Earth Sciences 240A - Lecture 28 - Mass Movement
Introduction
It’s the gravity, stupid!
Economics
Most expensive of
all natural phenomena
Gravity
Nomenclature: Force of cohesion and friction = ‘inertia’
[Abbott]
Components
Perpendicular to slope
Parallel to slope
Angle of repose
Importance of
lubricant (water)
Classification of
Mass Movement Processes
Creep
Slow (~3-4mm/y); Regolith affected
Frost heaving; Salt heaving
Never associated with catastrophe
Debris Flows/Mud Flows
Wide particle size variation
High content water
May travel ~320 km/h
Lahars are in this
category
Free-fall of blocks
Vertical to near-vertical slopes
Commonly dislodged by frost, rain
Rock Slides
Motion from planes of weakness: Joints,
foliation, faults
Most catastrophic
Examples
Frank Slide
Vaiont
Slide
1963, Italian
Construction
Concrete Hydro Dam
Terrible
geological site
Solution cavities
in foundation rock
Increased side
slope creep with filling of reservoir
1960: 1 million m3
slide
1963: creep 1 cm/d
to 39 cm/d to 80 cm/d
240 million m3
slide
Over top of dam;
‘tsunami’ in reservoir
Subsidence
Vertical collapse Driven by gravity
Water usually
plays a role
Categories
Human induced
Water,
oil/gas, coal, etc.
Natural
Sinkholes, caves, Karst topography
Groundwater and Limestone
Rain:
H2O + CO2 = H2CO3
Weak carbonic
acid
Limestone reaction
H2CO3 + CaCO3 =
Ca2+ + 2HCO-3
Both attach to
water molecules
Cavity forms plus Salactites/salactites
Karst
topography
Salt Solution
Example:
Barge oil drill punched into salt
mine
Rapid solution of NaCl
Plate Tectonics/Subsidence
Flooding of ‘failed arm’ of
Basis
for the Moses sea-parting?
Next
Prerequisite: Hydrosphere & Atmosphere