Under the pressure of its own weight and the forces of gravity, a glacier will begin to move, or flow, outwards and downwards. Valley glaciers flow down valleys, and continental glaciers (ice sheets) flow outward in all directions from a central point.

Glaciers move by internal deformation and/or by sliding at the base. Internal deformation occurs when the weight and mass of a glacier causes it to spread out due to gravity.

Sliding occurs when the glacier slides on a thin layer of water at the bottom of the glacier. This water may come from glacial melting due to the pressure of the overlying ice, or from water that has worked its way through cracks in the glacier. Glaciers can also readily slide on a soft sediment bed that has some water in it. Basal slip may account for most of the movement of thin, cold glaciers on steep slopes, or only 10 to 20 percent of the movement of warm, thick glaciers lying on gentle slopes.

When a glacier moves rapidly, internal stresses build up in the ice which cannot be relieved by deformation alone, and cracks (called crevasses) form at the surface of the glacier.

Glaciers dramatically impact their surrounding environment by reshaping the underlying and surrounding landscape as they move, through both erosion and deposition.

Glaciers erode the rock underneath them. A glacier can "carve" a valley, wearing away rocks and soil through abrasion and plucking up and moving large pieces of rock and debris. The glacier pushes this earth and rock forward as it advances, almost like a conveyor belt, and dumps it to the side along the way or at the end of the glacier (deposition). Depositional features include moraines, drumlins, and eskers.

The glacier story concludes as the glacier stops growing and actually begins to move In Retreat.