Geo 104 project

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.