Volcanoes
What are volcanoes? A volcano is an opening in Earth that erupts gases, ash, and lava.
How do volcanoes form? Magma is less dense than the rock around it, so it is forced toward the surface Vent: Opening that magma flows through Crater: The steep-walled depression around a volcano’s vent
Where do volcanoes occur? Divergent Plate Boundaries Iceland Mid-Atlantic Ridge Convergent Plate Boundaries Oceanic Plate slides beneath Continental Plate Andes mountains in South America Erupt more violently Oceanic Plate slides beneath Oceanic Plate
Where do volcanoes occur?
Where do volcanoes occur? Hot Spots Areas between Earth’s mantle and core that are unusually hot. Hot rock forces toward the crust where it melts partially to form a hot spot. Hawaiian Islands Pacific Plate moving over a stationary hot spot.
Hot Spot Occurrence
What controls eruptions? Trapped Gases Composition of Magma Silica Poor Silica Rich Varying Silica Content
Liquid Hot Magma!!!!
What controls eruptions? Silica Poor: quiet eruption Basaltic Magma, Pahoehoe flows Silica Rich: explosive eruption Granitic Magma, Mount St. Helens, WA Intermediate Silica: Quiet / explosive eruption. Andesitic Magma, Convergent Plate Boundaries, Krakatau, South America
Forms of Volcanoes Shield Volcano Quiet eruptions of basaltic lava spread out in flat layers Layers buildup and form a broad volcano with gently sloping sides Hawaiian Islands
Forms of Volcanoes Cinder Cone Volcanoes Explosive eruptions throw lava and rock high into the air When rock and ash land, it forms a steep-sided, loosely packed volcano Paricutín, Mexico
Forms of Volcanoes Composite Volcano Varying explosions depend on amount of silica and trapped gases. Alternating layers of lava and ash form a volcano Mount Rainier, WA
Violent Eruptions 1883: Krakatau, Indonesia 1906: Vesuvius, Italy 1983: Kilauea, Hawaii 2000: Popocatepetl, Mexico
Volcanic Activity Reports http://volcano.und.edu/vwdocs/current_volcs/current.html http://www.volcano.si.edu/reports/usgs/