Geologic activity around the plate boundaries on the ocean floor provide evidence of plate tectonics. At the ocean ridges such as the Mid-Atlantic Ridge, the plates are moving apart which is called a divergent boundary. At these ridges you can actually observe lava pouring out of cracks on the ocean floor that follow the ridge. Volcanoes form on the floor at the ridges and grow to form islands such as Iceland. In other areas of the ocean floor there are features called trenches. At trenches plates come together, called a convergent subducting boundary. Here one plate is forced under another and the ocean floor is dragged down forming the deepest part of the ocean floor and trenches. Example of a trench is the Marianas Trench.