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

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Size of landslideF

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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