Mississippi River Valley Geology Relation to River Regime

The Mississippi River alluvial valley developed concurrently with the advance and retreat of the final stage of continental glaciation. Sea level dropped as the ice accumulated, and the Mississippi River system eroded a deeply entrenched valley system. A rise in sea level when the ice melted reduced stream gradient, the river was forced to drop its load, and the valley system became filled with a gradational sequence of alluvium. Characteristics of the alluvial deposits show that the river was an overloaded braided stream most of the time that sea level was rising and that the river did not take on its meandering habit throughout the entire length of the valley until sea. level reached a stand about 5,000 years ago. The river has developed and abandoned several courses, the positions of which are still visible in traces of river migration or well-defined zones of meander belts. Each ancient course is marked by an alluvial ridge along its meander belt and by a characteristic pattern of distributary streams in its delta area.