Which process or processes change the size and shape of the oceans?

Answer 1

The movement of continental "plates" across the surface of the Earth. This is a very slow process, but is accompanied by earthquakes and volcanoes.

For example, the Hawaiian Islands are all volcanic; each island is a volcano. As the Pacific plate moves northwest, a static "hot spot" in the mantle forms new islands. The Big Island is the current one, but a new submarine volcano is erupting to the southeast that will, someday, form a new island.

In the Atlantic Ocean, the North American plate is moving away from the European plate, and the Atlantic is getting wider. (VERY slowly!) The Mid Atlantic Ridge is the place where the plates are separating, and building new mountains and new seafloor.

Answer 2

The main process that changes the size and shape of oceans is plate tectonics, which involves the movement of Earth's lithospheric plates. This movement can cause the formation of new ocean basins or the closing of existing ones. Additionally, sea-level rise due to factors like melting ice caps and thermal expansion of seawater can also impact the size and shape of oceans.