soil - erosion Flashcards
how do soil and weathering products move across the land?
mass movment - by gravity - movement of soild rock
transport by water - runoff/ streams
transport by wind
name 4 mass movements processes
flow
fall
slide
creep
define FALL - ROCKFALL
single loosened rock tumbles downhill
form talus slopes - pile
define FALL - EARTHFALL
forms when steep slopes of soil and sediment are undercut - action of sea or river
beach cliffs or river cutbanks
define SLIDES - ROCKSLIDES
large numbers of rocks cut loose at once and slide downhill
trapped air beneath rock cause large large speeds
define SLIDES - ROTATIONAL SLUMP - LANDSLIDE
chunks of earth slide of hill in block
creates a cliff called scarp where ruptured occurred
define SLIDE - DEBRIS SLIDE - LANDSLIDE
a mass of water, rock and earth slides as a disintegrated plug
large hazard to life
define SLIDE - MUDSLIDE
describes all kinds of slides and flows
correctly means the sliding of soil and fine grained sediment and water
eg Oso, 2014 deaths
define FLOW- EARTHFLOW
friendliest flow
earth acts as liquid and slowly moves down hill - leaves scarp
gradual
speeds of cm-m per hour
define FLOW- DEBRIS FLOW
earth, water and rock mixed into fast moving liquid
speeds miles per hour
Clear creek, colorado
define FLOW-MUDFLOW
fine material and water flowing
speeds like free flowing water
can be triggered by ice and snow melt - lahars
name trigger mechanisms for slides and flows
heavy rain saturates soil
earthquakes cause liquefaction
removal of plant roots by deforestation or fire
graudal weathering causes spontaneous failure
describe liquefaction
earthquake causes soil to vibrate which weakens friction between sediment grains
less cohesion
sediment able to flow like liquid
similar to quicksand
define what creep is
material flowing downhill due to diffusional mechanisms
very slow
mechanism disrupts soil and gravity will pull more soil downslope
name 4 creep mechanisms ?
freeze thaw cycles (solifluction) - as soil freezes it expands and when it warms it collapses - creates pattern on ground
tree throw pulls soil out when it falls down hill
Rain splash- falls downhill due to gravity
animal burrowing or hoofs disperse soil
where does each mass movement mechanism operate?
rockfall and earthfall - very steep slope 60’
rotational slump, debris slide and mud slide - mid steep slope 60-20’
creep - any slope but only process to occur on <35’
how does water move sediment ?
Dissolved load- invisible
suspended load - small silt/clay
saltation - bouncing
rolling
bed load - bigger rocks and sand
drainage overland flow
soil fully saturated so soil can’t infiltrate down
water puddles on surface which carries sediment
sheetwash
water runs overland carrying sediment as heavy rain saturated soils and created overland flow
surface lowering
water dried up and exposes erosion degrdation
dry area
drainage and flows - rills
water flow becomes channelized into small channels
sediment transported often to stream
rills can dry up - seasonal
drainage and flow - gullies
rilles created into larger and deeper channels
lots of soil carried away
they can dry up and become eroded
drainage and flow - streams
runoff sustained by ground water
sediment moved by rills and gullies ends up here
sediment moved by massmovement will end up in stream
all year around transportation - doesn’t dry up
where is the zone of deposition
at the mouth of river
lots of sediment here
where is zone of transpotation
in the middle
where the trunk stream is
where is zone of production (erosion)
upand headwaters
near tributaries
what can a flat surface on river profile be due to?
Dam
flat valley that glacier carved eg Yosemite
effects of a dam
distrupts flow of normal sediment
builds up behind dam so water carries no sediment
river will then be ‘hungry water’ which accumulates sediment from rest of river
effects in change in topography
may be due to tectonic uplift this creates waterfall
knickpoint created
becomes eroded and creates flat land again
where does wind erosion occur most
arid environments where sediment is loose and less water for cohesion
loose and dry material gets carried by wind
what does wind do to sediment?
bigger boulders creep and roll along bottom
sand jumps via saltation
clay and silt suspended in air as smallest particles and can create dust storm - suspension or aerial dispersion
how is aerial dispersion bad
not good for respiratory health
difference between aerial dispersion and saltation
AD - finer material they create big dust storms up into sky
saltation - lower lower not as big - larger sand particles
how much of earth is degraded?
15%
size of china and india
30 years ago so probz increased
how much degradation does deforestation cause to land?
113ha
how much degradation does overgrazing cause to land?
75ha
how much degradation does poor cropping cause to land?
83ha
name locations with high wind erosion?
open deserts or coasts
locatiosn with high water erosion?
south africa
grrece
name 4 consqunces or erosion?
deforested land
landslide blocks road
gully erosion eats into cropland
bridge destroyed by floods
name 4 erosion and preventative methods?
reforest land
gully erosion haulted by check dam points and trees planted
steep land benched terraced
river navigagtion improves fish catch
describe dry, damp and wet sand?
dry sand bound together by friction
damp sand - small amounts of water increase cohesion in grains
wet sand - saturation reduces friction and sand flows
