Volcanic eruptions and other igneous activity

Viscosity – mobility of magma (resistance to flow)

Factors affecting viscosity:

• temperature• composition

• silica content• dissolved gases

Factors affecting viscosity

Volcanic eruptions and other igneous activity

Low viscosity(high mobility)

High viscosity(low mobility)

High temp

Low temp

Low SiO2

High SiO2

Low gas content

High gas content

Importance of dissolved gases

Volcanic eruptions and other igneous activity

Low viscosity(high mobility)

High viscosity(low mobility)

Low violence eruption

High violence eruption

High pressure

Low gas content

High gas content

Low pressure

Materials extruded during an eruption

Volcanic eruptions and other igneous activity

• Lava flows• pahoehoe flows• aa flows• block lavas• pillow lavas

• Gases• Pyroclastic materials accdg to size

• ash and dust (welded tuff)• pea to walnut sized (lapilli, cinders)• blocks• bombs

• Pyroclastics accdg to texture• scoria (from basaltic magma)• pumice (from felsic magma)

Materials extruded during an eruption

Volcanic eruptions and other igneous activity

Lava flows – pahoehoe vs aa flows

Pahoehoe flows

Materials extruded during an eruption

Volcanic eruptions and other igneous activity

Lava flows – pahoehoe vs aa flows

aa flows

Materials extruded during an eruption

Volcanic eruptions and other igneous activity

Hardened pahoehoe flows = lava tubes

Materials extruded during an eruption

Volcanic eruptions and other igneous activity

Block lavas

Materials extruded during an eruption

Volcanic eruptions and other igneous activity

Pillow lavas

Materials extruded during an eruption

Volcanic eruptions and other igneous activity

Pillow lavas

The study of pillow lavas is important in reconstructing Earth’s geologic history. Can you tell why?

Materials extruded during an eruption

Volcanic eruptions and other igneous activity

Gases

Water vapor 70%CO2 15Nitrogen 5Sulfur dioxide 5

(low amounts of)ChlorineHydrogenArgon

Why is the study of volcanic gases very important?

Materials extruded during an eruption

Volcanic eruptions and other igneous activity

Gases

Materials extruded during an eruption

Volcanic eruptions and other igneous activity

Gases

Materials extruded during an eruption

Volcanic eruptions and other igneous activity

Pyroclastic materials – welded tuff

Materials extruded during an eruption

Volcanic eruptions and other igneous activity

Pyroclastic materials – welded tuff

Materials extruded during an eruption

Volcanic eruptions and other igneous activity

Pyroclastic materials – welded tuff

Materials extruded during an eruption

Volcanic eruptions and other igneous activity

Pyroclastic materials – welded tuff

Materials extruded during an eruption

Volcanic eruptions and other igneous activity

Pyroclastic materials – lapilli or cinders

From Vesuvius

Materials extruded during an eruption

Volcanic eruptions and other igneous activity

Pyroclastic materials – blocks

Materials extruded during an eruption

Volcanic eruptions and other igneous activity

Pyroclastic materials - bombs

Materials extruded during an eruption

Volcanic eruptions and other igneous activity

Pyroclastic materials (accdg to texture) - scoria

• Basaltic magma• Darker• Denser

Materials extruded during an eruption

Volcanic eruptions and other igneous activity

Pyroclastic materials (accdg to texture) - pumice

• Silica-rich magma• Lighter color• Less dense

Anatomy of a volcano

Volcanic eruptions and other igneous activity

Anatomy of a volcano - caldera

Volcanic eruptions and other igneous activity

Anatomy of a volcano - caldera

Volcanic eruptions and other igneous activity

Anatomy of a volcano - caldera

Volcanic eruptions and other igneous activity

Anatomy of a volcano – parasitic cones

Volcanic eruptions and other igneous activity

Anatomy of a volcano – fumaroles

Volcanic eruptions and other igneous activity

Volcano types – shield volcano

Volcanic eruptions and other igneous activity

• fluid basaltic lavas, often a few meters thick• broad, slightly domed structure• very few pyroclastic ejecta• lava tends to be more viscous as volcano matures

Volcano types – shield volcano

Volcanic eruptions and other igneous activity

Mauna Loa and Mauna Kea (upper white smudge) are 2 (of 5) overlapping shield volcanoes that make up Hawaii’s Big Island.

