Geological Hazards
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Transcript of Geological Hazards
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