Glacial landform

Lore & Background

Glacial landforms are divided into erosional and depositional types. Erosional landforms result from glaciers crushing, abrading, and scouring surfaces as they expand due to accumulating snow and ice. These include striations, cirques, glacial horns, arêtes, U-shaped valleys, roches moutonnées, overdeepenings, and hanging valleys. Striations are grooves in rock outcrops formed by scraping of small sediments, showing the glacier's direction. Cirques are bowl-shaped indentations left after mountain glaciers melt. U-shaped valleys, when filled with ocean water, become fjords. Depositional landforms arise when glaciers retreat, leaving behind glacial drift—unsorted sediments called till. Examples include moraines, eskers, kames, drumlins, and ribbed moraines. Fluvioglacial landforms are deposited by meltwater and are more size-sorted than till. Glacial erratics, rocks dragged far from their source, are found in New England stone walls.

Reader's Guide

Glacial landforms are significant because they record past ice sheet movements and climate conditions. Erosional features like striations and U-shaped valleys reveal glacier flow directions and extent. Depositional features such as moraines mark glacier termini and retreat stages. The disputed origin of some landforms, like roches moutonnées, suggests that pre-glacial jointing and weathering may contribute to their shape, and similar forms exist in tropical areas. The glacial buzzsaw effect, proposed to explain elevated flat surfaces, has been rejected for Norway and West Greenland, as cirques do not align with paleic surface levels. The Gulf of Bothnia and Hudson Bay depressions are more tectonic than glacial. Glacial lakes, including kettle lakes, tarns, and paternoster lakes, form from ice blocks or moraine dams. These landforms help reconstruct past environments and inform understanding of ongoing glacial processes.

Did You Know?

• Striations are grooves in rock outcrops formed by scraping of small sediments on the bottom of a glacier.
• U-shaped valleys, when filled with ocean water, are called fjords.
• The stone walls of New England contain many glacial erratics dragged miles from their bedrock origin.
• The glacial origin of roches moutonnées has been questioned, as similar forms exist in tropical areas like East Africa and Australia.