Volcanic processes Magma encounters external water Yes Volcanic

Magma encounters « external » water Yes Volcanic processes and types No Magma contains

• Dynamic types related to magma/water interactions • Dynamic types related to dissolved

Magma viscosity Figure 4 -1. a. Calculated viscosities of anhydrous silicate liquids at one

Mount Saint-Helens: The post-18 May dome

Figure 4 -7. Schematic cross section through a lava dome.

Dome growth and collapse • Cortex of the dome « chills » , interior

Montagne-Pelée, Martinique (lesser Antilles)

Piton de la Fournaise (Réunion, Indian Ocean)

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

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

Multiple lava flows Piton de la Fournaise (Réunion, Indian Ocean)

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Volcanic processes

Magma encounters « external » water Yes Volcanic processes and types No Magma contains dissolved gas Submarine, surtseyan, phreatomagmatic types Yes No Magma is viscous Plinian eruptions « grey » volcanoes More explosive Andesitic Subductions Yes No Domes and block-and-ash flows (Pelean) Flows and scoria cones (Strombolian, hawaian) « 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

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 Mc. Birney, 1973), Geol. Soc. Amer. Bull. , 84, 3563 -3592. c. Variation in the viscosity of rhyolite at 1000 o. C with increasing H 2 O content (after Shaw, 1965, Amer. J. Sci. , 263, 120 -153).

Mount Saint-Helens: The post-18 May dome

Figure 4 -7. Schematic cross section through a lava dome.

Secondary ash fall (+local surges)

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!!

Montagne-Pelée, Martinique (lesser Antilles)

Saint-Pierre, before

Saint-Pierre, after