Geological HazardsGeological Hazards

Volcanoes, Earthquakes, Volcanoes, Earthquakes,

and Tsunamiand Tsunami

Session 3Session 3

Journey to the Center of the EarthJourney to the Center of the Earth

CoreCore MantleMantle CrustCrust

Cross Section of EarthCross Section of Earth

CoreCore

Inner Core: solid, iron, 13.5 g/cmInner Core: solid, iron, 13.5 g/cm³³ Outer Core: molten, iron, 10.7 g/cm³Outer Core: molten, iron, 10.7 g/cm³ Water: 1.0 g/cm³Water: 1.0 g/cm³ Mercury: 13.0 g/cm³Mercury: 13.0 g/cm³

MantleMantle

Iron oxides, magnesium, and silicatesIron oxides, magnesium, and silicates Lower and Upper MantleLower and Upper Mantle

Upper MantleUpper Mantle

Asthenosphere (plastic-like, hot tar)Asthenosphere (plastic-like, hot tar) Source of magmaSource of magma Lithosphere (rigid)Lithosphere (rigid) Top of Lithosphere is Mohorovicic Top of Lithosphere is Mohorovicic

Discontinuity (Moho)Discontinuity (Moho) Seismic waves change due to density Seismic waves change due to density

and material contrastsand material contrasts

CrustCrust

OceanicOceanic ContinentalContinental

Oceanic Oceanic

Averages 3 miles in depthAverages 3 miles in depth Composed primarily of silica (49.8%) Composed primarily of silica (49.8%)

and alumina (16.7%)and alumina (16.7%) SimaSima Rock is basalt (non-explosive)Rock is basalt (non-explosive) 3.0 gm/cm3.0 gm/cm³³

ContinentalContinental

19 miles interior, 31-37 miles under 19 miles interior, 31-37 miles under mountainsmountains

Silica (60.1%) and alumina (15.6%)Silica (60.1%) and alumina (15.6%) Rock is granite (continents formed of Rock is granite (continents formed of

this material)this material) 2.7 gm/cm2.7 gm/cm³³ SialSial

Plate TectonicsPlate Tectonics

Lithosphere moving over the Lithosphere moving over the asthenosphereasthenosphere

Movement and interaction of platesMovement and interaction of plates Tectonic cycle: magma from Tectonic cycle: magma from

asthenosphere, seafloor spreading, asthenosphere, seafloor spreading, subductionsubduction

Approximately 250 million yearsApproximately 250 million years

Continental DriftContinental Drift

German climatologist Alfred Wegener German climatologist Alfred Wegener proposed theory in early 1900sproposed theory in early 1900s

Pangaea: supercontinentPangaea: supercontinent Jigsaw puzzleJigsaw puzzle

PangaeaPangaea

Changes in Continents Over TimeChanges in Continents Over Time

Subduction ZonesSubduction Zones

Pacific Ocean PlatesPacific Ocean Plates

Plate BoundariesPlate Boundaries

DivergentDivergent ConvergentConvergent TransformTransform

Spreading CenterSpreading Center Pulls apartPulls apart Usually in oceanic ridgeUsually in oceanic ridge Shallow earthquakesShallow earthquakes Volcanic activityVolcanic activity Adds material from asthenosphereAdds material from asthenosphere

Divergent ZonesDivergent Zones

Divergent ZonesDivergent Zones

Subduction ZonesSubduction Zones

Oceanic Trenches and RidgesOceanic Trenches and Ridges

Convergent ZonesConvergent Zones

Plates moving in opposite directionsPlates moving in opposite directions One plate subducts the otherOne plate subducts the other Remove part of crustRemove part of crust

Convergent LandformsConvergent Landforms

Mountain rangesMountain ranges VolcanoesVolcanoes Deep ocean trenchesDeep ocean trenches

Convergent ExamplesConvergent Examples

Subduction ZonesSubduction Zones

““Recycling” of crustal material in the Recycling” of crustal material in the lithospherelithosphere

Convective processConvective process Powerful earthquakes with strong Powerful earthquakes with strong

compressive forcescompressive forces Due to strong rocks under Due to strong rocks under

compression, store greater energy compression, store greater energy before rupturingbefore rupturing

Subduction AnimationSubduction Animation

http://www.classzone.com/books/earth_science/terc/content/visualizations/es0902/es0902page01.cfm

http://oceanexplorer.noaa.gov/explorations/03fire/logs/subduction.html

Transform BoundariesTransform Boundaries

Plates slip past each other laterallyPlates slip past each other laterally Vertical fractures called transform Vertical fractures called transform

faultsfaults Many boundaries near midocean Many boundaries near midocean

ridgesridges California (San Andreas)California (San Andreas)

Transform ExampleTransform Example

What is Vulcanism?What is Vulcanism?

