Geomorphology Flashcards
The largest component of earths materials
Rock
Earths circumference and radius
Circumference = 40,000 km
Radius = 6,371mm
Planets with high mass and low density (Jovian)
Outer, cooler planets
Planets with low mass and high density (terrestrial)
Inner, hotter planets
Earths compositional layers
- Core: high density metallic
- Mantle: high density rock
- Crust: low density rock
Layering based on physical properties
Inner core: solid
Outer core: molten
Mesosphere: hot, strong
Asthenosphere: hot, plastic
Lithosphere: cool, rigid
Exogenic energy/heat flow
Solar radiation
Endogenic energy/heat flow
Nuclear reactions within the earth
The outcomes of energy and heat flow within the earth (thermogenesis)
- Convection currents
- Changes in solid/liquid/gas phases of rock
- Creation of magma
The rock cycle is a _____ material system
Closed
Dual drivers of rock cycle
- Endogenic processes
- Exogenic processes
Crust is made up of how many major plates
Seven
What drives the motion of plate tectonics
- Thermally driven heat from the core
- Gravitationally driven
Founder of the theory of tectonic plates
Alfred Wegener
The most recent and most sucessful concept that uniies ideas about the nature of the earths crust
Theory of plate tectonics
Evidence of tectonic plate motion
- Landmasses fitting like a jigsaw puzzle
- Fossil patterns across continents
What does thermally driven plate tectonics entitle
- Partial melting under pressure (10% liquid)
- Convection currents in the mantle
- Coupling/decoupling at the 50-100km depth (Litho-Asthenosphere boundary)
Results of gravitationally driven tectonic plates
- Ridge-push
- Slab-pull
Large scale topographic evidence of plate tectonic motion
- Mountains
- Mid oceanic ridges
- Trenches
Basic large-scale processes of plate tectonic motion
- Rifting
- Sea-floor spreading
- Subduction
- island arcs
- Continental collision
- Orogenesis
Three types of plate boundary
- Divergent
- Convergent (destructive, collision)
- Transform
Forms of convergent plate margins
- Steady state
- Collision
- Oceanic-oceanic crust
- Oceanic-continental crust
- Continental-continental
crust
What happens at a oceanic-continental plate boundaries
- Subduction of oceanic plate bneath a continental plate
- Frictional heating leads to a rising magma plume
- Granite intrusions are emplaced within the mountain mass and volcanic activity develops
What happens at transform margins
Relative plates sliding past each other can grip and create oblique-slip margins causing earthquakes.
The alpine fault and its two subduction zones
The pacific plate is subducted in the north
The Indo-Australian plate is subducted in the south
What visible features occur at
1. Continental-continental margins
2. Oceanic-oceanic margins
3. Oceanic-continental margins
- Suture zones exhibited, where one continental margin subducts below the other and form a mountain range with an extensive upland plateau on one side and a longitudinal river system parralel to the range on te other side
- Oceanic plate subducts below another oceanic plate creating a volcanic arc and an adjacent deep sea trench
- Oceanic plate subducts below continental plate resulting in terrestrial volcanic arcs and a deep trench just offshore.
Collisional plate boundaries result in
- Orogenesis
- high rates of crustal deformation
- high rates of incision
- steep slopes and frequent landslides
- very high rates of landscape change
Southern alps average motion
40mm of transform motion per year
22mm of convergence per year
Southern alps rising rates
11mm uplift per year
11mm erosion per year
Outcomes of mountain ranges on subduction zones
- Uplift
- Thickenening
- Increased relief
- Steeper slopes
- Decreased slope stability
- Development of faults
- Decrease in strength
Endogenic-exogenic interactions
- Slope processes
- Fluvial processes
- Glacial processes
- Coastal processes
Evolution of ocean basins key dates
Break up of Pangaea 225 mya
Continental seperation 180 mya
What has caused the pacific to shrink
Formation of the Atlantic from the seperation of America and Africa
Atlantic growth +160%
Pacific growth -35%
Ocean basin architecture
- Ridges
- Abyssal planes
- Seamounts
- Continental shelves
- Trenches
Oceanic ridges
Symmetrical ridge and trough structures 100-1000 km wide, produced by sea floor spreading
Abyssal plains
4000-6000m deep flat plains between ridges, trenches or continental shelves that are made up of cool older ocean crust
Seamounts
Submarine mountains that were former volcanos that can break the surface and develop reefs
Continental shelves
Shallow areas beyond continental margins covered in terrigenous sediment that are most affected by sea level changes
Trenches
Created at subduction zones where the oceanic plate subducts under another plate
