Circular depression formed in the bed of an upper course river is known as

Step 1: Analyze the question The question asks for the name of a circular depression in the bed (floor) of a river in its upper course.

Step 2: Explain the concept In the upper course, rivers have steep gradients and a lot of energy. They cut downward (vertical erosion). Pebbles and stones get trapped in small hollows on the river bed and are swirled around by eddies. This grinding action, called abrasion (corrasion), drills out deep, rounded holes. These are called potholes.

Step 3: Check each option

• A. Interlocking spurs: These are ridges of high land that jut out alternately from each side of a V-shaped valley, and the river winds around them. They are not depressions in the bed.
• B. Plunge pools: These are deep basins at the foot of a waterfall, formed by falling water and rocks. They are circular-ish, but they form below a waterfall, not just anywhere in the river bed. The question describes a general circular depression in the bed, which is better matched by potholes.
• C. Rapids: These are stretches of fast, turbulent water over steeply sloping or uneven rock. They are not depressions.
• D. Potholes: These are circular hollows drilled into the river bed by swirling pebbles. This matches the description exactly.

Step 4: Answer The correct answer is **D.

Tip: Think "pot" = a round container. A pothole is a round hole in the river bed made by stones spinning around (abrasion). Plunge pools are linked to waterfalls, so remember "plunge = waterfall."