The four main types of landforms are mountains, plateaus, plains and hills. A landform is defined as any natural feature on the Earth's surface, which includes other minor landforms such as valleys, buttes, basins and canyons.
Landforms are generally created by the movement of tectonic plates and through erosion. For instance, the collision between two tectonic plates can cause the Earth's crust to fold and create huge mountains. It can also lead to the formations of volcanoes, which can both create and destroy new landforms. Erosion is responsible for breaking down landforms and turning one type into another. Over time, wind and water can erode away rock and soil to create valleys or eventually turn mountains into hills.
Both erosion and tectonic plate movement occur over a period of thousands or millions of years. It took the Colorado River more than 6 million years to carve out the Grand Canyon, while Mt. Everest and most other mountains are far older than that.
Despite their name, landforms can also occur under water, especially in oceans and seas. These underwater landforms often take the form of large mountain ranges, volcanoes or basins. At a depth of nearly 37,000 feet, the Mariana Trench is the deepest landform in the world.