Definition of an Esker
An esker is a long, winding ridge of stratified (layered) sand and gravel, deposited by meltwater streams flowing within or beneath a glacier. These distinctive landforms resemble embankments or railway beds, often extending for many kilometers across landscapes that were once covered by ice sheets.
Formation Process
Eskers form when glacial ice begins to melt. The meltwater carves tunnels and channels within the ice, or flows at the base of the glacier. These subglacial rivers carry sediment – sand, gravel, and pebbles – which is deposited on the tunnel floor as the water loses energy. When the surrounding glacial ice eventually melts away, these riverbed deposits are left behind as a raised ridge, often preserving the sinuous path of the ancient waterway.
Characteristics and Composition
Typically, eskers are composed of well-sorted and rounded sediments, indicating water transport and abrasion. Their internal structure often shows cross-bedding, a characteristic of fluvial (river) deposition. Eskers can vary greatly in size, from a few meters high and wide to tens of meters tall and several hundred meters wide, and can stretch for hundreds of kilometers in length.
Importance and Applications
Eskers are valuable geological indicators, providing insights into past glacial movements, meltwater drainage patterns, and sediment transport dynamics. They are also economically significant as sources of high-quality sand and gravel, which are quarried for construction materials. Their elevated, well-drained nature can also make them preferred sites for roads and settlements in otherwise flat or swampy terrain.