mass wasting
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California State University, Fullerton *
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Course
101
Subject
Geology
Date
Dec 6, 2023
Type
Pages
7
Uploaded by GeneralGoat3664
Geology 101 think questions on mass wasting
Explain what mass wasting is and why it occurs on a slope
Mass
all downhill rock and soil movement due to gravity. occurs when a
slope is too steep ( past the angle of repose ) to remain stable with
existing material and conditions. Loose rock and soil, called regolith,
are what typically move during a mass-wasting event.
Explain the basic triggers of mass-wasting events and how they occur
changes that oversteepened slope angles and weaken slope stability,
such as rapid snow melt, intense rainfall, earthquake shaking, volcanic
eruption, storm waves, stream erosion, and human activities
Identify types of mass wasting
-Flows (are mass wasting events containing a large volume of water)
-slides (movements of mass along the surface of a slope.)
-slumps(occurs when a chunk of rock or soil slides downhill along a
curved failure surface. Failure surfaces are often planes of weakness.)
-creep (is the slow downslope movement of rock and soil under the
influence of gravity. Creep moves only the surface layer of the land
and is never catastrophic.)
-falls (occur when rock or debris breaks free from a steep slope and
falls through the air)
Identify risk factors for mass-wasting events
steepness of slopes, increased rainfall in the area, loss of vegetation,
and earthquakes
Discuss how water content and slope steepness affect slope stability.
Ground water has a pore water pressure which can lead to uplift force,
thus lowering the shear strength and causing a landslide slope.
A high water content leads to instability
-The angle of repose refers to the steepest stable slope angle that a
material can hold Slopes steeper than this angle will slide
-Cohesion is the tendency of a material to stick together under normal
conditions Cohesion is greatly affected by water content
Describe creep and slumps.
A slump is the sudden movement of large blocks of rock and soil down
a slope. Creep is the very slow movement of rock and soil down a
slope. It causes trees, fence posts, and other structures to tilt downhill.
Creep is the imperceptibly slow, steady, downward movement of
slope-forming soil or rock.
Describe the fast-moving mass-wasting processes in terms of water
content and speed.
Rock falls are the fastest form of mass wasting. This is because falling
rocks can attain speeds in excess of 60 miles per hour. Falling rocks
can attain these speeds because they experience relatively little air
resistance.
Differentiate between stress and strain
Stress refers to the force applied to a material per unit area, while
strain is a deformation or change in the shape of the material that
results from the applied force.
Identify the three major types of stress
Confining stress Non-directional stress resulting from burial; also
called lithostatic stress
Tensional stress Stress that pulls objects apart into a larger surface
area or volume; stretching forces.
Shear stress Stress within an object that causes a side-to-side
movement within an internal fabric or weakness.
Differentiate between brittle, ductile, and elastic deformation
Elastic deformation A type of deformation that reverses when the
stress is removed.
Ductile deformation A bending, squishing, or stretching style of
deformation where an object changes shape smoothly.
Brittle deformation A style of strain in which an object suddenly
breaks, fractures, or otherwise fails.
Differentiate the three major fault types and describe their associated
movements
Normal faults occur when two plates, one on top of the other, slide
past each other and create the fault. Reverse faults occur when one
plate slides under the other, creating a vertical offset. Strike-slip faults
happen when two plates move horizontally past each other.
Know where faults, folds, and joints are formed on this diagram.
Normal Fault ( Tensional stress/Divergent)
-Reverse fault (Compression stress/Convergent)
-Strike-slip faulting (Shear stress/transform
Name and describe different fold types
anticlines, synclines, and monoclines
Be able to describe confining stress and the three types of directed
stress (compressional, tensional, and shear).
Stress causes the build-up of strain, which causes the deformation of
rocks and the Earth's crust. Compressional stresses cause a rock to
shorten. Tensional stresses cause a rock to elongate, or pull apart.
Shear stresses cause rocks to slip past each other.
What is the difference between brittle and ductile deformation?
