Dynamic Processes in the Missouri River Below is a photo from the meandering channels at Missouri Headwaters State Park, in southwest Montana. At this location, the Missouri River is formed at the confluence of the Gallatin, Madison, and Jefferson Rivers. This river flows 2, 341 miles before joining the Mississippi River, and is considered the longest river in the United States. Different processes influence the lateral migration of a meandering channel in its valley. Erosion, transport, and deposition all play significant roles in shaping a river through time. Focus on the locations in the channel where velocity is fast and slow, where along the channel erosion and deposition is occurring, and which direction the channel will migrate through time. Drag the appropriate labels to their respective targets. Not all labels will be used.