Understanding Landforms Created by River Erosion

The question asks to identify a specific landform: a flat or gently sloping surface that remains after river erosion has occurred, sometimes featuring areas of harder rock that resisted erosion (resistant remnants).

Analyzing the Options

Let's examine each option to see which best fits the description:

• Monadnock: This is an isolated hill or mountain that stands out from a surrounding plain. While it can be a resistant remnant, it is not the flat or gently sloping surface itself.
• Plateau: A plateau is a large, relatively flat area of land that is significantly higher than the surrounding area. While plateaus can be shaped by erosion, the definition doesn't specifically describe a surface left behind *after* erosion in the way the question implies, nor does it inherently include resistant remnants as part of its primary definition.
• Floodplain: A floodplain is a low-lying, nearly flat area next to a river that is formed by the sediment deposited during floods. It's primarily a depositional feature, not a surface shaped and left behind by erosion.
• Peneplain: This term, derived from Latin meaning "almost a plain," describes a low-relief, almost flat, or gently undulating landscape formed over a long period by erosion. It represents a late stage in the erosion cycle. Crucially, peneplains often preserve resistant rock outcrops as resistant remnants, fitting the description perfectly.

Defining Peneplain

A peneplain is essentially the end product of extensive river erosion acting over geological time scales. It's a surface worn down close to base level, characterized by its lack of significant relief. The presence of resistant remnants, which are areas of harder rock that erode more slowly, is a common feature, distinguishing it from a perfectly flat, featureless plain.

Conclusion

Based on the definition, a flat or gently sloping surface resulting from prolonged river erosion and often containing resistant remnants is best described as a peneplain.