ASBOG Practice Exam

When a geological bed dips upstream, how does the width of the V compare to the contours of the topography?

1. Narrower

2. Wider

3. Equal

4. Variable

The correct answer is: Wider

When a geological bed dips upstream, the resulting V-shaped valley typically has a width that is wider than the contours of the surrounding topography. This occurs because as the geological layers incline, they cause the valley walls to extend more broadly apart than the horizontal or slightly sloping contour lines would suggest. In a situation where beds dip upstream, they often produce a broader valley as the erosion process shapes the landscape. Water flow in rivers or streams also tends to gradually erode the banks and floor of the valley, often leading to a wider cross-section as it carries material downstream. This effect results in the valley widening relative to the steeply dipping geological formations, creating a noticeable difference between the valley width and the topographic contours, which may be more closely aligned with the surface elevations. Thus, the relationship between the dip of geological beds and valley width illustrates the interaction between geological processes and topographical features, leading to the correct understanding that the width of the V is wider in comparison to the contours of the topography.