copyright (c) 2005 pearson education canada, inc.4-1 powerpoint presentation stan hatfield....

Copyright (c) 2005 Pearson Education Canada, Inc. 4-1

PowerPoint PresentationStan Hatfield . Southwestern Illinois College

Ken Pinzke . Southwestern Illinois College

Charles Henderson . University of Calgary

Chapter 4: Part 2

Volcanoes and Other Igneous Activity

PowerPoint Presentation

Stan Hatfield . SW Illinois College

Ken Pinzke . SW Illinois College

Charles Henderson . University of Calgary

Tark Hamilton . Camosun College

Copyright (c) 2005 Pearson Education Canada Inc. 4-2A size comparison of the three types of volcanoes

Volcanic Structures and Eruptive Styles

Copyright (c) 2005 Pearson Education Canada Inc. 4-3

Types of Volcanoes• Composite cone (Stratovolcano)

– Most are located adjacent to the Pacific Ocean (e.g., Fujiyama, Pinatubo, Mt. St. Helens, El Chichon, Mt Hudson)

– Monte Vesuvio destroyed Pompeii & Herculaneum

– Large, classic-shaped volcano (> hundreds of metres high & > several kilometres wide at base)

– Composed of interbedded lava flows & pyroclastics



Eruption of Vesuvius in AD 79

Victims of Pompeii & Herculaneum

Casts of several victims of the AD 79 eruption of Mount Vesuvius.

Living in the Shadow of a Composite Cone


Living in the Shadow of a Composite Cone– The Lost Continent of Atlantis and Santorini

Thera blew 1627 BCE & destroyed Crete. Santorini was rebuilt in the caldera.


Ammoudi Beach, >60 m ash covers ruins


Nueé Ardente: A Deadly Pyroclastic Flow also called a Welded Ash Flow or Welded Tuff

– Most violent type of activity (e.g., Mount Vesuvius 79 AD, Mt. Pelee 1902 and Mount St. Helens 1980)

– A nueé ardente: (glowing avalanche cloud at night)– Fiery pyroclastic flow made of hot gases infused with

ash and other debris– Move down the slopes of a volcano at speeds up to

200 km per hour– Unlike other ash falls, this one fuses as it collapses

– May also produce a lahar, which is a volcanic mudflow



Calderas• Steep-walled collapse depressions at the summit

(Crater Lake is an example)• Size exceeds 1 km in diameter• Hawaiian-Type Calderas• Yellowstone-Type Calderas

Kilauea Caldera

Copyright (c) 2005 Pearson Education Canada Inc. 4-9Sequence of events that formed the caldera at Crater Lake, Oregon

Mt. Mazama – Crater Lake Caldera


Fissure Eruptions and Lava Plateaus• Fluid basaltic lava extruded from crustal fractures

called fissures• CRB: Columbia River Plateau; ~12.5 Ma flood

basalts also occur in the Chilcotin, S-central BC• Several Massive Extinction Events – Bio-Geological

Period Boundaries coincide with Flood Basalts– Deccan Traps, Siberian Traps, Karoo SA, Parana

CRBRoza Member

Frenchman Springs

ChilcotinChasm Provincial Park


Lava Domes• Bulbous mass of slowly extruded, congealed lava• Most are associated with late stages of an explosive

eruption of gas-rich magma• These are slow but dangerous and can spawn block

& ash flows

Volcanic pipes and necks• Pipes are short conduits that connect a magma

chamber to the surface• Often they remain as buttes after the pyroclastics

& cone erode away

Other Volcanic Landforms

Copyright (c) 2005 Pearson Education Canada Inc. 4-12 A lava dome forms on Mt. St. Helens following the eruption.

Other Volcanic Landforms: Lava Domes


Volcanic pipes and necks continued• Volcanic necks (e.g., Shiprock, New Mexico) are

resistant vents left standing after erosion has removed the volcanic cone since ~27 Ma

• Tow Hill, Graham Island is a ~5 Ma volcanic neck

Other Volcanic Landforms


Nature of Intrusions• Orientation with respect to the host (surrounding)

rock– Discordant – cuts across sedimentary rock units, or

other existing structures

– Concordant – parallel to sedimentary rock units

Intrusive Igneous Activity



Most magma is emplaced at depth in the Earth• An underground igneous body, once cooled and

solidified, is called a pluton• There is lots more inside than surface to the crust!

Nature of Intrusions• Shape

– Tabular (sheetlike: ~horizontal, sill, laccolith) both concordant to strata

– Tabular (sheetlike: ~vertical to inclined, dyke) cross cutting as planes, cones, rings

– Massive (irregular mass: pluton) cross cutting

– Cylindrical: Plugs, Pipes, Buttes when eroded

Copyright (c) 2005 Pearson Education Canada Inc. 4-16 Some intrusive igneous structures.

