Chapter 6 – VOLCANOES

Volcanoes & volcanic hazards• Volcano

– Vent where lava, solid rock debris, volcanic ash, & gases erupt from inside Earth onto its surface

– Can be explosive or non-explosive• Mt. St. Helens• Kilauea

Volcanoes & volcanic hazards

• Lava– Molten rock that reaches

Earth’s surface• Magma

– Molten rock, which may include fragments of rock, volcanic glass & ash, or gas• Beneath Earth’s surface

Volcanoes & volcanic hazards

Eruptions, landforms & materials• Eruption types:

Hawaiian– Shield volcano

• Broad, flat volcano with gently sloping sides

– Largest volcanoes

• Built of successive lava flows

• May also produce flood basalts or lava plateaus

Eruptions, landforms and materials• Eruption types:

Strombolian– More explosive

than Hawaiian– Create loose

volcanic rock called spatter cones or cinder cones• Smallest volcanoes

Eruptions, landforms and materials• Eruption types: Vulcanian

– More explosive than Strombolian

– Can generate clouds of ash up to 10 km

– Produce pyroclastic flows• Hot volcanic fragments

(tephra) that flow very rapidly

Eruptions, landforms & materials• Eruption types: Plinian

– Most violent eruptions; ash columns over 20 km

– Produce stratovolcanoes• Composed of alternating

layers of solidified lava & pyroclastic material

• Steep sided

Eruptions, landforms & materials

Eruptions, landforms & materials• Viscosity

– Degree to which substance resists flow• Less viscous =

runny• More viscous =

thick

• Dissolved gases– Up to ~10% of

magma• Water vapor, carbon

dioxide, sulfur dioxide, etc.

Eruptions, landforms & materials• Volcanic materials

– Pyroclasts– Tephra

• Ash• Agglomerates• Tuff

Eruptions, landforms & materials• Volcanic

materials– Pahoehoe flows– A’a flows– Lava tubes– Vesicles– Columnar

jointing– Pillow

structures

Eruptions, landforms and materials• Other volcanic features

– Crater– Caldera– Resurgent

dome

Eruptions, landforms and materials• Other volcanic features

– Thermal spring– Geyser– Fumarole

Eruptions, landforms and materials• Other volcanic

features– Fissure eruptions

• Flood basalt• Lava plateau

Volcanic hazards• Primary effects

– Lava flows– Pyroclastic flows– Volcanic gases

Volcanic hazards• Secondary effects

– Fires– Flooding– Mudslides (lahars)– Debris avalanche

Volcanic hazards• Tertiary and beneficial effects

– Landscape changes– Climate changes; regional &

global– Benefits:

• Replenishes minerals & fertility• Geothermal energy• Specific mineral deposits

Predicting Eruptions• Establish

volcano’s history– Active– Dormant– Extinct

Predicting Eruptions• Monitor changes & anomalies

– Microseismicity– Tilting or bulging– Volcanic gases– Changes in ground or surface

water temperature