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Types of Plate Boundaries
When two continental plates collide, they form one of the three primary types of plate boundaries, called a convergent boundary, or zone. Convergent boundaries represent areas where the Earth's crust is being recycled. A second type of plate boundary is called a divergent zone. Contrary to convergent zones, divergent zones represent areas where two plates are spreading apart. Convergent boundaries represent areas where new crust is being created. The final primary type of boundary is called a transform, or conservation, boundary. Here, two plates are horizontally sliding past one another. Transform boundaries produce fault lines, such as the San Andreas fault zone in California.
Convergent Plate Boundaries
There are three types of collisions that can occur between tectonic plates. When oceanic plates collide in a convergent zone, the older plate is forced under the newer, lighter plate, in a process called subduction. The Marianas Trench is an example of this type of convergent zone. When an oceanic plate collides with a continental plate, the oceanic plate subducts under the more buoyant continental plate. The third type of convergent zone is produced when two continental plates collide, similar in nature to the collision of two massive icebergs.
Collisions Between Continental Plates
Convergent boundaries involving continental plates, also known as collisional boundaries, result in tremendous pressure. Because the two continental plates are both light and relatively low in density, neither of the plates is able to easily force the other to subduct. Instead, the two plates compress together under tremendous pressure, ultimately buckling. The results of this collision include large horizontal shearing and dramatic upward thrusts. The forces created in collisional boundaries form the largest mountain ranges on the planet.
Examples of Continental Plate Collisions
An example of the types of formations that occur in a continental plate collision can be observed at the location where the Indian Plate is colliding with the Eurasian Plate. The Indian Plate has buckled to create the Himalayas. This mountain range reaches heights as high as 29,000 feet, the highest continental mountains on the planet. The Eurasian Plate has been raised, producing the Tibetan Plateau. This plateau, sometimes referred to as the "Roof of the World," is characterized by an average elevation of over 16,000 feet. The height of this plateau, which represents an area equal to half of the lower 48 United States, exceeds all but two of the peaks in the Alps, and is higher than almost all the peaks in the U.S.