Refers to all phenomena connected Refers to all phenomena connected with the origin and movement of with the origin and movement of molten rockmolten rock

Magma vs. LavaMagma vs. Lava

Magma: molten rock under the Magma: molten rock under the surfacesurface

Lava: molten rock above the surfaceLava: molten rock above the surface

ExtrusiveExtrusive

Magma expelled on the surface while Magma expelled on the surface while still moltenstill molten

VolcanismVolcanism

IntrusiveIntrusive

Magma solidifies in the shallow crust Magma solidifies in the shallow crust near the surfacenear the surface

PlutonicPlutonic

Magma solidifies deep inside the Magma solidifies deep inside the EarthEarth

VolcanoVolcano

Mountain formed by the Mountain formed by the accumulation of erupted lava and/or accumulation of erupted lava and/or volcanic ashvolcanic ash

Classifying VolcanoesClassifying Volcanoes

Appearance (size and slopes)Appearance (size and slopes) Magma compositionMagma composition Volatile contentVolatile content

Types of VolcanismTypes of Volcanism

Silicic: explosiveSilicic: explosive Basaltic: non-explosiveBasaltic: non-explosive

Explosive Eruption StylesExplosive Eruption Styles

Phreatic: Violent steam-driven explosionsPhreatic: Violent steam-driven explosions Phreatomagmatic: magma more than Phreatomagmatic: magma more than

steamsteam Strombolian: rapidly expanding steam Strombolian: rapidly expanding steam

bubbles in magma forms a cinder conebubbles in magma forms a cinder cone Vulcanian: ash-fall dominatedVulcanian: ash-fall dominated PelPeléan: high ash columns and ash flowséan: high ash columns and ash flows Plinian: silica-rich ash falls, large volume of Plinian: silica-rich ash falls, large volume of

magma potentially causes a collapsemagma potentially causes a collapse

Volcanic Explosivity IndexVolcanic Explosivity Index

Silicic VolcanismSilicic Volcanism

Source is subduction zones consists of Source is subduction zones consists of basalt and silicate sediment (high silica basalt and silicate sediment (high silica content)content)

Requires large amount of heat to meltRequires large amount of heat to melt Results in cooler magma temperatures Results in cooler magma temperatures

(870(870˚ C)˚ C) Gases can’t dissolve due to lower Gases can’t dissolve due to lower

temperatures, trapped in bubblestemperatures, trapped in bubbles Magma near surface, confining pressure Magma near surface, confining pressure

results in explosive releaseresults in explosive release

Basaltic VolcanismBasaltic Volcanism

Low silica contentLow silica content Higher magma temperatures (1200Higher magma temperatures (1200˚ ˚

C)C) Greater heat dissolves most of the Greater heat dissolves most of the

gasesgases Lava is more fluid than explosiveLava is more fluid than explosive Non-explosive, large quantities of Non-explosive, large quantities of

lava (basaltic flood)lava (basaltic flood)

Temporal PatternsTemporal Patterns

Active: relatively recent or frequent Active: relatively recent or frequent activityactivity

Dormant: quiet for some time but Dormant: quiet for some time but considered potentially activeconsidered potentially active

Extinct: not known to erupt since Extinct: not known to erupt since discoverydiscovery

Can go from extinct to dormant to Can go from extinct to dormant to activeactive

Major CategoriesMajor Categories

ShieldShield StratovolcanoStratovolcano Lava DomesLava Domes Cinder ConesCinder Cones

Volcanic TypesVolcanic Types

Shield VolcanoesShield Volcanoes

Categorized as BasalticCategorized as Basaltic Broad, gently sloping mountainsBroad, gently sloping mountains Structure are from layers of lava Structure are from layers of lava

flowsflows ““Quiet” eruptions of fluid lavaQuiet” eruptions of fluid lava

Shield ExamplesShield Examples

Mauna LoaMauna Loa KilaueaKilauea Mount EtnaMount Etna

StratovolcanoesStratovolcanoes

Composite or AndesiticComposite or Andesitic Medium to Large, medium-to-steep-Medium to Large, medium-to-steep-

sided, with a symmetrical conesided, with a symmetrical cone Moderate viscosityModerate viscosity Moderate to high volatile contentModerate to high volatile content

