Which term describes a sudden gain or loss of land due to natural events?

The term that describes a sudden gain or loss of land due to natural events is avulsion. Avulsion occurs when there is a rapid change in the landscape, such as during a flood or landslide, that leads to the relocation of land boundaries. For example, if a river floods and alters its course abruptly, land that was previously adjacent to the river may suddenly become part of the waterway or vice versa, resulting in a significant alteration of property lines.

In contrast, adverse possession refers to a legal doctrine allowing a person to claim ownership of land under certain conditions, generally involving continuous, open, and notorious use over a period of time. Condemnation is the process by which a government entity takes private property for public use, usually with compensation to the owner. Erosion, on the other hand, involves a gradual wearing away of land due to natural forces, which does not lead to the sudden changes characteristic of avulsion. Thus, avulsion distinctly captures the essence of sudden land changes due to natural events, making it the correct answer.