Intro Flashcards
Geomorphology is the science of what?
Science of Scenery
- Study of Earth surface materials, processes and resulting landforms
- Interactions between Earth’s spheres at a variety of temporal and spacial scales
What are the spheres of interaction that geomorphology studies?
Atmosphere, Lithosphere, Hydrosphere, Cryosphere, Biosphere
What is involved in an empirical science?
Observation, measurement, description
Relevance of Geomorphology?
- Land use and planning
- Agriculture, forestry, mining, parks
- Stream/watershed management
- hydrology, flood control, water resources
Geological hazards - Volcanic hazards
- Resources for construction or mineral exploration
Geomorphology pre - 1850
- Leonardo da Vinci
- Studied topography of Arno River Northern Italy
- Drew 1st contour map of a whole river basin
- Believed rivers carved valleys and shaped topo
- Wanted to regulate river for agriculture and transport
Nicholas Steno
- Principle of original horizontality
- Law of superposition
- found shark teeth on mountains indicated SL originally higher
Law of Superposition
- Oldest at the bottom
James Hutton
- Theory of the Earth
- Uplift, erosion, consolidation of rock
- Had a lot of jobs (lawyer, chemist, physician, farming)
Sir Charles Lyell
- Uniformitarianism
- Principles of Geology in 3 volumes (1830)
- Stratigraphic principle that rock layers correlate according to fossils
- Glaciers not icebergs transport erratics
Uniformitarianism
- slow geological processes have occurred throughout history and are still occurring today
- present is the key to the past
- contrasted to accepted theory of catastrophism
Catastrophism
- theory that Earth’s features formed in a single catastrophic event and remained unchanged thereafter
- Accepted theory for a long time
- Contrasted to Lyell’s uniformitarianism
Two main geomorphic principles of Hutton and Lyell
- Landforms and landscapes evolve
- Event frequency and magnitude control landscape development
Modern Geomorphology from 1850 - 1950
- Uniformitarianism accepted but the gradualism was overstated (some events catastrophic)
- expansion of knowledge of Earth history and processes
- descriptive studies of landforms emerged (drainage basins)
Powell (1870s)
- USGS
- Colorado river exploration
- Base level of river systems
Gilbert (1878)
- Dynamic equilibrium
- Henry Mountains Utah
- Weathering, erosion, debris transport mechanisms, graded streams
- dynamic adjustment between form and process
Davis (1909), Penck (1924), King (1953)
- Cycle of Erosion
- Theories of Landscape Evolution
Cycle of Erosion
- youthful (Downcutting)
- mature (Very topographic)
- old (Eroded to bedrock, flatter)
- youthful
- Universal down-wearing to peneplain
- Increase in entropy of the system (toward equilibrium)
- uplift occurs rapidly, continuous landscape evolution through stages of erosion and decreasing slope gradients
Concept of Base Level
- The lowest elevation to which a stream can erode
- Usually coincident with sea level
Graded Stream
- over a period of years a slope is adjusted to yield the velocity required for transportation of the load supplied from the drainage basin
What were Penck and King’s contributions to the Cycle of Erosion?
- Uplift occurs gradually and continuously, not only at end of a cycle
Peneplain
final stage once base level of erosion has been reached
What was the knowledge shift in the 1950’s to present?
Shift to Process geomorphology
- Measurement based research and theory development
- Realized uniformitarianism was overstated
- understanding of processes with physics
What was the overstated uniformitarianism replaced with?
- Frequency and magnitude relations
- Equilibrium
- Thresholds
What are landforms viewed as in process geomorphology?
- Interacting Systems
- Dynamic processes of mass and energy exchange over space and time
- Landforms strive to attain equilibrium in form/function over time
- Landforms linked to larger landscape changes
Unit of measurement for frequency
Hertz, s^-1
Unit of measurement for Force
Newton, kg m s^-2
Unit of measurement for pressure, stress, momentum flux
Pascal, kg m^-1 S^-1, N m^-2
Unit of measurement for work, energy
Joule, kg m^2 s^-2, N m
Unit of measurement for power
Watt, kg m^2 s^-3, J s^-1
Force
Phenomenon causing motion of mass with both magnitude and direction
What is the driving force
vs resisting force?
moving vs keeping in place
What is an example of resisting force?
friction
What is an example of driving force?
Pressure
Newtons 2nd Law
F = m x a = Newton
- Force required to move and accelerate 1kg to 1ms^-2
- All motion results from force
Gravitational acceleration
9.81 m s^-2
Gravitational Force
9.81 kg m s^-2
Work
- Force moving mass over a certain distance in direction of applied force
- w = F x d = m x a x d
- Requires E in Joules (N m)
What are the 5 fundamental considerations of process geomorphology?
- Time
- Space
- Process
- Morphology
- Composition
Space/scale considerations
- micrometer to sub-continental scale (<10km)
- spatial distribution and morphology of features
- Temporally limited to human timescales while most large events are outside of human record
- Rely on theory and interpretation
- artificial entry point, must use care in interpreting given limited spatio-temporal perspective
What is a major limit to scale for geomorphic studies?