Stratovolcano ExamplesStratovolcano Examples

Mount St. HelensMount St. Helens Mount FujiMount Fuji Mount VesuviusMount Vesuvius

Lava DomesLava Domes

RhyoliticRhyolitic Small to moderate size, high magma Small to moderate size, high magma

viscosity, steep flanks, and low to viscosity, steep flanks, and low to moderate volatile contentmoderate volatile content

Usually erupts only once but can be Usually erupts only once but can be replaced by another domereplaced by another dome

Lava Dome ExampleLava Dome Example

On Mount St. HelensOn Mount St. Helens Mount PelMount Peléeée

Cinder ConesCinder Cones

Small, steep-sided cones, low Small, steep-sided cones, low viscosity, and moderate volatile viscosity, and moderate volatile contentcontent

Rising basalt magma meets Rising basalt magma meets groundwatergroundwater

Pyroclastics ejected from a central Pyroclastics ejected from a central vent and occasional lava flowsvent and occasional lava flows

Cinder Cone ExamplesCinder Cone Examples

Haleakala CalderaHaleakala Caldera ParicutParicutínín

Volcanic HazardsVolcanic Hazards

Lava FlowsLava Flows TephraTephra Pyroclastic FlowsPyroclastic Flows LaharsLahars Poisonous GasesPoisonous Gases

Lava FlowsLava Flows

Minimal loss of life but considerable Minimal loss of life but considerable damage to property and cropsdamage to property and crops

Pahoehoe: smooth tops with a Pahoehoe: smooth tops with a billowy surfacebillowy surface

Aa: Rubble on the surfaceAa: Rubble on the surface

Pahoehoe and AaPahoehoe and Aa

TephraTephra

Fine-grained fragmented debris and Fine-grained fragmented debris and ash that contains bits of volcanic ash that contains bits of volcanic glass and is very abrasiveglass and is very abrasive

Potential for structural damage from Potential for structural damage from roof collapse and mechanical failure roof collapse and mechanical failure due to clogging of air intakesdue to clogging of air intakes

Breathing problemsBreathing problems

Pyroclastic FlowsPyroclastic Flows

Most deadly geohazardMost deadly geohazard Hot volcanic ash and steam that pour Hot volcanic ash and steam that pour

downslopedownslope Hot and plastic like material and Hot and plastic like material and

become sheets of welded ashbecome sheets of welded ash Incinerate anything in the pathIncinerate anything in the path

LaharsLahars

Hot MudflowsHot Mudflows Flow downslope at very fast speeds Flow downslope at very fast speeds

with the density of wet concretewith the density of wet concrete Gathers rocks during downhill Gathers rocks during downhill

journeyjourney

Poisonous GasesPoisonous Gases

Carbon dioxide: concentrates in Carbon dioxide: concentrates in depressionsdepressions

Suffocates people and animals Suffocates people and animals without warningwithout warning

Sulfur dioxide: sharply acrid smell Sulfur dioxide: sharply acrid smell and choking effectand choking effect

Reacts with oxygen to form sulfur Reacts with oxygen to form sulfur trioxide which reacts with water trioxide which reacts with water vapor to make sulfuric acidvapor to make sulfuric acid

Volcano Case StudiesVolcano Case Studies

Mt. St. HelensMt. St. Helens KilaueaKilauea

Earthquakes 101Earthquakes 101

““Shaking of the Earth by seismic Shaking of the Earth by seismic waves radiating away from a waves radiating away from a disturbance, most commonly a fault”disturbance, most commonly a fault”

““Shaking of the ground, usually Shaking of the ground, usually caused by rocks rupturing under caused by rocks rupturing under stress”stress”

VulnerabilityVulnerability

Which state is #1 in earthquakes?Which state is #1 in earthquakes?

Ranking of Earthquakes by StateRanking of Earthquakes by State

Key TermsKey Terms

Focus: place within the Earth where Focus: place within the Earth where the rock breaks (aka as hypocenter)the rock breaks (aka as hypocenter)

Foci occur from 435 mi. (700 km) in Foci occur from 435 mi. (700 km) in depth to the surfacedepth to the surface

Epicenter: point on the Earth’s Epicenter: point on the Earth’s surface directly above the focussurface directly above the focus

Most damage usually most severe at Most damage usually most severe at or near the epicenteror near the epicenter

Earthquake DepthsEarthquake Depths

Shallow Focus: Surface to 100 km Shallow Focus: Surface to 100 km (62 mi)(62 mi)

