The force per unit area imposed vertically by a glacier on its bed. For a cold-based glacier, it is effectively equal to the weight of the overlying ice. This is expressed as:

where N is the effective water pressure, p is the density of the ice, g is the acceleration due to gravity, and h is the ice thickness. However, if water is present at the glacier bed, the effective normal pressure is reduced by an amount equal to the subglacial water pressure. The higher the subglacial water pressure, the more it can counteract the pressure of the ice. The equation then becomes:where N is the effective water pressure, p is the density of the ice, g is the acceleration due to gravity, h is the ice thickness, and wp is the subglacial water pressure. This is true for flat-bedded glaciers. Effective normal pressure is modified by the flow of ice over obstacles, increasing upstream of the obstacle and decreasing to its lee.