What typically happens to a river's elevation in its longitudinal profile?

In a river's longitudinal profile, elevation does indeed vary along its length. This variation occurs due to several factors, including the river's gradient, the underlying geology, and the influence of tributaries and other landscape features.

Generally, as a river flows from its source in the mountains or higher elevations toward its mouth, which is often at sea level or close to it, the elevation typically decreases. However, this decrease is not uniform, as the river may encounter varying landscapes, such as hills, valleys, and plateaus, leading to fluctuations in elevation along its course.

These variations may include sections where the river flows over steep gradients, resulting in higher elevations, and sections that meander through flatter terrain, lowering its elevation. Additionally, local geological structures and sediment deposition can further influence the river's path and elevation.

Hence, the correct response highlights the complexity and dynamic nature of river systems, where multiple factors contribute to the changes in elevation along their longitudinal profiles.