Volcanoes and Other Igneous Activity Mr. Coyle Harwood Union High School

Volcanoes and Volcanoes and Other Igneous Other Igneous

ActivityActivity

Mr. CoyleMr. CoyleHarwood Union High SchoolHarwood Union High School

The Nature of Volcanic EruptionsThe Nature of Volcanic Eruptions

► Factors determining the “violence” or Factors determining the “violence” or explosiveness of a volcanic eruptionexplosiveness of a volcanic eruption

►Temperature of the magma Temperature of the magma ►Composition of the magmaComposition of the magma►Dissolved gases in the magmaDissolved gases in the magma

► The above three factors actually control the The above three factors actually control the viscosityviscosity of a given magma which in turn of a given magma which in turn controls the nature of an eruption controls the nature of an eruption


► ViscosityViscosity is a measure of a material’s resistance is a measure of a material’s resistance to flow to flow

► Factors affecting viscosityFactors affecting viscosity►TemperatureTemperature - Hotter magmas are less - Hotter magmas are less

viscousviscous►CompositionComposition - Silica (SiO - Silica (SiO22) content) content

Higher silica content = higher viscosity Higher silica content = higher viscosity (e.g., (e.g., felsicfelsic lava such as rhyolite, lava such as rhyolite,

granite)granite)Lower silica content = lower viscosity or more Lower silica content = lower viscosity or more

fluid-like behavior (e.g., fluid-like behavior (e.g., maficmafic lava such as lava such as basalt)basalt)


►Factors affecting viscosity continuedFactors affecting viscosity continued►Dissolved GasesDissolved Gases

Gas content affects magma mobilityGas content affects magma mobility Gases expand within a magma as it nears the Gases expand within a magma as it nears the

Earth’s surface due to decreasing pressureEarth’s surface due to decreasing pressure The violence of an eruption is related to how easily The violence of an eruption is related to how easily

gases escape from magmagases escape from magma


►Factors affecting viscosity continuedFactors affecting viscosity continuedIn SummaryIn Summary►Fluid basaltic lavas generally produce quiet Fluid basaltic lavas generally produce quiet

eruptionseruptions►Highly viscous lavas (rhyolite or andesite) Highly viscous lavas (rhyolite or andesite)

produce more explosive eruptionsproduce more explosive eruptions

Materials extruded from a Materials extruded from a volcanovolcano

►Lava FlowsLava Flows►Basaltic lavas are much more fluidBasaltic lavas are much more fluid

►Types of basaltic flowsTypes of basaltic flows PahoehoePahoehoe lava (resembles a twisted or ropey lava (resembles a twisted or ropey

texture)texture) AaAa lava (rough, jagged blocky texture) lava (rough, jagged blocky texture)

A A PahoehoePahoehoe lava lava flowflow

a a typicaltypical aaaa flow flow

Materials extruded from a volcanoMaterials extruded from a volcano

► Pyroclastic materials – “Fire fragments”Pyroclastic materials – “Fire fragments”Types of pyroclastic debrisTypes of pyroclastic debris

►Ash and dust - fine, glassy fragmentsAsh and dust - fine, glassy fragments►PumicePumice - porous rock from “frothy” lava - porous rock from “frothy” lava►LapilliLapilli - walnut-sized material - walnut-sized material ►Cinders - pea-sized material Cinders - pea-sized material ►Particles larger than lapilliParticles larger than lapilli

BlocksBlocks - hardened or cooled lava - hardened or cooled lava BombsBombs - ejected as hot lava - ejected as hot lava

A volcanic bombA volcanic bomb

Bomb is approximately 10 cm long

VolcanoesVolcanoes►General FeaturesGeneral Features

►Opening at the summit of a volcanoOpening at the summit of a volcano CraterCrater - steep-walled depression at the summit, - steep-walled depression at the summit,

generally less than 1 km diametergenerally less than 1 km diameter CalderaCaldera - a summit depression typically greater - a summit depression typically greater

than 1 km diameter, produced by collapse following than 1 km diameter, produced by collapse following a massive eruptiona massive eruption

