Natural Disasters 1

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Within North America, every location is at risk from at least one hazardous process

West coast:

East coast:

Mid-continent:

All areas:

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Earthquakes, landslides

Hurricanes

Tornadoes, blizzards

Drought

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internal forces within the earth

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Driven by internal energy of Earth (plate tectonics)

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External forces on surface

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Driven by sun's energy (atmospheric)

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Gravitational attraction

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Driven by the force of gravity

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Natural hazard:

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A natural process that poses a potential threat to people and property/possessions

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Risk

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Probability of an event multiplied by the impact on people or property (higher risk are more immediate)

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Consequences

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Damage to people, property, environment, economy

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Disaster

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A brief event that causes great damage or loss of life

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Hazard

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Potential threat

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Catastrophe

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Massive disaster

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Prediction

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A specific time, date, location, and magnitude of the date

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Forecast

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A range of probability for the event (more general)

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Impact

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Function of both magnitude and frequency

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Magnitude-frequency concept

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Inverse relationship between magnitude and frequency - intense hazards happen less frequently

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Tectonic cycle

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Creation, movement and destruction of tectonic plates (outer shell of the earth)

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Rock cycle

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Igneous, sedimentary and metamorphic rocks

Igneous comes from volcanic activity

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Hydrologic cycle

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the movement and exchange of water among the land, atmosphere and oceans by changes in state

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Residence time

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Length of time that a substance spends in a specific part of the natural system

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Direct effects

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Deaths, injuries, displacements of people, damage to property

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Indirect effects

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Crop failure, starvation, emotional distress, loss of employment

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Reactive approach

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Recovery, search and rescue, providing emergency water and shelter

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Proactive approach

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Land-use planning, building codes, insurance, evacuation etc

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Inner core

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Extremely hot and solid

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Asthenosphere

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Composed of hot magma with some flow

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Litosphere

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Thin and brittle crust

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Oceanic crust vs continental crust

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Oceanic: Dense, thin

Continental: relatively buoyant, thick

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Divergent

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Spread apart, move away - new land is created at these locations, results in seafloor spreading and causes oceanic ridges to form

Mid-atlantic ridge

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Convergent

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Oceanic and continental crust, moving towards each other

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Subduction zones

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Different plated hit each other, resulting in dense ocean plate sinking and melted magma rising to form volcanoes

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Collision boundaries

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When the same plates hit each other, resulting in rising land such as mountains

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Transform

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Side by side movement, slide horizontally past each other

San andreas fault

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Hot spots

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Magma rises from mantle, never changes location. Plate moves across hot spot

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Accreted

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Stuck to landscape

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Moment magnitude scale

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Determined by the area ruptured along a fault, the amount of movement along the fault, the elasticity of the crust and the focus

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Modified Mercali Scale

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Qualitative scale based on damage to structures around the affect on people

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Blind faults

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Located below the surface

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Strike-slip faults

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Displacementes are horizontal

Occur along transform faults

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Dip-slip faults

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Displacements are vertical

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Types of dip-slip faults

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Reverse: hanging-wall has moved up relative to the footwall, angle is steep

Thrust: Angle is less than reverse

Normal: Hanging-wall has moved down relative to the footwall

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Active faults

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Movement during the past 11,600

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Potentially active

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Movement during the past 2.6 million years

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Inactive

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No movement during the past 2.6 million years

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Body waves

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Include P waves and S waves

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P waves

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Primary waves, compressional waves, faster or first wav to arrive - compress in and out or push.pull movement. Travel through solids or liquids

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S waves

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Secondary or shear waves, move slowly in an up and down motion and can only travel through solids

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Surface waves

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When P and S waves reach the earth's surface and then move along it

Responsible for damage near the epicenter

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Factors that determine the shaking experienced

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Magnitude, distance to epicentre, focal depth, direction of rupture, local soil and rock type, local engineering and construction practices

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The distance to the epicentre is calculated:

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at 3 different seismic stations, triangulation

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Local soil and rock types

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Dense homogenous crust can transmit eathquake energy. this means that earthquakes in Eastern North America are felt over larger distances that those in Western North America

