Mass Movements
Mass Movements
• Mass Movement - The transfer of rock and
soil downslope due to gravity
http://www.google.com/imgres?sa=X&biw=1242&bih=564&tbm
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Triggers of Mass Movements
• Gravity is the force behind mass movements.
• Several factors make slopes more susceptible
to the pull of gravity.
Factors that Trigger Mass Movements
1.
2.
3.
4.
Saturation of surface materials with water
Over steepening of slopes
Removal of vegetation
Earthquakes
Water as a Trigger for Mass
Movement
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• Heavy rains and rapid
snowmelt can saturate
surface materials and
trigger a mass movement.
• Example – 1998 Hurricane
Mitch produced torrential
rains, causing devastating
mudflows.
http://www.google.com/imgres?biw=12
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Water as a Trigger for Mass
Movement
• When pores in sediment
become filled with water, the
particles slide past each
other more easily.
Water as a Trigger for Mass
Movement
• When sand grains are slightly
moist they will stick together,
even on a relatively steep slope.
• If you add enough water
however, the pores between the
grains will fill with water and
the sand-water-mixture will
ooze downhill
Over-steepened Slopes
http://www.google.com/imgres?biw=1242&bih=564&tbm=isch
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15
• Loose soil particles can
maintain a relatively
stable slope up to a
certain angle.
• The slope angle ranges
between 25 and 40
degrees, depending on
the size and shape of the
particles.
Over-steepened Slopes
• An over-steepened slope is a slope which
exceeds the stable angle for the type of
material in the location.
http://www.google.com/imgres?biw=1242&bih=564&tbm=isc
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Over-steepened Slopes
• An over-steepened slope can result when a
stream undercuts a valley wall or waves
pound against the base of a cliff.
• People can create over-steepened slopes
during excavation for roads or other
structures
http://www.google.com/imgres?biw=1242&bih=564&tbm=isch&tbnid=TFrHAp6GUrNGbM%3A&imgrefurl=h
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Removal of Vegetation
• Plants make slopes more stable because their
root systems bind soil and regolith together.
• When plants are removed by forest fires or
human activities such as logging or farming,
the likelihood of mass movement increases.
http://www.google.com/imgres?hl=en&biw=1242&bih=564&tbm=isch&tbnid=s5crK
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Removal of Vegetation
http://www.google.com/imgres?sa=X&hl=en&biw=1242&bih=56
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age=1&start=0&ndsp=15
• In Menton France,
farmers replaced olive
trees, which have deep
roots, with carnations, a
more profitable but
shallow rooted crop.
• Planting the carnations
made the slopes less
stable.
• A landslide on one of the
slopes killed 11 people
Earthquakes
• Earthquakes are one of the most dramatic
triggers of mass movements.
• An earthquake and its aftershocks can
dislodge enormous amounts of rock and soil.
• The landslide in the
picture was triggered by
an earthquake
Types of Mass Movements
• Geologists classify mass movements based on
the kind of material that moves, how it
moves, and the speed of the movement.
• There are 5 main types of mass movement
Rockfalls, slides, slumps, flows, and creep
Rockfalls
• A rockfall occurs when rocks or rock
fragments fall freely through the air.
• This type of mass movement is common on
slopes that are too steep for loose material to
remain on the surface.
http://www.google.com/imgres?sa=X&hl=en&biw=1242&bih=564&tbm=isch&tbnid
=j3drk6LnBQtCCM%3A&imgrefurl=http%3A%2F%2Fgeology.campus.ad.csulb.edu%2
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Rockfalls
• Many rockfalls result from the mechanical
weathering of rock caused by freeze-thaw
cycles or plant roots.
• Rockfalls sometimes trigger other mass
movements.
Slides
• In a slide, a block of
material moves
suddenly along a
flat, inclined surface.
• Slides that include
segments of bedrock
are called rockslides.
Rockslides
• Rockslides are among the fastest mass
movements, reaching speeds of over 200 km
per hour.
