UNIT 9 Mass movement Flashcards
what are the types of mass movement
Solufluction and creep
Slumping
Lahars and mudflows
debris flows
rockfalls and rockslides
what is a mass movement
the downslope movement of rock, regolith, snow or ice driven by gravity
You can distinguish Mass movements by
Material
velocity
Character
Environment
What are the types of material in a mass movement
snow, rock, mud, ice
What are the characters of sediment in mass movement
coherent or chaotic
wet or dry
what are the mass movement environments
subaeriel submarine
What is creep
slow downhill movement of regolith caused by seasonal expansion and contraction
What is evidence of creep
Tilted telephone poles, sagging foundation, curving tree trunks
WHat is solufluction
Tundra Creep where melted permafrost slowly flows over deeper frozen soil
What are rock glaciers
rock glaciers are mixtures of rock fragments imbedded in ice
think breccia or conglomerate cemented in ice
because ice is relatively week it can flow slow down steep slopes
what is slumping
mass movement by sliding of regolith in coherent blocks
have a head scarp (exposed failure)
and a bulging toe (material pile up)
What is a mud flow
Mostly mud mass movement, depends on water content and slope angle
what is a debris flow
mud flow mixed with pebbles and cobbles
what are lahars
same process as a mudflow or debris flow but with volcanic ash instead of weathered regolith
super hot and scary and stuff
what is a rock/debris slide
non vertical,
rock can move at 300km/h
rock slide if rock
debris slide if regolith
what is an avalanche
the best beaver tail flavour
a turbulent cloud of debris and air
snow or other debris like rock or marine sediment
wet snow avalanche speed
30km/h
dry snow avalanche speed
20km/h
avalanches flow through….
channels down mountains or underwater
What is a rock / debris fall
vertical Freefall of mass
falls rapidly
caused by road cuts
what happens in submarine slumps and debris flow
sediment breaks loose and flows down a canyon
the turbidity current slows and deposits sediment in a submarine fan
in a turbidity current..
sediment and water flow chaotically downslope
physics of mass movement
moves when the downslope force is greater than the resisting force
which is caused by many factors like chem bonds electrostatic attraction friction and surface tension
sand angle of repose
35 deg
coarse sand angle of repose
40 deg
angular pebbles angle of repose
45 deg
what are weak surfaces
saturated sand or clay layers
joints parallel to surface
weak sedimentary bedding
metamorphic foliation
what triggers mass movement
shocks
vibrations
liquefaction
changes in slope loads, steepness and support
changes in slope strength
what causes shocks and vibrations
earthquakes
storms
trucks
blasting
what is liquefaction
when wet sediment shakes, grains can behave like fluid, solid sediment turns into a slurry
what can cause changes in slope loads
addition of weight above a slope
water infiltration
construction
what can cause changes in steepness (MM)
rivers and road cuts
what can cause changes in support (MM)
undercutting may remove support and create a steeper slope
what can cause changes in slope strength
weathering
vegetation
water content
what happened in the vajont dam
water table rose above the dam and overflowed causing massive destruction
what magnitude was the 1929 NFL earthquake
7.2
Where do slope failures occur
HIGH RELIEF AREAS
revers glaciers waves
HIGH RAIN AREAS
weathering heavy soil
TECHTONIC AREAS
how do you identify mass movement
look for indications of past mass movement such as head scarps, overtight power lined, dead or tilted trees
how does vegetation prevent mass movement
the roots stabilize the potential failure plane
what is regrading
cutting terrace steps to remove load and catch debris
What is drainage in mass movement prevention
lowering the water table below a potential failure plane dries the plane and makes it stronger
how can you reduce undercutting
divert a stream further from a cliff
place riprap to absorb wave energy
What are some ways engineered structures to help prevent the effects of mass movement
Retaining walls
Jock bolts
avalanche sheds
When do you use controlled blasting
if a slide is inevitable,Avalanches usually
what is nessecary to set a mass movement in motion
weathering, relief, a triggering event
