Landscape shaping processes PDF

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Summary

Rolf Aalto
• Mass conservation
• Equilibrium
• Process-form feedbacks
• Sediment transport laws
• Equilibrium landscape forms
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Description

GEO1212 EARTH SYSTEM SCIECNE (FUTURE) TERRESTRIAL SPHERE PROF. ROLF AALTO LANDSCAPE SHAPING PROCESSES: • Mass conservation • Equilibrium • Process-form feedbacks • Sediment transport laws • Equilibrium landscape forms Principle of mass conservation -Mass cannot be created or destroyed (Antoine Lavoisier came up with this idea under normal circumstances) - Change in land surface elevation = Amount of uplift or subsidence + Balance between sediment supply and removal -Height change due to erosion = Volume removed/Surface area (m3/m2=m) Sample exam questions: Sediment budget calculations: Q1: Each year 20,000 m3 of sediment is eroded from a mountain catchment with a drainage basin area of 4 km2 * What is the net rate of surface lowering in the catchment (not considering isostatic recovery)? * What is the net rate of surface lowering in the catchment allowing for isostatic recovery of the crust? Concepts of Equilibrium: Landscapes are in equilibrium when they experience no net change in form (elevation) over time This occurs when Sediment input – sediment output + uplift = 0 OR Uplift = Denudation Applying the concept of equilibrium Long term evolution of mountains… uplift = erosion Short term evolution of rivers… Sediment in = Sediment out Implication of WM Davis’ evolutionary approach is that the landscape is never at equilibrium

Over deeper time you have a gradual decline in equilibrium Looking at a century at a time you can see droughts and floods either side of the equilibrium Looking at a time frame of a couple of months it appears that there is static equilibrium - What appears to be in steady state, changes may still be occurring but at a rate slower than the time scale of your observation

Form, process and equilibrium GK Gilbert pioneered the concept of ‘mutual adjustment between form and process’ towards equilibrium Feedback between landform and process is critical to explaining both EROSION & DEPOSITION OF SEDIMENT

FORM (SHAPE OF RIVER)

DISTRIBUTION OF WATER

TRANSPORT

The slope of a river channel: = 6.03 X 10-5 [d/A]0.6

Where = Channel slope, A= catchment area and d = median grain size.

Form- Process Feedbacks and Equilibrium Landscapes - Feedbacks can be either positive or negative - Positive feedbacks amplify initial disturbances - Negative feedbacks dampen initial disturbances Smithson et al (2008)

Fundamentals of the Physical Environment Chapter 1 (p15-19)

SUMMARY:  Environmental processes are the means by which the physical landscape is being shaped. The processes involve physical, chemical and biological reactions taking place above, at and underneath the surface of Earth. Present-day processes are governed by present-day factors, and also by factors which have been inherited from the history of the landscape being studied.  Such is the complexity of physical environments that a systems approach helps us to understand them. The use of morphological systems, cascade systems and process-response systems is well established in physical geography, and leads t studies of equilibrium, positive feedback and negative feedback which have proved useful in helping us to understand how human beings interact with their environment.  Paradigm shifts in the history of the discipline have come though the visions of key workers in the sub disciplines of geomorphology and earth history, climatology, biogeography and conservation.  Not all environmental systems behave in an equilibrium manner. Chaotic and nonequilibrium conditions exist which are completely unpredictable.

Holden (2008)

An Introduction to Physical Geography and the Environment Chapters 8 & 9 For more detail on equilibrium concepts see: Summerfield (1994) Global Geomorphology Chapter 18...