Sea level fluctuations
- Short term
- tides and waves
- minutes-years
- Intermediate term
- eustatic changes
- Isostatic changes
- 10-100,000 years
- Long term
- tectonic changes
- 1-100 ma
Eustatic sea level changes
Global, immediate, ocean volume changes which can be steric or coupled
Steric eustatic changes
Density changes (temperature and salinity), loss in density equals loss in sea level
Coupled changes
Water storage changes (glacial and interglacial periods)
Isostatic sea level changes
Results from isostasy:
- gravitational equillibrium
- bouyancy
- thin, low density crust “floats” on high density crust
Loading and unloading of the crust
- Removal and addition of rock mass (erosion/deposition)
- Removal and addition of water/ice (ice sheet growth/decay)
Is fresh or salt water more dense and basic than the other
Salt water
Denudation methods
- Wearing away the land surface
- surface lowering
- weathering, mass movement, erosion, transportation
- Potentential energy
- uplift
- Kinetic energy
- solar powered
- water movement
Denudation
The process of the earths surface being eroded
Weathering
- Physical and chemical alteration of rock at the earths surface
- A passive process distinguished from the dynamic role of fluids, wind and ice
- An equillibrium process
- rocks formed in one environment moved to another
- instability
- reduced to more stable forms
- Does not involve transportation of materials
Physical weathering
Physical break up of rocks caused by a variety of processes which generate stresses within or upon rock masses
Types of physical weathering
- Freeze-thaw activity
- Crystal growth
- Hydration
- Pressure release
Chemical weathering
Decomposition of minerals in rocks with reactions between air, water and minerals
Regolith
Residual materials that have resisted weathering (soil)
Types of chemical weathering
- Hydrolosis - breakdown of silicate minerals
- Oxidation - reaction of O2 forming oxides (rusting)
- Carbonation - water reacts with c02 forming weak carbonic acid
- Solution - water dissolving a mineral
Karst landscapes
Landscapes particularily susceptible to chemical weathering
Karst landscape requirements
- CaCo3 rich limestone
- Joint patterns to allow water penetration
- Aerated zone between ground and water table
- Vegetation cover
Factors controlling the amount of dissolved Co2
- Concentration of Co2 in the air
- Temperature (cooler water absorbs more Co2 than warmer water)
- Biological processes (decaying humus source of Co2)
Three components of shear strength
- Friction characteristic (angle of friction)
- Effective normal stress
- Cohesive forces
Coulumb-Terzaghi shear strength equation
Shear strength = Cohesion + effective normal stress x tan angle of friction
Driving and resisting forces
Driving: gravity acting on slope materials
- weight
- size, shape
- moisture
- slope angle
Resisting: friction
- cohesion
- frictional strength (weight component)
Slope instability is
Episodic (progressive)
Types of mass movementa
- Fall - material airbourne
- Avalanche - snow/debris is falling/tumbling
- Landslides - cohesive materials planar or curved to slope
- Flow - high moisture content
- Creep - slow, expansion
Cohesive materials
Materials stuck together ie soil
Anhropogenic effects on slope unstability
Deforestation, overgrazing, drainage, earthworks
Sedimentary part of the rock cycle driven by
Exogenic processes (weathering, erosion, depositon)
Clastic sediments
Composed of particles (clasts) from:
1. Pre existing rocks
2. Weathered products of igneous, metamorphic and sedimentary rocks
3. Weathered products transported away by running water, wind or ice
Sediment characterization
Size, shape, variability, colour, lithology
Grain size techniques
Φ scale, sieves, settling tubes, laser
Statistical description of grain size
- Mean
- Sorting (standard deviation)
- Skewness of distribution
- Kurotosis (peakedness)
Sorting statistical description
Coarse, poorly sorted, subangular
What does shape and size of grains tell us
- More rounded = more abrasion
- Smaller = more communition over time
- Better sorting = viscosity of fluid
Diagram that explains transportation in water
Hjulstrom curve
Higher water velocities =
Larger particles
Sediment transport in water requires energy that
- Can initiate transportation
- Can maintain transportation
- Allows deposition
Biological sediments
Composed of animal and plant remains
Carbonate sediments
Made of CaCO3 such as limestone
Terrestrial sediments
Peats, (plant matter, moss) coal
Chemical sediments
Minerals precipitated from lake or sea water
Chemical sediments from least soluble to most soluble
Calcite - CaCO3
Gypsum - CaSO4
Halite - NaCl
Cave precipitites
Speleotherms
- stalagmites, stalactites, travertine (flowstone)
