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