Geomorphology - 3 Flashcards
Low intensity events …
Happen a lot but don’t do very much
High intensity events …
Do a lot but don’t happen very much
Leopold
1964
Bank full discharge
Maximum discharge that can be contained in a channel without over topping its banks
Dominant discharge
Single steady discharge that would produce the same morphology and dimensions as produced by the actual flow regime
Effective discharge
Discharge or range of discharges that transports the largest proportion of sediment load over the long term
Gumbel
Log distribution curve
Extreme events recorded in the landscape
Static equilibrium
Inputs and outputs are balanced
Stable equilibrium
If disturbed, landscape may recover back towards its original state
Stable equilibrium example
Linear dunes by climatic fluctuations
Vegetating
Devegetating
Moving
Re vegetating
Meta stable equilibrium
New recovery state/trend when thresholds are crossed
E.g stream transport in a landslide
Steady state equilibrium
If the system constantly fluctuates around the mean equilibrium state
Dynamic equilibrium
Mean variations around a definite trending change
Glacial Erosion
Wainwright
2006
Wainwright 2006
Is equilibrium just a metaphor ?
As equilibrium is untestable by process it functional geomorphology
Threshold definitions (2)
1) BOUNDARY CONDITIONS - where geomorphic systems change from equilibrium to disequilibrium state
2) LIMIT OF STABILITY
Threshold controlled by external factors
Extrinsic
Intrinsic threshold
Gradual changes when external factors remain constant
Geomorphic threshold
Stability of a landform itself, amount of slow accumulated change a landform can taken before it moves into a new system
Lag time
Delay between controls changing and landscape responding
Relict landform
Landforms created under previous climatic conditions
Exceeding a particular threshold can lead to more than one geomorphic process responding
What is this?
COMPLEX RESPONSE
Dominant landform events
Occur with moderate frequency and moderate magnitude
CONCEPT OF MAGNITUDE AND FREQUENCY
Events control what the landscape looks like in between events: either recovery or adjustment
CONCEPT OF EQUILIBRIUM OR STEADY STATE
Landscape response (form change) to process forcing varies
Notions of THRESHOLDS and equilibrium
Recent changes in geomorphology technologies
5
1) improved technologies for remote sensing and surveying
2) important developments of absolute dating techniques
3) advent of personal and large scale computation
4) recognition that geomorphology is a system science
5) reintegration it tectonics into geomorphology, consideration of landscape history
6) increasing dominance of human agency in modification of Earths surface
How can we stimulate the evolution of a topographic surface ?
By using a set of driving erosion and sedimentation processes
Challenges in modelling landscape change
3
- need to extrapolate geomorphical information in a landscape
- need to reconcile theories/ models with different scales
- need to integrate human impacts into landscape evolution models
Case study of human influences effecting models
1830 - 1928
200 years of extracting deposits to extract water from coal mines
West Midlands
Landscape Evolution Models
CYBEROSION
Cells define local characteristics
E.g. animal agents, human agents, soil properties
Equifinality
Notion that the same landforms may be produced by more than one mechanism
Implications of equifinality
3
1) can’t work out history of landscape in its present state
2) can attempt to work out response if you understand the process
CANT WORK OUT PROCESS FROM THE RESPONSE
3) LEMs are over simplified in dependency and condition to stop people’s own predictions
Wolman and miller
1960
Relationship between rate of transport, applied stress and frequency of stress
Wainwright 2006
Represent equilibrium as a metaphor as it is an untestable process or by functional geomorphology
Schumm
1985
Limit of stability
Boundary conditions at which geomorphic systems can change from equilibrium to disequilibrium state
Wainwright 2010
Agent based models - over come limitations of existing approaches
Grid based cellular model, identifies features that can vary through time and human interactions
Helps to understand complex landscape responses and form policy related decisions
