GEOLOGY 102
Lecture 28 – Mass Wasting (Movement)
a) Mass wasting - the movement of material _________________ under the influence of gravity, without the aid of a _________________ medium i)
Commonly referred to as “_________________” ii) Most important process of __________________________________
(1) Shapes the landscape
(2) Provides _________________ to streams and glaciers iii) Can occur very ____________ to very slowly
a) Development of relief - creates slopes down which masses move i) ______________ - difference in elevation between one place and another ii) _________________ tries to pull material at higher elevations down to
_______________ elevations iii) The _________________ the slope, the faster the movement will be b) Fracturing and _________________ - weakens materials at the Earth’s surface i) Jointed rock, broken rocks, and regolith – much ______________ than intact rock c) Slope Stability - the battle between _________________ force and
_________________ force i) Stable slopes
– sliding is _________________ ii) ______________ slopes
– sliding will likely happen iii) Slope _________________ - movement on an unstable slope iv) Failure depends on the balance between 2 forces:
(1) _________________ force
– caused by gravity
(2) resistance force - ______________ sliding
(3) downslope force > resistance force  _________________ v) What causes _________________ force?
(1) _________________ (unattached block)

(2) _________________ charges and friction (dry regolith)
(3) _________________________ (slightly wet regolith)
(4) Surface tension in damp sand ____________ particles
(5) Dry particles bound by ______________ and friction
(6) Saturated particles _________________ by water, lose
_________________ vi) Angle of Repose - the angle of the _________________ slope granular debris piles up to
(1) _________________
(2) Angle depends on shape and ____________ of grains d) Glide Horizon - separates a substrate below from unstable rock or debris above i) Different materials have different kinds of glide horizons:
(1) _________________ - slippery wet clay
(2) Massive rocks - _________________
(3) _________________ rocks – surface between beds, ____________ and evaporites also may preferentially slip
(4) _________________ rocks - foliation planes, especially those defined by
__________ ii) glide horizons parallel to the slope are much more likely to ____________ than layers that dip ___________ the surface
a) Shocks & Vibrations

i) _________________ tremors, storms, passing of large trucks,
_________________ in construction sites, liquefaction ii) ___________ any remaining _________ that hold the mass in place and/or cause the mass and slope to separate slightly, decreasing _______________ iii) _________________ force decreases, and the downslope force sets the mass in _________________ b) Changing slope angle, slope load, and slope support i) Factors that make a slope _________________ or _________________ may ultimately cause it to fail ii) Increase _________________ forces iii) Processes:
(1) _________________ at the foot of a hill or mountain
(2) Undercutting
(3) _________________________ slope c) Changing the slope strength: the effects of _________________, vegetation, and _________________ i) Stability of the slope depends on _________________ of the material ii) _________________ weakens rock iii) _________________ tends to strengthen slope, roots hold unconsolidated grains together and ______________ water iv) _________________ in large quantities (i.e. heavy rains, rising floodwaters,
…) decreases _________________ of grains, can lead to liquefaction d) Gros Ventre Slide, Grand Teton NP, Wyoming – Spring 1925 i) Why?
(1) _________________ parallel to the slope
(2) Sandstone _________________ by river
(3) Soft _________________ underlying sandstone – acted as a glide horizon
(4) Excess water - rain and snowmelt -
_________________ glide horizon, also added
_________________

(5) _________________ felt June 21 st & June 22 nd in Yellowstone
– slide occurred June 23 rd
4)
a) Different types of mass wasting based on: i) _____________ of material involved (_____________, ______________,
___________) ii) Velocity of the movement (fast, intermediate, or slow) iii) _________________ of the moving mass (chaotic cloud, slurry, or coherent block) iv) _________________ in when the movement occurs (subaerial or
_________________________) b) Flow vs. Slide i) Presence or absence of a discrete _________________ surface ii) ___________ - failure surface (______________________________),
_________________ movement iii) ___________ - no failure surface, _________________ movement c) Falls - occur when a mass _________________ from a steep (vertical) cliff i) If rock fragments - _____________________ ii) If rock and regolith - _____________________ iii) Associated with freeze/thaw processes, shaking, or joints iv) _________________ and collision with other rocks bring blocks to a halt v) _________________ - a sloping apron of rocks along the base of a cliff d) Landslides - a sudden movement or rock and debris down a
_________________ slope along a glide horizon i) If only rock - _________________ ii) If only regolith - _________________ iii) Leaves a ________________________ iv) Generally occurs along a ____________ surface v) Velocities up to _________________ vi) Debris piles up at the base of the slope

e) Slump - downward _________________ of rock or regolith along a curved surface i) Moving mass - _________________ ii) Slid surface - __________________
_________________________ iii) Slump scar - ________________ iv) Slumps come in all sizes v) Move at speeds of mm/day to 10’s m/min vi) Typically ________________ as they move, including structures built on them f) Flows - water and air mix with a material to create a _________________ that moves down slope i) Moves as a _______________ fluid with little resistance to _____________ ii) _____________ is a function of (_________________________ & water content)
(1) Higher the angle & the more water/air

