Date post: | 10-Nov-2014 |
Category: |
Education |
Upload: | cari-lutkins |
View: | 486 times |
Download: | 3 times |
GEO 104 FINAL PROJECTCARI GRACE LUTKINS – REAGAN SNYDER – HANNAH MILLER – WOOD COLLINS
EARTHQUAKES
Sudden movement of a block of Earth’s crust along a geologic fault; the movement releases
accumulated strain in the rocks.Focus
Point along a fault where rock rupture occurs
Epicenter Geographic location of
the place directly above the Earthquake focus
Earthquakes are compared based on:
Magnitude Amount of energy released, measured on a logarithmic
scale
Moment Magnitude Area of rupture along fault Amount of movement (slippage along fault) Rigidity of the rocks at a point of failure
Richter Magnitude Developed for Southern CA by Charles Richter No longer commonly used for seismologists
Ground shaking increases by 10x for each unit
Earthquakes are compared based on:
(Cont.)Intensity
Effects on people and structures
Measured by the Modified Mercalli Scale Qualitative scale (I-XII) based on damage to structures &
people’s perception of shaking Modified Mercalli Intensity Maps show where the damage is
most severe
Intensity based on: Distance from Epicenter Depth of focus/slip direction Local geologic conditions
Fault Types
Strike-Slip Crust moves in horizontal direction
Dip-Slip Vertical movement Include 2 walls defined by miners as:
Footwall (Where miners put their feet) Hanging wall (Where they hang their
lanterns) Named by which direction (up or down) the
hanging wall moves relative to the footwall
Normal Fault Hanging wall moves down relative to footwall
Reverse Fault Hanging wall moves down relative to footwall
Blind Fault Are not visible from the surface
Secondary Effects
• Liquefaction• Similar to quick sand, can
produce sand blows
• Common in >5.5M earthquakes
• After shaking stops, ground re-compacts & becomes solid
• Elevation Changes• Regional uplift & subsidence
• Can cause substantial damage on coasts & streams
• Fires• Displacements cause power &
gas lines to break/ignite
• Hard to put out because water lines are often broken
• Disease• Caused by a loss of sanitation
& housing, contaminated water supplies, and disruption of public health services
Interaction with Earthquakes
Human Interaction
Reservoir-Induced Seismicity The weight from water
reservoirs may create new faults
Deep well disposal Liquid waste disposal deep
in the Earth can increase fluid pressure on faults
Nuclear Explosions Can cause the release of
stress along existing faults
Minimizing the hazard
Focused on forecast & warning
Estimating seismic risk Hazard maps
Short-Term Prediction Gives timeframe &
location. Relies on precursors, pattern & frequency, deformation of ground surface, Seismic gaps, & geophysical changes
VOLCANOES
Volcanoes are directly related to plate tectonics
Most are near plate boundaries; some associated with hot spots Active plate boundaries: Subduction zones,
Convergent Boundaries, Divergent Boundaries Magma formed at Plate boundaries turn into
lava at the surface
MAGMAThree Types:
• Basaltic (40-55% silica)
• Ocean Islands
• Andesitic (55-65% silica)
• Island & Volcanic arcs
• Rhyolitic (>65% silica)• Continental volcanoes
Volatile content determines how explosive the eruption
will be. • Increases with increasing
silica content
• High volatile content =explosive eruption
Viscosity affects the flow of lava & therefore shape
and eruption style• Low viscosity = water, honey
• High viscosity = peanut butter
Volcanic Structures
Shield Volcanoes Largest in the world Form oceanic islands Low viscosity, low volatile
content Rapidly flowing lava; non-
explosive Resembles warrior shield; low
gradient Examples: Hawaiian Islands,
Iceland
Composite Volcanoes Magma more viscous; higher
volatile content Mixture of explosive activity &
lava flows Forms typical cone shape Also called Stratovolcanoes Produces island arcs, volcanic
arcs Responsible for most death &
destruction Examples: Mt. Rainer & Mt. Fuji
Volcanic Structures; cont.