75% shallow focus75% shallow focus Intermediate: 100-300 km (62-186 Intermediate: 100-300 km (62-186

mi)mi) Deep: 300-700 km (186-435 mi)Deep: 300-700 km (186-435 mi)

FaultsFaults

Breaking apart of rocksBreaking apart of rocks Rock is broken with accompanying Rock is broken with accompanying

displacement (actual movement of displacement (actual movement of the crust on one or both sides of the crust on one or both sides of fault)fault)

Vertical, horizontal, or bothVertical, horizontal, or both

Four Main TypesFour Main Types

NormalNormal ReverseReverse Strike-slipStrike-slip OverthrustOverthrust

Types of FaultsTypes of Faults

Fault AnimationFault Animation

http://www.classzone.com/books/earth_science/terc/content/visualizations/es1103/es1103page01.cfm

http://www.iris.washington.edu/gifs/animations/faults.htm

Seismic WavesSeismic Waves

Energy released when Earth shakesEnergy released when Earth shakes Measured by seismometerMeasured by seismometer Body WavesBody Waves Surface WavesSurface Waves

Body WavesBody Waves

FastestFastest Short-periodShort-period Most energetic for short distances Most energetic for short distances

close to epicenterclose to epicenter Primary WavesPrimary Waves Secondary WavesSecondary Waves

Primary WavesPrimary Waves P waveP wave Fastest and first to reach recording Fastest and first to reach recording

stationstation Move in push-pull or compressional Move in push-pull or compressional

motion (slinky)motion (slinky) Table bump with bowl of soupTable bump with bowl of soup Similar to sound waves but moves Similar to sound waves but moves

through solids, liquids, and gasesthrough solids, liquids, and gases Sonic boom phenomena-window rattlingSonic boom phenomena-window rattling

Secondary WavesSecondary Waves

S wavesS waves Second (slower) wave to reach recording Second (slower) wave to reach recording

stationstation Transverse waves with motion at right Transverse waves with motion at right

angles to direction of movementangles to direction of movement Lift end of table rapidly up and downLift end of table rapidly up and down Only travels through solids, reflected back Only travels through solids, reflected back

into rock or another form if it hits liquid or into rock or another form if it hits liquid or gasgas

Causes severe damageCauses severe damage

Surface WavesSurface Waves

Body waves disturbing the surfaceBody waves disturbing the surface Rock in water with ripplesRock in water with ripples Slower than body waves, more land Slower than body waves, more land

movement, more damagemovement, more damage Love WavesLove Waves Rayleigh WavesRayleigh Waves

Love WavesLove Waves

Similar to S waves but motion is side-Similar to S waves but motion is side-to-side in a horizontal plane more or to-side in a horizontal plane more or less parallel to Earth’s surfaceless parallel to Earth’s surface

Faster than Rayleigh wavesFaster than Rayleigh waves Don’t move through liquids or gasesDon’t move through liquids or gases

Rayleigh WavesRayleigh Waves

Forward-rotating waves (lift table up Forward-rotating waves (lift table up and down and rotate simultaneously)and down and rotate simultaneously)

Moves ground up and down along Moves ground up and down along with side-to-sidewith side-to-side

Most shaking feltMost shaking felt More shallow the epicenter, more P More shallow the epicenter, more P

and S energy, more energy into and S energy, more energy into RayleighRayleigh

Wave AnimationWave Animation

http://www.classzone.com/books/earth_science/terc/content/visualizations/es1002/es1002page01.cfm?chapter_no=visualization

Measuring EarthquakesMeasuring Earthquakes

MagnitudeMagnitude IntensityIntensity AccelerationAcceleration

MagnitudeMagnitude

Richter ScaleRichter Scale Measures amplitude of seismic Measures amplitude of seismic

waveswaves Non-linear scaleNon-linear scale Each whole unit represents a ten-fold Each whole unit represents a ten-fold

increase in wave amplitude and a 32 increase in wave amplitude and a 32 fold increase in energyfold increase in energy

Most commonMost common

Descriptor Descriptor Magnitude Magnitude Average Average Annually Annually

GreatGreat 8 and 8 and higherhigher

1 ¹1 ¹

Major Major 7 - 7.9 7 - 7.9 17 ² 17 ²

Strong Strong 6 - 6.9 6 - 6.9 134 ² 134 ²

Moderate Moderate 5 - 5.9 5 - 5.9 1319 ²1319 ²

Light Light 4 - 4.9 4 - 4.9 13,00013,000(estimated)(estimated)

Minor Minor 3 - 3.9 3 - 3.9 130,000130,000(estimated)(estimated)

Very Minor Very Minor 2 - 2.9 2 - 2.9 1,300,0001,300,000(estimated)(estimated)

¹ Based on observations since 1900. ¹ Based on observations since 1900. ² Based on onservations since 1990.² Based on onservations since 1990.