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The earthquake cycle

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Inactive period

Period where strain produces minor earthquakes

Period of foreshocks - prior to major release of stress (doesn't always occur)

Period where the mainshock occurs allowing the fault to release built up stress

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Plate boundary earthquakes

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Earthquakes that occur on faults separating litospheric plates

Strike-slip - thrust and normal

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Thrust earthquakes

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Subduction earthquakes, strongest, occur on faults that separate converging plates

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Intraplate earthquakes

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An earthquake on a fault in the interior of a continuant, far from a plate boundary

Smaller than plate boundary earthquakes

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Primary effects of earthquakes

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Ground shaking, surface rupture, these are physical effects

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Secondary effects of earthquakes

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Liquefaction, land-level change, landslides, fire, tsunamis

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Ground rupture

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Fault scarps can be produced that extend for kilometres

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Liquefaction

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Transformation of water-saturated sediment from solid to liquid

water pressure becomes high enough to suspend particles of sediment

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Haiti Earthquake

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Transform fault, M7.0

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Precursors to earthquakes

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Pattern and frequency of earthquakes (foreshocks and microearthquakes)

Land-level change (GPS stations)

Seismic gaps along faults (no recent quakes)

Physical and chemical changes

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Tsunami is japanese word for

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harbour wave

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Events capable of triggering tsunamis

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earthquakes

landslides

volcano flank collapse

submarine volcanic eruptions

meteorites

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Earthquakes can cause tsunamis in two ways

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displacement of the seafloor (M7.5)

triggering a landslide that enters water

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Run-up

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Maximum horizontal and vertical distances that the largest wave of a tsunami reaches as it travels inland

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distant tusnami

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Tele tsunami, travels thousands of kilometers across the open ocean

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Local tsunami

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Short distance, little warnings, shorelines affected within 100km

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Areas at risk for tsunamis

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Coasts located near subduction zones, Pacific ocean and mediterranean sea

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Primary effects of tsunamis

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Flooding and erosion destroy beaches, coastal vegetation and infrastructure

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Secondary effects of tsunamis

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Generally occur after event is over

Fires may develop due to ruptured gas lines

Water supplies contaminated

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Tsunameters

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Rest on the sea floor and measure changes in water pressure

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Outbreak

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Simultaneous, related occurrance of several cases

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Epidemic

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An uncontrolled outbreak of communicable (contagious) disease

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Pandemic

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International or wide-travelling simultaneous epidemics of the same condition

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Epidemiology

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the study of the distribution and determinants of health related events in the human population

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Agent

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The actual cause of the disease

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What is a primary effect of a tsunami?

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Beach erosion

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To locate the epicentre of an earthquake what is the minimum number of seismographs needed?

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3

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Most volcanoes are found near:

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plate boundaries, both convergent and divergent zones produce volcanoes

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Magma

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Found deep within the crust and upper mantle

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Lava

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Found flowing from an erupting volcano

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Most abundant elements in magma

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Silicon and oxygen, combined = silica

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Types of volcanic rocks from low to high silica content

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basalt, andesite, dacite, rhyolite

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High silica content magma

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Cooler, more viscous, more gases

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Low silica content magma

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hotter, less viscous, fewer gases

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Volcanoes with ____ silica content produce the most explosive eruptions

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High

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4 types of volcanoes

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Shield, composite, volcanic dome, cinder dome

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Shield volcanoes

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Largest volcanoes, shaped like broad arcs, basaltic magma

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Tephra

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Fragmented volcanic material blown out during an eruption

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Composite volcanoes

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Cone-shaped, stratovolcanoes, andesite or dacitic

Eruptions are more dangerous/explosive but less frequent than shield

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Volcanic domes

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Highly viscous rhyolite magma

Steep-sided, form around vents

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Cinder cone volcanoes

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Small, composed of small pieces of tephra

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Maars

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Circular volcanic crater produced by an explosive eruption and filled with water

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Jokulhlaups

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Volcanoes beneath glaciers that melt large quantities of ice producing floods

