Results of plate tectonics: 1.volcanism2.diastrophism3.earthquakes

Volcanism

Volcanism movement of molten rock from earth’s interior through a conduit or opening to, or near, the surface movement of molten rock from earth’s interior through a conduit or opening to, or near, the surface

Types of volcanism: A. Extrusive 1. Volcanoes  a) shield  b) composite  c) cinder cone 2. Lava Flows  flood basalts B. Intrusive

A. Extrusive Volcanism Magma reaches the surface (lava) and cools above the surface. Magma reaches the surface (lava) and cools above the surface. 1. Volcanoes: hills or mountains of volcanic material that was released under pressure from a vent –>500 active (4/5 “ Ring of Fire”) - subduction, rift valleys, mid-oceanic ridges, hot spots

Types of Volcanoes: a) Shield Volcanoes –broad, gently sloping surfaces  examples: Hawaii, Azores, Mt. Hekla in Iceland –tallest mountains on earth are shield volcanoes from the ocean floor –effusive eruption  nonviolent eruption due to type of magma –low viscosity; 2200 degrees F, little gas in magma –Iron, magnesium, low in silica: from asthenosphere  Primarily basalt

b) Composite Volcanoes –steep-sided –alternating layers of pyroclastics and lava  pyroclastics: rock pieces ejected: –Tephra: pulverized rock –Scoria: cindery vesicular rock –ash falls and lava flows –subduction zones  examples: Mt. St. Helens, Mt. Rainier, Mt. Fuji, Mt. Hood –explosive eruption due to type of magma  higher viscosity, 1600 F; contains gases  from melting of lithosphere: more silica

Types of volcanism: A. Extrusive 1. Volcanoes  a) shield  b) composite  c) cinder cone 2. Lava Flows  flood basalts B. Intrusive

Composite = stratovolcano Composite = stratovolcano

Insert map of volcanoes

CALDERA: landform associated with some composite volcanoes CALDERA: landform associated with some composite volcanoes –large bowl-shaped depression left after a composite volcano blows; mountain collapses inward –Example: Crater Lake

c) Cinder Cones c) Cinder Cones –steep, cone-shaped hills of pyroclastics –moderately explosive –most abundant and smallest (<1500 ft. high) –central crater –form rapidly, erode rapidly  example: central Arizona; Paricutin, Mexico; Idaho Snake River Plain

Types of volcanism: A. Extrusive 1. Volcanoes  a) shield  b) composite  c) cinder cone 2. Lava Flows  flood basalts B. Intrusive

2. Lava Flows Effusive (nonviolent) eruptions Effusive (nonviolent) eruptions spreading boundaries and hot spots spreading boundaries and hot spots lava spreads out over surface; coming out of fissure (rift) lava spreads out over surface; coming out of fissure (rift) –example: Lake Superior shore  1.2 billion yrs BP can accumulate layer upon layer : FLOOD BASALT can accumulate layer upon layer : FLOOD BASALT –examples: Columbia Plateau (Washington), Deccan Plateau (India)

B. Intrusive Volcanism Magma solidifies beneath surface; intrudes into cracks in crust Magma solidifies beneath surface; intrudes into cracks in crust –intrusions can later be exposed at surface; more resistant than surrounding rock

Intrusive landforms Neck: narrow steep-sided peak, formed in central vent of an extinct volcano Neck: narrow steep-sided peak, formed in central vent of an extinct volcano –E.g., Ship Rock, Devil’s Tower Dike: thin layer of igneous rock ; vertical; cuts across other rock layers Dike: thin layer of igneous rock ; vertical; cuts across other rock layers Sill: thin layer of igneous rock between rock layers Sill: thin layer of igneous rock between rock layers Plutons: large igneous bodies at depth Plutons: large igneous bodies at depth –batholiths –laccolith: dome-shaped