An area with a collection of closed depressions, some of which are filled with water, is NOT likely the result of which process?

• A. Subsidence due to hydro compaction in an unconfined aquifer
• B. Karst dissolution
• C. Weathering front retreat
• D. Evaporation ponds from mining

Answer: (A)

Closed depressions that can trap water point to processes that create pits or basins through dissolution, differential weathering, or human-made ponding. Karst dissolution fits here because soluble rocks dissolve to form sinkholes and circular to irregular hollows that often collect water. Weathering front retreat can leave behind recessed areas as the weathered material retreats, producing closed depressions. Evaporation ponds from mining are intentional, surface basins that are water-filled and closed off from drainage.

Subsurface hydro compaction in an unconfined aquifer, on the other hand, produces land subsidence from loss of pore water and sediment compression. This tends to generate broader, more diffuse subsidence patterns rather than a field of discrete, well-defined closed depressions. The water table may drop, but the surface features aren’t typically a collection of distinct pits that stay water-filled, which is why this process is less likely to explain the observed landscape.