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 SiO 2 High SiO 2 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% CO 2 15 Nitrogen 5 Sulfur dioxide 5 (low amounts of) Chlorine Hydrogen Argon 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, discordant Sills – tabular, concordant Laccoliths – tabular, concordant Batholiths

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