Outline the differences between constructive and destructive plate margins.

Tectonic plates are in constant motion. When two plates are moving away from one another, magma upwells and new land is formed. This is known as a constructive plate margin, an example of which can be found at the boundary between the North American and Eurasian Plates. On the other hand, when an oceanic plate and a continental plate are moving towards each other, it is common for the denser (oceanic) plate to be subducted under the less dense (continental) plate which can cause melting of rock and subsequently the formation of volcanic ridges. An example of this type of plate boundary can be found at the along the margin between the Nazca and South American Plates.