Types of sedimentary environments
- Continental
- Coastal and marine
Stream flow characteristics
- Driving forces and resisting forces
- Material characteristics
- Velocity
- Discharge
Stream flow driving force and resistence
Driving force: gravity
Resistence: friction and sediment transport, channel boundary, water/particle
Discharge continuity equation
Discharge = flow width x flow depth x mean flow velocity
Q = w.d.v
Stream power (potential to do work) equation
Stream power = density of water x acceleration due to gravity x discharge x channel gradient
Ω = p.g.Q.S
Types of sediment transport depending on stream velocity and sediment characteristics
- Solution
- Suspension
- Saltation
- Traction
Bed rock channels
Erosion of the channel boundary
Channel boundary erosion processes
Abrasion, Plucking, Cavitation
Direct sediment into bed rock channels supplied by
Slope processes into streams
Alluvial channels
Unconsolidated fluvial channel systems
Stream power > sediment supply =
Stream power < sediment supply =
Channel degradation
Channel aggradation
Channel degradation and aggradation
Degradation is the lowering of a stream channel caused by increase in stream power carrying sediments away
Aggradation is the deposition of material in the stream
How are sediments in alluvial channels transported
Bed and suspended load dominated
Alluvial fans
Fan shaped accumulations of stream deposit
Meandering streams result when
Sinuosity > 1.5
Sinuosity = channel length/valley length
Flood plain morphology
Levees, oxbow lakes, crevasse splays, abandoned channels
Braided streams
Channel multiplicity that is formed ans dissected by bars
Braided stream characteristics
- high width/depth ratio
- high slope
- high sediment load
- bed load dominated
Recorders of environmental change
Terraces through their, precipitation, vegetation, hydrology, sediment supply.
Why do people modify river channels
For flood control, drainage improvement and reduction of bank erosion.
Types of channelization
- Re-sectioning - increase width/depth to increase channel capacity
- Reallignment - Straightening channels to increase gradient velocity
- Diversions - alteration of natural course
How do lined channels help channel velocity
Low roughness = less resistence = high velocity channels
Primary source of coastal energy
Waves
Components of a wave
Height, length, steepness, period
Mass sediment transport in the surf zone
- Swash and backwash
- Littoral currents
- Rip currents
Storm surges result in
High tide, low atmospheric pressure, landward mass transport
Forms of tidal coasts
Microtidal - wave dominant
Mesotidal - wave and tide co dominant
Macrotidal - tidal dominant
Products of deposition at deltas
- Aggradation
- Progradation (extension of deltas)
Hard coasts
Unprotected by barriers and has direct wave attack, creating seaside cliffs, arches and stacks
Glacier types
Valley glaciers, ice sheets, ice shelves
Cold vs warm vs thermally complex glaciers
Cold - frozen at bed
Warm - water at bed
Thermally complex = bed partially frozen
Glacier mass balance/ inputs and outputs
Inputs:
Snow, rainfall, avalanching, regelation ice
Outputs:
Surface melt, basal and englacial melt, sublimation, deflation, calving, avalanching
Glaciers can be split into two sections
Accumulation zone and Ablation zone with equillibrium line to sperate them
How does the equillibrium line move in glaciers
- Positive mass balance = glacier thickens/advances and Equillibrium line moves down the glacier
- Negative mass balance = glacier thins/retreats and Equillibrium line moves up the glacier
Ice flow three componenets
Internal deformation, Sliding, Subglacial sediment deformation
Equation for general glacial flow
Glens flow law
Glens flow law equation
Strain rate = constant for ice hardness x shear stress^empirical exponent
Basal shear stress equation
Shear stress = ice density x gravitational acceleration x ice thickness x sin glacier surface slope
Glacial internal deformation
Occurs in all glaciers where frozen bed ‘creeps’ down the valley
Glacial sliding
Water acts as lubricant at glacier bed and slides glacier down valley
Subglacial sediment deformation
Mobile or deforming bed moves glacier down valley
Where is material transported through glaciers
- Supraglacial (on top)
- Englacial (internal, streams)
- Subglacial (bed erosion)
Glacial depositional processes
Active deposition (lodgement)
Passive deposition (melt out, flow)
Both result in poor sorting with wide range of particle sizes
Outcomes of milankovitch cycles
- Seasonal assymytries in annual radiation reciept, creating a variable pattern of solar radiation distribution
- Radiation reciept in low latitudes mainly affeced by eccentricity and procession
- In high latitudes, radiatio reciept is mainly affected by tilt
