plate tectonics

Describe formation of pillowlavas.

When hot lava emerges on the sea floor it cools very quickly and solidifies to form globules that appear as pillows stacked up on each other.

Note

The ocean water around the vents are mineral rich especially sulfurous materials.

Describe sea floor spreading.

The crust moves away and magma upwells, gaining the magnetism of the Earth that existed at the time of its formation.

Divergent plate boundaries

Results in the formation of riff valleys cg. East American riff valley

Magma is forced upward between the two plates, hardens and forms a new strip of crust.there are these kinds of plates between each of the world's oceans eg. Mid Atlantic ridge.

Covergent with 2 oceanic

When the North American and Caribbean plates collide the denser American are sinks back into the mantle. The point at which it re- enters the earth exerts a frictional drab on the Caribbean plate. As a result a trench is formed-it cracks and other lines of weakness form when magma is ejected.

Describe the formation of an island arc.

Magma is ejected creating islands along the convergent plate margin.both North and South boundaries are transform plate margins. There is a kink in the northern boundary resulting in a small area of divergent.

Convergent with an oceanic and continental

When the oceanic Nazca Plate collides with the continental South American the denser plate subsides. On reentering the earth it melts - this point is called subduction zone therefore a frictional drab is create on the continental plate - thus a trench is formed. The continental plate folds and crumples up to form fold mountains. Lines of weakness form volcanoes and ocean floor can be pushed up to form saline lakes.

Transform with an oceanic and continental.

It is believed that the indo-australian plate broke away from Gondwanaland and moved across the Tethys sea towards the Eurasian plate. Layers of sediment were collected across the Tethys sea door and as it got narrower the sediment layers began folding. The sea floor was pushed up and out of existence to form the Himalayas

Note

Peninsula India was also formed which attached to the Eurasia continent. The indo-austrailian plate continues to push into the Eurasian plate - therefore the entire North American plate is earthquake prone

Transform with 2 continental

Both the North American and pacific plate are moving in a northwesterly direction. The pacific plate is moving at a faster rate of 6 cm per year leaving behind the other plate at 1cm it therefore gives the impression that the plates are moving in the opposite direction

Transform plate margins are formed where

Plates move in opposite directions eg. North + South boundaries on Caribbean plates

Same direction but different rates eg. San Andreas fault.

Faults or cracks tend to develop along the boundaries of the plates

Example of a trench - 2 oceanic

Puerto Rican and Cayman trench

Volcano- 2 oceanic

Kick' em Jenny of the coast of Grenada and soufriere in St. Vincent

Trench example - continental and oceanic

Peruvian Chilean trench

Fold mountain example continent and oceanic

The Andes mountains

Volcanoes example

Chimborazo and Cotopaxi in Ecuador

Saline lake example

Lake titicaca

Example of fault formation by transform plate margin

San Andreas fault.

What is a plate?

A rigid segment of the earth's crust which can float across the heavier semi- molten rock below.

Plate margin

Where the boundary of 2 plates meet

Plate tectonics

Is the study of the plates which make up the earth's crust and how their movements affect land forms at the surface.