Volcanoes

volcano: place where magma reaches the surface

magma: liquid, molten rock underground lava: magma that reaches the surface lost gas, gained rock

MID-OCEAN RIDGE: occurs where plates are moving apart lava flows out smoothly and fluidly from cracks

SUBDUCTION ZONE: occurs at subduction boundaries usually explosive and erupted material is mostly lava

HOT SPOTS: areas of volcanic activity in lithospheric plates

Hawaiian Islands are an example

- Temperature - Composition • Viscosity: the measure of a material's resistance to flow (Ex: water is thin, so it has a low viscosity) • Factors affecting viscosity of lava: - Temperature - Composition

two types of lava: felsic: much silica, light-colored, slow moving (continental crust)

mafic: low silica, dark-colored, fast moving (oceanic crust)

Aa Lava Pahoehoe Lava

Pahoehoe

Aa

Aa

Pillow lava from Hawaii Click me!

many magmas contain dissolved gases that are given off water vapor, carbon dioxide (CO2), sulfur (S) magmas with more gases have more explosive eruptions

tephra: solid fragments ejected from a volcano ash (fine, glassy fragments) lapilli (walnut sized particles) blocks (hardened lava) bombs (ejected as hot lava) Sometimes called pyroclastic material

• Composition of the magma • Temperature of the magma  Factors that determine the violence of an eruption: • Composition of the magma • Temperature of the magma • Dissolved gases in the magma

Examine video clips of erupted materials.

Other Volcanic Hazards 1) Ash in the atmosphere can disrupt air travel and, in severe instances, affect climate. Mount Pinatubo, Philippines - Plane on its tail because of weight of ash in 1991 Lascar (northern Chile) erupted in 1993. Eruptions such as this can send large amounts of fine ash particles high into the atmosphere, where they sometimes remain for years. The ash particles scatter incoming sunlight, shading and slightly cooling Earth's surface. Some very large eruptions can have a measurable effect on climate worldwide.

http://www. livescience. com/31127-iceland-volcano-ash-plume-trouble http://www.livescience.com/31127-iceland-volcano-ash-plume-trouble.html

Other Volcanic Hazards 2) Lahars - Mudflows made up of volcanic debris. They flow like liquids, but because they contain suspended material, have a consistency similar to wet concrete. Lahars can travel at speeds of over 50 mph and reach distances dozens of miles from their source.

Other Volcanic Hazards 3) Volcanic Gases - Most of the gas released in an eruption is harmless water vapor (H2O), but volcanoes also produce carbon dioxide, sulfur dioxide, hydrogen sulfide, fluorine gas, and other gases. All of these can be deadly. Lake Nyos, Cameroon – 1986. 1,700 people and 3,500 livestock died when suffocated by CO2 from the lake bottom.

composed of quiet lava flows Shield Volcano composed of quiet lava flows form gently sloping, dome- shaped mountain basaltic (mafic) magma

largest = Mauna Loa in Hawaii

Made mostly of pyroclastic material Formed from explosive eruptions Cinder Cone Volcano Made mostly of pyroclastic material Formed from explosive eruptions Not very high, narrow base, steep sides Granitic (felsic) magma

http://volcano.oregonstate.edu/cinder-cones

http://www.bbc.co.uk/science/earth/collections/mount_vesuvius

built up of alternating layers of rock and lava Composite Volcano (Stratovolcano) built up of alternating layers of rock and lava explosive eruptions at first with tephra, then quiet with lava forms large, cone-shaped mountains made of felsic and mafic magma

Mount Rainier (left) and Mount Hood (right)

Mount Fuji