ERTH2404 L9 Volcanoes Upload

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ERTH2404

Lecture 9: Volcanoes

Dr. Jason MahUSGS



Reading assignment

• Please read Kehew’s book to complement the

material presented in this lecture:

Chap. 4;

2



Lecture objectives

• To learn the mechanics of a volcanic eruption

• How do volcanoes erupt?

• Relationship between plate tectonics and

earthquakes• To learn the relation between magma

composition, eruptive style, eruption type andvolcanic landforms

• Eruptive styles and landforms

• Volcanic hazards and mitigation

3



20% of the population live near a volcano

4



How do earthquakes erupt?

• Step 1: Melt the solid rock

• What can cause solid rock to melt?

• Decompression melting (decrease in P, most important)

• Increase in T

• Increase in water content

• Magma rises to continental crust

5




• Decompression melting

6

(oceanic)




• Step 2: Fractures

• Phase change from solid to liquid leads to increase

in volume

• Fractures develop in overlying rocks

• More hot material rise

• More rocks liquefy

7




• Step 3: Volatiles

• Volatiles gradually come out of solution

• Gas bubbles push magma upward

• Step 4: Magma fragments

• When bubbles ≥ 75% volume

• Powerful gas jet expels magma in the

atmosphere

8




• Volcanic eruption: sudden occurrence of a

violent discharge of volcanic materials

9



Eruption

10 R e f . : A b b o t t , P . L . 2 0

0 4 . N a t u r a l D i s a s t e r

s .

4 t h E

d i t i o n . F i g . 6 . 8 .

S h o w n w i t h p e r m i s

s i o n .

Conduit

Central vent



• The relationship between plate

tectonics and volcanoes

11



Plate tectonics

• Theory of plate tectonics is central to

understanding natural disasters related to the

Earth’s internal energy

• Volcanoes and earthquakes do not occur

randomly

• Coincide with plate boundaries

•90% of volcanoes found at the edge of plates• Classic example: "Pacific Ring of Fire"

12



Ring of Fire

13



Plate tectonics and volcanoes

• Relation between tectonic environment,

magma composition and eruptive style

• In general:

14

Environment Magma

composition

Volume of

magmaEruptive style

Basaltic Peaceful

Andesitic

Rhyolitic

Explosive

Spreading centers Basaltic 80% Peaceful

Transform faults

Convergent zones Andesitic

Rhyolitic10% Explosive

Hot spots 10%



Hot spot volcanoes

• Chain of volcanoes

• Aligned in the direction of plate motion

• Age increasing with distance from hot spot

• Oldest likely to be extinct on the seafloor

• Variable eruptive style

• Example: Hawaii

• Animation 1

15



Hot spot volcanoes

16

R e f . : A b b o t t , P . L . 2 0 0

4 . N a t u r a l D i s a s t e r s .

4 t h E

d i t i o n . F i g . 2 . 1 4 .

S h o w n w i t h p e r m i s s i o

n .



Hot spot volcanoes

17

R e f . : A b b o t t , P

. L . 2 0 0 4 . N a t u r a l D i s a s t e r s .

4 t h E

d i t i o n . F i g . 2 . 1 4 . S h o w n w i t h p e r m i s s i o n .



Volcanoes at spreading centers

• Peaceful eruptions

• Magma directly derived from asthenosphere

• Basaltic lava: low % SiO2

•Very high T

• Low viscosity

• Pull-apart movement of plates creates zone of lowpressure

• Rocks melt partially• Magma rises and flows easily

• Examples: volcanoes of Iceland

18



Volcanoes at spreading centers

19

Ref.: Abbott, P.L. 2004. Natural Disasters.

4th Edition. Fig. 6.3. Shown with permission.



Volcanoes at convergent zones

• Continent-continent collision zones

• Little volcanism

• Subduction zones

• Widespread volcanism

• Role of water

• H20 from down going plate lowers the melting point of

rock

• Partial melting is induced in the overlying plate

• Magma rises and erupts

20




21






• Volcanic mountains formed at the edge of thecontinents where one plate subducts beneathanother

• 10% of magma on the Earth’s surface • Andesitic to rhyolitic magma

• Examples:

• Volcanoes of the Andes

• Mount Baker, Mount St. Helens (USA)

22



Subduction zones

23

Source: USGS

Examples:

Japan, Aleutians Western North and SouthAmerica

Oceanic-oceanicconvergence

Oceanic-continentalconvergence



• Eruption styles and their

characteristics

24



3 V’s

• Factors controlling volcanism:

• Viscosity

• Volatiles

• Volume of magma

25



Viscosity

Viscosity: internal resistance of a liquid to flow

Low High

Water maple syrup honey toothpaste

• Most important property controlling magmabehavior and, therefore, eruptive style

Low High

Peaceful eruption Explosive eruption

26

Viscosity

Magma Viscosity



Magma Viscosity

• What controls magma viscosity?