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Crater

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Depressed formed by the explosion or collapse of a volcano top

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Vent

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Opening on the surface through which lava and pyroclastic debris erupt

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Caldera

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Circular to oval depression formed during the collapse of a volcano - can be up to 25 km in diameter

Eruptions that form these are largest and deadliest on Earth

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Geyser

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Water boils in an underground chamber to periodically produce a release of steam/water

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Supervolcano

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Ejected material covers many of thousands of square km

Over a hot spot, not a subduction zone

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Mid-ocean ridges

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Composed of basaltic magma that originates in the asthenosphere

Shield volcanoes are found here

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Hot spots beneath oceans

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Chains of shield volcanoes containing basaltic magma form as a plate moves over a hot spot

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Hot spots beneath continents

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Produce explosive eruptions composed of rhyolitic and dacitic magma

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Primary effects of volcanoes

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Lava flows, lateral blasts, pyroclatsic flows, ash falls, poisonous gases, sector collapse, lahars

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Secondary effects of volcanoes

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Landslides, floods, fires, tsunamis

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VEI scale

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from 0 to 8, based on tephra ejected, logarithmic scale

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Pahoehoe lava

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Low viscosity (few km per hour), high temperature, when hardened it as a smooth texture

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Aa lava

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High viscosity, lower temperature, when hardered it has a blocky texture

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Lateral blasts

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Eruption directed away from a volcano where materials are blown parallel to the surface

Mt st helens is an example

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Pyroclastic flowos

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Avalanches of ash, gas, and rock fragments that travel down the slopes of volcanoes during an eruption

Speeds can reach 150km/h 30km from the source

Kills most people

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Hazards of ash fall

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Destroys vegetation

Contaminates surface water

Health hazards to people and animals

Causes aircraft engine failure

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Lahar

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Indonesian word for a large amount of material that becomes saturated with water and moves downslope

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Bombing

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Blocking a channel to force lava to take alternate route

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Hydraulic chilling

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Water used to chill lava

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Wall construction

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Redirect lava flow

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What is usually the first sign of an impending volcano eruption?

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Small earthquakes

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4 variables of landslides

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Mechanism of movement

Type of material

Amount of water present

Speed of movement

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3 mechanisms of landslides

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Fall - steep angle, dropping off a cliff

Slide - discrete failure plane, curved vs straight

Flow - movement of particle semi-independently of one another, aid of water

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Rock fall

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Caused by fall mechanism

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Slump

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Caused by slide mechanism

Failure plane is curved upward

rotational slide

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Creep

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Caused my flow mechanism, very slow

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Driving forces

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Move material downslope, based on weight of material from vegetation, water

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Resisting forces

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Oppose downslope movement; they are based on the shear strength of the material

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Factor of safety

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Ratio of resisting forces to driving forces

Rf/Df

Over 1, slope is stable

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Rotational slide

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Material moves downslope along an upward curving surface

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Translational slide

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A type of landslide where material moves downslope along a discrete plane

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Topographic relief

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Height of hill or mountain above land around it

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Talus

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Fragments of rock that have moved downslope and accumulated at its base

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Tiltmeters

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Detect movement along a slope

Some rock fences are linked to signal systems

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Two types of avalanches

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Travelling as a coherent block, or becoming wider as it travels downslope

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Point-release avalanches

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Begin as an initial failure after a heavy snowfall, sliding snow causes more failures causing the trough to widen

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Slab

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Occur when a snowpack fractures along a weak layer parallel to the surface

Move as cohesive blocks leaving behind a scarp

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Hoar

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Can form deep in the snowpack, have less strength than the rest of the snowpack

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Slope angle

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Angles below 25 degrees, snow doesn't slide, but between 25 and 60 is where most avalanches occur

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Compression test

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Vertical force is placed on the top of the snowpack to detect weak layers

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Shovel test

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Assess the strength by isolating a column of snow and applying force on the uphill side

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Rutschblock test

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Skier pushes and jumps on a column of snow to detect cohesion - best test

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Run-out zone

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Deceleration area of the avalanche