1. Alteration of any part of the earth's surface by passage of a glacier, chiefly by glacial erosion or deposition; distinguish from glacierization. 2. As used in many texts, particularly with respect to the ice ages, same as glacierization, for example, “Pleistocene glaciation. ” 3. The transformation of cloud particles from supercooled water drops to ice crystals. Thus, a cumulonimbus cloud is said to have a glaciated upper portion.