Landforms, Landscape Evolution, and Fluvial and Karst Processes

Landform

A small to medium tract or parcel of the earth's surface.

Landscape

A landscape is made up of several related landforms, representing a large tract of the earth's surface.

Geomorphic agents

They perform erosion and cause changes on the earth's surface.

Changes in landforms

Changes occur due to erosion, deposition, climatic conditions, and movements of landmasses.

Deposition

Deposition follows erosion, leading to changes on the earth's surface.

Stages of landform evolution

Stages include youth, mature, and old age, reflecting the development of landforms over time.

Most important geomorphic agent in humid regions

Running water is the most important geomorphic agent in humid regions with heavy rainfall.

Components of running water

1. Overland flow as a sheet 2. Linear flow as streams and rivers

Stream channels over steep gradients

They turn gentler due to erosion, losing velocity and facilitating deposition.

River slope and deposition

The gentler the river channel's slope, the greater the deposition.

Hills and valleys due to lateral erosion

They are reduced to plains.

Sheet erosion

Overland flow causes sheet erosion.

Concentration of overland flow

Small and narrow rills that develop into gullies and valleys.

Peneplain

A type of plain formed as a result of stream erosion, almost flat.

Youth stage of landscape development

Few streams, shallow V-shaped valleys, and no floodplains.

Mature stage of landscape development

Streams are plenty, valleys are deep V-shaped, and floodplains are wider.

Old stage of landscape development

Gentle gradients, free meandering streams, and broad flat divides.

Valley development

From small rills to gullies, then to valleys.

Gorge

A deep valley with steep to straight sides.

Canyon vs. gorge

A canyon is wider at the top than at the bottom; a gorge is equal in width.

Potholes

Circular depressions formed by stream erosion and abrasion of rocks.

Shallow depressions due to flowing water

Pebbles and boulders get collected and rotated, causing the depressions to grow.

Joining of depressions

The stream valley gets deepened.

Plunge pools

Large, deep holes at the base of waterfalls.

Incised or entrenched meanders

Deep and wide meanders cut in hard rocks, formed in steep gradient streams.

River terraces

Old valley floor or floodplain levels due to vertical erosion.

Paired terraces

River terraces at the same elevation on either side of the river.

Alluvial fans

When streams from higher levels break into foot slope plains of low gradient.

Stream load over mountain slopes

Very coarse load that gets dumped on gentler gradients.

Deltas

Landforms formed where rivers dump sediments into the sea, accumulating as a low cone.

Difference between deltas and alluvial fans

Deltas develop at river mouths into the sea, while alluvial fans are formed on land.

Materials settling first in a delta

Coarsest materials settle first, followed by finer fractions like silts and clays.

Floodplain

A major landform of river deposition formed by the deposition of sediments during flooding.

Types of deposits in an inactive floodplain

Flood deposits and channel deposits.

Materials carried by slow-moving waters in a floodplain

Fine-sized materials like sand, silt, and clay.

Active floodplain

The river bed made of river deposits.

Natural levees

Elevated landforms along riverbanks formed by sediment deposition during floods.

Point bars

Deposits of sediment on the inside bends of river channels.

River channels in plains

They shift laterally and change courses, leaving cut-off channels.

Difference between natural levees and point bars

Natural levees are found along river banks, while point bars are found on the concave side of meanders.

Meanders

Loop-like channel patterns developed by rivers over flood and delta plains.

Concave bank in meanders

It experiences active deposition and is known as the cut-off bank, showing a steep scarp.

Convex bank of meanders

Erosion leads to a long, gentle profile.

Meanders growth

They may get cut-off due to erosion, forming ox-bow lakes.

Role of groundwater in landform evolution

It contributes to the erosion of landmasses and the evolution of landforms.

Factors contributing to the formation of meanders

Water flowing over gentle gradients, unconsolidated alluvial deposits, and Coriolis force acting on water.

Rocks allowing water to percolate well

Permeable rocks, thinly bedded rocks, highly jointed and cracked rocks.

Movement of water causing erosion in rocks

Downward movement and horizontal movement through bedding planes or joints.

Rocks showing significant effects of groundwater action

Limestones and dolomites rich in calcium carbonate.

Landforms produced by groundwater action in limestone

Karst topography.

Processes active in developing karst topography

Solution and precipitation deposition.

Small depressions in limestone

Swallow holes.

