Landforms and Their Evolution
1. Learning Objectives
After reading these notes, you will be able to:
2. Introduction β Landforms and Evolution
3. Running Water β Landforms
πΏ Stages of Landscape Development by Running Water
| Stage | Streams | Valleys | Divides | Other Features |
|---|---|---|---|---|
| Youth | Few, poor integration, steep gradient | Shallow V-shaped; narrow/no floodplains | Broad and flat with marshes, swamps, lakes | Waterfalls, rapids; meanders may develop on broad uplands |
| Mature | Plenty, good integration | Still V-shaped but deep; wider floodplains; meanders confined within valley | Sharp divides; swamps and marshes disappear | Waterfalls and rapids disappear |
| Old Age | Few tributaries, gentle gradients | Streams meander freely over vast floodplains; natural levees, oxbow lakes | Broad and flat with lakes, swamps, marshes | Landscape at or slightly above sea level |
ποΈ A. Erosional Landforms by Running Water
ποΈ Valleys
Start as rills β gullies β valleys. Types: V-shaped valley (most common), Gorge (deep, very steep to straight sides, almost equal width top and bottom β forms in hard rocks), Canyon (steep step-like side slopes, wider at top than bottom β forms in horizontal sedimentary rocks). Canyon is a variant of gorge.
π Potholes and Plunge Pools
Potholes = circular depressions on rocky beds of hill-streams; formed by stream erosion aided by abrasion of rock fragments. Pebbles rotate in depression β depression grows. At the foot of waterfalls, large deep holes form due to sheer impact of water + rotation of boulders = Plunge Pools.
γ°οΈ Incised/Entrenched Meanders
Deep and wide meanders cut in hard rocks. Form due to active lateral erosion by streams on gentle slopes over time. Very deep and wide meanders in hard rocks = incised or entrenched meanders.
πͺ River Terraces
Surfaces marking old valley floor or floodplain levels. May be bedrock surfaces or alluvial terraces. Result of vertical erosion by stream into its own depositional floodplain. Many terraces at different heights = former river bed levels. Same elevation on both sides = paired terraces.
ποΈ B. Depositional Landforms by Running Water
π Alluvial Fans
Formed when streams from higher levels break into foot slope plains of low gradient. Coarse load too heavy to carry over gentler gradient β dumped as a broad, low to high cone-shaped deposit. Streams shift position β form many channels = distributaries. Humid areas β low cones with gentle slope; Arid areas β high cones with steep slope.
ποΈ Deltas
Like alluvial fans but develop at a different location β where rivers meet the sea. Load dumped into the sea; if not carried away, spreads as a low cone. Unlike alluvial fans, delta deposits are very well sorted with clear stratification. Coarsest materials settle first; finer silts and clays go further. River distributaries increase in length as delta grows.
πΎ Floodplains
Major landform of river deposition. Active floodplain = river bed made of river deposits. Inactive floodplain = floodplain above the banks. Contains flood deposits (fine silt/clay) and channel deposits (coarse). Floodplains in a delta = delta plains. Channels shift laterally leaving cut-off courses filled gradually.
π Natural Levees
Found along banks of large rivers. Low, linear, parallel ridges of coarse deposits along river banks. Quite often cut into individual mounds. Form during floods when coarser material deposits on banks.
π΅ Point Bars (Meander Bars)
Found on concave side of meanders of large rivers. Sediments deposited in linear fashion by flowing water along the bank. Almost uniform in profile and width; contain mixed sizes of sediments.
γ°οΈ Meanders and Ox-bow Lakes
Meanders = loop-like channel patterns over flood and delta plains. Not a landform β only a type of channel pattern. Active deposition on convex bank (slip-off bank); undercutting on concave bank (cut-off bank). As meanders grow into deep loops β get cut-off β left as ox-bow lakes.
4. Groundwater β Karst Topography
π³οΈ A. Erosional Landforms (Karst)
π§ Swallow Holes
Small to medium sized, round to sub-rounded shallow depressions on limestone surface formed through solution.
π³οΈ Sinkholes
Opening circular at top, funnel-shaped at bottom. Size: few sq. m to a hectare; depth: half metre to 30 m or more. Two types: Solution sinks (form by solution alone β more common) and Collapse sinks / Dolines (form when roof of underground cave collapses).
