VolcanoA naturally occurring opening

in the surface of the Earth through which molten,

gaseous, and solid material is ejected.

~Encarta

EXPLORE CHAPTERS

Introduction

Etymology

Plate Tectonics & Hotspots

Types of Volcanoes

Lava Composition

Lava Behavior

Types of Eruptions

Ring of Fire

2009 AFWA Issued volcano products

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IntroductionIntroduction

As a METSAT analyst, it is your job to explore all available information tools to help determine the location of a volcanic eruption of ash and the extent of the height and direction of where the ash will travel.

*It is important to note that while it is important to observe where lava is flowing, advisory products will only be issued

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Make note of everything that can eject from a volcano and think about how each can impact the local population and aircraft flying near or

through the eruption cloud.

INTRODUCTION

EtymologyEtymology

• The word volcano is derived from the name of Volcano, a volcanic island in the Aeolian Islands of Italy whose name in turn originates from Vulcan, the name of a god of fire in Roman mythology.

• The study of volcanoes is called volcanology.

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Plate Tectonics & Hotspots

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Divergent plate boundaries

Convergent plate boundaries

Hotspots

The pulling apart of plates, causing

molten rock to come to the top of

the mantle. Causes mainly

submarine volcanic activity and creates new oceanic crust.

The collision of plates, causing Subduction or

one plate to submerge

beneath the other.

Located away from tectonic plates, over

mantle plumes where pipes vent

magma. Volcanoes formed

over hotspot go dormant and new ones are formed

when plates move overhead.

Divergent Plate Boundaries Most divergent plate boundaries are at the bottom of the

oceans, causing most of the volcanic activity to be submarine, thus forming new seafloor.

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Convergent Plate Boundaries

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When two plates (usually an oceanic and continental plate) collide, causing the one plate to submerge under the other plate (called subducting). In the case of oceanic-continental, a deep trench just off shore is formed.

When the viscous magma, high in silica content, reaches the surface, a volcano is formed.

*This is what caused the typical Ring of Fire volcanoes.*

Oceanic - Oceanic convergenceContinental - Continental convergenceOceanic - Continental convergence

PLATE TECTONICS

How Plate Tectonics Work

1 – Lithosphere: Continental & Oceanic2 – Asthenosphere3 – Softened, dense rock flows slowly4 – Convection currents bring hot material up toward the surface5 – Convection currents diverge at base of lithosphere; pulls on the solid plate. Tension causes solid plate to break apart (divergent plate boundary)6 – Space fills with molten rock (magma). Seawater cools magma and solidifies, forming new oceanic lithosphere. Over time mid-ocean ridge gets larger.7 - The older part of plate moves away from the ridge, where the new lithosphere has been added. 8 – The further away the plate moves from the spreading ridge, it cools. The colder the plate, the heavier it becomes. The furthest edge from the ridge becomes denser than asthenosphere beneath it.

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How Plate Tectonics WorkCont’d

9 – The dense plate sinks beneath another, causing a subduction zone to form. 10 – The sinking edge pulls the rest of the plate behind it.11 – Subduction zones are a form of convergent plate boundary. The less dense continental plate floats above the more dense asthenosphere.12 – Extreme heat and pressure at depth of the subducting plate cause fluids to sweat, which percolate upward and melts overlying solid mantle above the plate to form pockets of magma.13 – The new magma is less dense than surrounding rock and rises toward surface. It cools and solidifies as large intrusive rocks. When exposed by erosion, forms the cores of great mountain ranges (i.e. Sierra Nevada & Andes)14 – Some molten rock reaches Earth’s surface to erupt , forming volcanic rocks. Accumulation of layers over time construct volcanic mountain ranges (i.e. Cascade range)

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HotspotsLocated over a mantle plume, where the convection of the Earth’s mantle creates a column of hot material that rises until it reaches the crust. Pipes

form in the crust, which vents magma.

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Ring of Fire

Result of plate tectonics and the movement and collisions of crustal plates. Area where large numbers of earthquakes and volcanic eruptions occur in a 40,000km horseshoe shape. Associated with a nearly continuous series of activity. Contains 452 volcanoes, with over 75% of worlds active and dormant volcanoes.

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4 Main Types of Volcanoes4 Main Types of Volcanoes Cinder Cones (Volcanic cones)

Composite volcanoes (Stratovolcanoes)

Shield Volcanoes

Lava domes

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Shield Volcanoes• Named for their broad,

shield-like profiles.• Formed by the eruption of

low-viscosity lava that can flow a great distance from a vent, but usually not a catastrophic explosion.

• Gradual buildup and near continuous characteristics.

• More common in oceanic settings.

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Lava Domes• Formed by small, bulbous

masses of lava too viscous to flow a great distance.

• Lava piles over and around its vent, and the dome grows by expansion within.

• Commonly found within craters or on flanks of large composite volcanoes.

HOMEVOLCANO TYPES

Volcanic (Cinder) Cones• Built from particles of congealed lava ejected from a single vent.• Gas-charged lava blows violently into the air, breaks into small fragments and fall once solid as cinders around the vent. • Most have a bowl-shaped crater at the summit, and rarely rise more than 1K feet above surroundings.

HOMEVOLCANO TYPES

Stratovolcanoes (Composites)

• Steep-sided, symmetrical cones. Formed by alternating layers of lava flows, volcanic ash, cinders, blocks, and bombs.

• May rise 8K or more feet above surroundings.

HOMEVOLCANO TYPES

Supervolcanoes• Occurs when magma in the

Earth rises into the crust from a hotspot but cannot break through the crust. Pressure builds until the crust can no longer contain it.

• Can produce devastation on an enormous scale.

