What landform is primarily found at the mouth of the Mississippi River?

The landform primarily found at the mouth of the Mississippi River is a delta. This delta is created by the accumulation of sediment carried by the river as it flows into a larger body of water, in this case, the Gulf of Mexico. As the river slows down upon meeting the ocean, it deposits various materials, leading to the formation of new land that expands outward in fan-like shapes.

The Mississippi River Delta is particularly significant not only for its size but also for its ecological importance. It serves as a crucial habitat for a diverse array of wildlife and acts as a vital fishing area. Additionally, deltas like this one are geologically dynamic, constantly changing due to river sediment deposition, erosion, and other natural processes.

In contrast, the other options represent different types of landforms that do not specifically describe the features at the mouth of the Mississippi. For example, a plain is a flat area of land that is not necessarily near a river mouth, a peninsula is a landform that is surrounded by water on three sides, and an estuary is a transitional area where freshwater from rivers meets and mixes with saltwater from the sea but does not specifically describe the accumulation of sediment characteristic of a delta.