What is an aquifer?

An aquifer is defined as an underground layer that stores water, which aligns perfectly with the correct choice. This subsurface layer is typically composed of materials such as sand, gravel, or porous rock that can hold significant amounts of water. Aquifers are vital for supplying water to wells and springs, making them critical for both natural ecosystems and human water use.

Understanding the characteristics of aquifers helps in managing water resources effectively. They can vary in size and capacity, influencing the sustainability of water supply in a given area. Factors such as the permeability of the surrounding materials, the recharge rate from precipitation, and the overall geology of the region all play a role in how an aquifer functions.

The other options describe different water-related features but do not accurately define an aquifer. For instance, an elevated water table refers to the surface of the groundwater level but does not indicate stored underground layers specifically. A water-bearing surface river implies surface flow rather than the underground storage capacity of an aquifer. Lastly, a layer of rock that prevents water movement refers to an aquitard, which serves as a barrier to groundwater flow rather than a storage medium for water. Understanding these distinctions is important for effectively discussing groundwater resources and their management.