• Most dangerous kind and can cool global temperatures for years after eruptions due to the volume of sulfur and ash.

HOMEVOLCANO TYPES

Submarine volcanoes• Located on the ocean floor. • Active ones in shallow

water may shoot steam and rocky debris into the air.

• Deep eruptions may be prevented by the weight of the water.

• Rapid cooling by the water causes the erupted materials to solidify, often creating pillow lava.

• That is how many islands were developed.

HOMEVOLCANO TYPES

Subglacial volcanoes (glaciovolcano)

• Develop under icecaps.• During an eruption, the

heat of the lava melts the overlying ice. The water cools the lava, creating pillow lava shapes.

• Most common in Iceland & Antarctica and have a flat top with steep sides.

HOMEVOLCANO TYPES

Lava CompositionLava Composition

Oxygen (O)Silicon (Si)Aluminum (Al)Iron (Fe)Magnesium (Mg)

Titanium (Ti)Calcium (Ca)Sodium (Na)Potassium (K)Phosphorous (P)

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10 elements make up most magmas:

O & Si are the two most abundant elements in magma and are therefore described by silica content (SiO2). Click on the types of lava below for more information on each.

Felsic• High percentage of silica (>63%)• Highly viscous• Erupted as domes or short, stubby flows.• Typically forms stratovolcanoes or lava domes.• The viscosity traps gases, which cause more catastrophic eruptions . • Spurs pyroclastic flows and leaves thick layers of deposits, sometimes several meters deep.

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Pyroclastic flows

• Temperatures as high as 1,200 ⁰C

• Will incinerate anything flammable in their path, while leaving a thick layer of pyroclastic flow deposit.

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Andesitic

• Lower in aluminum and silica, usually richer in magnesium and iron.

• Form andesite domes and block lavas.• Temperatures between 750 and 950 ⁰C and are less viscous.

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Mafic• Erupt at temperatures above 950 ⁰C.• High in iron and magnesium, with lower aluminum and silica. • Low viscosities.• Typically forms low-profile shield volcanoes.

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Lava BehaviorLava Behavior

Highly viscous• Flows slowly, clogs, and

forms semi-solid blocks which resist flow.

• Tends to entrap gas, which forms bubbles within the rock.

• Correlates to explosive eruptions and is associated with pyroclastic flows.

Low viscous• Tends to flow easily,

forming puddles, channels and rivers of molten rock.

• Tends to easily release bubbling gases as they’re formed.

• Rarely pyroclastic.• Tend to form broad shields

rather than steep cones.

Viscosity of lava determines how the lava will behave.

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Types of EruptionsTypes of Eruptions

Non-explosive• Flood lavas• Hawaiian style• Mid-ocean ridges

Explosive• Strombolian• Vulcanian• Surtseyan• Vesuvian/Plinian• Peléan• Bandaian

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Non-explosive

• Flood lavas: basaltic & can be highly voluminous

• Hawaiian style: with some tephra and fast-moving fluid lavas; often channelized.

• Mid-ocean ridges: largely restricted to spreading center rifts as small cones and sheet flows.

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Explosive Strombolian

• Low-level eruptions, consists of ejection of incandescent cinder, lapilli and lava bombs to altitudes of tens to hundreds of meters.

• Small to medium in volume, with sporadic violence.1 – Ash plume2 – Lapilli3 – Volcanic ash rain4 – Lava fountain5 – Volcanic bomb6 – Lava flow7 – Layers of lava and ash8 – Stratum9 – Dike10 – Magma conduit11 – Magma chamber12 - Dike

HOMEERUPTION TYPES

Explosive Vulcanian

• Eruption characterized by a dense cloud of ash-laden gas exploding from the crater and rising high above the peak.

• Increased silica content of magma (which has increased viscosity) means increased explosiveness.

1 – Ash plume2 – Lapilli3 – Lava fountain4 – Volcanic ash rain5 – Volcanic bomb6 – Lava flow7 – Layers of lava and ash8 – Stratum9 – Sill10 – Magma conduit11 – Magma chamber12 - Dike Sakurajima, Japan

HOMEERUPTION TYPES

Explosive Surtseyan

• Takes place in shallow seas or lakes.• Commonly phreatomagmatic (a result of interaction

between water and magma) representing violent explosions.

1 – Water vapor cloud2 – Cupressoid ash3 – Crater4 – Water5 – Layers of lava and ash6 – Stratum7 – Magma conduit8 – Magma chamber9 – Dike

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Explosive Vesuvian/Plinian• Displays as columns of gas and volcanic ash extending

high into the stratosphere and eject large amounts of pumice.

• Can last less than a day to months. May collapse top of volcano, resulting in a caldera, and fine ash will deposit over large areas.

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Redoubt

ERUPTION TYPES

Explosive Peléan

• Characteristics include presence of a glowing avalanche of hot volcanic ash and formation of lava domes, short flows of ash or the creation of pumice cones.

• Collapse of ash columns.

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1 – Ash plume2 – Volcanic ash rain3 – Lava dome4 – Volcanic bomb5 – Pyroclastic flow6 – Layers of lava and ash7 – Strata8 – Magma conduit9 – Magma chamber10 – Dike

ERUPTION TYPES

Classification of volcanoes

• Volcanoes that erupt regularly.

• Actual lifespan can last from months to several million years.

Dormant• Volcanoes that have

erupted in historical times, but now quiet.

• Considered when eruptions have been historically many (possibly thousands or more) years apart and could erupt again. (Pompeii and previously Soufriere Hills)

Active Extinct• Volcanoes that

have not erupted in recorded historical times

• Scientists consider them to be unlikely to erupt again because there is no longer a lava supply.

ERUPTION TYPESHOME

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