The ridge is the seam that split the ancient continents to form the Atlantic ocean 180 million years ago. Ocean rock forms by cooling magma and moves symmetrically away from the ridge. The oldest ocean rocks are closest to the continents and the youngest are at the ridge. All oceanic volcanos have relatively quiet eruptions because the magma is low in silica and therefore is fluid. Where plates meet and move toward each other, something has to give, so one plate usually slides under the other in a process called subduction.
Ocean floor is dense so it slides under the edge of an adjacent continent.
This process is called subduction. Subduction forms a broad fault zone with many sheared fragments of ocean floor rock forming a mixture we call melange. The faults are like a cuisinart, cutting up and mixing different vegetables. Cool, descending crust acts like a heat sink, so conditions of high pressure but fairly low temperature prevail, forming odd metamorphic minerals. Subduction pushes rock deeply into the hot regions of the earth which melts to form magma.