The term 'glacial ice block' is a reference to a type of large, block-shaped mass of ice that forms in glaciers. The term 'serac' is a French word meaning 'block of ice' and is used to describe these large blocks of ice. Seracs are formed when the pressure of the glacier causes the ice to break into large chunks. These chunks can range in size from a few meters to hundreds of meters in length. They are often found in crevasses or other areas of the glacier where the pressure is greatest.