Volcanic EruptionsVolcanic Eruptions

Mafic Lava Dark coloredRich in magnesium and ironFormed from oceanic crustCools rapidly

Felsic Lava

Light coloredRich in silicaFormed from continental crust

Eruptions

Composition of lava determines the force of the eruption

Oceanic Eruptions

Erupt on the ocean floor and oceanic islandsMafic lava

Very hotVery thin (watery)Flows easily

Continental Eruptions

Erupt on the landFelsic lava

CoolerThickerContains large amounts of gases

Carbon dioxide and water vaporExplosive

Mafic Lava

Pyroclastic material (tephra)-rock fragments ejected from volcanoesVolcanic ash- less than 2 mmVolcanic dust- less than .25 mmBoth can travel around the Earth in the

atmosphere

Volcanic Cones

Piles of volcanic material around the vent

Volcanic cones

Shield conesCover wide areasBroad at the baseGentle slopeQuiet eruptionsExample Hawaiian Islands

Shield cones

Volcanic cones

Cinder conesExplosive eruptionsVery steep slopesRarely more than a few hundred meters high

Cinder cones

Volcanic cones

Composite conesDevelop into high volcanic mountainsAlternating types of eruptionsExamples: 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

EarthquakesTemperature changes in rock around ventBulging of the surface of the volcanoChange in gases given off