• % SiO2

• Magma with high % SiO2 has more silicate chains,

sheets and 3D structures• More bounds between atoms increase viscosity

27

Basalt Andesite Rhyolite

% SiO2

Viscosity



Low-viscosity magmas

• Tend to reach the Earth’s surface

• Erupt peacefully

•

Characteristics:• Basaltic magma

• 80% of magma reaching the surface is basaltic

• High T (1000-1250°C)

• Low volatile content

• At high T, volatiles escape easily

28



High-viscosity magmas

• Tend to form intrusive bodies

• When reaching the surface, erupt explosively

•

Characteristics:• Andesitic and rhyolitic magma

• Low T (600-900oC)

• High volatile content

• Volatiles are "trapped" in magma and have to burst to

escape

29



Viscosity and Density

• Density of magma:

• Magma density > crust density

• Mafic magma

• Low viscosity

• Magma density < crust density

• Felsic magma

•

High viscosity• Animation 2

30



Eruptive styles and landforms

31

Eruptive style Eruption type Bas And Rhy

Icelandic

Hawaiian

Flood basalts

Strombolian

VulcanianPlinian

Caldera

Peaceful

Explosive

Magma composition

• Eruption style and associated igneous rock



32

Eruptive styles and landforms

Volcanic

Eruption type Bas And Rhy Viscosity Volatiles Volume Landform

Icelandic Low Low Small Lava plateauHawaiian Low Low Large Shield volcano

Flood basalts Low Low Very large Province

Strombolian Medium Medium Small Scoria cones

Magma composition Control factors



Peaceful eruption style

• Icelandic-type: small volume

• Landform: lava plateau

• Hawaiian-type: large volume

• Landform: shield volcano

• Flood basalts: very large volume

• Largest volcanic events on Earth

• None occured in "recent" geological time

• Landform: flood basalt province

33



Lava plateau

34



• Land forming• Plate boundaries diverge

• Basaltic lava pours peacefully from long fissures

• Submarine volcanic activity forming new sea

floor



Shield volcano

35

http://mail.colonial.net/~hkaiter/volcanoes.html



Shield volcano: Mauna Loa, Hawaii

USGS

Shield volcano

36 R e f . : A b b o t t , P . L . 2 0 0 4 . N a t u r a l D i s a s t e r s .

4 t h E

d i t i o n . F i g . 6 . 1 6

. S h o w n w i t h p e r m i

s s i o n .



Shield volcanoes

37

• Peaceful lava flows

• High volume

• Gas emissions

• Faults, earthquakes,tsunamis

• Hawaii

• 3 active volcanoes• 1 dormant

• 1 extinct

Kohala (extinct)

Mauna Kea

(dormant)

Kilauea

Mauna Loa

Hualalai



Kilauea

38

• Shield volcano erupting since Jan 3, 1983

USGSUSGS, March 2008



Kilauea

39

• Kalapana region, Jan 1987



Strombolian-type eruptions

• "Intermediate" case…

• Peaceful eruptive style in convergent zoneenvironment

•

Mafic composition: basaltic to andesitic• Medium viscosity

• Medium volatiles

•

Gas build up• Eruptions generate pyroclastic materials

• Lava pours out of a crater

40




• Small volume

• Pressure accumulate quickly in subsurface

• Released in separate short-duration bursts

• Daily activity

• Bursts not strong enough to destroy the volcanic

edifice

• Eruptive phase of a few years duration untilvolcanic conduit clogged

41




• Scoria cone: volcano in the shape of a conical

hill formed by pyroclastic debris piled up next

to a volcanic vent

• Also known as Cinder cone

• Destroyed quickly by erosion

• Pyroclastic debris weak and unstable

•Harder volcanic conduits remain creatinga volcanic neck

42




• Named after Stromboli volcano, Italy• Erupting for past 2400 years

43

USGS



Monogenetic volcano

• Monogenetic volcanic field: collection of cinder cones

• El Parícutin volcano, Mexico• Grows quickly, 5 stories in a week

• Born, developed and died (1943-1952)

• « The new volcano in Mexico is a unique geologicalphenomenon: for, before our eyes, it has sprung into

existence and has grown to a very respectable heightof 1,500 feet, all within a period of 8 months. »• Dr. Parker D. Trask (USGS), Science, December 1943

44



El Parícutin volcano, Mexico

45



• Ash found in Mexico City, 400 km away




46

P h o t o : C . S a m

s o n , C a r l e t o n U .