Sinkhole

An opening that is circular at the top and funnel-shaped at the bottom.

Erosional landforms in karst areas

Pools, sinkholes, lapies, limestone pavements.

Solution sink

A depression formed by solution action, often covered by soil and may appear as shallow water pools.

Collapse of a sinkhole

It leaves a large hole opening into a cave or void below, known as a collapse sink.

Valley sinks or Uvalas

Long, narrow to wide trenches formed when sinkholes and dolines join due to material slumping or cave roof collapse.

Lapies

Ridges formed due to differential solution activity along parallel to sub-parallel joints in limestone.

Formation of caves

By water percolating down through rocks and dissolving limestone along bedding planes, creating gaps.

Stalactites

Icicle-shaped formations hanging from cave ceilings, broad at the base and tapering towards the end.

Stalagmites

Formations rising from the floor of caves, created by dripping water from stalactites above.

Chief chemical in limestone

Calcium carbonate, which is soluble in carbonated water.

Formation from evaporating water carrying calcium carbonate

Calcium carbonate is deposited, leading to formations like stalactites and stalagmites.

Glaciers

Masses of ice moving as sheets over land or as linear flows down mountain slopes.

Cause of glacier movement

Glaciers move due to the force of gravity.

Movement of glaciers

Glaciers move due to the force of gravity.

Cirques

Deep, long, and wide troughs or basins found at the heads of glacial valleys.

Landscape changes due to glaciers

They cause abrasion and plucking, reducing mountains to low hills and plains.

Lakes in cirques

Cirque or tarn lakes.

Movement speed of glaciers

A few centimeters to a few meters a day, or even less or more.

Erosional effects of glaciers

Glaciers can cause significant damage to rocks and alter landscapes.

Types of glaciers

Continental glaciers and mountain glaciers.

Erosion effects on hills and valleys

They are reduced to plains as lateral erosion increases.

Cause of sheet erosion

Overland flow causes sheet erosion.

Stages of landscape development in running water regimes

Youth, Mature, Old.

Youth stage of stream landscapes

Streams are few, with shallow V-shaped valleys and no floodplains. Waterfalls and rapids may exist where hard rock is exposed.

Mature stage of stream landscapes

Streams are plentiful with deep V-shaped valleys. Floodplains are wider, and waterfalls and rapids disappear.

Old stage of stream landscapes

Streams meander over vast floodplains with gentle gradients. Most of the landscape is at or slightly above sea level.

Formation of valleys

Valleys start as small rills, developing into gullies, then deepening into various valley types like V-shaped valleys, gorges, and canyons.

Difference between a gorge and a canyon

A gorge has steep sides and equal width at the top and bottom, while a canyon has steep, step-like sides and is wider at the top.

Formation of potholes in hill-streams

Potholes form from stream erosion aided by the abrasion of rock fragments over rocky beds.

Formation in shallow depressions due to flowing water

Pebbles and boulders get collected and rotated, enlarging the depressions.

Products of river terraces

Vertical erosion by the stream into its own depositional floodplain.

Load carried by streams over mountain slopes

It becomes too heavy to carry over gentler gradients and gets dumped.

Types of floodplains

Active floodplain: Made of river deposits. Inactive floodplain: Contains flood deposits and channel deposits above the banks.

Inactive floodplains

Contain flood deposits (finer materials like silt and clay) and channel deposits (coarse deposits from abandoned channels).

Flood deposits

Carry finer materials like silt and clay.

Channel deposits

Consist of coarser materials left by shifted river channels.

Meander bars

Another name for point bars, found on the concave side of river meanders.

Meander

A loop-like channel pattern that develops in rivers over flood and delta plains.

Cut-off bank

The concave bank of a meander, characterized by a steep scarp due to erosion.

Ox-bow lakes

Lakes formed when meanders are cut off due to erosion at inflection points.

Groundwater

Contributes to the erosion of landmasses and the evolution of landforms.

Coriolis force

Deflects flowing water, influencing meander patterns in rivers.

Permeable rocks

Rocks that allow water to percolate well.

Erosion in rocks

Caused by the downward and horizontal movement of water through bedding planes and joints.

Karst topography

Landforms produced by groundwater action in limestone or dolomitic regions.

Swallow holes

Shallow depressions formed on limestone surfaces through solution.

Collapse sinks

Sinkholes that form when the roof of an underground void collapses, creating a large opening.

Doline

Another term used to refer to collapse sinks.