π Valley Sinks / Uvalas
When sinkholes and dolines join together due to slumping of materials or roof collapse of caves, long, narrow to wide trenches called valley sinks or Uvalas form.
π‘οΈ Lapies and Limestone Pavements
Most of limestone surface gets eaten away by pits and trenches leaving it extremely irregular with a maze of points, grooves and ridges = lapies (form due to differential solution along parallel joints). Lapie field may eventually turn into limestone pavements.
ποΈ Caves
Water percolates through cracks/joints and dissolves limestone along bedding planes β long and narrow to wide gaps = caves. Caves at different elevations depending on limestone beds. Caves with openings at both ends = tunnels.
π B. Depositional Landforms (Karst)
π§ Stalactites
Hang as icicles from the roof of caves. Broad at base, tapering towards free ends. Form as calcium carbonate deposited by dripping water from cave roof.
π§ Stalagmites
Rise up from the floor of caves. Form due to dripping water from surface or through the thin pipe of the stalactite. May take shape of column, disc, rounded bulging end or miniature crater.
ποΈ Pillars / Columns
When stalactites and stalagmites eventually fuse β they give rise to columns and pillars of different diameters.
5. Glaciers β Landforms
ποΈ A. Erosional Landforms by Glaciers
π Cirque
Most common landform in glaciated mountains. Found at heads of glacial valleys. Deep, long and wide troughs or basins with very steep concave to vertically dropping high walls at head and sides. Lake forming within cirque after glacier disappears = cirque lake / tarn lake. Two or more cirques in stepped sequence may exist.
β°οΈ Horns
Form through headward erosion of cirque walls. When 3 or more radiating glaciers cut headward until their cirques meet β high, sharp pointed and steep sided peaks = horns. Examples: Matterhorn (Alps) and Mount Everest (Himalayas).
π‘οΈ ArΓͺtes (Serrated Ridges)
Divides between cirque side walls/head walls get narrow due to progressive erosion β turn into serrated or saw-toothed ridges = arΓͺtes. Very sharp crest and zig-zag outline.
ποΈ Glacial Valleys / Troughs
Trough-like and U-shaped with broad floors and smooth, steep sides. May contain moraines, lakes (gouged out of rocky floor or formed by debris). Hanging valleys occur at elevation on sides of main glacial valley β spurs truncated to form triangular facets. Very deep glacial troughs filled with sea water at high latitudes = fjords/fiords.
π» B. Depositional Landforms by Glaciers
ποΈ Moraines
Long ridges of deposits of glacial till. Types: Terminal moraine = long ridge at the end (toe) of glacier; Lateral moraine = along sides parallel to glacial valley; Ground moraine = irregular sheet of till over valley floors left by retreating glaciers; Medial moraine = in the centre of glacial valley flanked by lateral moraines (imperfectly formed).
γ°οΈ Eskers
When glaciers melt, water flows and accumulates beneath the glacier. Very coarse materials settle in the valley of ice beneath the glacier. After ice melts β found as a sinuous (winding) ridge = esker.
ποΈ Outwash Plains
Plains at the foot of glacial mountains or beyond continental ice sheets. Covered with glacio-fluvial deposits (broad flat alluvial fans) of gravel, silt, sand and clay joining to form outwash plains.
π₯ Drumlins
Smooth oval shaped ridge-like features composed mainly of glacial till with some gravel and sand. Long axes parallel to direction of ice movement. Size: up to 1 km long, ~30 m high. Stoss end (facing glacier) = blunter and steeper; Tail = gentler. Indicate direction of glacier movement.
6. Waves and Currents β Coastal Landforms
ποΈ A. Erosional Landforms (Coastal)
ποΈ Sea Cliffs
Waves break with great force against land β shape hill sides into steep cliffs. With constant pounding, cliffs recede. Range from few metres to 30 m or more.
ποΈ Wave-Cut Platform / Terrace
As cliff recedes β leaves a flat or gently sloping platform in front of the sea cliff. Platform occurring above average height of waves = wave-cut terrace.
π³οΈ Sea Caves
Lashing of waves against base of cliff + rock debris β hollows created β widened and deepened β sea caves.
πΏ Sea Stacks
Retreat of cliff may leave remnants of rock standing as small isolated islands just off the shore. Resistant masses originally part of a cliff or hill = sea stacks. Also temporary β eventually disappear due to wave erosion.
