Slope Processes and Development Flashcards
describe a slope in an arid area?
jagged or straight due to mechanical weathering or shestwash
describe a slope in a humid area?
rounder
due to ecumenical weathering
soil creep
and fluvial transport
describe a slope in the tropics?
humid weather means domination of chemical weathering
due to hot wet conditions and avalibility of organic acids
deep flat produced favouring low slope angles
what is revoking?
the superficial and unconsolidated material at earths surface
including soil scree weathered bedrock and deposited material
prone to downslope movement (due to unconsolidated nature)
clay rich are particularly unstable due to ability to hold water
how can soil structure and texture influence slope development?
clay soils hold more water
dee clay on a slope where vegetation has been removed will offer very little resistance to mass movement
how can vegetation affect slope development?
can decrease surface runoff through storage and interception
deforested slopes are exposed to intense erosion and filleting
vegetarion can increase chance of major landslides
dry mass movement
rock fall
fluid mass movement
mud flow
very slow mass movement
soil creep
fast mass movement
avalanche
what is mass movement
large scale movements on the earths surface not accompanied by a moving agent such as a river or ocean wave
what are the most important factors in determining mass movement
gravity
slope angle
pore pressure
what factors influence slope development
rock type climate regality soil aspect vegetation
what two factors cause slope failure
reduction in internal resistance SHEAR STRENGTH of slope
Increase in SHEAR STRESS of the slope (the forces attemption to pull the material downslope)
what is the effect of gravity on mass movement
moves material downslope
sticks partciles to slope
where do slip planes occur
at the junction of two layers at fault lines at a joint along a bedding plane when shear stress is rested than shear strength
Heave/creep
slow
small scale
occurs mostly in winter
indidcual soil particles are pushed to surface by wetting heating or freezing of water
particles move at right angles to the surface as it is the path of least resistance
fall under the influence of gravity when the particles have dried, cooled or water has thawed
net movement downslope
Talus creep
slow movement of fragments on scree slope
what does the majority of soil creep movement come from
75% induced by moisture and so volume change
how are individual soil particles heaved to surface?
wetting
heating
freezing
what feature can heave form
terracettes
what are the initial causes of falls
weathering e.g. freeze thaw or disintegration
or erosion prising open lines of weakness
how can the length of rock fall influence scree
long - rounded scree
short - relatively straight
what do falls cause on rock faces
retreat
where do falls occur
steep slopes
greater than 40 degrees
especially bare rock faces
where joints are exposed
when do slides occur
when an entire mass of material moves along a slip plane
different types of slides
rotational slides - producing series of massive steps or terraced
rockslides or landslides or material rock or regith
when do slides commonly occur
weak rocks
steep slopes
active undercutting
change in the water content of slipe
or very cold conditions
what type of rock is vulnerable to slip planes and why
clay because it has little shear st engraved
slip plane is concave curve and the slide occurs the mass will be rotated backwards
when do loose rocks stone and soil move downslope
when downslope force exceeds resistance produced by friction and cohesion
when does a landslide occur
when material moves downslope due to shear failure at the boundary of the moving mass
what are landslides sensitive to and why
water content
reduced the strength of the material by increasing internal pressure
this pushes particles apart
weakening the links between them
water adds weight to mass increasing downslope force
what type of rocks do slumps occur on
weaker rocks
especially clay
how do slumps and flows differ from landslide
high water content
smaller particles
how does a flow differ from a slump
flows are
more continuous
less jerky
more likely to contort mass
material involved is predominately fine particles e.g. deeply weathered clay
when does a slump occur
when clay absorbs water
becomes saturated
exceeds liquid limit
flows along a slip plane
frequently the base of a cliff has been undercut and weakened by erosion thus reducing its strength
example of a slump
Average
21 October 1966
144 killed
116 of which were school children
fact about the material in a slump
33% is fine grained
how does the speed of flows vary
mudlflows are much faster than earth flows
and more fluid
higher water content enables material to flow across gentler angles
what are avalanches
rapid movements of snow ice rock or earth down a slope
snow and ice may pick up rocks and or earth
in mountainous steep areas how does a rock fall differ from a rock avalanche
rock avalanche is large scale movement to material
rock fall could be individual rocks
where are avalanches common
steep slopes over 22 degrees especially on north facing slopes where the lack of sun inhibits stabilisation of snow
mountainous areas
dry acalanche
newly fallen snow falls off older snow
winter
wet avalanche
in spring partially melted snow moves often triggered by skiing
what is a debris avalanche
rapid mass movement of sediment often associated with saturated ground conditions
