Short answers, pulled from the story.
Geomorphology is the scientific study of how physical, chemical, and biological processes shape the surface of our planet. It examines features ranging from the deepest ocean trenches to the highest mountain peaks through the interaction of the lithosphere with the hydrosphere, atmosphere, and biosphere.
The term geomorphology seems to have been first used by Laumann in an 1858 work written in German. It was brought into general use by John Wesley Powell and W. J. McGee during the International Geological Conference of 1891.
The geographical cycle or cycle of erosion model was developed by William Morris Davis between 1884 and 1899. This theory posited that tectonic uplift creates a river valley that gradually erodes until side valleys flatten the terrain, after which uplift starts the cycle over again.
A revolution in geomorphology began in the middle of the 20th century when the field was put on a solid quantitative footing. Key figures included William Walden Rubey, Ralph Alger Bagnold, Hans Albert Einstein, Frank Ahnert, John Hack, Luna Leopold, A. Shields, Thomas Maddock, Arthur Strahler, Stanley Schumm, and Ronald Shreve.
The primary agents include aeolian processes from wind, rivers and streams that transport sediment, and glaciers that cause abrasion and plucking. Hillslope processes move soil and rock downslope under gravity, while biogeomorphologic processes involve living organisms influencing surface changes.
Planetary geomorphology studies the surfaces of other terrestrial planets such as Mars, Venus, Titan, and Iapetus using Earth analogues. Indications of wind, fluvial, glacial, mass wasting, meteor impact, tectonics, and volcanic processes are analyzed to understand the geologic and atmospheric history of those planets.