12Flood BasaltsOccur when basaltic magma flows onto the surface of the earth through large cracks called fissures.When the magma cools, it covers large areas with thick igneous rock.Accounts for largest volume of erupted volcainc material on Earth.Examples:Columbia PlateauNew ocean floor
14Cinder Cone VolcanoForm when tephra fall to the ground and form a loosely-packed steep-sided structure.Tephra consist of bits of rock or solidified lava drpped from the air.Includes volcanic ash, cinders, and larger rocks called bombs and blocksExample:Paricutin – Feb 20th, 1943
16Types of Tephra Volcanic Ash Volcanic Dust Lapilli Tephra particles less than 2 mm in diameter.Volcanic DustParticles less than 0.25 mm in diameter.LapilliLarger tephra particles, less than 64 mm in diameter.Generally fall near the vent.
17Types of Tephra Volcanic Bombs Volcanic Blocks Tephra particles with round or spindle shape.Volcanic BlocksSolid rocks blasted from a fissure.
18Composite VolcanoFormed from alternating quiet and explosive eruptions, depending on the amount of trapped gases and silica content at the time of eruption.Result is alternating layers of tephra and lava.Examples:Convergent boundaries – Mount St. Helen’s, Mount Raineer
20Krakatau Island in the Sunda Straits near Indonesia. Erupted in August of 1883, causing the “island” to collapse into the empty magma chamber (caldera-forming).More than 36,000 people were killed (mainly by a tsunami)Global temps dropped as much as 1.8 degrees Celsius for five years.
22Effects of Eruptions Lava flows Collapse of buildings from ash fall Air pollution (lung disease/stress)Acid rainPyroclastic flowsHuge, hot, fast rush of ash and debris down the mountain (can result in fires)Permanent/Temporary Evacuation