Introduction
Glaciated landforms originate from the dynamic movement of ice masses and meltwater operating through the dual processes of erosion and deposition. Glacial erosion acts predominantly through frost shattering, plucking (quarrying), and basal abrasion, while deposition involves direct placement of unstratified till or stratified glacio-fluvial reworking. Together, these processes carve distinctive alpine and continental landscapes.
1. Erosional Landforms (Abrasion and Plucking)
Glacial erosional processes modify pre-existing fluvial topography through basal grinding and quarrying of bedrock blocks.
- Cirque and Horn: Cirques are steep-sided, armchair-shaped bedrock hollows excavated by headwall frost shattering and rotational plucking. Where three or more cirques erode headward towards a central point, an isolated pyramidal peak or horn (such as the Matterhorn) is formed.
- U-Shaped Valleys and Hanging Valleys: Pre-existing V-shaped river valleys are deepened, straightened, and widened into flat-floored, steep-walled U-shaped troughs by basal glacial abrasion. Tributary glaciers with lesser erosive power carve shallower troughs, leaving tributary valleys stranded high above the main valley floor as hanging valleys.
- Nunataks: High, exposed, ice-free bedrock summits or ridges protruding above an surrounding ice cap or valley glacier. They remain unglaciated but undergo severe periglacial freeze-thaw weathering.
- Roche Moutonnée: Asymmetrical bedrock hummocks produced by bedrock resistance against moving ice. The up-glacier (stoss) side exhibits smooth abrasion and striations, while the down-glacier (lee) side undergoes steep, jagged plucking.
2. Depositional Landforms (Till and Meltwater Action)
When glaciers retreat or melt, debris entrained within or on top of the ice is deposited as unstratified till or sorted glacio-fluvial outwash.
- Moraines: Linear ridges composed of unsorted, unstratified glacial till deposited at ice margins. They are classified by position into lateral moraines (along valley walls), medial moraines (formed by merging lateral moraines), and terminal/end moraines (marking the maximum glacial advance).
- Drumlins: Inverted spoon-shaped or streamlined teardrop hills composed primarily of glacial till. Typically occurring in swarms to form a 'basket-of-eggs' topography, their blunt ends face up-glacier and tapered tails indicate the down-glacier direction of flow.
- Glacio-fluvial Features (Eskers and Kames): Stratified deposits formed by sub-glacial and pro-glacial meltwater streams. Eskers are sinuous, winding ridges of sorted sands and gravels deposited by tunnels beneath stagnant ice, whereas kames are steep, conical mounds of sorted debris slumped into hollows at retreating ice fronts.
Conclusion
Glacial geomorphology is inherently sensitive to climatic fluctuations. As noted in the IPCC Sixth Assessment Report (AR6), accelerating global cryospheric retreat is destabilizing glacial landscapes into fragile paraglacial systems, significantly raising the frequency of hazards such as Glacial Lake Outburst Floods (GLOFs) behind unstable terminal moraines.