1. Initial period (20 Feb – 18 Oct 1943)

• 10-19 February: underground noises, vapors

• 20 February: fissure

•

22 February: first lava flows

• Rapid growth of scoria cone

• 24 hours 30 m

• 72 hours 60 m

• 6 days 120 m

• 1 month 148 m

• 4 months 200 m

47




48

24 February 1943 26 February 1943




2. Development of the Sapichu cone (smaller

cone)

• Secondary conduit

• 18 Oct 1943 – 8 Jan 1944

4920 February 1944




3. Reactivation of the principal cone

• 8 Jan 1944 – 12 Jan 1945

5020 March 1944

Church of San Luis

Parangricutiro




• Church of San Luis Parangricutiro

51




• Growth profile

52




4. Gradual decline in activity,

• Jan 1945 – Feb 1952

• Erosion several cm/year

53



Explosive eruptive style

54

Volcanic

Eruptive style Eruption type Bas And Rhy Viscosity Volatiles Volume Landform

Vulcanian Med/High Medium Large

Med/High High LargeHigh Low Small Lava dome

Caldera High High Very large Caldera

Explosive

Stratovolcano

Plinian

Magma composition Control factors



Vulcanian-type eruptions

• Eruptions alternate between:

• Medium/high viscosity lava of varied composition

• Pyroclastic material covering a large area

• Often preceeding a more violent plinian-type

eruption

• Landform: stratovolcano

55



Stratovolcano

• Stratovolcano: A large volcanic cone built of

alternating layers of viscous lava and pyroclastic

debris

• Steep-sided• Symmetrical

• Also known as stratovolcano

• Surface rupture: central vent

Examples: Mount Fuji, Kilimanjaro, Mount Etna

56



Stratovolcano

57

R e f . : K e h e w , A . E . 1 9 9 8 . G e o l o g y f o r E n g i

n e e r s &

E n v i r o n m e n t a

l

S c i e n t i s t s . 2 n d E

d i t i o n . F i g . 3 . 2 0 . S h o w n w i t h p e r m i s s i o n .



Stratovolcano

58

Mt. St. Helens, Washington

October 1, 2004



Plinian-type eruptions

• Volatile-powered vertical eruption

carrying pyroclastic debris

• Plume up to 50 km in the atmosphere reach

stratosphere

• Lots of pumice

• Continued development of stratovolcano

59




60

R e f . : A b b o t t ,

P . L . 2 0 0 4 . N a t u r a l D

i s a s t e r s .

4 t h E

d i t i o n . F i g . 6 . 1 6 . S h o w n w i t h

p e r m i s s i o n .




• During final phase of eruptive sequence:

• High viscosity

• Lava behaves like a "paste" forming a plug in the

volcanic conduit• Few volatiles remain

• Landform: lava dome

61




• Mount Vesuvius, Naples Italy• Buried Pompeii in 79 A.D.

• Ash 33km high

• 1.5M tonnes per second• 16 000 deaths

62




•

Mount Vesuvius, Naples Italy• Debris/ash cloud moving at > 100 km/hr, > 100°C

• Over 1000 casts found

63www.bbc.uk

h t t p : / / w w w . n s f . g o v /



Lava dome

• Lava dome: volcanic cone with a highly

viscous blob of lava forming a half-ball shape

over the vent

(Note: sometimes the term is only applied tothe blob of lava)

• Lava is too viscous to flow far from the vent

•In many cases, the dome continues to growupward until it collapses

64



Lava dome

65

S o u r c e : U S G

S

Newberry Volcano, Oregon



Caldera-type eruptions

• Largest explosive volcanic eruptions• Method 1

• Collapse of an existing stratovolcano into the partiallyemptied magma chamber

• Usually follows a sustained Plinian-type eruption thatopened void space below the volcano

• Piston-like action of collapsing volcano cause very largevolume of magma to flow outward as pumice-rich sheets

•

Example: Crater Lake, animation

- OR -

66




67






• Method 2

• Cataclysmic explosion litterally blows the existing

volcano apart completely

• Examples: Santorini, Krakatoa

68




• Krakatoa, Indonesia• Eruption 416AD

• Created of 7km wide caldera, currently submersed

• Remnanents formed islands, baby volcanoes formed

• Eruption 1883

• Eruption heard 4800 km away

• Shock wave recorded around the world

• Destroyed baby volcanoes

• Generated 40 m high tsunami travelling 2.5 km inland• Approximately 35 000 people killed

• Underwater caldera

69




• Krakatoa,

caldera

70



• Volcanic hazards

71



Volcanic hazards and mitigation

72

P h o t o : Y . G i g u è r e . S h o w n w i t h p e r m i s s i o n .



