geomorphology Flashcards
why is earth considered a ‘goldilocks planet’
- not too hot or cold
- water can be in all 3 states
exogenic processes
- external to earth
- driven by sun/solar radiation
endogenic processes
- internal to earth
- thermally driven (nuclear reactions)
sedimentary cycle
- continental crust forms, exposed to atmosphere, becomes unstable, weathering/erosion occurs, debris created, transported, deposited
igneous cycle
- rock solidifies from molten state, turned into magma
- magma is high pressure high temperature and can be objected into a solid
- it is then either intrusive or extrusive
if magma cools beneath rock…
intrusive
if magma breaks outside of rock and cools…
extrusive
main plate tecontic points
- 7 major plates
- plates are mobile
- thermally-driven
- gravitiationally-driven
- proof in large scale topography
7 major plates are…
- pacific
- indo-australian
- north american
- south american
- african
- eruasian
- antarctic
plates move __ per year
7cm
ridge push
plates spread with gravity, move from high to low
slab pull
leading descending edge pulls rest of plate down. disconnects from other plate and forms a trench
mountains occur when…
2 plates collide and converge
mid oceanic ridges occur when…
plates are divergent
trenches occur when…
one plate subducts beneath another
subduction zone
when one plate goes under another
divergent boundary
plates moving apart
convergent boundary
plates moving together
transform boundary
plates sliding past
movement in southern alps
avg 40mm transform, 22mm convergence per year
alpine fault links…
2 subduction zones
- to north, south plate subducted
- to south, indo-aus plate subducted
orogenesis
mountain building processes
high mountains means…
high rates of erosion
steep slopes means…
unstable
deep gorges means…
high sediment loads
interaction of endo/exo results in…
- slope processes
- fluvial processes
- glacial processes
weathering is…
physical and chemical alteration of rock at the earths surface
once rock is exposed to atmosphere…
unstable and break down
physical weathering includes what processes?
- freeze-thaw activity
- crystal growth
- hydration
- pressure release
freeze-thaw activity
- physical weathering process
- liquid to solid phase change
crystal growth
- physical weathering process
- crystal grows inside rocks and displaces volume
hydration
- physical weathering process
- material swells up with water
pressure release
- physical weathering process
- rock relaxes at greater volume and may break
what is physical weathering?
physical breakdown of rock
what is chemical weathering?
- decomposition of minerals in rocks
- driven by reactions in air, water and minerals
regolith
product left behind after weathering
what are slopes responsible for?
- mass movement/wasting
- graviational movements of debris
driving forces on a slope
- gravity
- weight
- size
- shape
- moisture
- slope angle
resisting forces on a slope
- friction
- cohesion
- frictional strength
coulomb equation
shear stregnth equation
shear strength = cohesion + effective normal stress x coefficient of plane sliding friction
fall
- material airborne at some stage
eg rockfall
avalanche
- material falling and tumbling
- material partly airborne
eg snow, debris
landslide
- cohesive/semi-cohesive material
- moisture plays role
creep
- slow movement
flow
- high moisture content
- turbulent
- high sudden moisture supply
how people impact slopes to make them unstable
- deforestation
- overgrazing
- drainage
- earthworks
how is sediment/particles transported
- gravitational processes - eg slopes
- fluids - water, ice, wind/air
hjulstrom curve
shows particles eroded, transported and deposited
what is described on the left of the hjulstrom curve
cohesion
what is described on the right of the hjulstrom curve
mass effect
erosion on slopes is defined by the balance between…
erodability of rock/soil and erosive power of water
driving forces of stream flow
gravity
resisting forces of stream flow
- friction
- channel boundary
- sediment tranport
how does velocity of a stream work
- friction at bed slows water
- air friction at top of river also slows water
- as you move away from bed and air, there is less friction, so velocity increases
entrainment occurs when…
bed shear stress exceeds friction of material on bed
channel DEGREDATION in alluvial channels
stream power > sediment supply
channel AGGRADATION in alluvial channels
stream power < sediment supply
processes of erosion in rock channels
- abrasion
- plucking
- cavitation
how does abrasion work in rock channels
scraping/wearing away
how does plucking work in rock channels
pulling material off bed
channelization definition
all processes of river engineering for purposes of flood control/protection
types of channelization
- re-sectioning
- realignment
- diversions
- embankments
how does re-sectioning work in a channel
- increase width or depth
- increases cross-sectional area
- increases channel capacity
how does realignment work in a channel
- straightening channel by making cuts
- increases gradient velocity
- decreases flood levels
how do diversions work in a channel
alteration of natural course
how do embankments work in channel
- banks built adjacent to river channel
- confines floodwaters
what makes a positive mass balance in a glacier
inputs
- snow
- rainfall
- avalanching
what makes a negative mass balance in a glacier
outputs (erosion)
- melt - surface, basal, englacial
- sublimation
- calving
- avalcnhing
- deflation
what happens at accumulative zone of a glacier
ice formation in a glacier
what happens at ablation zone in a glacier
ice loss in a glacier
