GEOS 3310 Lecture Notes: Volcanoes

Dr. T. Brikowski

Fall 2008

file:volcanoes.tex,v (1.17, March 31, 2008), printed September 29, 2008

Introduction

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Introduction

Volcanoes have a number of common features:

• they are formed by the emergence of molten rock

(underground magma becoming lava on the surface)

• different magma compositions (mostly with varying silica,

SiO2 content) have distinctive eruptive styles

• magma composition is generally controlled by the tectonic

setting

• knowing something about the volcano type helps predict the

potential hazard

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Historical Volcanic Events

Figure 1: Historical volcanic events, associated damage and eruption type

[Tbl. 6.1, ?].

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Volcanoes in the U.S.

Figure 2: Volcanoes and major cities in the Western U.S. [Fig. 6.3, ?].

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Magma TypesTable 1: Magma types, their silica content and explosivity (correlates

primarily to volatile content). Lighter colors indicate higher silica content.

Rock images from CSULB.

Type Image Silica Content Water Content

Basalt 50% low

Andesite 60% moderate-high

Rhyolite 70% moderate-high5

Silica and Magma Viscosity

Figure 3: Viscosity vs. magma type (after UBC). Increasing silica content

leads to increased polymerization of magma (via mineral-like SiO2 chains )

and higher viscosity. Also increasing water (gas) content leads to increased

explosivity.

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Silica Framework in Magma

Figure 4: Silica framework in quartz. In magma, the more SiO2, the more

extensive the framework, and the higher the viscosity. The corner of each

tetrahedron is a shared oxygen, the center of each contains an Si4+ bonding

the oxygens together. From UWGB .7

Tectonic Setting and Volcanism

Figure 5: Tectonic setting and volcanism [Fig. 6.11, ?]. Increasing

contribution of continental crust leads to higher silica content.

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Types of Volcanoes

Figure 6: Summary of volcano types [Tbl. 6.2, ?].

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Videos of Eruptive Types

IACEVI has released clips of eruptive types:

• ash flow

• slow basalt/andesite flows

And other sites

• Japanese geological survey Mt. Unzen ash flow from the air

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Shield Volcanoes

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Mauna Loa: Shield Volcano

Figure 7: Mauna Loa, Hawaii, classic shield volcano form, after

USGS.12

Inflation and Tilting Mechanism

Figure 8: Inflation mechanism at shield volcanoes (Kilauea)

[Fig. 8.30a, Keller, 2000].

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Inflation and Tilting at Kilauea

Figure 9: Inflation and tilting record during eruptions at Kilauea. Upward

progression of earthquakes and subsequent tilting allows prediction of

eruptions, [Fig. 8.30b, Keller, 2000]. See also USGS14

Composite Volcanoes

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Mt. Fuji

Figure 10: Ring of Fire around Pacific Ocean, representing a

nearly [Fig. 8.7, Keller, 2000].

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Ring of Fire

Figure 11: Ring of Fire around Pacific Ocean, representing a nearly

continuous band of subduction around the ocean rim [Fig. 8.3, Keller,

2000].17

Tectonic Setting of Cascade Range

Figure 12: Tectonic setting of Cascade Range [Fig. 8.11, Keller, 2000].

Subducting plate and deep crust melt, providing moderately siliceous magma

and creating composite volcanoes.18

Mt. St. Helens

Figure 13: Mt. St. Helens, the most active volcano in the

continental U.S. This scene from 1980 prior to its collapse [Fig.

8.1, Keller, 2000].19

MSH - Bulge Development

Figure 14: Development of pre-eruption bulge at Mt. St.

Helens [Fig. 8.25a, Keller, 2000].

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MSH - Eruption Begins

Figure 15: Slope failure and beginning of May 1980 eruption

[Fig. 8.25b, Keller, 2000].

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MSH - Lateral Blast

Figure 16: Lateral blast stage of May 1980 eruption [Fig. 8.25c, Keller,

2000]. This phenomenon was poorly understood prior to this eruption.

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MSH - Vertical Eruption

Figure 17: Full vertical eruption stage of May 1980 eruption [Fig.

8.25c, Keller, 2000]. This phenomenon was poorly understood prior to this

eruption. See animation .23

MSH - Animated Eruption Images

Figure 18: Animation of Mt. St. Helens eruption images, after

USGS.

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MSH - Direct Eruption Effects

Figure 19: Mt. St. Helens direct eruption effects [Fig. 8.26b,

Keller, 2000].

