Classroom presentations to accompany

Understanding Earth, 3rd edition

prepared by

Peter Copeland and William Dupré

University of Houston

Chapter 5Chapter 5Volcanism

Fig. 5.1

Plumbing System of a Volcano

May 1990 Eruption of Kilauea, Hawaii

James Cachero/Sygma

Volcanic Volcanic rocksrocks

Major difference between plutonic

and volcanic rocks is texture, a

reflection of cooling rate.

Material ejected from Material ejected from volcanoesvolcanoes

Nonvolatile material

• Lava: magma that has flowed on the surface of the Earth.

• Tephra: fragments that solidified in the air during eruption.

Types of Types of LavaLava

aaaa

pahoehoepahoehoe

Kim Heacox/DRX Fig. 5.3

Pahoehoe Pahoehoe LavaLava

Aa LavaAa Lava

Martin G. Miller Fig. 5.2

Columbia Plateau Flow Basalts

TephrTephraa

• Pyroclastic flow

• Air-fall

• Mudflow (lahar)

PyroclasticPyroclastic flow flow

((nueé ardentenueé ardente))

Mixture of hot gases, ash, and rocks

forming a super-heated and dense

current capable of moving 150 km/hr.

R.S.J. Sparks

Pyroclastic Flow from the 1998 Pyroclastic Flow from the 1998 Eruption on MontserratEruption on Montserrat

AP/Wide World Photos Fig. 5.9

Escaping a Pyroclastic

Flow at Mount Unzen, Japan,

1991

Science Source/Photo Researchers Fig. 5.7

Volcanic Bomb

Doug Sokell/Visuals Unlimited Fig. 5.8

Volcanic Breccia

Submarine eruptionsSubmarine eruptions

• Pillow basalt

• Phreatic explosions

Woods Hole Oceanographic Institute Fig. 5.4

Pillow LavaPillow Lava

Maritime Safety Agency, Japan Fig. 5.18

PhreaticExplosion

in the Pacific

Glen Oliver/Visuals Unlimited Fig. 5.5

Vesicular Basalt

Gregory G. Dimijian/Photo Researchers Fig. 5.6

Pyroclasic Eruption at

Arenal Volcano,

Costa Rica

Eruptive styles and Eruptive styles and landformslandforms

• Shield volcanoes

• Stratovolcanoes (composite)

• Domes and cones

• Fissure eruptions (flood basalts)

• Submarine eruptions

Shield volcanoesShield volcanoes• Low-viscosity lava flows

–Low-silica magma — mafic–Basalt

»Pahoehoe»Aa

• Gently sloping flanks — between 2 and 10 degrees• Tend to be very large

• Spatter cone — minor feature

Shield Volcano

Fig. 5.10

NASA, Viking Orbiter 1

Olympus Mons Shield Volcano

Cinder conesCinder cones

• Formed of pyroclastics only

• Steep sides — ~30 degrees

• Relatively small

• Short duration of activity

Fig. 5.12

Cinder Cone

Mark Hurd Aerial Surveys Fig. 5.13

Cerro Negro Cinder Cone,

near Managua, Nicaragua

in 1968

Volcanic domesVolcanic domes

• Forms above a volcanic vent

• Viscous lava — usually silica-rich (or cooler magma)

• Associated with violent eruptions

Fig. 5.11

P. L. Kresan

Inyo Obsidian Domes-California

Lyn Topinka/USGS

Fig. 5.11

LavaDome

Composite volcanoComposite volcano• Alternating pyroclastic layers and lava

flows

• Slopes intermediate in steepness

• Intermittent eruptions over long time span

• Mostly andesite

• Distribution– Circum-Pacific Belt (“Ring of Fire”)

– Mediterranean Belt

Fig. 5.14

Composite Volcano

Raga/The Stock Market Fig. 5.15

Mt Fujiyama, Japan

Emil Muench/Photo Researchers

Before May, 1980

David Weintraub/Photo Researchers

After May, 1980

CalderCalderaa

• Depression at top of volcano produced during an eruption

• May have younger domes within it

Fig. 5.16

Greg Vaughn/Tom Stack Fig. 5.17

Crater Lake, Oregon

Fred Padula Fig. 5.19

Shiprock, New Mexicoan exposed volcanic pipe

(diatreme)

Fissure Fissure eruptionseruptions

When low-viscosity lava is

issued from cracks in the Earth

tens of kilometers long.

1971 Fissure Eruption, Kilauea, Hawaii

Fig. 5.20

Fissure Eruptions Form Lava Plateaus

Tony Waltham Fig. 5.21

Laki fissure (Iceland) erupted

in 1783 extruding the

largest lava flow in human history.

Lava floodsLava floods

• Mafic lava — solidifies to basalt

• Fissure flows

–Plateau basalts

• Columnar structure or jointing

Fig. 5.22

Martin G. Miller Fig. 5.2

Columbia Plateau Flow Basalts

Welded Tuff: California

Gerals and Buff Corsi/Visuals Unlimited Fig. 5.231 foot

S. Aramaki Fig. 5.24

Ash-flow Sheets Draping Topography, Japan

Caution: Volcanologist at Work

Maurice Krafft/Photo Researchers Fig. 5.25

Volcanic Mudflow Volcanic Mudflow ((laharlahar):):

A mixture of water and pyroclastic

material in a concrete-like slurry

capable of moving up to 100

km/hour!

Barbara and Robert Decker

23,000 killed in 1985 by volcanic mudflows, Nevada del Ruiz

Other material ejected from Other material ejected from volcanoesvolcanoes

Volatile material

• Steam (H2O)

• Carbon dioxide (CO2 )

• Hydrogen sulfide (H2S)

• Many other constituents

Christian Grzimek/Photo Researchers Fig. 5.26

Sulfur-encrusted fumerole:Galapagos Islands

Simon Fraser/Photo Researchers

Fig. 5.27

Stokkur geyser in Iceland

Tectonic setting of Tectonic setting of volcanoesvolcanoes

• Convergent plate boundaries

• Divergent plate boundaries

• Within plate “hotspots”

The World’s Active Volcanoes

Fig. 5.28

Fig. 5.29

Cross Section of the East Pacific Rise

Volcanism Associated with Plate Tectonics

Fig. 5.30

Effects of volcanoes on Effects of volcanoes on humanshumans

• Growth of Hawaii• Geothermal energy• Effect on climate• Volcanic catastrophes

»Mt. St. Helens»Vesuvius»Krakatoa»Mt. Pelée»Montserrat

Types of Volcanic Types of Volcanic HazardsHazards• Lava Flows: e.g. Hawaii, 1998

• Gas: e.g. Lake Nyos (Cameroon), 1984– 1700 people killed

• Ash fall: e.g. Mt. Pinatubo, 1991

• Pyroclastic flows: e.g. Mt. Pelee, 1902– 28,000 killed

• Lahars (mudflows): e.g. Nevado del Ruiz, 1985– 23,000 killed

• Tsunami: e.g. Krakatoa, 1883– 36,417 killed

E. Tad Nichols

San Juan, Mexico, Buried by Paricutin Lava Flows

Roger Ressmeyer/Corbis Fig. 5.31

Scientists Investigate Mt. Pinatubo’s Caldera

U.S. Active Volcanoes