Volcanic Eruptions

Mafic Lava Dark colored Rich in magnesium and iron Formed from oceanic crust Cools rapidly

Felsic Lava Light colored Rich in silica Formed from continental crust

Eruptions Composition of lava determines the force of the eruption

Oceanic Eruptions Erupt on the ocean floor and oceanic islands Mafic lava Very hot Very thin (watery) Flows easily

Continental Eruptions Erupt on the land Felsic lava Cooler Thicker Contains large amounts of gases Carbon dioxide and water vapor Explosive

Mafic Lava Pyroclastic material (tephra)-rock fragments ejected from volcanoes Volcanic ash- less than 2 mm Volcanic dust- less than .25 mm Both can travel around the Earth in the atmosphere

Volcanic Cones Piles of volcanic material around the vent

Volcanic cones Shield cones Cover wide areas Broad at the base Gentle slope Quiet eruptions Example Hawaiian Islands

Shield cones

Volcanic cones Cinder cones Explosive eruptions Very steep slopes Rarely more than a few hundred meters high

Cinder cones

Volcanic cones Composite cones Develop into high volcanic mountains Alternating types of eruptions Examples: Mount Fuji, Mount Hood, Mount St. Helens

Composite cones

Crater Funnel shaped pit at the top of a volcanic vent

Caldera Large basin shaped depression caused by an explosive eruption Magma chamber below a vent, causing the volcanic cone to collapse

Predicting Volcanoes Earthquakes Temperature changes in rock around vent Bulging of the surface of the volcano Change in gases given off