Volcanic Domes Most viscous; highly
explosive Small domes often form
within crater after large eruption
Examples: Mt. St. Helens
Cinder Cones Built from accumulation of
tephra Small pieces of vesicular
black or red lava (cinders) Forms when lava meets
water Common on the flanks of
larger volcanoes & normal faults
Examples: Paricutin, Mexico
Primary Effects
Pyroclastic Flows Avalanches of hot ash, rock,
volcanic glass fragments, & gas that move rapidly down the sides
Known as Nuee Ardentes Incinerate everything in it’s path
Ash Fall Vegetation destroyed, surface
water contaminated Accumulation on roofs cause
structural damage Irritation of respiratory system &
eyes Engines of jet aircraft may
“flame out”
Poisonous Gases Water vapor, CO2, CO, SO2, H2S Carbon dioxide gas is odorless &
heavy; can accumulate & suffocate animals and people
Chemicals can contaminate soil & plants
Can cause air pollution: Vog (volcanic smog)
Secondary Effects
• Lahars• Loose tephra becomes
saturated with water, becomes unstable & moves downward. Types:• Mud Flows
• Debris Flow
• Sources of water: melted snow & rainfall
• Landslides• May be triggered by
events other than eruptions; Can cause tsunamis
• Earthquakes• Accompany volcanic
eruption
• Fires• Hot lava may ignite plants
& structures
• Climate Change• Ash & SO2 reflect sunlight
Human Interaction• Land surface monitoring• Monitoring volcanic gas
emissions• Mapping & dating of volcanic
deposits
• USGS Alert Notification System
• Hydraulic chilling: Attempt to control lava flow with water
Landslides
Rapid downslope movement of rock or soil as a coherent mass (Also refers to mass wasting) Include earth flows, rock falls, & avalanches
Slopes
Types of slopes: Convex Slope Straight Slope Concave Slope
The driving forces on slopes are a big factor in the causes of landslides
Weight of the slope (such as vegetation, buildings, fill material) causes downslope movement
Steepness of the slope causes the driving force to be greater
Vegetation provides a protective cover that slows surface erosion
Climate• Arid regions are more
prone to rock falls, debris flows, & soil slips
• Humid Regions are more prone to complex landslides, earth flows, and creep
Snow Avalanches
• Downslope movement of snow & ice
• Thousands occur each year in the U.S.
• Snow slopes greater than 25 degrees are unstable depending to temperature & wetness of snow grains
Landslide Prevention
25 People are killed each year from landslides, and the damages are worth over $1 Billion
Drainage Control Keeps the water from infiltrating a slope and
the drains can divert the water elsewhere
Retention Walls Concrete or filled wire baskets Can be placed at the base, middle, or near the
top of the slope
FLOODING
The natural process of overbank flow
Primary effect of hurricanes
Secondary effect of earthquakes and landslides
Factors that cause
flooding:• The amount and distribution of precipitation in the drainage
basin• The rate at
which the precipitation
soaks into the earth
• How quickly surface runoff
from that precipitation
reaches the river
Velocity, Discharge, Erosion & Deposits
Streams are the primary transportation & erosional agent in the Rock Cycle
Amount of erosion & deposition depends on: Velocity: Speed of the water Discharge: Volume of water flowing through a cross sectional area
of the stream channel p/unit time Discharge increases downstream because of the addition of water
from tributary streams to the main channel Changes in channel area lead to changes in velocity Narrow channels have higher velocity than wide ones
Stream flow widens & slows when moving from high to low gradient Deposited sediment forms an alluvial fan or delta
Flood Characterizations
Flood discharge Discharge of the stream at
the point where water overflows the channel banks A graph showing changes
in stream discharge, water depth, or state over time is called a hydrograph
Flood Stage Used to indicate that the
elevation of the water surface has reached a level likely to cause damage to personal property
Flash Floods Produced by intense rainfall of
short duration over a relatively small area Most common in arid &
semiarid environments plus areas with steep topography or little vegetation
Effects of FloodsPrimary effects (Directly
caused by the flood) Injury & loss of life Damage caused by
currents, debris, and sediment
Erosion & deposition of sediment
Secondary Effects (Indirect effects of the flood) Short-term pollution of
streams Hunger & Disease Displacement &
homelessness
Natural Service Functions
• Fertile Lands• Floods deposit
sand, silt, clay & organic matter
• Aquatic Ecosystems• Help flush out
stream channels & remove debris
• Sediment Supply• Helps keep
the elevation of a landmass above sea-level
Human Interaction
Land Use Changes Amount of water or sediment
received by a stream changes it’s gradient or cross-sectional shape, effecting the velocity of the water Streams & rivers maintain
Dynamic Equilibrium
Dam Construction Upstream the water will slow down
& deposit sediment, downstream can carry additional sediment & cause erosion
Urbanization Rate of increase is determined by
percentage of land covered with roofs, pavement, and cement
Minimizing the hazard
Physical barriers Levees Flood Walls Reservoirs to store water On-site storm water retention
basins
Channelization Straightening, deepening,
widening, clearing, and or lining existing stream channels
Summary of Risk
Earthquake Ground Rupture
Shaking
Liquefaction
Elevation
Changes
Landslides
Fires
Disease
Volcano Lava Flow
Ash Fall
Pyroclastic Flow
Gases
Debris Flow
Mudflow
Landslides
Tsunamis
Global Cooling
Floods
Fires
Flooding
Injury; Death
Damage caused by currents, debris, sediment
Erosion & deposition of sediment
Short-term pollution of streams
Hunger; disease
Displacement, homelessness
Landslide Damage to
homes, roads, & utilities
Block roads, impeding travel
Block streams, shipping lanes
People hit with or buried by falling debris
Flooding upstream
Recommendation for Building Project
We recommend the neighborhood of Walnut Heights for the building project site because of its lowest risk associated with volcanoes,
landslides, floods, and earthquakes compared to all other
neighborhoods of Hazard City.