Volcanoes and Seismic Volcanoes and Seismic HazardsHazards

VolcanoesVolcanoes

I. What is a volcanoI. What is a volcano? ?

• Opening in EarthOpening in Earth’’s crust through which s crust through which molten rock, gases, and ash erupt.molten rock, gases, and ash erupt.

Volcano FormationVolcano Formation: :

CraterCrater – a basin-like rimmed structure at top – a basin-like rimmed structure at top or on flanks of a volcanic cone.or on flanks of a volcanic cone.

VentVent – opening at earth – opening at earth’’s surface through s surface through which volcanic material is extruded.which volcanic material is extruded.

Magma ChamberMagma Chamber – reservoir of magma in – reservoir of magma in the shallow part of the lithospherethe shallow part of the lithosphere

II. Magma Formation:II. Magma Formation:3 conditions that allow 3 conditions that allow magma to form magma to form

Example of Example of location this location this would occurwould occur

Decrease in pressure lowers Decrease in pressure lowers melting temperature of melting temperature of materials in asthenospherematerials in asthenosphere

Rift valley at mid-Rift valley at mid-ocean ridge ocean ridge

Temperature increase can Temperature increase can cause materials to melt cause materials to melt

Asthenosphere at Asthenosphere at a hot spot a hot spot

Increase in amount of water in Increase in amount of water in asthenosphere can lower asthenosphere can lower melting temperature of melting temperature of materials there materials there

Asthenosphere at Asthenosphere at subduction subduction boundaries boundaries

What Controls the Type What Controls the Type of Magma and Eruption of Magma and Eruption

Style?Style? - The viscosity of the magma- The viscosity of the magma

• What effects viscosity?What effects viscosity?

- Temperature of magma – hotter, lower - Temperature of magma – hotter, lower viscosity, more fluidviscosity, more fluid

- Composition of magma (amount of silica) – - Composition of magma (amount of silica) – more silica, higher viscosity, more resistant to more silica, higher viscosity, more resistant to flow.flow.

What Makes Magma/Lava What Makes Magma/Lava Erupt?Erupt?

• Magma is a liquid, less dense than Magma is a liquid, less dense than surrounding material.surrounding material.

• Gases within magma rise to surfaceGases within magma rise to surface

• Low viscosity lava: gases easily rise and are Low viscosity lava: gases easily rise and are gently releasedgently released

• High viscosity lava: gases build up – explosive High viscosity lava: gases build up – explosive eruptionseruptions

III. Types of MagmaIII. Types of MagmaCharacteristicCharacteristic Basaltic Basaltic

Magma Magma (Mafic)(Mafic)

Andesitic Andesitic MagmaMagma

Rhyolitic Rhyolitic Magma Magma (felsic)(felsic)

Silica contentSilica content ≤ ≤ 50% 50% ≈ ≈ 60% 60% ≈ ≈ 70% 70%

Gas contentGas content LeastLeast IntermediateIntermediate MostMost

ViscosityViscosity LeastLeast IntermediateIntermediate MostMost

Type of Type of eruptioneruption

Rarely Rarely explosiveexplosive

Sometimes Sometimes explosiveexplosive

Usually Usually explosiveexplosive

Melting Melting temperaturetemperature

HighestHighest IntermediateIntermediate LowestLowest

LocationLocation Rifts, oceanic Rifts, oceanic hotspotshotspots

Subduction Subduction boundariesboundaries

Continental Continental hotspotshotspots

Basaltic Magma: Basaltic Magma: KilaueaKilauea

Andesitic Magma: Mt. St Andesitic Magma: Mt. St HelensHelens

Rhyolitic Magma: Rhyolitic Magma: Yellowstone Caldera (rim)Yellowstone Caldera (rim)

IV. Ejected Material:IV. Ejected Material:A. Lava: A. Lava: liquid molten rockliquid molten rock

1. Pahoehoe – ropelike lava1. Pahoehoe – ropelike lava

2. Aa – crumbly lava2. Aa – crumbly lava

3. Pillow lava – thought to have 3. Pillow lava – thought to have

formed under water formed under water

B. Solid Pyroclastic Material:B. Solid Pyroclastic Material: 1. Ash – microscopic solids 1. Ash – microscopic solids

Cinders – pea-sizedCinders – pea-sized

2. Lapilli – walnut size2. Lapilli – walnut size

3. Blocks/Bombs – 3. Blocks/Bombs –

football size or biggerfootball size or bigger

4. Pyroclastic flow – avalanche of burning ash4. Pyroclastic flow – avalanche of burning ash

V. Volcanic LandformsV. Volcanic Landforms

• Cinder Cone: Cinder Cone: steep-sided, formed steep-sided, formed by explosive by explosive eruption of cinderseruption of cinders

• Small height, short Small height, short livedlived

• Sunset crater, Sunset crater, Arizona Arizona

Composite Volcano Composite Volcano (Stratovolcano)(Stratovolcano)Steep-sided, built by lava Steep-sided, built by lava

flows and pyroclastic flows and pyroclastic deposits (tephra)deposits (tephra)

alternating layers, alternating layers, intermediate composition intermediate composition

(andesitic), most (andesitic), most dangerousdangerous

Osorno volcano in the Osorno volcano in the Chilean AndesChilean Andes

Steep-sided, built by lava Steep-sided, built by lava flows and pyroclastic flows and pyroclastic

deposits (tephra)deposits (tephra)

alternating layers, alternating layers, intermediate composition intermediate composition

(andesitic), most (andesitic), most dangerousdangerous

Osorno volcano in the Osorno volcano in the Chilean AndesChilean Andes

Shield VolcanoShield VolcanoGentle slope, resembles a warriors shield, quiet Gentle slope, resembles a warriors shield, quiet eruptions of fluid lava flows (basaltic), largest eruptions of fluid lava flows (basaltic), largest landforms on earth landforms on earth Mauna LoaMauna Loa

CalderaCalderaCrater-shaped basin formed after top of a volcano Crater-shaped basin formed after top of a volcano collapsescollapsesCrater Lake, OregonCrater Lake, Oregon

Match description to type Match description to type of eruption and volcanoof eruption and volcano

• 1. Thin mafic lava flows, gentle slopes of hardened 1. Thin mafic lava flows, gentle slopes of hardened lava layers lava layers shield.shield.