ποΈ B. Depositional Landforms (Coastal)
ποΈ Beaches
Characteristic of deposition-dominated shorelines. Most sediment comes from land (rivers) or wave erosion. Temporary features β sandy beach of one season may reduce to narrow coarse pebbles in another. Most beaches = sand-sized materials. Shingle beaches = small pebbles and cobbles.
π¬οΈ Sand Dunes (Coastal)
Sands lifted and winnowed from beach surfaces β deposited just behind the beach as sand dunes. Long ridges parallel to coastline β very common along low sedimentary coasts.
π Bars and Barrier Bars
Off-shore bar = ridge of sand and shingle in sea, parallel to coast. Barrier bar = off-shore bar exposed above water due to further sand addition. Commonly form across mouth of river or entrance of bay.
π‘οΈ Spits
Barrier bar that gets keyed up to one end of a bay or headland = spit. Also develop attached to headlands/hills.
ποΈ Lagoons
When barrier bars and spits form at mouth of a bay and block it β a lagoon forms. Lagoons gradually get filled by sediments from land β eventually become a coastal plain.
7. Winds β Desert Landforms
ποΈ A. Erosional Landforms (Desert/Wind)
ποΈ Pediments and Pediplains
Pediments = gently inclined rocky floors close to mountains at their foot, with or without thin debris cover. Form through lateral erosion by streams and sheet flooding. Through parallel retreat of slopes (backwasting), pediments extend backwards at expense of mountain front β mountain gets reduced β leaving an inselberg (remnant). Eventually all high relief is reduced to low featureless plains = pediplains.
π Playas
In basins surrounded by mountains β drainage towards centre β gradual deposition β nearly level plain at centre. When water is sufficient β covered by shallow lake = playa. Water retained for short duration (evaporation). Playas often contain good deposits of salts. Playa plain covered by salts = alkali flats.
π³οΈ Deflation Hollows and Caves
Persistent wind removes weathered mantle β creates shallow depressions = deflation hollows. Wind also creates small pits over rock surfaces. Blow outs become deeper and wider β caves.
π Mushroom, Table and Pedestal Rocks
Rock outcrops susceptible to wind deflation and abrasion get worn out leaving remnants of resistant rocks polished in the shape of a mushroom (slender stalk + broad rounded cap), a table top, or a pedestal.
ποΈ Inselberg
Remnant of a mountain left behind after parallel retreat of slopes (backwasting) reduces the surrounding landscape to a pediplain. An isolated hill standing in a flat desert landscape.
π¬οΈ B. Depositional Landforms (Desert/Wind) β Sand Dunes
| Dune Type | Shape | Condition |
|---|---|---|
| Barchan | Crescent-shaped; wings/points directed downwind | Constant and moderate wind; uniform surface; no vegetation |
| Parabolic | Like reversed barchan; wings directed upwind | Sandy surfaces partially covered with vegetation; same wind direction as barchan |
| Seif | Like barchan but with only one wing; lone wing can grow very long and high | Shift in wind conditions |
| Longitudinal | Long ridges β considerable length but low in height | Poor supply of sand; constant wind direction |
| Transverse | Aligned perpendicular to wind direction; long and low | Constant wind; sand source elongated at right angles to wind |
Summary β Quick Revision
Landform = small-medium tract of Earth’s surface. Landscape = several landforms together. Landmass passes through Youth β Mature β Old Age. A peneplain with monadnocks = final stage.
Running water erosional forms: Valleys (V-shaped, Gorge, Canyon), Potholes, Plunge Pools, Incised Meanders, River Terraces (paired terraces).
Running water depositional forms: Alluvial fans, Deltas, Floodplains, Natural Levees, Point Bars, Meanders, Ox-bow Lakes.
Karst topography = limestone regions. Erosional: Swallow holes, Sinkholes (solution/collapse/dolines), Uvalas, Lapies, Limestone pavements, Caves. Depositional: Stalactites (roof), Stalagmites (floor), Pillars.
Glacial erosional forms: Cirque (tarn lake), Horns (Matterhorn, Everest), ArΓͺtes, U-shaped valleys, Hanging valleys, Fjords/Fiords.
