Rusk Glacier is located on the eastern face of Mount Adams in the U.S. state of Washington. Starting at an elevation of over at just below The Castle, the glacier flows eastward down slope. A significant portion of the glacier is covered by rock debris and in the middle of the glacier, at about , there is a small ice-free island of rock. The glacier terminates at about at its rock-covered moraine. The glacier has decreased in surface area by 23 percent between 1904 and 2006.