What is a glacier?

A glacier is indeed defined as a mountain of ice that moves on land. This movement occurs due to the immense weight of the ice, which causes it to flow slowly under the influence of gravity. Glaciers are formed from accumulated snow that compacts into ice over long periods, and they play a crucial role in the Earth's ecosystem and hydrology. They can carve landscapes, contribute to sea level changes as they melt, and store large amounts of fresh water.

The other options refer to different bodies of water or formations. For instance, underground bodies of water represent aquifers, which are not related to glacier characteristics. An area where fresh water is stored might describe lakes or reservoirs but does not capture the unique features of glaciers. Lastly, a large river that flows into an ocean is a riverine system and does not encompass the defining aspects of glaciers. Understanding glaciers is essential in the context of climate science as they react sensitively to temperature changes and thus provide important indicators of environmental shifts.