Brittle Deformation = rock breaks while undergoing elastic strain.
Ductile Deformation = rock breaks while undergoing plastic strain.
Pressure, temperature, and rate of deformation determine brittle
versus ductile deformation.
You should be able to read the stress vs. strain graph and locate
regions of elastic, ductile, and brittle behavior.
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Can you tell the difference between a left-lateral strike-slip fault and a
right-lateral strike-slip fault? What type is the San Andreas Fault?
Depending upon the direction of shearing Standing on one side of the
fault and looking across, did the other side move right or left? San
Andreas fault is a right-lateral strike-slip fault.
Describe anticlines and synclines, and know which has the older or
younger rocks in the center and on the limbs of the fold.
Anticlines are arch-like folds where the oldest rock layers are found in
the center. Synclines are the opposite of anticlines and are concave
up, with the youngest rock layers found in the center.
How do monoclines form?
Monoclines are folds where one limb of the fold is practically
horizontal, while the other limb is steeply dipping.
Explain how elastic rebound relates to earthquakes
Describe different seismic wave types and how they are measured
Body waves can travel through the Earth's inner layers, but surface
waves can only move along the surface of the planet like ripples on
water. Earthquakes send out seismic energy as both body and surface
waves.
The body waves (P and S) and surface waves are recorded by
a seismometer
. P waves travel fastest and are the first to arrive from
the earthquake. In S or shear waves, rock oscillates perpendicular to
the direction of wave propagation. In rock, S waves generally travel
about 60% of the speed of P waves, and the S wave always arrives
after the P wave.
Describe how seismographs work to record earthquake waves
the recording device on the mass records the relative motion between
itself and the rest of the instrument, thus recording the ground motion.
A pen hangs from the weight, and a rotating drum with paper sits
below it on the base. The tip of the pen touches the drum. When the
earth shakes from an earthquake, the drum rotates, and the weighted
pen moves back and forth due to the motion of seismic waves. The
pen records the movement of the drum.
From seismograph records, locate the epicenter of an earthquake
to find an earthquake epicenter you need at least three seismographs.
Find the distance from each seismograph to the earthquake epicenter.
The interception of the three circles is the epicenter.
Explain the difference between earthquake magnitude and intensity
Magnitude is a measure of earthquake size and remains unchanged
with distance from the earthquake. Intensity, however, describes the
degree of shaking caused by an earthquake at a given place and
decreases with distance from the earthquake epicenter.
List earthquake factors that determine ground shaking and destruction
the main factors affecting earthquake shaking intensity are
earthquake depth, proximity to the fault, the underlying soil,
Identify secondary earthquake hazards
tsunamis, fires, contamination of water supplies, gas leaks, and
power outages.
Compare and contrast the properties of P-waves and S-waves.
P waves can travel through liquid and solids and gases, while S
waves only travel through solids.
Given a seismogram, be able to identify the P-wave, S-wave, and
surface wave arrivals.
What does the Moment Magnitude Scale measure?
Total energy released
What does the Modified Mercalli Intensity Scale measure?
The effects on people
Describe the various hazards associated with earthquakes.
Ground Rupture. Deformation on the ground that marks, the
intersection of the fault with the earth's surface. …Ground Shaking.
Disruptive up, down and sideways vibration of the ground during an
earthquake
. ...
Liquefaction
. ...
Earthquake-induced Landslide
. ...
Tsunami.
Where do earthquakes occur? Describe the earthquakes (e.g., depth,
magnitude) that occur at the three types of plate boundaries.
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Shallow fault earthquakes. A fault is a break in the rock beneath our
feet
. ...
Subduction zone earthquakes. The largest earthquakes ever recorded
are subduction zone earthquakes. …
Divergent , convergent transform
shallow, intermediate, and deep.
At divergent plate boundaries, earthquakes tend to be weak and
shallow. Transform plate boundaries, have shallow, but very powerful
earthquakes. At convergent plate boundaries, where two continental
plates collide earthquakes are deep and also very powerful.