Which one of the following is not an erosional landform?

Question

Accepted Answer

Esker is not an erosional landform. Here's why:

*   **Esker:** An esker is a long, winding ridge of stratified sand and gravel. It is a depositional landform formed by meltwater streams flowing within or beneath a glacier or ice sheet. As the glacier retreats, these streams deposit their sediment load, creating the esker. Therefore, it's a result of deposition, not erosion.

Now, let's explain why the other options are incorrect (i.e., why they *are* erosional landforms):

*   **Cirque:** A cirque is a bowl-shaped, amphitheater-like depression carved into the side of a mountain by glacial erosion. It's formed by the freeze-thaw action (frost wedging) and abrasion by the glacier itself. This makes it a classic erosional feature.

*   **Plunge pool:** A plunge pool is a deep basin at the base of a waterfall. It's formed by the erosive power of the falling water, which scours out the bedrock below. The force of the water and the abrasion by sediment carried in the water are the primary erosional agents.

*   **Mesa:** A mesa is an isolated flat-topped elevation or hill, bounded from all sides by steep escarpments. Mesas are formed by differential erosion. A resistant caprock protects the underlying softer rock layers. Over time, the surrounding softer rock is eroded away, leaving the mesa standing. While deposition might play a small role in the caprock formation, the overall shape and isolation of the mesa are due to the *removal* of surrounding material, making erosion the dominant process.