Ice sheet

In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacialice that covers surrounding terrain and is greater than 50,000 km (19,000 sq mi).

Ice sheets are the largest glacial bodies on Earth, distinguished from smaller ice caps, ice fields, and glaciers. Ice sheets can have multiple ice domes, the topographic highs from which ice flows outwards, and are typically drained by ice streams and outlet glaciers around their periphery. The two extant ice sheets on Earth are the Antarctic ice sheet and the Greenland ice sheet.

Although the surface is cold, the base of an ice sheet is generally warmer by means of geothermal heat. In places, melting occurs and the melt-water lubricates the ice sheet so that it flows more rapidly. This process produces fast-flowing channels within the ice sheet called ice streams. Ice sheets are continually in motion as the ice gradually flows outward from the highest points of the ice sheet towards its margins. The slope of the ice sheet is low around the plateau but increases steeply at its margins.

The growth of ice sheets is a signature of glacial periods, which occur during ice ages. There have been many different ice sheets over Earth's history. At the maximum of the Last Glacial Period, the historic Laurentide and Cordilleran ice sheets merged with the Greenland Ice Sheet to cover much of North America. In the same period, the Weichselian Ice Sheet covered Northern Europe and the Patagonian Ice Sheet covered southern South America. The retreat and disappearance of these ice sheets marked the beginning of the current Holoceneinterglacial period, and the ongoing retreat and future fate of the Greenland and Antarctic ice sheets plays a major role in climate change and sea level rise.