Volcano types – shield volcano

Volcanic eruptions and other igneous activity

Mauna Loa is over 9 km high (more than Everest’s 8.7km)

Volcano types – cinder cones

Volcanic eruptions and other igneous activity

• built from ejected lava fragments known as cinders or scoria• ash to walnut-sized ejecta

Volcano types – cinder cones

Volcanic eruptions and other igneous activity

• single eruptive episode = small cones• lava pipe is often immediately sealed with congealed lava• lava flows seldom happen; only at base, away from summit crater

Volcano types – composite cones

Volcanic eruptions and other igneous activity

• large, nearly symmetric structure of both lava and pyroclastic deposits• silica-rich magma travels only a short distance• gas-rich magma often produces violent eruptions

Volcano types – composite cones

Volcanic eruptions and other igneous activity

• steep summit with gently sloping flanks are due to lava flows• when young, lava tends to be more viscous, hence traveling farther to make a bigger base• mature volcanoes produce more viscous lava with increase the summit’s angle

Volcano types – hazards of composite cones

Volcanic eruptions and other igneous activity

sudden, often unexpected eruptions

Volcano types – hazards of composite cones

Volcanic eruptions and other igneous activity

Nuee ardente (glowing avalanches)

Volcano types – hazards of composite cones

Volcanic eruptions and other igneous activity

Lahar (mudflows of pyroclastic material)

Other volcanic landforms - Calderas

Volcanic eruptions and other igneous activity

Crater lake-type caldera

Other volcanic landforms - Calderas

Volcanic eruptions and other igneous activity

Hawaiian-type caldera

Other volcanic landforms - Calderas

Volcanic eruptions and other igneous activity

Yellowstone-type caldera

Other volcanic landforms – Fissure eruptions and basalt plateaus

Volcanic eruptions and other igneous activity

Fissure eruptions

Other volcanic landforms – Fissure eruptions and basalt plateaus

Volcanic eruptions and other igneous activity

Basalt plateaus

Other volcanic landforms – Lava dome

Volcanic eruptions and other igneous activity

Other volcanic landforms – Volcanic pipes

Volcanic eruptions and other igneous activity

Kimberlite diamond mines are volcanic pipes

Other volcanic landforms – Volcanic necks

Volcanic eruptions and other igneous activity

Volcanic necks are exposed pipes (erosion has long since removed the surrounding volcanic structure)

Intrusive igneous activity – plutons

Volcanic eruptions and other igneous activity

According to shape• Tabular• Massive

According to orientation• Discordant• Concordant

Dikes – tabular, discordantSills – tabular, concordantLaccoliths – tabular, concordantBatholiths

Other volcanic landforms – Dikes

Volcanic eruptions and other igneous activity

Other volcanic landforms – Sills

Volcanic eruptions and other igneous activity

Other volcanic landforms – Sills

Volcanic eruptions and other igneous activity

Other volcanic landforms – Sills

Volcanic eruptions and other igneous activity

Other volcanic landforms – Sills (columnar joints)

Volcanic eruptions and other igneous activity

Other volcanic landforms – Laccoliths

Volcanic eruptions and other igneous activity

Other volcanic landforms – Batholiths

Volcanic eruptions and other igneous activity

Other volcanic landforms – Batholiths (xenoliths)

Volcanic eruptions and other igneous activity

Other volcanic landforms – Stocks

Volcanic eruptions and other igneous activity

Stocks are smaller batholiths

Plate tectonics and igneous activity

Volcanic eruptions and other igneous activity

Igneous activity at convergent plate boundaries

Volcanic eruptions and other igneous activity

Volcanic island arcs

Igneous activity at convergent plate boundaries

Volcanic eruptions and other igneous activity

Igneous activity at convergent plate boundaries

Volcanic eruptions and other igneous activity

Continental volcanic arcs

Igneous activity at convergent plate boundaries

Volcanic eruptions and other igneous activity

Costa Rica coastal plains

Igneous activity at divergent plate boundaries

Volcanic eruptions and other igneous activity

Oceanic ridges

Igneous activity at divergent plate boundaries

Volcanic eruptions and other igneous activity

East African Rift

Intraplate igneous activity

Volcanic eruptions and other igneous activity

Mantle plume

Intraplate igneous activity

Volcanic eruptions and other igneous activity

Sahara desert volcanoes