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Name: Matt
Status: Student
Grade: 6-8
Location: CA
Country: United States
Date: February 2008


Question:
I have been taught that the boundaries of Earth push, pull, and slide, but there is nothing about a plate moving in one certain direction or if the plate in different directions. This makes me wonder, do the plates move one certain direction and also, what causes move the plates?



Replies:
Matt-

There are some maps available which show the directions of plate movements. The mechanism for movement is complex, but scientists believe that the basic forces behind movements involve convection currents in the mantle. Here are a couple of web sites that may help:

http://www.ocean.udel.edu/deepsea/level-2/geology/plate.html

http://www.platetectonics.com/book/page_4.asp

Note that the plate movement maps in these sites are large-scale, and do not show many of the small-scale, very complex movements in some parts of the world. If you do a search on the Internet under “plate tectonics,” you will find many sites that may help you understand this fascinating topic.

Patricia Rowe


Dear Matt:

The plates are called that because they act as if each one were a separate piece of crust. Plates can move in a straight line and can also spin. We can actually measure the plates moving by bouncing laser beams off the moon and we have found that plates moves about as fast as your fingernail grows. The plates move against each other but are not all heading in the same direction.

Exactly how the plates are moved is a question that has not been completely answered but we are pretty sure it is movement in the mantle, the layer between Earth’s crust and the core.

Robert Avakian


The crust of the Earth is said to be made up of a number of Plates, which are composed of two types of material - which form different layer types. Oceanic layers are thin, are relatively dense, and make up the floor of the oceans. Continental layers are much thicker, but are composed of lighter material (relatively speaking). A single plate may have both oceanic and continental layers adjoining. There are seven large plates and a number of smaller ones. These plates move, and as they do, the edges bump into each other. If an oceanic plate collides with a continental plate, the heavier oceanic layer goes underneath the continent, and we get a subduction zone, usually with a deep ocean trench (See Marianas trench).

If a continent collides with a continent, neither wants to go underneath so you get a huge crumpling zone, and the material gets compressed and piles higher and higher (See Himalayas) Do they all move in the same direction? - NO. Each plate moves in a different direction, but that also means that no plate can move in two directions - It moves as a single piece. What drives all this movement? Mid Ocean volcanic ridges. If you look at a good atlas, or a globe, you will see a bumpy line, running down the middle of the Pacific Ocean. This is a mid ocean ridge, and it is actually a huge volcano (or series of volcanoes) in the shape of a slit. Lava from the volcanoes oozes out onto the ocean floor, pushing the two oceanic plates apart. This means that one half of the Pacific Ocean is moving toward Japan - where it gets pushed underneath. The other half is being pushed toward America, and the far edge of that plate is trying to go underneath and slide past the Western edge of America - and this is why California has so many earthquakes.

The Wikipedia Article on Plate Tectonics is a good place to begin your further research.

http://en.wikipedia.org/wiki/Plate_tectonics

Nigel Skelton



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