The Earth contains oceanic plates and continental plates. Therefore, there are three types of convergent plate boundaries: ocean to ocean, ocean to continent and continent to continent. In the first two cases, the convergence results in subduction of one of the plates, where one plate moves under the other and is recycled into the mantle. With a continent-to-continent convergent boundary, the continental crust is too light to be subducted.
At a continent-to-continent convergent plate boundary, as neither plate can be subducted, the crust tends to buckle and press upward, creating mountain ranges and plateaus. During the slow process, the plates may move only a few inches a year. However, the convergence of continental plates has formed some of the biggest mountain ranges in the world, including the Himalayas.
The Himalaya Range, which contains the world's tallest mountains, formed at the convergence boundary of the Indo-Australian Plate and the Eurasian Plate. Seventy million years ago, the Indo-Australian plate, moving northward, collided with the Eurasian plate. The Tethys seabed, which had separated the continents, was forced upward, forming folded longitudinal ridges. The Tibetan plateau also formed to the northeast. The Indo-Australian plate continues to move north at a rate of approximately 5 cm a year.
The Alps in Europe owe their existence to the collision of the African and European tectonic plates. Formation started 770 million years ago, with most of the process occurring between 34 million and 15 million years ago. The Appalachians were partially, although not completely, formed by continent to continent convergence. Three hundred million years ago, the collision of Africa and North America raised the Appalachians higher then the modern Himalayas. Time and erosion have since reduced the mountains to their present size.