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MSH - Topography Before and After

Figure 20: Mt. St. Helens topography before and after, looking

SSW. See animated version .

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MSH - Ash Distribution

Figure 21: Mt. St. Helens ash distribution [Fig. 8.26c, Keller,

2000].27

MSH - Post-eruption Dome Building

Figure 22: Mt. St. Helens dome-building eruption 2004-5, from USGS .

See also 2005-6 dome poster.28

Mt. Rainier Hazard Map

Figure 23: Potential hazards from Mt. Rainier, outside Seattle, WA [Fig.

6.24, ?].

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Nevado del Ruiz Hazard Map

Figure 24: Potential hazards from Nevado del Ruiz, Columbia [Fig. 8.23,

Keller, 2000].

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Rhyolitic Volcanoes/Calderas

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Typical Caldera (Aniakchak)

Figure 25: Typical geomorphology of a caldera, Aniakchak Caldera,

Alaska. Caldera is 10 km (6.2 mi) across, formed about 1300 years ago,

and is now partly filled with post-collapse domes and flows After USGS .32

Long Valley Caldera Cross-Section

Figure 26: Cross-section and map of Long Valley Caldera [Fig.

8.B, Keller, 2000]. Caldera collapse occurred during eruption

700,000 years ago (which deposited the Bishop Tuff).33

Distribution of Bishop Tuff

Figure 27: Distribution of Bishop Tuff/ash from Long Valley

Caldera [Fig. 8.B, Keller, 2000]. Deposited from eruption

700,000 years ago.34

Predicted Hazard from Long Valley Caldera

Figure 28: Predicted hazard from Long Valley Caldera [Fig. 6.17, ?].

Contours give probable depth of ash, red area and diagonal lines show area

of probable flow events.35

Warning Levels Long Valley Caldera

Figure 29: Warning and response plan, Long Valley Caldera [Tbl. 6.3, ?].

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Crater Lake, Oregon

Figure 30: Crater Lake, Oregon, looking at Wizard Island. This caldera

formed from the eruption of Mt. Mazama about 7000 years ago. After

USGS .37

Other Volcanic Phenomena

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Cinder Cones

Figure 31: Paricutin eruption, Mexico, 1943 [Fig. 8.0, Keller, 2000].

Several villages were completely overrun by basaltic lava flows (see book

cover), cinders represent the volatile “froth” ejected into the air at the vent.39

Geysers

Figure 32: Geyser eruption mechanism [Fig. 6.15b, ?]. Regular geometry

and infilling often causes predictable eruption interval.

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Predicting Eruptions

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Monitoring Methods

• tiltmeters (see Kilauea tilt slide )

• seismic monitoring

– monitor seismicity vs. depth (Fig. 33)

– watch for harmonic tremor

• infrared (Fig. 34)

• gas monitoring (Fig. 35)

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Seismicity vs. Depth: St. Helens

Figure 33: Seismicity vs. depth at Mt. St. Helens since 1997.

St. Helens renewed activity in Fall 2004. Image from USGS

CVO .43

Thermal InfraRed Imagery

Figure 34: Thermal infrared imagery of St. Augustine volcano,

Alaska [Power et al., 2006].

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Gas Monitoring: Long Valley

Figure 35: Gas monitoring and seismicity at Long Valley

Caldera. Note that gas peak appeared just before significant

seismicity. From USGS .

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Controlling Flows

• usually fruitless, but politicians need to be seen doing

something

• one successful blockade of a vent in Italy

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Useful Links

This is intended to be an ever-evolving list of useful links on

the general topic of this note set.

• videos of Hawaiian eruptions

– Pu’u O’o crater filling eruption

• New Zealand lahar formation .

• Smithsonian World Volcanism Program

• USGS Volcanism and Volcanic Hazards Program

• collection of IAVCEI film clips

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Bibliography

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E. A. Keller. Environmental Geology. Prentice Hall, Upper Saddle River, NJ, 8th edition, 2000.ISBN 0-13-022466-9.

J. A. Power, C. J. Nye, M. L. Coombs, R. L. Wessels, P. F. Cerveill, J. Dehn, K. L. Wallace,J. T. Freymuller, and M. P. Doukas. The reawakening of Alaska’s Augustine Volcano. EOS,87(37):373–377, 12 September 2006. URL http://www.agu.org/journals/eo/eo0637/2006EO370002.pdf.

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