• 2. Felsic thick lava flows, much pyroclastic 2. Felsic thick lava flows, much pyroclastic debris/steep slope debris/steep slope compositecomposite

• 3. Small steep-sided, formed by explosive eruption 3. Small steep-sided, formed by explosive eruption of cinders of cinders cinder conecinder cone

• 4. Mt. St. Helens 4. Mt. St. Helens composite volcanocomposite volcano

• 5. Mt. Pinatubo 5. Mt. Pinatubo part of a chain of composite part of a chain of composite volcanoesvolcanoes

• 6. Mt. Fuji 6. Mt. Fuji stratovolcano or compositestratovolcano or composite

• 7. Kilauea 7. Kilauea shieldshield

• 8. Craters on the Moon 8. Craters on the Moon lava flow field with cinder lava flow field with cinder conescones

Mt Ruapehu, New Mt Ruapehu, New ZealandZealand

• A cone A cone volcano –volcano –

• Very activeVery active

• Last Last erupted in erupted in 19951995

LaharsLaharsVolcanic mudflow Volcanic mudflow

often formed when often formed when hot ash mixes with hot ash mixes with water from melted water from melted snowand ice or a snowand ice or a

crater lake.crater lake.

Volcanic mudflow Volcanic mudflow often formed when often formed when hot ash mixes with hot ash mixes with water from melted water from melted snowand ice or a snowand ice or a

crater lake.crater lake.

Earthquake Earthquake DestructionDestruction

1. Ground Shaking1. Ground Shaking

There are several controls to amount of damage There are several controls to amount of damage any area may sustain:any area may sustain:

• Duration of shakingDuration of shaking

• Distance from epicenterDistance from epicenter

• Type of bedrock materialType of bedrock material

• Amount of slippage along faultsAmount of slippage along faults

2. Building Collapse2. Building CollapseEarthquakes donEarthquakes don’’t kill people, buildings kill t kill people, buildings kill people.people.

3. 3. FireFirePhotograph showing the great fire following the Photograph showing the great fire following the 1906 San Francisco Earthquake – magnitude 1906 San Francisco Earthquake – magnitude 8.1-8.2.8.1-8.2.

4. Landslides and Ground Subsidence4. Landslides and Ground SubsidenceDamage from the 1964 Alaskan Earthquake – a Damage from the 1964 Alaskan Earthquake – a massive earthquake where over 200 acres of massive earthquake where over 200 acres of land slid toward the ocean. (9.4)land slid toward the ocean. (9.4)

Liquefaction- Stable ground turns into Liquefaction- Stable ground turns into

fluid not capable of supporting structuresfluid not capable of supporting structures

5. Tsunami – 5. Tsunami – ““ Harbor Wave Harbor Wave””

• Most triggered by subduction-zone Most triggered by subduction-zone earthquake and earthquake induced earthquake and earthquake induced landslides.landslides.

• Wall of water is pushed up from the ocean Wall of water is pushed up from the ocean floor floor

• Can travel across ocean as a series of Can travel across ocean as a series of waveswaves

6. Ring of Fire6. Ring of FireEarthquakes and volcanoes Earthquakes and volcanoes are not distributed randomly are not distributed randomly – they occur in specific – they occur in specific

regions- usually along zones.regions- usually along zones. where plate boundaries where plate boundaries meet.meet.

7. Volcanic Hazards7. Volcanic Hazards

• Lava ash is deadlyLava ash is deadly• Mudflows (Lahars) Mudflows (Lahars)

are deadlyare deadly• Toxic gasesToxic gases• Pyroclastic bombs,Pyroclastic bombs,• Cause acid rainCause acid rain• LandslidesLandslides• Even though violent Even though violent

– often results in – often results in fertile soilfertile soil

(Ruapehu Lahar (Ruapehu Lahar emergency)emergency)

1953 Tangiwai disaster1953 Tangiwai disaster

Mt. St, Helens Mudflow and Pyroclastic Blast

Seismic Risk Map (USA)Seismic Risk Map (USA)

Geologic Hazards and Emergency Geologic Hazards and Emergency PreparednessPreparedness

• Millions live in hazardous areasMillions live in hazardous areas

• Many have no choiceMany have no choice

• Many choose to live thereMany choose to live there

• Risks and Benefits: volcanic ash creates fertile soilRisks and Benefits: volcanic ash creates fertile soil

• touriststourists

• geothermal energygeothermal energy

Scientists try to predict hazards in advanceScientists try to predict hazards in advance

- Monitoring escaping gas, Monitoring escaping gas,

- increased magma temperature, increased magma temperature,

- animal behavioranimal behavior

Good planning reduces the Good planning reduces the effects of the hazardeffects of the hazard

• Monitoring – warningMonitoring – warning

• Emergency suppliesEmergency supplies

• Families can organizeFamilies can organize

• Local emergency services be preparedLocal emergency services be prepared

• Information availableInformation available

• Buildings and roads designed to cope.Buildings and roads designed to cope.