There are numerous differences among plains as regards their mode of origin or structure. There are also differences regarding to the processes which modify them and their stage in the cycle of erosion.
Like all land surfaces, plains also undergo cycle of erosion. In fact, the origin and present topography of any large plain cannot be attributed to a single cause. Several processes have contributed to their formation.
In origin plains are most commonly the result of deposition of sediment, usually in water, and more often in ocean water.
Plains that have been built beneath the sea have often been brought above sea level by one of the relative changes in the relative level of sea and land. Such plains are called coastal plains.
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In addition, plains are formed by rivers, glaciers, lakes and also by volcanic outflows. They are also sculptured by the process of denudation, as when a land surface is worn to the state of old age, or when a river, moving back and forth levels the surface.
Such plains as are situated away from the sea, and those that were not formed due to relative changes is the sea level as well as land, are called inland plains. Actually this classification of plains into two broad categories is based on their location.