The force most responsible for causing changes in the Earth’s landforms is plate tectonics. Tectonic plates, which are essentially gigantic slabs of rock, lie underneath all of the world’s landmasses and seas, and occasionally these plates shift. The movements may be undetectable or may produce destructive events such as earthquakes or volcanoes. Over time, the amalgamation of these shifts reshapes the Earth’s surface, altering existing landforms and creating entirely new ones.
The Facts About Plates
When plates move, the landmasses or water bodies above them also move. Tectonic plates move very gradually, usually at rates of mere centimeters each year. For example, significant changes aren’t often seen over the course of a human lifetime, but today’s world would be virtually unrecognizable to an observer 200 million years ago, at which point all of the seven continents were combined into one single enormous continent. Individual plates range in size from the area of Saudi Arabia to larger than Africa. Some plates contain mostly land, while others contain mostly water. All plates, however, extend deep beneath the Earth’s surface, to a depth of at least 70 kilometers (over 40 miles). And there are no notable spaces between plates -- every plate directly adjoins at least two others.
Forms of Tectonic Interaction
There are three specific ways in which plates interact with one another, based on the type of boundary between them. Plates pull away from each other at divergent boundaries. Frequently found underwater, at these boundaries magma wells up from deep within the Earth, emerging through volcanoes or other vents and ultimately forming new land or seafloor. The island of Iceland was created by this type of tectonic activity. Plates push toward each other at convergent boundaries. Here, mountains or volcanoes often are created or pushed higher. The Himalayas and Andes are examples of this process. Plates slide past each other -- like subway trains on opposing lines -- at transform boundaries. This is occurring in Baja California, which geologists predict will someday become an island in the Pacific Ocean.