basin Scale– Justified theoretically but also
practically/logistically
What are natural Spatial Scales?
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Defining Spatial Systems - Representativeness
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Spatial Sampling Strategies
• Sampling often purposive - problems with statistical inference
• Necessity of stratification - recognition of scales of change e.g. vegetation/lithology
• Problems of autocorrelation
• These issues have rarely been defined formally in Geomorphology - something the Biogeographers have been better at!
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Upscaling from the mud beneath your boots
• Issues of representativeness
• Synthetic Landscapes
• Satellite Imagery
• Isotope dating of erosion
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Strategies for Scale Linkage
• Use of ratio/dimensionless data– e.g. stream flow frequency curves
• Smoothing/trend surface analysis
• Synthetic approach as described for timescales
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Linking time and Space
• Ergodic Hypothesis– Developed by Physicists observing molecular
motion….widely applied but not explicitly tested in Geomorphology
• Famous application…Savigears Cliffs– slope development after successive cut off from
wave action
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Necessary Linkage of time and Space Scales
• Cm to m ……….s to min (micro scale)
• m to km………. hours to days
• km to 102 km…….Years to 103 years (meso scale)
• 102-104 km…….104 to 105 years (macro scale)
• 105 - 106 km………..106 years