Iowa State Geology Practice Exam

The correct answer is radial drainage, which develops in landscapes where the surface slopes outward from a central point, typically found on cone-shaped mountains, like volcanic peaks or domes. In a radial drainage system, streams radiate outward from the summit, resembling the spokes of a wheel.

This drainage pattern occurs because water flows away from the high point in various directions, taking the path of least resistance due to gravity. The cone shape of the mountain facilitates this radiating effect, as the slopes taper downwards uniformly from the peak. The nature of radial systems allows for a variety of stream orientations as they descend the mountain, highlighting the diverse flow paths that can develop in this type of geological setting.

In contrast, the other drainage patterns—dendritic, rectangular, and trellis—are associated with different geological configurations. Dendritic drainage resembles a tree's branches and typically forms in regions with uniform rock types. Rectangular drainage features right-angle bends and forms over fractures or faults in a more structured landscape. Trellis drainage develops in regions with alternating hard and soft rock layers, leading to a more organized pattern. Thus, radial drainage is uniquely suited to the topography of cone-shaped mountains, making it the appropriate choice for this question.