Final answer:
A sinkhole is a depression in the ground caused by the collapse of a surface layer due to the dissolution of underlying bedrock, often limestone, by acidic water. This geological process can lead to the formation of cavities that, once too large, result in a collapse and the creation of a sinkhole.
Step-by-step explanation:
The correct answer to the student's question is A) Sinkhole. A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer, often associated with the dissolution of the underlying bedrock. This geological process can occur when acidic rainwater or groundwater, often containing dissolved carbon dioxide, reacts with limestone or other soluble rocks, such as dolostone or gypsum, leading to the gradual dissolution of the bedrock and the formation of cavities. When these cavities become too large to support the weight of the overlying ground, a sudden collapse can occur, leading to the formation of a sinkhole.
Sinkholes can also result from subsidence, which can be triggered by various factors including soil compaction, extraction of natural gas or other mineral resources, and withdrawal of groundwater. It is important to note that while sinkholes occur naturally, human activities such as excessive water withdrawal and construction can exacerbate their formation.