Glacial depositional forms: Glacial Till, Moraines (Terminal, Lateral, Ground, Medial), Eskers (sinuous ridge), Outwash Plains, Drumlins (stoss end + tail β indicate ice direction).
Coastal erosional forms: Sea Cliffs, Wave-cut Terrace/Platform, Sea Caves, Sea Stacks. West coast of India = high rocky (erosion dominant).
Coastal depositional forms: Beaches (shingle beach), Coastal Sand Dunes, Off-shore Bar, Barrier Bar, Spits, Lagoons β Coastal Plains. East coast of India = low sedimentary (deposition dominant).
Desert erosional forms: Pediments, Pediplains, Inselberg, Playas (alkali flats), Deflation Hollows, Blow outs, Caves, Mushroom/Table/Pedestal Rocks.
Desert depositional forms (Sand Dunes): Barchan (crescent, downwind wings), Parabolic (reversed barchan, vegetation), Seif (one wing), Longitudinal (long ridges, poor sand), Transverse (perpendicular to wind).
Important Terms to Remember
- Landform: Small to medium tracts or parcels of Earth’s surface, each with its own physical shape, size, materials and geomorphic history.
- Landscape: Large tracts of Earth’s surface made up of several related landforms together.
- Peneplain: An almost plain β lowland of faint relief formed as a result of long-continued stream erosion. Some resistant remnants (monadnocks) may still stand out.
- Monadnock: A low resistant rock remnant standing out in a peneplain β resistant to erosion while surrounding areas were reduced to plains.
- Sheet Erosion: Overland flow as a sheet removes materials uniformly from the land surface.
- Gorge: A deep valley with very steep to straight sides, almost equal width at top and bottom. Forms in hard rocks.
- Canyon: Characterised by steep step-like side slopes; wider at top than bottom. A variant of gorge. Forms in horizontal bedded sedimentary rocks.
- Potholes: More or less circular depressions on rocky beds of hill-streams formed by stream erosion aided by abrasion and rotation of rock fragments.
- Plunge Pools: Large, deep holes at the base of waterfalls formed by the sheer impact of water and rotation of boulders.
- Incised/Entrenched Meanders: Very deep and wide meanders cut in hard rocks due to continued active lateral erosion.
- River Terraces: Surfaces marking old valley floor or floodplain levels β result of vertical erosion by stream into its own floodplain.
- Paired Terraces: River terraces at the same elevation on either side of the river.
- Alluvial Fan: Broad, low to high cone-shaped deposit formed when streams flowing from higher levels break into foot-slope plains of low gradient and dump their coarse load.
- Delta: Fan-like deposit formed where river meets the sea. Deposits are well-sorted with clear stratification. Coarser materials first, finer silts and clays later.
- Distributaries: Smaller channels formed when a stream shifts its position across an alluvial fan or delta.
- Floodplain: Major landform of river deposition. Active floodplain = river bed; Inactive floodplain = above the banks.
- Natural Levees: Low, linear, parallel ridges of coarse deposits along the banks of large rivers. Form during floods.
- Point Bars (Meander Bars): Sediments deposited on the concave side of meanders of large rivers in a linear fashion.
- Meanders: Loop-like channel patterns that develop over flood and delta plains β a type of channel pattern, not a landform. Active deposition on convex bank; undercutting on concave (cut-off) bank.
- Ox-bow Lakes: Cut-off meander loops left as crescent-shaped lakes when meanders grow too deep and get cut off due to erosion at inflection points.
- Karst Topography: Landforms developed in limestone/dolomite regions by the action of groundwater through solution and precipitation. Named after the Karst region in the Balkans.
- Swallow Holes: Small to medium sized, round, shallow depressions on limestone surface formed by solution.
- Sinkholes: Circular at top, funnel-shaped at bottom openings in limestone areas. Solution sinks (by solution alone) and collapse sinks/dolines (by roof collapse).
- Uvalas (Valley Sinks): Long, narrow to wide trenches formed when sinkholes and dolines join due to slumping or roof collapse of caves.
- Lapies: Irregular surfaces with a maze of sharp pinnacles, grooves and ridges formed due to differential solution activity in limestone areas.
- Limestone Pavements: Smooth surfaces formed when lapie fields are further eroded and smoothened.
- Stalactites: Icicle-like deposits of calcium carbonate hanging from the roof of limestone caves. Broad at base, tapering at free end.