Click for
Rockslide
Video
Slumps
• A slump is the downward
movement of a block of
material along a curved
surface.
• The material in a slump
usually does not travel very
fast or very far.
• As the block moves, its
upper surface sometimes
tilts backward.
Slumps
• Slumps leave a crescentshaped cliff just above
the slump, which you can
see in the picture.
• They are common on
oversteepened slopes
where the soil contains
thick accumulations of
clay.
Flows
http://www.google.com/imgres?start=93&biw=1242&bih=564&
tbm=isch&tbnid=t0SIVOhvQdCXrM%3A&imgrefurl=http%3A%2F
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r=193&page=8&ndsp=16
• Flows are mass
movements of material
containing a large amount
of water, which move
downslope as a thick fluid.
• Flows that move quickly,
called mudflows, are
common in semiarid
mountainous regions, such
as parts of southern
California.
Mudflows
• In these regions, protective
vegetation is sparse. A
heavy downpour or rapid
snowmelt can flood
canyons with a mixture of
soil, rock, and water.
• The mixture may have the
consistency of wet
concrete.
Mudflows
• It follows the contours of the canyon, taking
large boulders and trees along with it.
• As you see in the photo, mudflows in
populated areas are very dangerous and
destructive.
Click photo for mudflow video
Earthflows
• Earthflows are flows that
move relatively slowly—
from about a millimeter
per day to several meters
per day.
• Their movement may
continue for years.
• Earthflows occur most
often on hillsides in wet
regions.
Earthflows
• When water saturates the soil on a hillside,
the material breaks away, forming a tongueshaped mass like the one shown
Creep
• The slowest type of mass
movement is creep,
which usually only
travels a few millimeters
or centimeters per year.
• One factor that
contributes to creep is
alternating between
freezing and thawing
http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=
images&cd=&cad=rja&docid=BiCGnUaxouhl5M&tbnid=pdzHjgTkhNn
jbM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.geogrify.net%2FG
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Creep
• Because creep is so slow,
you cannot observe it
directly.
• You can recognize the
effects of creep easily
however – creep causes
structures that were once
vertical to tilt downhill.
http://courses.missouristate.edu/EMantei/creative/WeathStrem/cre
ep.jpg
Click Photo for Landslides Videos
http://www.google.com/imgres?biw=1242&bih=564&tbm=isch&tbnid=BAmPBXiDDcL_TM%3A&imgrefurl=ht
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&iact=rc&dur=503&page=3&start=25&ndsp=15
Videos
Mudflow- https://www.youtube.com/watch?v=MM1TTzARW94
Creep- http://www.youtube.com/watch?v=l1jqDLiQXbs
Rockslide= http://www.youtube.com/watch?v=ZVYGJYnJTi0
Landslide=http://www.youtube.com/watch?v=K5pidzTZslo
https://www.youtube.com/watch?v=Z02coWd2ixI
References
• Adapted from Prentice Hall Earth Science Text
at
http://mhs.wcpss.net/teachers/murphy/earth
science/textbook/este053.pdf
Picture of the day!!!!
• http://epod.usra.edu/
Today’s Schedule
5 min-Bell ringer
30 min- Mass Wasting Notes and Videos
25 min Erosion & Deposition definitions
(cause & effect), examples matching
review
10 Exit – HASHTAG VOTES
Earth & Space Science
September 16, 2014
Homework
The Ever-Changing
Surface of the Earth Part 1: Erosion WKS
Essential Question
What are different types of deposition?
Vocabulary
*Creep *Mudflow *Earthflow *Rockslide
*Landslide
Today we will…….
ES.1.18 - Demonstrate the possible effects of atmospheric changes brought on by things such
as acid rain,
ES.1.26ES.1.26 - Differentiate among the processes of weathering, erosion, transportation of
materials, deposition, and soil formation.
ES.1.27ES.1.27 - Illustrate the various processes that are involved in the rock cycle and discuss
how the total amount of material stays the same through formation, weathering,
sedimentation, and reformation.