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

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