the ______________ the flow iii) Can carry l arge rocks, houses, cars, trees … iv) Specific types of flows:
(1) _________________ - turbulent clouds of debris mixed with air that rushes down steep hill slopes at high _________________
(a) Snow - __________________________________
(b) Fragments of rock and dust - ________________________________
(c) Fastest unconsolidated flow
(d) Rock Avalanche
(i) Relatively _______, extremely rapid movement of debris
(ii) Can travel enormous _________________ with little elevation difference
(iii) Travels on a cushion of _________
(e) Snow Avalanche
(i) Air-debris mass is ___________ than air & hugs ground
(ii) Acts like strong & _______________ _____________

(2) Flows with water
– water mixes with regolith to create a slurry that moves downslope
(a) Just mud - _________________
(b) Mud mixed with larger rock fragments - _________________
(c) Lahar - mix of volcanic ash (from ________________ eruption or
_______________ eruptions) & water (from ____________ & ice that
__________ in a volcano’s heat or from heavy _________________) g) Creep – gradual down slope movement of regolith i) Resultant movement after a ____________________ cycle is downslope ii) Tilt fences, gravestones, power line poles, curves trees iii) Upper cm’s of ground __________ during the winter, ______________ again in the spring iv) Water _______________ in volume (9.2%) when it ______________

regolith moves
______________ perpendicular to the slope v) During the spring, ice melts

_____________ makes the regolith sink vertically h) Cold Climate Mass Wasting i) Solifluction - _______, down slope movement of ___________-saturated
______________ sediment
(1) Common in areas with _________________
(2) Only the uppermost 1-3 m of the ground thaws in __________ regions
(3) Melted layer becomes soggy and weak, flowing down slope in overlapping
____________
(4) Produces distinct lobes
(5) Flow rates _________________ ii) Rock Glacier - a lobe of ______________________ rock debris that slowly moves downhill
(1) mostly rocks with ___________ between the blocks i) Types of Submarine Mass Movement

i) Submarine _________________ - semi-coherent blocks slip down slope on weak mud ___________
___________________
(1) Olistostrome ii) Submarine debris flows - a slurry containing large
_____________ suspended in a ___________ matrix iii) Turbidity currents - a _________________ cloud of suspended sediment avalanches down slope
(1) Graded beds j) Summary – Types of Mass Wasting i) Slowest (creep) to the faster (____________, flows, & ____________) to the fastest (avalanches, & _____________) ii) Velocity f(_________________ of slope & _________________ content) iii) Can start as one kind and ________________ into another iv) ______________ - material actually flies through the air in ______________ v) ______________ - material remains coherent and remains in
______________ with the underlying surface
(1) Difference between slumps and slides
(a) slump occurs along a ____________ glide horizon
(b) slide occurs along a ____________ glide horizon vi) _________________ - material mixes with air and rushes down steep slopes life a strong ___________ vii) Flows - material becomes ________________ jumbled as it moves, does not follow a __________________________
(1) Difference between avalanche and flow
(a) avalanche is air and rock/regolith (snow)
(b) ___________ is water and rock/regolith
a) Identifying regions at risk i) Natural Hazards

ii) Look for _________________ formed by ___________ movements:
(1) Slump _____________
(2) _________________ portions of forests in which the trees point downslope
(3) ____________ of loose debris at the base of hills
(4) _________________ land surfaces iii) Detect regions that are beginning to move:
(1) Roads, buildings, pipes begin to _________________
(2) Power lines may be too _____________ or too loose
(3) Visible ______________ on the ground (head of slump)
(4) _________________ ridges (toe of slump)
(5) _____________ trees
(6) ___________ trees or new ___________ due to changes in groundwater b) Prevention – stabilize the slope i) Revegetation: roots hold regolith together and prevent it from becoming
__________________________ with water ii) Reduce subsurface water: water weakens material beneath the slope and adds _____________ to the slope, remediate by improving
_________________ so that water does not enter subsurface or
_________________ water from the ground
(1) Stop irrigation or repair leaky _____________ iii) Regrading: regrade steep slopes so that it does not exceed the angle of
_________________
(1) Some mass upslope could be moved to a ______________ region, or the ground could be terraced so that the mass _________________ overall becomes stable iv) Prevent Undercutting:
(1) Where a river _________________ a cliff, engineers can divert the river
(2) Along coastal regions, engineers can build an offshore breakwater or pile
_____________ along the beach to ____________ wave energy before it strikes the cliff

v) Constructing Safety Structures: build structures that _________________ potentially unstable slopes or _____________ region downslope from
___________ if mass wasting does occur
(1) Ex: retaining wall, ______________________, chain link fencing, thin
_________________ sheet, avalanche _________________ vi) Controlled Blasting of Unstable Slopes: blast unstable ground loose at a time when its movement can do no harm
(1) _________________ avalanches