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Volcanic processes

Volcanic processes. Yes No YesNo Yes No « grey » volcanoes More explosive Andesitic Subductions « red » volcanoes Less explosive Basaltic Intra-plate

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Page 1: Volcanic processes. Yes No YesNo Yes No « grey » volcanoes More explosive Andesitic Subductions « red » volcanoes Less explosive Basaltic Intra-plate

Volcanic processes

Page 2: Volcanic processes. Yes No YesNo Yes No « grey » volcanoes More explosive Andesitic Subductions « red » volcanoes Less explosive Basaltic Intra-plate

Magma encounters « external » water

Submarine, surtseyan, phreatomagmatic types

Magma containsdissolved gas

Plinian eruptions Magma is viscous

Domes and block-and-ash flows

(Pelean)

Flows and scoria cones(Strombolian, hawaian)

Yes No

Yes No

Yes No

« grey » volcanoesMore explosiveAndesiticSubductions

« red » volcanoesLess explosiveBasalticIntra-plate

Volcanic processesand types

Page 3: Volcanic processes. Yes No YesNo Yes No « grey » volcanoes More explosive Andesitic Subductions « red » volcanoes Less explosive Basaltic Intra-plate

• Dynamic types related to magma/water interactions

• Dynamic types related to dissolved bubbles

• Dynamic types related to domes growth and collapse

• Dynamic types related to lava flows etc.• Destruction of volcanic edifices• Complex edifices

Page 4: Volcanic processes. Yes No YesNo Yes No « grey » volcanoes More explosive Andesitic Subductions « red » volcanoes Less explosive Basaltic Intra-plate

Magma viscosity

Figure 4-1. a. Calculated viscosities of anhydrous silicate liquids at one atmosphere pressure, calculated by the method of Bottinga and Weill (1972) by Hess (1989), Origin of Igneous Rocks. Harvard University Press. b. Variation in the viscosity of basalt as it crystallizes (after Murase and McBirney, 1973), Geol. Soc. Amer. Bull., 84, 3563-3592. c. Variation in the viscosity of rhyolite at 1000oC with increasing H2O content (after

Shaw, 1965, Amer. J. Sci., 263, 120-153).

Viscosity of Anhydrous Magma

Log

Vis

cosi

ty (

poi

se)

10

8

6

4

2

50 60 70Wt. % SiO2

1400o C1200o C1000o C

Oliv

ine

Bas

alt

Bas

alt

And

esite

Dac

ite

Rhy

olite

10

8

6

4

2 4 6 8 10Wt. % H2O

Rhyolite at 1000oC

Log

Vis

cosi

ty (

pois

e)

4

5

3

2

AllLiquid

T (oC)

IncreasingCrystallization

Basalt

Beg

inn

ing

of C

ryst

alliz

atio

n

2

Log

Vis

cosi

ty (

pois

e)

a cb

1400 1300 1200 1100

Page 5: Volcanic processes. Yes No YesNo Yes No « grey » volcanoes More explosive Andesitic Subductions « red » volcanoes Less explosive Basaltic Intra-plate
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Mount Saint-Helens:The post-18 May dome

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Page 8: Volcanic processes. Yes No YesNo Yes No « grey » volcanoes More explosive Andesitic Subductions « red » volcanoes Less explosive Basaltic Intra-plate
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Figure 4-7. Schematic cross section through a lava dome.

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Secondary ash fall (+local surges)

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Page 15: Volcanic processes. Yes No YesNo Yes No « grey » volcanoes More explosive Andesitic Subductions « red » volcanoes Less explosive Basaltic Intra-plate
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Page 17: Volcanic processes. Yes No YesNo Yes No « grey » volcanoes More explosive Andesitic Subductions « red » volcanoes Less explosive Basaltic Intra-plate

Dome growth and collapse

• Cortex of the dome « chills », interior still hot

• Steep slopes, local collapse– Breccias– Pyroclastic flows: « block and ash flow »

• Dense flow, rich in blocks

• Smaller scale than plinian!!

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Montagne-Pelée, Martinique(lesser Antilles)

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Saint-Pierre, before

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Saint-Pierre, after

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Page 22: Volcanic processes. Yes No YesNo Yes No « grey » volcanoes More explosive Andesitic Subductions « red » volcanoes Less explosive Basaltic Intra-plate
Page 23: Volcanic processes. Yes No YesNo Yes No « grey » volcanoes More explosive Andesitic Subductions « red » volcanoes Less explosive Basaltic Intra-plate
Page 24: Volcanic processes. Yes No YesNo Yes No « grey » volcanoes More explosive Andesitic Subductions « red » volcanoes Less explosive Basaltic Intra-plate
Page 25: Volcanic processes. Yes No YesNo Yes No « grey » volcanoes More explosive Andesitic Subductions « red » volcanoes Less explosive Basaltic Intra-plate

Magma encounters « external » water

Submarine, surtseyan, phreatomagmatic types

Magma containsdissolved gas

Plinian eruptions Magma is viscous

Domes and block-and-ash flows

(Pelean)

Flows and scoria cones(Strombolian, hawaian)

Yes No

Yes No

Yes No

« grey » volcanoesMore explosiveAndesiticSubductions

« red » volcanoesLess explosiveBasalticIntra-plate

Volcanic processesand types

Page 26: Volcanic processes. Yes No YesNo Yes No « grey » volcanoes More explosive Andesitic Subductions « red » volcanoes Less explosive Basaltic Intra-plate

• Dynamic types related to magma/water interactions

• Dynamic types related to dissolved bubbles

• Dynamic types related to domes growth and collapse

• Dynamic types related to lava flows etc.• Destruction of volcanic edifices• Complex edifices

Page 27: Volcanic processes. Yes No YesNo Yes No « grey » volcanoes More explosive Andesitic Subductions « red » volcanoes Less explosive Basaltic Intra-plate

Lava lakes

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Eruptive fissures

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Bubbles

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Scenic volcanoes!

Stromboli (Italy)

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Scoria cones

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Piton de la Fournaise (Réunion, Indian Ocean)

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Cones groupe in Réunion

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Puy de Pariou (France)(note also the pelean dome of Puy de Dome at the back)

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Scoria cones

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Disrupted cones

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Cones and lava flows

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Etna (Italy)

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Strange things lava flows do…

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No, there is nobody here – it is just a weird but completely natural shape…

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Multiple lava flows

Piton de la Fournaise (Réunion, Indian Ocean)

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Rift zone

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Aa and Pahoehoe

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Lava caves

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Prismation

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Scoria base

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