The flow of rivers is the primary geologic process affecting Iowa’s landscape today (note valleys on Landform. Many valleys, such as the Missouri and Mississippi alluvial plains, are much wider than the rivers within them, which indicates excavation by flood flows during glacial melting. Abundant gravel deposits along the valleys also reflect the power of meltwater to move coarse material. Even modern floods demonstrate how earth materials are eroded from one portion of a valley, sorted by flowing water, and redeposited downstream. Such episodes of sediment transport by rivers are an on-going part of the geologic evolution of Iowa.

Iowa’s earth history continues to be shaped by slow, gradual processes as well as by brief, intense events. We live on the surface of a deep geologic inheritance, whose materials and processes—past, present, and future—affect the lives of us all.

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