Science/geography help!!!?

Question

Hi, i have a really important science test tomorrow and dont understand a few topics, could you explain them in simple english. Thanks:

What is an oceanic ridge (how its formed. What it looks like...etc)?

What is an oceanic trench (" ")?

Need to know everything about subduction zones: what is causes, how it happens ABSOLUTELY EVERYTHING!

Thats about it thanks every1. I will go awsum in the exam with ur help becoz i have studied really hard.

Answer 1

And aoceanic ridge is formed (if you're talking about, like, the mid atlantic ridge), by a divergent plate boundary what happens is magma flows up when the plates diverge and creates the oceanic ridge.  

An oceanic trench is formed from a subduction zone.

A subduction zone is caused when continental and oceanic crust collide.  The oceanic crust (because it's more dense) will subduct (go under) the continental crust.  It will form an accretionary wedge.  Because there is crust subducting underneath the continental crust, and because it drags down some water, some of the oceanic crust will melt and form magma and therefore you normally get volcanic ridges off of the plate boundary.

There is probably more, but you can look up all of this by just searching "subduction zones" in google.