►VentVent – opening connected to the magma – opening connected to the magma chamber via a pipechamber via a pipe

VolcanoesVolcanoes

►Types of VolcanoesTypes of Volcanoes►Shield volcanoShield volcano

Broad, slightly domed-shapedBroad, slightly domed-shaped Composed primarily of basaltic lavaComposed primarily of basaltic lava Generally cover large areasGenerally cover large areas Produced by mild eruptions of large volumes of Produced by mild eruptions of large volumes of

lavalava Mauna Loa on Hawaii is a good exampleMauna Loa on Hawaii is a good example

Shield VolcanoShield Volcano

VolcanoesVolcanoes

►Types of Volcanoes continuedTypes of Volcanoes continued►Cinder coneCinder cone

Built from ejected lava (mainly cinder-sized) Built from ejected lava (mainly cinder-sized) fragmentsfragments

Steep slope angleSteep slope angle Rather small sizeRather small size Frequently occur in groupsFrequently occur in groups

Sunset Crater – a cinder Sunset Crater – a cinder cone near Flagstaff, cone near Flagstaff,

ArizonaArizona

VolcanoesVolcanoes►Types of volcanoes continuedTypes of volcanoes continued

►CompositeComposite ( (StratovolcanoStratovolcano)) Most are located adjacent to the Pacific Ocean (e.g., Most are located adjacent to the Pacific Ocean (e.g.,

Fujiyama, Mt. St. Helens)Fujiyama, Mt. St. Helens) Large, classic-shaped volcano (1000’s of ft. high & Large, classic-shaped volcano (1000’s of ft. high &

several miles wide at base)several miles wide at base) Composed of interbedded lava flows and layers of Composed of interbedded lava flows and layers of

pyroclastic debrispyroclastic debris

A composite volcanoA composite volcano

Mt. St. Helens – a Mt. St. Helens – a typical typical composite volcanocomposite volcano

Mt. St. Helens following Mt. St. Helens following the the

1980 eruption 1980 eruption

A size comparison of the A size comparison of the three three

types of volcanoestypes of volcanoes

VolcanoesVolcanoes

►Composites continuedComposites continued Most violent type of activity (e.g., Mt. Vesuvius)Most violent type of activity (e.g., Mt. Vesuvius) Often produce a Often produce a nuenueéé ardente ardente

►Fiery pyroclastic flow made of hot gases infused Fiery pyroclastic flow made of hot gases infused with ash and other debriswith ash and other debris

►Move down the slopes of a volcano at speeds up to Move down the slopes of a volcano at speeds up to 200 km per hour200 km per hour

May produce a May produce a laharlahar, which is a volcanic mudflow, which is a volcanic mudflow

A nueA nueé ardente on Mt. St. é ardente on Mt. St. HelensHelens

Other volcanic landformsOther volcanic landforms

►CalderasCalderas►Steep-walled depressions at the summitSteep-walled depressions at the summit►Size generally exceeds 1 km in diameterSize generally exceeds 1 km in diameter

►Pyroclastic flowsPyroclastic flows►Associated with felsic & intermediate magmaAssociated with felsic & intermediate magma►Consists of ash, pumice, and other fragmental Consists of ash, pumice, and other fragmental

debrisdebris

CalderaCaldera


►Pyroclastic flows continuedPyroclastic flows continued►Material is propelled from the vent at a high Material is propelled from the vent at a high

speedspeed►e.g., Yellowstone plateaue.g., Yellowstone plateau

►Fissure eruptionsFissure eruptions and and lava plateauslava plateaus►Fluid basaltic lava extruded from crustal Fluid basaltic lava extruded from crustal

fractures called fissuresfractures called fissures►e.g., Columbia River Plateau e.g., Columbia River Plateau


