Geography: Class 11 (Part 2) — Chapter 6: Landforms and Their Evolution

Introduction to Landforms and Landscapes

After weathering processes act on earth materials, geomorphic agents perform erosion and deposition, continuously reshaping the Earth's surface. Each landform has its own physical shape, size, and materials, evolving through stages comparable to life: youth, maturity, and old age.

Landform: Small to medium tracts or parcels of the Earth's surface.
Landscape: Several related landforms grouped together to form large tracts of the Earth's surface.
Peneplain: An almost featureless plain representing the final stage of fluvial erosion, occasionally featuring low-resistant remnants called monadnocks.

Summary Matrix of Landforms

The following table summarizes the erosional and depositional landforms produced by different geomorphic agents:

Geomorphic Agent	Erosional Landforms	Depositional Landforms
Running Water	Valleys (Gorges, Canyons), Potholes, Plunge Pools, Incised Meanders, River Terraces	Alluvial Fans, Deltas, Floodplains, Natural Levees, Point Bars, Ox-bow Lakes
Groundwater	Sinkholes, Swallow Holes, Valley Sinks (Uvalas), Lapies, Caves	Stalactites, Stalagmites, Pillars
Glaciers	Cirques, Horns, Serrated Ridges (Arêtes), Glacial Valleys/Troughs, Hanging Valleys, Fjords	Moraines, Eskers, Outwash Plains, Drumlins
Waves & Currents	Cliffs, Wave-cut Terraces, Sea Caves, Stacks	Beaches, Dunes, Bars, Barriers, Spits, Lagoons
Winds	Pediments, Pediplains, Playas, Deflation Hollows, Mushroom Rocks	Sand Dunes (Barchans, Seifs, Parabolic, Transverse, Longitudinal)

Running Water (Fluvial Landforms)

In humid regions, running water is the most active geomorphic agent. It has two components: overland flow (sheet wash) and linear flow (streams and rivers).

Stages of River Landscapes

Youth Stage: Characterized by a small number of streams with poor integration. Rivers flow over steep gradients in shallow, V-shaped valleys with no floodplains. Waterfalls and rapids are common.
Mature Stage: Streams are numerous with good integration. Valleys remain V-shaped but are deep. Wider floodplains develop, allowing rivers to flow in meanders. Waterfalls and rapids disappear.
Old Stage: Characterized by gentle gradients and few tributaries. Rivers meander freely over vast floodplains, forming natural levees and ox-bow lakes.

Erosional Fluvial Landforms

Gorge: A deep valley with very steep, nearly straight sides, almost equal in width at the top and bottom.
Canyon: A variant of a gorge characterized by steep, step-like side slopes, wider at the top than at the bottom.
Potholes: Circular depressions formed over rocky stream beds due to abrasion by rock fragments.
Plunge Pools: Large, deep potholes formed at the base of waterfalls due to the sheer impact of water.
Incised/Entrenched Meanders: Deep, wide meanders cut into hard rocks, typically found in steep gradient streams undergoing active vertical erosion.
River Terraces: Surfaces marking old valley floors or floodplain levels, resulting from vertical erosion by the stream.

Depositional Fluvial Landforms

Alluvial Fans: Cone-shaped deposits formed when streams flowing from steep mountain slopes break onto low-gradient foot slopes.
Deltas: Similar to alluvial fans but formed at the river mouth where sediments are dumped into the sea, showing well-sorted stratification.
Natural Levees: Low, linear, and parallel ridges of coarse deposits formed along the banks of large rivers.
Point Bars: Also known as meander bars, these are linear sediment deposits on the concave side of river meanders.

Groundwater (Karst Topography)

Groundwater acts chemically through solution and precipitation, primarily in regions rich in calcium carbonate rocks like limestone and dolomite. This landscape is known as Karst topography.

Erosional Karst Landforms

Swallow Holes: Small to medium-sized shallow depressions formed on limestone surfaces through solution.
Sinkholes: Funnel-shaped openings, circular at the top, varying in depth from a few meters to over thirty meters.
Uvalas: Long, narrow to wide trenches formed when multiple sinkholes and dolines collapse and join together.
Lapies: Highly irregular limestone surfaces characterized by a maze of sharp pinnacles, grooves, and ridges.
Caves: Long, narrow to wide underground gaps formed along bedding planes where limestone dissolves.