Number and Magnitude of QuakesNumber and Magnitude of Quakes

Moment MagnitudeMoment Magnitude

More accurate than RichterMore accurate than Richter Relies on amount of movement along Relies on amount of movement along

faultfault Used for big earthquakesUsed for big earthquakes

MagnitudMagnitude e ChangeChange

Ground Motion Ground Motion ChangeChange(Displacement)(Displacement)

Energy Energy ChangeChange

1.01.0 10.0 times10.0 times about 32 timesabout 32 times

0.50.5 3.2 times3.2 times about 5.5 about 5.5 timestimes

0.30.3 2.0 times2.0 times about 3 timesabout 3 times

0.10.1 1.3 times1.3 times about 1.4 about 1.4 timestimes

Change of Magnitude and EnergyChange of Magnitude and Energy

IntensityIntensity

Mercalli ScaleMercalli Scale Damage perceptionDamage perception QualitativeQualitative I to XIII to XII

Mercalli ScaleMercalli Scale

AccelerationAcceleration

Rate of change of velocityRate of change of velocity ““g” forceg” force Building design in earthquake areasBuilding design in earthquake areas Construction materials for periods of Construction materials for periods of

buildingsbuildings Geology and natural periods (hard Geology and natural periods (hard

rocks versus soft sediment)rocks versus soft sediment) Potential to amplify shakingPotential to amplify shaking

Comparison of Magnitude, Comparison of Magnitude, Intensity, and AccelerationIntensity, and Acceleration

Earthquake Case StudiesEarthquake Case Studies

Loma PrietaLoma Prieta New MadridNew Madrid

TsunamiTsunami

Sea wave generated by a major Sea wave generated by a major disturbance of the seafloor and disturbance of the seafloor and overlying wateroverlying water

Japanese word: tsu=harbor, Japanese word: tsu=harbor, nami=wavesnami=waves

No pluralNo plural Hard to detect on open oceansHard to detect on open oceans Narrow topography of shoreline forces Narrow topography of shoreline forces

higher waves higher waves

Various CausesVarious Causes

Deep ocean faultsDeep ocean faults Volcanic eruptionsVolcanic eruptions Caldera collapsesCaldera collapses LandslidesLandslides Meteorite impactsMeteorite impacts

Most Common CauseMost Common Cause

Earthquakes with fault movements Earthquakes with fault movements under the oceanunder the ocean

Vertical fault movements, primarily Vertical fault movements, primarily PacificPacific

Pronounced vertical offsets of the sea Pronounced vertical offsets of the sea floorfloor

Disturbs deep oceanDisturbs deep ocean Water can’t be compressed so it Water can’t be compressed so it

transmits energy as wavestransmits energy as waves

CharacteristicsCharacteristics

Waves have exceptionally long Waves have exceptionally long wavelengths (crest-to-crest distance)wavelengths (crest-to-crest distance)

Drag across ocean bottomDrag across ocean bottom Moves about 420-518 mph (435 avg. Moves about 420-518 mph (435 avg.

in Pacific)in Pacific) Width can be up to 60 mi (100 km), Width can be up to 60 mi (100 km),

wide as Lake Michiganwide as Lake Michigan

More CharacteristicsMore Characteristics

Low in open oceanLow in open ocean 1.5’ (.5 m)1.5’ (.5 m) Speed decreases near shore (shallow Speed decreases near shore (shallow

water depth) but height dramatically water depth) but height dramatically increasesincreases

Water commonly withdraws quickly Water commonly withdraws quickly from shorefrom shore

Water rises from offshore to form the Water rises from offshore to form the first tsunami wave to strike the coastfirst tsunami wave to strike the coast

Even MoreEven More

Successive tsunami may reach several Successive tsunami may reach several tens of meters in height depending on tens of meters in height depending on local conditionslocal conditions

Intervals of tsunami can be 15 Intervals of tsunami can be 15 minutes to an hour due to long minutes to an hour due to long wavelengthswavelengths

First tsunami often not the highestFirst tsunami often not the highest High tide more dangerous due to High tide more dangerous due to

higher water levelhigher water level

Tsunami Case StudiesTsunami Case Studies

1946 1946 Aleutian Earthquake and Tsunami

1964 Great Alaskan Earthquake