Major landforms include continents, islands, mountain ranges, deserts and plains. Major water forms include oceans, rivers and lakes. Most other landform terms refer to smaller formations or to modifications of one of the larger forms.
Geomorphology is the branch of physical geography dealing with the study of landforms and their origins and evolution. It includes the study of processes that create landforms, such as mass movement, weathering, fluvial processes and glaciation. All of these processes either erode the earth's surface or leave deposits on it; some do both. For example, glaciers erode valleys by grinding out rock and pushing it before them, creating U-shaped valleys. As glaciers melt, they deposit the stones and ground-up rocks, creating ridges called eskers and moraines depending on whether they form in stream beds beneath the glacier or along the glacier's sides.
William Morris Davis proposed the first model of geomorphology in the late 19th century. His model begins with uplifts of the earth's surface that create steep mountains and ridges. As water flows down steep slopes, it cuts channels and carries eroded material to lower altitudes. Over time, the slopes become flatter with erosion from water and wind and the landscape becomes gentler and more rounded in appearance. While Davis' model is insufficient to explain many landforms, it does point out the importance of the forces of erosion and deposition.