Depositional Karst Landforms

Stalactites: Icicle-like calcium carbonate structures hanging down from the roofs of caves.
Stalagmites: Calcium carbonate structures rising up from the cave floor, formed by dripping water from above.
Pillars: Columns formed when stalactites and stalagmites eventually fuse together.

Glaciers

Glaciers are massive sheets of ice moving slowly over land due to gravity. They cause immense erosion through abrasion and plucking.

Erosional Glacial Landforms

Cirque: Deep, long, and wide trough-like basins with steep, concave walls, often containing lakes called tarns.
Horns: Sharp, pointed, and steep-sided peaks formed when three or more radiating glaciers erode headward.
Arêtes: Serrated, saw-toothed ridges with sharp crests separating adjacent cirques.
Glacial Troughs: U-shaped valleys with broad floors and steep sides. Deep troughs filled with sea water in high latitudes are called fjords.

Depositional Glacial Landforms

Moraines: Long ridges of unassorted glacial till. They are classified as terminal, lateral, ground, or medial moraines.
Eskers: Sinuous ridges of coarse gravel and boulders deposited by meltwater streams flowing in tunnels beneath the ice.
Outwash Plains: Broad, flat plains covered with glacio-fluvial deposits at the foot of glacial mountains.
Drumlins: Smooth, oval-shaped, ridge-like features composed of glacial till, resembling inverted spoons, indicating the direction of glacier movement.

Waves and Currents (Coastal Landforms)

Coastal processes are highly dynamic. Coastal landforms depend on the configuration of the land and sea floor, and whether the coast is emerging or submerging.

High Rocky Coasts vs. Low Sedimentary Coasts

High Rocky Coasts: Highly indented coastlines where erosional features like cliffs, wave-cut platforms, and sea caves dominate.
Low Sedimentary Coasts: Smooth coastlines where depositional features like lagoons, bars, barriers, and spits dominate.

Erosional Coastal Landforms

Cliffs: Steep rock faces along the coast formed by wave action.
Wave-cut Terraces: Flat or gently sloping platforms at the base of sea cliffs.
Sea Caves: Hollows formed at the base of cliffs due to the constant lashing of waves.
Sea Stacks: Isolated, resistant rock pillars standing off the shore, left behind after cliff retreat.

Depositional Coastal Landforms

Beaches: Temporary accumulations of sand, gravel, or cobbles along the shoreline.
Bars: Long ridges of sand or shingle running parallel to the coast in the nearshore zone.
Spits: Barrier bars that are attached to the headland of a bay at one end.
Lagoons: Shallow bodies of water separated from the open sea by barrier bars or spits.

Winds (Aeolian Landforms)

Wind is a dominant geomorphic agent in hot deserts, acting through deflation, abrasion, and impact. Desert landforms are also significantly shaped by brief, torrential rains and sheet floods.

Erosional Aeolian Landforms

Pediments: Gently inclined rocky floors at the foot of mountains, formed by lateral erosion and sheet flooding.
Pediplains: Low, featureless plains formed by the coalescence of pediments in desert regions.
Playas: Shallow, temporary lakes in desert basins that leave behind salt-covered plains called alkali flats upon evaporation.
Deflation Hollows: Shallow depressions formed when wind blows away loose, weathered mantle.
Mushroom Rocks: Rock pillars with slender stalks and broad, rounded caps, polished by wind-borne sand abrasion.

Depositional Aeolian Landforms (Sand Dunes)

Barchans: Crescent-shaped dunes with points or wings pointing downwind, formed under constant wind direction.
Parabolic Dunes: U-shaped dunes formed when sandy surfaces are partially covered with vegetation, representing reversed barchans.
Seifs: Similar to barchans but with only one wing, formed when wind conditions shift.
Longitudinal Dunes: Long, low ridges of sand formed parallel to the wind direction when sand supply is poor.
Transverse Dunes: Long sand ridges aligned perpendicular to the constant wind direction, formed when sand is abundant.