Landforms of Erosion and Deposition: Rivers, Glaciers, Coasts and Deserts

Rivers, Groundwater and Ice at Work

Fluvial Landforms: Rivers at Work

• A gorge is a deep, steep-sided valley of similar width top to bottom. A canyon looks similar but is wider at the top than the bottom, in step-like layers. India’s own Gandikota Canyon, cut by the Pennar River in Andhra Pradesh, is a well-known exam example.
• In hilly terrain, a river can cut straight down through a meander loop instead of shifting sideways, forming an incised meander. Where a river later cuts into its own old floodplain, it leaves stepped river terraces standing on either bank.
• Rivers on gentle slopes curve into loops called meanders. Sediment piles up as a point bar on each bend’s inner, slower bank, while the river erodes the outer, faster bank. When a loop gets cut off from the main channel, it becomes a stranded, curved oxbow lake.
• A floodplain forms where a river deposits fine sediment beyond its banks during floods. Natural levees are low ridges of coarser deposits that build up right along the riverbank.
• An alluvial fan forms where a river suddenly drops its coarse load on reaching flatter ground. A delta is the same idea, but where a river meets the sea, like the Nile River does at its own famous delta.
• A river landscape ages through three stages. In youth, streams are few, with shallow V-shaped valleys. In maturity, many streams cut deep valleys with sharp divides. In old age, few streams remain and floodplains grow wide.

Karst Topography and Glacial Landforms

• Karst topography develops only in soluble rock, like limestone, where groundwater dissolves the rock over time. It is named after the Karst region of the Balkans.
• Sinkholes are the most common karst feature, circular depressions where rock has dissolved from below. Caves form along bedding planes, with stalactites hanging from the ceiling and stalagmites rising from the floor. Where a stalactite and a stalagmite meet, they fuse into a single column called a pillar.
• Among karst depressions, a polje is the largest, far bigger than a sinkhole, a swallow hole, or the mid-sized uvala.
• A cirque is a deep, steep-walled basin cut by ice at the head of a glacial valley, often holding a small lake called a tarn. Where three or more cirques cut into one peak, a sharp horn forms, like the Matterhorn; a narrow ridge between two cirques is an arete.
• Moraines are ridges of debris dropped by a glacier. An esker is a winding ridge left by a stream that once flowed under the ice, and a drumlin is a smooth, spoon-shaped hill of till. Deep glacial valleys flooded by the sea become fjords, like Norway’s own Geirangerfjord, and explored further in our dedicated Fjords article.

Coasts, Deserts and the Exam Angle

Coastal and Desert Landforms

• Waves pounding a rocky coast carve steep sea cliffs. As the cliff retreats, it leaves a flat wave-cut terrace of rock debris in front of it. When a sea cave’s roof collapses, an isolated pillar of rock left standing offshore becomes a sea stack.
• A bar is a ridge of sand parallel to the coast; a spit is a bar attached at one end to the land. When a spit or bar closes off a bay, it traps a lagoon behind it. India’s rocky west coast favours erosion features, while its low, sedimentary east coast favours deposition like deltas.
• A pediment is a gently sloping rock floor cut back at the foot of a mountain. As pediments grow and the mountain shrinks, an isolated rocky remnant called an inselberg is left standing, a pattern also visible across much of the Sahara Desert.
• A barchan is a crescent-shaped dune with its points trailing downwind, forming where wind direction stays steady on fairly flat ground. A seif is like a barchan with only one wing, formed when wind direction shifts; a parabolic dune is the reverse shape, anchored by vegetation instead of trailing free.
• Longitudinal dunes form as long ridges running parallel to a steady wind, where sand supply is scarce. Transverse dunes run perpendicular to the wind instead, where sand is abundant.