- Stalagmites: Calcium carbonate deposits rising up from the floor of limestone caves. Form due to dripping water from the stalactite above.
- Glaciers: Masses of ice moving as sheets over land (continental/piedmont) or as linear flows down mountain slopes (mountain/valley glaciers). Move due to gravity.
- Cirque: Most common glacial erosional landform. Deep, long and wide trough or basin with very steep concave walls at head and sides. Found at heads of glacial valleys. Lake forming in cirque = cirque/tarn lake.
- Horns: High, sharp pointed and steep-sided peaks formed when 3 or more radiating glaciers cut headward until their cirques meet. Examples: Matterhorn (Alps), Everest (Himalayas).
- ArΓͺtes: Serrated or saw-toothed ridges with very sharp crests and zig-zag outline formed when divides between cirque walls get progressively eroded and narrow.
- Glacial Valleys/Troughs: U-shaped valleys with broad floors and steep sides carved by glaciers. May have hanging valleys, truncated spurs (triangular facets).
- Fjords/Fiords: Very deep glacial troughs filled with sea water, making up shorelines at high latitudes.
- Glacial Till: Unassorted coarse and fine debris dropped by melting glaciers. Rock fragments are angular to sub-angular.
- Outwash Deposits: Glacio-fluvial deposits carried and deposited by meltwater streams. Roughly stratified and assorted; rock fragments somewhat rounded.
- Moraines: Long ridges of glacial till deposits. Types: Terminal (at toe of glacier), Lateral (along sides), Ground (irregular sheet left by retreating glacier), Medial (in centre flanked by lateral moraines).
- Eskers: Sinuous (winding) ridges formed when coarse materials settle in subglacial stream channels beneath a glacier and are revealed after the ice melts.
- Outwash Plains: Broad flat plains at foot of glacial mountains covered with glacio-fluvial deposits of gravel, silt, sand and clay.
- Drumlins: Smooth oval-shaped ridge-like features of glacial till. Long axes parallel to ice movement direction. Stoss end = blunter/steeper (facing glacier); Tail = gentler. Indicate direction of glacier movement.
- Wave-cut Terrace/Platform: Flat or gently sloping platform left in front of a receding sea cliff, above the average height of waves.
- Sea Stacks: Isolated, resistant rock masses standing just off the shore β remnants of cliffs or hills after wave erosion caused retreat of coastal cliffs.
- Off-shore Bar: Ridge of sand and shingle in the sea in the off-shore zone lying parallel to the coast.
- Barrier Bar: An off-shore bar exposed above water due to further addition of sand.
- Spit: A barrier bar keyed up to one end of a bay or headland.
- Lagoon: A body of water enclosed when barrier bars and spits form at the mouth of a bay and block it. Eventually filled by sediments to form a coastal plain.
- Deflation: Lifting and removal of dust and smaller particles from rock surface by wind β one of the three ways wind acts in deserts.
- Pediment: Gently inclined rocky floor close to mountains at their foot, with or without thin debris cover. Forms through lateral erosion by streams and sheet flooding.
- Pediplain: Low featureless plain formed when high desert relief is reduced through parallel retreat of slopes (backwasting).
- Inselberg: Isolated hill or remnant of a mountain standing in a flat desert pediplain after surrounding areas have been reduced by backwasting.
- Playa: Shallow lake at the centre of a desert basin that retains water only for short duration due to evaporation. Often contains salt deposits.
- Alkali Flats: Playa plains covered up by salts left behind after evaporation.
- Deflation Hollows: Shallow depressions created when wind persistently blows away weathered mantle from over rocks or soil in one direction.
- Barchan: Crescent-shaped sand dune with wings/points directed downwind. Form where wind is constant, moderate, and surface is uniform.
- Parabolic Dunes: Reversed barchans with wings directed upwind. Form when sandy surfaces are partially covered with vegetation.
- Seif: Sand dune similar to barchan but with only one wing or point. Form when there is a shift in wind conditions.
- Longitudinal Dunes: Long ridges of sand, considerable in length but low in height. Form when sand supply is poor and wind direction is constant.
- Transverse Dunes: Sand dunes aligned perpendicular to wind direction. Form when wind is constant and sand source is elongated at right angles to wind.