Convergent Boundaries

At a convergent boundary, two plates move toward each other and collide. This is the destructive counterpart of the divergent boundary: instead of new crust being created, crust here is destroyed. As the plates push together, one of them is forced down into the mantle, and the place where this sinking happens is called a subduction zone. The plate that goes under is eventually melted and recycled back into the Earth's interior, which is why convergent boundaries are described as places where the crust is consumed.

The book identifies three distinct ways in which convergence can occur, depending on the type of plates involved.

• Oceanic and continental plate: The denser oceanic plate is pushed beneath the lighter continental plate. This produces a deep trench offshore and volcanic mountain ranges on the continental edge, like the Andes.
• Two oceanic plates: The older, denser oceanic plate subducts beneath the younger one. This creates a deep trench and a chain of volcanic islands called an island arc, such as Japan or the Philippines.
• Two continental plates: Since both plates are light and buoyant, neither subducts easily. Instead, the collision crumples and thickens the crust, pushing up massive mountain ranges. The Himalayas are the classic example of this type of convergence. …