Earth+Science

-**plate tectonics is the study of the formation and movement of plates -plates are composed of lithosphere (continental=thick, oceanic=thin) 12 major and several minor plates -plates move because of convection cells in the atmosphere
 * PLATE TECTONICS
 * -**convection cells- a circulatory motion in a liquid or gas transferring heat energy

-****DIVERGENT**- place where two plates are pulling apart from each other a)Mid Atlantic Ridge-sea floor spreading at the mid ocean ridges recorded by the reversal of the magnetic poles in mineral grains -paleomagnetism- the study of magnetism in ancient rocks --polar wandering-as metallic mineral grains align themselves with their magnetic poles rock records show that the grains reverse the direction in which they point -**CONVERGENT-****when two plates move towards each other ** -collision-when two plates carrying continents collide they push up usually causing mountains (EX.HIMALAYAS) -subduction-when both plates do not contain continents, one of the plates iss forced to sink under the other one more dense plate is always the one that is subdued **-ocean-ocean**- one plate will subdue to the other one usually causing a deep trench (EX. Mariana's Trench)**
 * Types of Plate Boundaries
 * -ocean continent-the ocean floor is more dense so it subdues to the continental causing ofshore trenches, mountains or volcanoes (EX. Western Coast of South America)

Transform Plate Boundary -**when plates slide past one another usually causing a build up of pressure which is released in the form of an earthquake -San Andreas Fault-** many earthquakes are common along the fault where the North American Plate is sliding past the Pacific Plate To learn more about plate boundaries, you may visit this website: http://www.platetectonics.com/book/page_5.asp

__**Earth Quakes and Volcanic Activity**__
 * -**the ring of fire**-string of volcanoes along the pacific ocesn

__Volcanism__ -magma-molten rock, underground -felsic-magmas with relatively high silica are thick, light colored, and slow moving -mafic-relatively low silica content, thinner, darker, and flow more easily -magma contains dissolved gasses that are given off as the magma erupts. The most important of these gases are water vapor, carbon dioxide, and sulfur -magmas containing large amounts of dissolved gases tend to produce more explosive eruptions - lava- molten rock that has reached the surface - felsic lava- thick and stiff called AA Lava. Produce explosive eruption - mafic lava- thin and fluid called Pahoehoe laval. Lava pours out smoothly

tephra-**solid fragments of lava produced from explosive eruptions -small to large-ash, lapilli, bombs
 * __Lava Fragments__

__**Kinds of Eruptions**__ ** -**Rift Eruptions-occur at long, narrow fractures in the crust such as mid-ocean spreading centers -when lava flows out smoothly and fluidly it forms a volcanic mountain with a broad base and gently sloping sides called a shield cone -these eruptions are more exploive due to the large amount of gases in the magma. forms a **cinder cone** with very steep sides
 * -subduction boundary eruptions**- are the result of thick magma that forms at subduction boundaries.

-hot spots are areas of volcanic activity in the middle of lithospheric plates -similar to rift eruptions. smooth flowing lava and shield cones. -**the hot spot stays in the same locations as the lithospheric plate above it moves** ** **
 * __Hot Spots__