- Understanding complexities is difficult, especially rare events
- Many large events (EQ’s and floods happen outside of human timescale
- ex. 2013 Calgary flood had no historical record to predict severity
Time considerations
- Landforms develop over longer timespans than human
- Often focused on human timescales
- Not all are active
- Study models of present or past
- define relevant timescales
- extrapolate short records over long spans
Process considerations
- Mass and Energy drive morphodynamics
- relate form to process to explain landform dynamics and change
- But erosion eliminates past forms/processes, records discontinuous
- Rely’s on fundamental principles (uniformitarianism, stratigraphy, fluid dynamics)
Morphology considerations
- Describe, measure, model
- Link process to form using theoretical or conceptual frameworks (facies models, class schemes)
- Hypothesis then test with evidence
- Theory plus observation plus pre-existing evidence
Composition considerations
- Controlled by what is inside (Sedimentology)
Critical concepts in modern geomorph
- Delicate balance between process and landform
- Balance of driving and resisting forces
- Change in driving force can push past threshold and change landform
- Balance and thresholds are all scale dependent
What are the 2 types of temporal scales?
- Time dependent
- Time independent
Spatial and Temporal scale graph
- y-axis = increasing length (m)
- x-axis = increasing time scale (yrs)
- sand-bed streams to increased channel width and depth to gravel-bed streams to increased meander wavelength to increased reach gradient to increased profile concavity and gradient
Time-independent
- landforms are open systems constantly adjusting to inputs and outputs of matter and energy striving to attain equilibrium
- Characteristic-form models are used to describe landform states after some period of adjustment (b/c steady state is never reached)
- Gilbert’s dynamic graded stream concept
Time-dependent
- landforms adjust in response to initial disturbance or change input (climate change, tectonism)
- landforms reflect a developmental stage in a gradual evolution at increasingly slower rates (entropic)
- Davis’ cycle of erosion
Davis (1909)
“sudden” uplift then erosion
Penck (1924)
Gradual uplift then erosion
King (1953)
dominant lateral erosion not uplift
Frequency
occurrences per unit time
Magnitude
Energy used or Mass moved per unit time by a geomorphic process
- level a river reaches each year
- (rate of movement?)
how is how often an event of a certain magnitude expressed?
- Recurrence interval R = (n + 1)/m (n = # records, m = magnitude ranking, 100 yr flood)
- Probability P = (R - 1) x 100
How are magnitude and frequency related?
Inversely
Which types of events do the most Work in geomorphic systems?
Moderate does the most Work b/c HighMag-LowFreq aren’t frequent enough for long-term transport rates and LowMag-HighFreq don’t do enough Work.
Steady Time
- Engineering Time
- mins-yrs
- Time- independent, some components unchanging
- Steady base flow in a river
Graded Time
10^2 years
- Time-dependent and independent
- Sediment load and channel gradient over hundreds of yrs and discharge over a year
- Fluctuating dynamic equilibrium as system approaches some steady state
Cyclic (Geologic) Time
10^3 - 10^6
- Time-dependent
- Time is independent variable (also climate, initial relief and geology)
- All landform responses depend on these
Equilibrium in Geomorph
- Static
Stationary or unchanging
Equilibrium in Geomorph
- Stable
Revert to previous state after disturbance (feedback)
Equilibrium in Geomorph
- Unstable
Small disturbance causes movement away from equilibrium toward a new (stable?) state
Equilibrium in Geomorph
- Metastable
Incremental change from one to another state of equilibrium (threshold)
Equilibrium in Geomorph
- Steady State
- Fluctuation about an average
- No obvious trend
- Caused by numerous small-scale disturbances
- Long-term
- ex. Weather
Equilibrium in Geomorph
- Thermodynamic
- tend toward max entropy
- Long-term
Equilibrium in Geomorph
- Dynamic-Metastable
- Fluctuation about a trending mean with abrupt shifts to new equilibrium states (threshold)
- system jumps after threshold
- Very common
Equilibrium in Geomorph
- Dynamic
- Fluctuation about a trending, non-repetitive mean
- Quasi-equilibrium
Threshold
- Limit w/in a landform or process beyond which equilibrium cannot be maintained
- Defines ability to respond and adjust to changing Mass or Energy conditions
- Natural part of most geomorphic systems
What are the 2 types of thresholds
- Intrinsic
- Extrinsic
Intrinsic Threshold
- No external
- Changes occur w/o a change in, or influence from, an external variable
- ex. Slope angle
Extrinsic Threshold
- Respond to external
- Response of a system to external influence
- Ex. rain or landslides
Reaction and Relaxation times
Response to a threshold often lags behind initial disturbance or change in process
Reaction Time
Lag from disturbance (change in Energy) to morphological response (change in Mass)
Relaxation Time
Adjustment time of landform/process to new equilibrium or another threshold
Feedbacks and 2 types
- Response to change in M and/or E causing shift from (+) or back (-) to equilibrium
- Processes affect the landscape, but through feedback, the landscape also affects those processes
- Positive
- Negative
Positive Feedback
- Self-amplifying
- Increases trend away from equilibrium
- Landslide continuing
- Faulting increases stream slope, increases erosion, reduces slope
Negative Feedback
- Self-regulating
- Decreases trend away from equilibrium
- Landslide stabilizing to new slope
Over long time periods, what type of feedback do most geomorphic systems experience?
