geomorphology, study of the origin and evolution of the earth's landforms, both on the continents and within the ocean basins. It is concerned with the internal geologic processes of the earth's crust, such as tectonic activity and volcanism that constructs new landforms, as well as externally driven forces of wind, water, waves, and glacial ice that modify such landforms. Geomorphology developed from the works of James Hutton and James Playfair in the 18th cent.; G. K. Gilbert described landform evolution; William Morris Davis developed the geomorphic cycle, set forth in his Geographic Essays (1909). By the 1970s, geomorphology had grown to include the environmental problems involved in landform processes, including subsidence, landslides, and coastal processes (see coast protection), which all affect humans who live in certain susceptible regions. Satellite images and data help geomorphologists to describe and map landforms and observe rapid or slow changes on the earth's surface. Development of mathematical models of landform processes have influenced the direction of modern geomorphic research. Geomorphology principles also have been applied to the study of landform development of other planets and moons of the solar system, based on images sent back to earth by flyby and orbiting satellites.