A.M.D.G Geography 08/07/13

CONVERGENT PLATE BOUNDARIES

· Planet is not getting any bigger so if new land is created other land has to be destroyed.

· These boundaries are also called destructive plate boundaries.

· This happens where plates dive into mantle

· Solid rock of crust melts

· This is part of tectonic cycle.

3 Convergent Boundaries

· Continental -> Oceanic

· Oceanic ->Oceanic

· Continental-> Continental

· Oceanic meets continental

· Oceanic material (sima) is heavier than continental (sial)

· Oceanic dives beneath continental and about 70km melts.

· The plate (lithosphere) becomes part of the mantle (asthenosphere).

· Hence it is called a destructive boundary

· Stress of this collision causes the continental plate to buckle to form mountains.

· The melting plate mixed with gases from the sea water may also cause violent volcanic activity Pacific Plate North America -> Mt St Helen’s and Rockie Mts.

· Oceanic meets Oceanic

· Older heavier plate dives under.

· This is subduction long, deep, narrow trench developed.

· Marianas trench (Pacific and Philippines) about 11km at deepest.

· Crystal rock destroyed.

· Magma formed volcano activity occurs. A line of volcanic islands appear along boundary.

· These are Island Arcs.

· Philippines and Japanese Islands

· Part of Pacific Rim

· Continental meets Continental

· Two continental plates collide head on.

· Light but very thick.

· The lithosphere subducts but plates collide and all sediments at edges of plates are swept up and deformed causing mountain ranges.

· Indian sub plate collided with Eurasian 50-20 million years ago resulting in Himalayas.

· Ireland: Cadedonian mts Donegal

· Faulting, thrusting and folding occur.

· Huge amounts of deposited material from rivers.

· They collided recently therefore mountains are still high i.e. ->not worn down by weathering and erosion.

· Very destructive earthquakes occur along fault lines within Himalayas.

Conservative Plate Boundaries

· Plates slide past

· Along fault

· Transform faults

· Crust neither created nor destroyed

· Therefore a passive or conservative boundary

· Intense earthquake activity

· San Andreas Fault, California 1200km long move about 5cm a year

Plate Boundary Summary

Direction

Name

Created

Moves apart

Divergent or Constructive

Crust created Continents split

Move together/Collide

Convergent or Destructive

Fold Mts., Earthquakes, Volcanoes, Island Arcs and crust destroyed

Moves alongside/past

Transform, neutral, passive

Earthquakes

Move over hot spot

Mid plate

Volcanic Island

	Created by sebastiankavanag almost 11 years ago

Geography Note on Convergent_Plate_Boundaries, created by sebastiankavanag on 15/07/2013.

Convergent_Plate_Boundaries