Volcanic hazards

• 50-60 eruptions worldwide each year

• 2-3 eruptions/year in North America

• Aleutian chain (Alaska)

• Volcanoes become hazardous when peopleare in close proximity

• 100 000 killed in last 100 years

• Tendency for people to inhabit fertile soils onflanks

73



Primary hazards

• Primary hazards result directly from the

eruption

• Examples:

• Pyroclastic flows

• Volcanic gas

• Lava flows

• Pyroclastic fall (ballistic projectiles and ash)

74



Pyroclastic flows

• Synonym: "nuée ardente" (glowing cloud)

• Pyroclastic flow: avalanche of hot gas, ash androck fragments moving down the sides of a

volcano• T ≈ 1000°C

• Velocity 10 – 300 m/s

• High-density flows follow valleys

• Low-density, more dilute flows can move up andover ridges

75



Nuée ardente

• One of the earliest

photographs of a nuée

ardente.

• Photograph taken atMont Pelée,

Martinique, on 16

December 1902 by A.Lacroix.

76

S o u r c e : U S G S



Pyroclastic flows

• Direct effects:• Responsible for the largest number of fatalities

related to volcanism

•

Highly destructive to infrastructure due to mass,high To and great mobility

• Indirect effect: fires

• Examples:

• Pompeii (79 AD)

• St-Pierre de la Martinique (1902)

77



Volcanic gas

• Volcanic gases come out of solution and

increase in volume when magma erupts

• Main driving force of explosive eruptions

• Most abundant: H2O, CO2, SO2

• Can also be present: H2S, H2, CO, HCl, HF, He

• Concentrated near vent

• Distribution controlled by prevailing wind

78

l



Volcanic gas

• Direct effects:

• Heavier-than-air gas (e.g. CO2) accumulate in

depressions, causing suffocation

• Example: Lake Nyos (Cameroon, 1986)

• S, Cl, F react with water, forming poisonous

acids

79

fl



Lava flows

• Hazardous nature related to speed of advance

• Controlling factors:

• Rate of lava production at the vent

• Slope steepness

• Lava viscosity

• Fluid basaltic flows, ≈ km/hr

• Viscous andesitic-rhyolitic flows, ≈ cm/hr

• Whether lava flows as a broad sheet, through a

confined channel, or in a lava tube

80

fl



Lava flows

• Direct effects: lava flows destroy everything in

their path

• Bury, crush, burn objects

• Most lava flows move slow enough to allowevacuation of people

81

P l i f ll



Pyroclastic falls

• Ballistic projectiles: falling fragments of lapilli

and scoria (particle size > 2 mm)

• Fall close to the volcano

82

P l i f ll



Pyroclastic falls

83

Photo: J. Aristimuño. Shown with permission.

A h f ll



Ash fall

• Volcanic ash (particle size < 2 mm)

• Tiny jagged pieces of rock and glass

• Properties: hard, abrasive, mildly corrosive, does

not dissolve in water• Can be transported 100-1000s km downwind

84

A h f ll



Ash fall

• Direct effects:

• Vegetation destroyed

• Surface water contaminated

• Respiratory health issues

• Structural damage to buildings

85

A h f ll



Ash fall

•

Isopach map of volcanic ash [cm], MountPinatubo, Philippines

86

R e f . : K e h e w

, A . E . 1 9 9 5 .

G e o l o g y f o r E n g i n e e r s & E n v i r o n m e n t a

l S c i e n t i s t s .

2 n d E

d i t i o n . F i g . 3 - 3 7 . S h o w n w i t h

p e r m i s s i o n .

Photo: USGS

V l i h



Volcanic ash

• Indirect effects:

• Atmospheric dust affects aircraft engines

• 1982, British airways flight flew through

volcanic ash and all 4 engines shut down

• Eyjafjallajökull Volcano, Iceland

• Eruption 14 April 2010

• 6 day travel ban, over 100,000 flights canceled

87

V l i h



Volcanic ash

88

S d h d



Secondary hazards

• Secondary hazards result from theenvironment created by the volcano

• Hazardous conditions can persist long after

eruptive phase is over• Examples:

• Floods: lava flows can dam rivers and modifydrainage relationships

• Lahars

• Atmospheric dust

89

S d h d L h



Secondary hazards: Lahars

• Lahar: type of mudflow that originates on theslopes of volcanoes when volcanic ash anddebris become saturated with water and flowrapidly downslope