Shallow Intrusive Igneous Activity

Laccolithconcordant

Caldera

Stock < 1 km3

1<Pluton<1010<Batholith<100

Dykecross cutting

Butte


Nature of Intrusions• Dyke – a tabular, discordant pluton

– Forms in brittle rocks or from fast intrusion ~km/sec

• Sill – a tabular, concordant pluton (e.g., Palisades Sill in New York/Jersey ~205 Ma opening of Atlantic, rifting of Pangea)

– Forms in ductile rocks, pliable sediments, easier to inflate than to intrude higher, buoyancy or gas lost

• Laccolith – Shonkin Sag, Montana– Similar to a sill but domed convex up

– Lens or mushroom-shaped mass

– Arches overlying strata upward



Nature of Intrusions• Batholith

– Largest intrusive body

– Surface exposure of 100+ square kilometres (smaller bodies are termed stocks or plugs)

– Frequently form the cores of collisional mountains


Exfoliation Sheet JointsTensional cooling structuresIn coarse grained granites

Little Rock Texas


Emplacement of Batholiths• Magma at depth is much less dense than the

surrounding rock– Increased temperature and pressure causes solid rock to

deform plastically

– The more buoyant magma pushes aside the host rock and forcibly rises in the Earth as it deforms the “plastic” host rock



Emplacement of Batholiths• At shallower depths, the host rock is cooler and

exhibits brittle deformation– Movement of magma here is accomplished by fractures

in the host rock and stoping

– Inclusions in the host rock or xenoliths are evidence supporting the movement of magma through solid rock

– We saw some of these as deformed mafic clasts or enclaves in the lighter coloured granitic rocks of the Devonian Tyee Stock at Finlayson Point



Plate Tectonics and Igneous Activity

Global distribution of igneous activity is not random

• Most volcanoes are located within or near ocean basins

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


Igneous Activity at Convergent Plate Boundaries • Subduction zones

– Occur in conjunction with deep oceanic trenches

– Descending plate partially melts

– Magma slowly moves upward

– Rising magma can form either

– A volcanic island arc (island arc) if in the ocean

– A continental volcanic arc if subducted under continental lithosphere



• Subduction zones – Associated with the Pacific Ocean Basin

– Region around the margin is known as the “Ring of Fire”

– Most of the world’s explosive volcanoes are found here

– Stratocones & Calderas both occur in this setting



Igneous Activity at Divergent Plate Boundaries• Spreading centres

– The greatest volume of volcanic rock is produced along the oceanic ridge system

– Mechanism of spreading

– Thermal bulge on top of Mantle from upwards convection

– Lithosphere pulls apart and slides downhill to both sides

– Less pressure on underlying rocks, mantle upwells to fill in

– Results in partial melting of mantle (decompression melting)

– Large quantities of basaltic magma are produced

– The process lasts 10’s to 100’s of Ma

– Older ideas like “Ridge Push” clash with the extensional setting



Intraplate Igneous Activity• Activity within a tectonic plate

• Associated with mass of hotter than normal mantle called mantle plumes

• Form localized volcanic regions in the overriding plate called a hot spot

– Produces basaltic magma sources in oceanic crust (e.g., Hawaii and Canary Islands)

– Vast outpouring of mafic lava creating large basalt plateaus like Columbia Plateau and Deccan Plateau in India (latter may have affected climate in Upper Cretaceous)


Copyright (c) 2005 Pearson Education Canada Inc. 4-29Three zones of volcanism with central volcanoes


Island Arc, fluxJapan, Aleutians

Continental Arc, fluxAndes, Coast Ranges

HotspotDecompressionHawaii, Iceland

Copyright (c) 2005 Pearson Education Canada Inc. 4-30Three zones of extensional volcanism from decompression.


Mid Atlantic Ridge

East African Rift

Deccan Traps K/T Flood BasaltsPlume Head

Copyright (c) 2005 Pearson Education Canada Inc. 4-31Model of a mantle plume and associated hot-spot volcanism.

Plate Tectonics and Igneous ActivityLarge Igneous Provinces (LIPS) also form Oceanic Plateaux: Caribbean, Ontong Java, Kerguelen


Can Volcanoes Change Earth’s Climate?

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

In Troposphere Months-Years, Stratosphere >>

Examples of volcanism affecting climate• Did Deccan Traps 65 Ma end Cretaceous Hothouse• Mount Tambora & Indonesia – 1815 (caldera)• Krakatau, Indonesia – 1883 (caldera)• Mount Pinatubo, Philippines – 1991 (stratocone)


Eruptions can emit great quantities of sulphur dioxide gases, which combine with water to form sulphuric acid particles called aerosols; they reflect solar radiation back to space.

The answer is Yes. They are regarded as an explanation for some aspects of Earth’s climatic variability.

When aerosols penetrate the stratosphere with its rapid jet stream the entire heat balance in the atmosphere can shift, changing the rest of atmospheric convection.

Can Volcanoes Change Earth’s Climate?


End of Part 2 ofChapter 4Volcanism

copyright (c) 2005 pearson education canada, inc.4-1 powerpoint presentation stan hatfield....

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eruptive stylescopyright

composite conecopyright

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welded ash flow

nue ardente

eruption of mount vesuvius