Download CHAPTER 5.3 MASS MOVEMENTS

CHAPTER 5.3 MASS MOVEMENTS
“The transfer of rock and soil downslope due to gravity.”
Year:
2009
Year:
2020
Year:
Year:2050
2070
Some types of mass
movement are so
slow you can’t see
them moving.
CHATER 5.3 MASS MOVEMENTS
“The transfer of rock and soil downslope due to gravity.”
Some types of mass
movement are very
sudden.
Triggers of Mass Movement
When pores in sediment
Saturation by Water
become filled with water.
Saturation provides a
slippery medium upon
which the soil particles
can slide.
Saturation adds weight
to the soil causing it to
break loose and slide
downslope.
Triggers of Mass Movement
Oversteepened Slopes
Slopes that are steeper
than about 40 degrees.
Soils can remain stable
on slopes up to about
25-40 degrees.
Can be caused by wave
action or human
construction processes.
40 degree slope
Triggers of Mass Movement
Removal of Vegetation
Plant roots bind
soil and regolith
together.
Cutting or replacement of
plants that secure the soil.
Removal of plants removes the
“rope” that holds the soil in place.
Triggers of Mass Movement
Earthquakes Rapid movement of tectonic plates.
Triggers abrupt and often
violent mass movement.
Can dislodge large
amounts of soil at once.
Types of Mass Movements
Geologists classify mass movements based on…
… the kind of material that
moves (rocks, mud, snow)
… how the material moves
(slides, flows, slumps)
… the speed of the
movement (creep)
Types of Mass Movements
Rockfalls …
• occur when rocks or
rock fragments fall
freely through the air.
Rockslides …
• occur when a block
of material moves
suddenly (fast) along a
flat, inclined surface.
Types of Mass Movements
Slumps …
• occur when material
moves downward along
a curved surface.
• leave a crescent
shaped cliff just above
the slump.
Types of Mass Movements
Flows …
• occur when material
containing a large
amount of water move
downslope as a thick
fluid
• “mudflows” move
quickly
• “earthflows” move
slowly
Types of Mass Movements
Creeps …
• moves only a few
millimeters or
centimeters per year.
• affected by freezing
and thawing
• cannot be observed
directly as it happens
(too slow)
1 mm
A
B
Types of Mass Movements
Creeps …
HSW: Geography Basics: Five Ways Lands Change
Sideling Hill
Assignment:
Read pgs 148-149.
Answer the questions under “ASSESSMENT” on pg 149.
DO NOT do Question 5(c).