• Speed: 1 – 40 m/s

• Spread over long distances

90

S d h d L h



Secondary hazards: Lahars

• Almost always occur on stratovolcanoes

• Steep flanks

• Tall cones often snow covered

• Constructed of weakly consolidated material

• Triggering mechanisms:

• Melting of snow and ice

• Heavy rainfall

91

Mount St Helens 1982 eruption



Mount St. Helens, 1982 eruption

92

Mount St Helens



Mount St. Helens

93

• Mudline on tree

• Geologist is 6ft

Case Study



Case Study

• Nevado del Ruiz volcano, Columbia

• Major eruption on 10 November 1985

melts ice cap

• Lahar triggered, travelling at 60 km/h

• Town of Armero buried

• 23,000 fatalities

94

Case Study



Case Study

• Could this disaster have been prevented?• Historical records: lahars in 1595 and 1845

• Hazard map published one month before thedisaster

• But poorly distributed

• Volcano awakes in 1984

• Small scale volcanic activity

• Government is warned

95

Case Study



Case Study

96

Ref.: Kehew, A.E. 1998. Geology for Engineers & Environmental Scientists.

2nd Edition. Fig.3-36. Shown with permission.

Case Study



Case Study

• Currently…

• 500 000 people living in the region

• Volcano is monitored heavily

• Evacuation plans in place

97

Tertiary hazards



Tertiary hazards

• Tertiary hazards result from the destabilizinglong-term effects of the volcanic eruption onsociety

• Famine

• Atmospheric dust affects global climate

• Extensive crop damage and loss of livestock

• Diseases

• Breakdown of sewage and water systems

• Effects of tertiary hazards can be felt several yearsafter the eruption

98

Rabaul caldera Papua New Guinea 1994



Rabaul caldera, Papua New Guinea, 1994

• Shuttle photograph of eruption column(18 km above ground)

99 S o u r c e : U S G S

Rabaul caldera Papua New Guinea 1994



Rabaul caldera, Papua New Guinea, 1994

• Ash fall from Rabual caldera

100

Photo: USGS

Summary of Volcanic hazards



Summary of Volcanic hazards

101 R e f . : A b b o t t , P . L . 2 0 0 4 . N a t u r a l D i s a s t e r s .

4 t h E

d i t i o n . F i g . 7 . 2 0

. S h o w n w i t h p e r m i s s i o n .

Mitigation



Mitigation

• Volcanic eruptions are one of the mostdifficult natural hazards for which to mitigate

• Low frequency, high magnitude events

• Exact combination and timing of events difficult topredict

• Especially for explosive volcanoes

102

Can lava flows be diverted?



Can lava flows be diverted?• Wall building

• The city of Catania successfully blocked the lava flow of Mount Etna in 1669 (USGS)

• But the diverted flow headed to the town of Paterno

• The citizens of Paterno prevented Catania frommaintaining their artifical breach

103

Mt. Etna diversion, 1983

w w w . w o r l d a t l a s . c o m





• Aerial bombing

• Unsuccessful in Hawaii, Mauna Loa in 1935 and

1942

104www.pha.jhu.edu/~chiu/hawaii2001index.html

USGS

Hilo

Volcanic activity classification



Volcanic activity classification

• Active: volcano which has erupted in historictimes

• Dormant: volcano that has not erupted inhistoric time but is capable of erupting in the

future• Extinct: volcano that is not expected to erupt

again

•

Rather "subjective" classification including anelement of prediction• Different vulcanologists use different criteria

105

Canadian volcanoes?



Canadian volcanoes?

• All triangles < 2 Ma• All big triangles < 10,000

years old!

• All due to interaction

between lithospheric plates

106

Garibaldi and Baker



Garibaldi and Baker

• Garibaldi is dormant withseismic activity, no gas activity• Hazards: lavas, ash clouds,

mudflows

107

Garibaldi area,[email protected]

Mt. Baker from the Fraser Valley

• Active with ash explosions(1840’s), abundant recent gasactivity

• Hazards: lavas, landslides, ashclouds, mudflows

Monitoring volcanic activity




• Compilation of baseline data when thevolcano is dormant

• Seismic activity

•

Thermal monitoring• Sampling of gas, lavas, etc.

• Warnings issued when changes occur

108





• USGS Volcanoes and Current Activities Alert:• http://volcanoes.usgs.gov/

• USGS Observatories

• http://volcanoes.usgs.gov/observatories/cvo/

http://volcanoes.usgs.gov/

http://volcanoes.usgs.gov/observatories/cvo/






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