Final answer:
Magma that hardens beneath the surface creates landforms through volcanic activity. Diverging tectonic plates can produce magma, which rises to the surface and forms mid-ocean ridges. Converging plates can lead to subduction and the release of water, triggering mantle melting and the formation of volcanoes and mountains.
Step-by-step explanation:
When tectonic plates diverge, the underlying mantle experiences reduced pressure, causing magma to be produced. This magma can then rise to the surface and create new landforms, such as mid-ocean ridges.
On the other hand, when tectonic plates converge and one plate subducts below another, hydrated minerals in the subducting plate release water, which can then trigger melting of the mantle and the production of magma. This magma can result in the formation of volcanoes and mountain ranges.