Answer:
Plate interactions
Step-by-step explanation:
When two plates collide and one goes under the other, trenches are formed like the trenches in the Pacific Ocean. These can also form volcanoes due to the melting of the plate as is goes under the other.
When two plates collide and neither give way to the other, mountains are formed like the Himalayas.
When two plates are pulling away from each other, they form ridges because of the molten magma that is dragged up with the plates. One ridge is found in the Atlantic Ocean.