- Negative feedback
- Changes are resisted and tendency towards equilibrium is maintained
General Systems Theory
- Framework for conceptualizing and modelling complex phenomena
- inputs, throughputs and outputs matter and/or energy
- ex. Hydrological cycle is conceptual framework using systems approach
System
- Set of objects, attributes, and processes that form a functioning whole
- A model, simplification of a very complex reality
- Components operate together as a functioning whole
System Objects
Landform elements, defined spatially (drainage basin, mountain slope etc.)
System Attributes
Physical properties, measurable (slope gradient, soil texture, etc.)
System Processes
Functional relationships between elements that affect or control attributes (water flow, exertion of wind stress, land sliding etc.)
When is a system positive or negative?
- Based on the # of Negatives in system
- Odd # = Negative
- Even # = Positive
Qualitative/Conceptual Models
- Descriptive models of key components in a land system
- Based on observed data, graphs, maps, hypotheses
- Qualitative
- Useful for generalizing observations and applying elsewhere
Morphological Models
- Forms, attributes, patterns
- Little quantification of process or Matter and/or E exchange
Cascading Model
- M and/or E transfer btwn components via directional pathways
- Little consideration of morphological implications
- Doesn’t really loop back on itself
- Atm moisture to precipitation to surface water to infiltration to soil water
Process-response Model
- Integrate characteristics of both morphological and cascading systems
- Form & process interactions
- Useful for modelling responses to changing events over time
- Feedback between components
- Most common approach
Positive feedback =
Amplification
Negative feedback =
Regulation
Process-Control Models
- Deliberate human control/replication of geo processes to better understand key forces, responses, M and E exchanges
- Scientific research, engineering, management or planning
Analogue Models
- Physical scaled models of forms and/or processes
- Geometric (form) scaling is easy while dynamic (process) scaling is very difficult
Geometric (form) scaling is easy while dynamic (process) scaling is very difficult.
Why?
- Need big labs to mimic nature for process
Mathematical Models
- Model complex phenomenon using # and eqn’s
- Quantitative
- Great precision
- Accuracy depends on knowledge of phenomenon
Advantages of Systems approaches
1) Recognize relations btwn form and process (encourages process-based study where records lack)
2) Logical framework and wholistic view for study of complex, multivariate systems (allows for dynamic variations in response to changing processes over time)
3) Application/linkage to broader geographic study (Climate change)
What are the disadvantages of Systems approaches ?
- Models are abstractions, not reality
- Simplified
- Ground in theory/frameworks
So: - Recognize simplifications/limitations
- verify/validate
Landforms as process-response geological systems
- Matter Exchange/ Rock Cycle to
- Energy Exchange/ Geomorphic Process to
- Morphological Response (Landforms)
Matter Exchange/Rock Cycle
- Magma
- Lithification
- Rocks
- Weathering
- Debris
- Erosion/Transport
- Load
- Deposition
Energy Exchange/ Geomorphic Process
- Tectonics (Folding, faulting, uplift, subsidence)
- Physical Disintegration/ Chemical decomposition
- Entrainment and Transport by wind, water, ice
- Deposition by wind, water, ice
Structural Landforms
Mountains, faults, rift valleys
Weathering landforms
Karst topo, talus cones
Erosional Landforms
River/glacial valleys, Gullies
Depositional Landforms
Sand dunes, bars, deltas, floodplains
Two fundamental types of geomorphic processes
- Endogenic
- Exogenic
Endogenic geomorphic process
- Energy from inside the Earth
- Landforms built by tectonic/volcanic processes
- Intrusive landforms (batholiths)
- Extrusive (volcanic) landforms
- Tectonic landforms (folded and faulted mountains)
Exogenic geomorphic process
- Process driving by gravity and atmospheric forces
- Landforms modified by sedimentary forces
- Colluvial, fluvial, glacial, eolian, coastal processes
- Resultant landforms are relatively small scale but widespread
Batholiths
- Roots of continents
- form from intrusive rocks, coarse crystalline, magma derived
- Exposed by later erosion
- Solid, well jointed rocks
Structural Landforms
- Folding (Plastic deformation of rocks under compressional stress)
- Most common/obvious in sed rocks at convergent margins
- Faulting (brittle fracture, normal, reverse, overthrust, strike slip)
- Used in tectonic geomorphology, assess tectonic activity
Volcanic Landforms
- Built by magma extrusion
- Lava and tephra
- Occur at divergent/convergent boundaries and hotspots
Related landforms in Convergent margins
Calderas, cinder cones, lava domes
