Three types of convergent plate boundaries

Callen Bentley introduces the concept of convergent boundaries within the context of plate tectonics, explaining that the Earth's lithosphere is broken into plates that move relative to each other. Convergent boundaries are specifically where plates move towards one another, contrasting with divergent (moving apart) and transform (sliding past) boundaries. The Alps are presented as an initial example of mountain formation resulting from these interactions.

The first type of convergent boundary discussed is oceanic lithosphere meeting continental lithosphere. Due to oceanic lithosphere being denser than continental lithosphere, it subducts beneath the continental plate. This process leads to the loss of water from the subducting plate, triggering partial melting in the overlying mantle and producing magma. This magma rises to form a chain of volcanoes on the continent, known as a continental volcanic arc.

The second type involves two oceanic plates converging. In this scenario, one oceanic plate subducts beneath the other. Generally, the older, colder, and thus denser oceanic plate is the one that subducts. Similar to oceanic-continental convergence, this subduction generates magma, which rises and erupts through the overriding oceanic lithosphere, forming a chain of volcanic islands known as a volcanic island arc.

The third type occurs when two continental plates collide. Continental lithosphere is too buoyant to subduct significantly. Instead, as the continents converge, they crunch into one another, resulting in intense folding and faulting that shoves rock both upwards and downwards. This process thickens the crust significantly, leading to the formation of massive mountain ranges, such as the Himalayas and the Alps.

The video concludes by revisiting the Alps as an example of continental-continental collision between the African and Eurasian plates. It also references the Appalachian Mountains as a past example. Mount Shasta, a composite volcano in Northern California, is presented as an example of a continental volcanic arc, indicating an oceanic-continental convergent boundary where oceanic crust is subducting beneath continental crust.