►Lava DomesLava Domes►Bulbous mass of congealed lavaBulbous mass of congealed lava►Most are associated with explosive eruptions of Most are associated with explosive eruptions of

gas-rich magmagas-rich magma

A lava dome on Mt. St. A lava dome on Mt. St. HelensHelens


►Volcanic pipesVolcanic pipes and and necksnecks►Pipes are short conduits that connect a Pipes are short conduits that connect a

magma chamber to the surfacemagma chamber to the surface►Volcanic necks (e.g., Ship Rock, New Volcanic necks (e.g., Ship Rock, New

Mexico) are resistant vents left standing Mexico) are resistant vents left standing after erosion has removed the volcanic after erosion has removed the volcanic conecone

Formation of a volcanic Formation of a volcanic neckneck

Shiprock, NM – a Shiprock, NM – a volcanic neckvolcanic neck

Plutonic igneous activityPlutonic igneous activity

►Most magma is emplaced at depth in the Most magma is emplaced at depth in the EarthEarth

►An underground igneous body, once cooled An underground igneous body, once cooled and solidified, is called a and solidified, is called a plutonpluton

►Classification of plutonsClassification of plutons►ShapeShape

Tabular (sheetlike)Tabular (sheetlike) MassiveMassive


► Types of intrusive igneous featuresTypes of intrusive igneous features►DikeDike – a tabular, discordant pluton– a tabular, discordant pluton►SillSill – a tabular, concordant pluton (e.g., Palisades Sill – a tabular, concordant pluton (e.g., Palisades Sill

in New York)in New York)►LaccolithLaccolith

Similar to a sillSimilar to a sill Lens or mushroom-shaped massLens or mushroom-shaped mass Arches overlying strata upwardArches overlying strata upward Mt. Kahtadin, MaineMt. Kahtadin, Maine

Some intrusive igneous Some intrusive igneous structuresstructures

A sill in the Salt River A sill in the Salt River Canyon, ArizonaCanyon, Arizona


►Intrusive igneous features continuedIntrusive igneous features continued►BatholithBatholith

Largest intrusive bodyLargest intrusive body Surface exposure of 100+ square kilometers Surface exposure of 100+ square kilometers

(smaller bodies are termed stocks)(smaller bodies are termed stocks) Frequently form the cores of mountainsFrequently form the cores of mountains

Batholiths of western Batholiths of western North America North America

Plate tectonics and igneous Plate tectonics and igneous activityactivity

►Global distribution of igneous activity is not Global distribution of igneous activity is not randomrandom

►Most volcanoes are located within or near Most volcanoes are located within or near ocean basinsocean basins

►Basaltic rocks are common in both oceanic and Basaltic rocks are common in both oceanic and continental settings, whereas granitic rocks are continental settings, whereas granitic rocks are rarely found in the oceansrarely found in the oceans

Distribution of some of the Distribution of some of the

world’s major volcanoes world’s major volcanoes

Distribution of magnitude Distribution of magnitude 5 or greater earthquakes, 5 or greater earthquakes,

1980 - 19901980 - 1990

Deep-focus earthquakes Deep-focus earthquakes occur along convergent occur along convergent

boundariesboundaries

Volcanoes and climateVolcanoes and climate

►Explosive eruptions emit huge quantities Explosive eruptions emit huge quantities of gases and fine-grained debris into the of gases and fine-grained debris into the atmosphere which filter out and reflect a atmosphere which filter out and reflect a portion of the incoming solar radiationportion of the incoming solar radiation

►Examples of volcanism affecting climateExamples of volcanism affecting climate►Mount Tambora, Indonesia – 1815Mount Tambora, Indonesia – 1815►Krakatau, Indonesia – 1883Krakatau, Indonesia – 1883►Mount Pinatubo, Philippines - 1991Mount Pinatubo, Philippines - 1991

Documents

Volcanoes and Other Igneous Activity Mr. Coyle Harwood Union High School