Plate Boundaries

The Theory Of Plate Tectonics States: The Lithosphere is divided into ten major plates and a number of smaller plates.

Hess’ Theory about Sea Floor Spreading explains how all of the plates (not just oceanic ones) could be set in motion. It would also make sense that they all then collide in some way at the other end . . .

The “dynamic” parts of earth (Volcanoes, Earthquakes and Mountain Building) occur along Plate Boundaries where plates collide.

There are three types of plate boundaries: DIVERGENT (moving apart) CONVERGENT (coming together) TRANSFORM (moving sideways past each other) **We will abbreviate the types of plates “O” for ocean, and “C” for continental

Divergent boundaries Plates moves apart New crust is created as hot magma rises up from the mantle. Mountains associated with divergent boundaries are called RIDGES

Divergent Boundary Motion:

Examples of Divergent Boundaries: Mid-Atlantic Ocean Ridge, East African Rift, and Red Sea

DIVERGENT BOUNDARY TYPES: (Mid Atlantic Ridge) (East African Rift) O-O Divergent C-C Divergent

Iceland is a growing country, because it’s got a divergent boundary right in the middle of it. . . It will stretch, thin, have some mild volcanic activity increase, and then eventually have ocean water move in. . (RIFT VALLEY)

Convergent Boundaries Plates move toward each other and collide. A plate will always be subducted. MOTION: Either the lighter plates will “buckle” and fold, or the denser one will get pushed beneath the other.

CONVERGENT BOUNDARY TYPES: (Japanese Islands) (Himalayan Mountains, Alps) O-O Convergent C-C Convergent (Andes Mountains, Cascade Mountains) O-C Convergent

Because of subduction, the plate being melted creates excess magma, heat, and pressure. Volcanic activity and earthquake activity are common at convergent boundaries.

O-O Convergent Boundary Formed when one ocean plate is subducted beneath another The location of the subduction forms a deep trench The melting oceanic plate creates an island arc (ARCHIPELAGO) on the overhanging plates

The Pacific Ocean is a major site of ocean plate convergence The Pacific Ocean is a major site of ocean plate convergence. . . Which gave rise to Japan and the Phillipines

C-C convergent boundaries used to have an ocean between them which has long since dissappeared/subducted. Because of the forces of the collision, these mountains are typically taller and more jagged than other ranges. MOUNTAIN BUILDING = “OROGENY”

India Is still moving into Asia Today

O-C Convergent Boundaries: The heavier oceanic plate will sink under the lighter continental plate. The convergence causes the continental plate to buckle up, forming mountains. As the heavier oceanic plate subducts, it melts in the mantle and hot magma rises up forming volcanoes called a Volcanic Arc on the continental plate. Examples: Mt. St. Helens and Lassen Peak in the Cascade Mountain Range and the Andes Mountains

O-C Collision Motion:

Mt. St. Helens Lassen peak

Transform Boundaries At transform boundaries plates slide past each other. Crust is neither being destroyed nor created. Transform boundaries act like stress fractures resulting from other plate boundaries. There are O-O, O-C, and C-C transform boundaries.

(San Andreas Fault System) (San Andreas Fault System). . . As the Pacific Plate moves North, it’s possible that LA could be West of us some day!

San Andreas Fault System

Identify the Plate Boundaries below and their related structures formed: A. B. C. D. E. Types: C-C Divergent, O-O Divergent, O-O convergent, O-C convergent, C-C convergent, Transform