time, space and landscape. do landscapes evolve or do they adjust to characteristic forms? w.m....
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Time, Space and Landscape
Do Landscapes Evolve or do they adjust to Characteristic Forms?
W.M. Davies – the Cycle of ErosionEvolution of Landscape
Characteristic Form
• Shift from constant degradation (reducing energy) to open system approach with balance between inputs and morphology
Process studies: ruling paradigm or selective myopia
Massive shift in time (and space) scales of investigation
Equilibrium
Continual adjustment toexternal stimuli at a range of time scales
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
Relaxation Time and Sensitivity
Sensitivity
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
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
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
• Drainage Basin Scale– Justified theoretically but also
practically/logistically
What are natural Spatial Scales?
Defining Spatial Systems - Representativeness
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!
Upscaling from the mud beneath your boots
• Issues of representativeness
• Synthetic Landscapes
• Satellite Imagery
• Isotope dating of erosion
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
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
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