The term 'River of Ice' is a poetic name for a GLACIER, which is a large mass of ice that moves slowly down a mountain or valley. Glaciers are formed over many years as snow accumulates and compacts into ice. As the GLACIER moves, it erodes the landscape, creating unique features such as U-shaped valleys, moraines, and cirques. Glaciers are important sources of freshwater and can be found in many parts of the world.