Pertaining to, or produced by, sheets of ice or glaciers. A glacial landscape is one left behind when a glacier melts. A glacial epoch or ice age is a period of time when ice sheets expanded and contracted over large areas of the surface of the Earth. Glacial processes and deposits are the reason why the soils of the northern hemisphere above a latitude of about 45 degrees, are young and of high inherent fertility, by contrast with the soils of the tropical and sub-tropical zones.