LANDFORMS (Due To Surface Processes)

INTRODUCTIONStudy of surface features of the Earth, caused by rivers; wind, glaciers, groundwater or Coastal processes.

Evolution and structure of various landforms related to mountains, plains, plateaus, valleys and basins are specialized field of study within geomorphology.

RIVER (FLUVIAL) SYSTEMRiver (Channelized Running water) is the most important agent of erosion on the continents and the stream valleys are the most common landforms.

Rivers flowing to the oceans drain about 68 % of the Earth's land surface. The remainder of the land either is covered by ice or drains to closed inland basins (Lakes).

Rivers gradually mould the land by eroding away the material in some place and depositing it in other.

River System: A river system consists of a main channel (trunk stream) and all of the tributaries that flow into it or joining the trunk stream.

Parts of stream:Upstream: Towards headwater (up the regional slope of erosion).Downstream: Towards mouth of river (delta).Tributary:A stream flowing into or joining a larger stream.Distributaries: Numerous streams branches into which a river divides where it reaches its delta.River Terminology Stream is smaller than a River. It is also an umbrella term used in the scientific community for all flowing natural waters, regardless of size.Stream system has a number of components defined in terms of their stream order as explained in figure.

River System

RIVER SUBSYSTEMSA River system can be divided into three subsystems:

Collecting system (branches) -- Consisting of a network of tributaries in the headwater region, collects and funnels water and sediment to the main stream.

Transporting system (trunk) -- The main trunk stream, which functions as a channel through which water and sediment move from the collecting area toward the ocean. (Erosion and deposition also occur in a river's transporting system).

Dispersing system (roots) -- Consists of a network of distributaries at the mouth of a river (delta), where sediment and water are dispersed into an ocean, a lake, or a dry basin.

Dendritic Pattern: Irregular branching pattern (tree like) in many direction.It is common in massive rocks and in flat lying strataDue to strong resistance of rocks headward development of valley is negligible.Drainage PatternParallel pattern:Parallel or sub-parallel drainage formed on sloping surface.Common in terrain with homogeneous rocks.Development of parallel narrow channels are commonly seen on gently sloping surface

Radial Pattern: Streams radiates out from the center of the topograhic high

common in Volcanic terrain / dome structure.Rectangular Pattern: Channels marked by right-angle bends. Commonly due to presence of joints and fractures in the massive rocks or foliation in metamorphic rocksCentripetal pattern: Streams converge toward a central depression, such as a volcanic crater or caldera, a structural basin, basin created by dissolution of carbonate rock.

Trellis Pattern: Rectangular arrangement of channels in which principal tributary streams are parallel and very long. This pattern is common in areas where the outcropping edge of folded sedimentary rocks form long and nearly parallel belts.

Annular Pattern: Streams follow nearly circular or concentric paths along belts of weak rocks that ring a dissected dome or basin (where erosion has exposed successive belts of rock of varying degrees of erodibility).

River through its course

Form at the base of topographic features where there is a marked break in slope.Alluvial fans tend to be coarse-grained at their mouths. However, they can be relatively fine-grained at their edges.FLUVIAL LANDFORMS- ALLUVIAL FAN: Fan-shaped deposits of water transported material (alluvium).

Braided Rivers exhibit numerous channels that split off and rejoin each other to give a braided appearance. They typically carry coarse-grained sediment down a steep gradient. FLUVIAL LANDFORMS- BRAIDED RIVER:

As it flows, it deposits sediment on inside of curves (point bar deposits), and erode the banks on the outside of curves.FLUVIAL LANDFORMS- MEANDERING RIVER:In contrast to braided rivers, meandering rivers typically contain one channel that winds its way across the floodplain.

The Ganga and Brahmaputra Rivers combined have formed one of the largest deltas in the world, comprising approximately 105 640 km2. Bay of BengalDELTAThe fluvial sediment that accumulates where a stream enters a lake or ocean.

Undercutting by rivers & formation of new Terraces:Flat-topped, steep-sided benches elevated above floodplain.

Form due toRelative base level fall (e.g. uplift)Change in discharge: sediment yield.

Base level: The level upto which a river can cut its base.

Aeolian LandformsAeolian landformis a feature of theEarth's surface produced by either the erosive orconstructive action of theWind.

This process is not unique to earth but it has been observed and studied on other planets, most notablyMars.

In aeolian processes, wind erodes, transports and deposits particles ofsediment.

Deflation: The removal of loose, fine-grained particles.

Abrasion: The wearing down of surfaces by the grinding action andsandblastingof windborne particles.Aeolian Erosional Processes

Aeolian erosional landforms

Aeolian Transport Processes

Aeolian Depositional LandformsTypes: DUNES: Linear ridges - (Transverse & Longitudinal). BARCHAN (Crescent shaped)Dunes: It is the mound or ridge of sand or other loose sediment formed by the wind in a desert due to any obstacle in its flow.

Types of Dunes (contd.) Barchans: Migrating crescent dune with horns pointing downwind; form where strong winds blow in a consistent direction. Move fast. Common in central Asia and Sahara. Can reach hundreds of feet in height. Barchans

Types of Dunes (contd.)Transverse Dunes : parallel waves of crescent dunes perpendicular to wind direction; migrate downwind. Found in areas with large supply of sand.Transverse Dunes

Types of Dunes (contd.)Seifs : multiple very long narrow, parallel dunes. May be caused in areas with at least two dominant wind directions. Can be tens of miles long.Longitudinal dunes (Seifs)

Aeolian Processes summaryErosion :Winderodesthe Earth's surface by deflation (the removal of loose, fine-grained particles), by the turbulent eddy action of the wind and byabrasion (the wearing down of surfaces by the grinding action andsandblastingof windborne particles).

Transportation :Particles are transported by winds through suspension,saltation, andcreep.

Deposition: Wind-deposited materials hold clues to past as well as to present wind directions and intensities. These features help us understand the present climate and the forces that molded it. Wind-deposited sand bodies occur as sand sheets, ripples, anddunes.

GLACIAL LANDFORMS

Definition:Glacier is a large, slow moving mass of ice, formed by compacted layers of snow that slowly deforms and flows in response to gravity.

Snow Granular snow (in Large amounts)Granular snow Firn

Firn Ice

Ice Flowing ice (Glacier)SNOW TO GLACIERS1. Precipitation in the form of SNOW in higher reaches (e.g. Himalayas) & latitudes (e.g. Polar areas). FORMATION OF GLACIERS(one melt season or more)

FORMATION OF GLACIAL ICE For a glacier to form the following requirements must be met:

Precipitation in the form of SNOWMust fall on a surface where it can accumulate in large volumes;It must accumulate in an area where the temperature regime allows the snow to remain through at least one melt season; andThe snow must undergo metamorphism which changes it to glacier ice.

In general, these conditions are found in higher latitudes and high altitudes.

As layers of snow accumulate, the older snow becomes compacted due to the weight of overlying snow. Eventually most of the air is squeezed out, and the result is glacial ice.

ANATOMY OF GLACIERS

Zone of AccumulationUpper part of the glacier with highest elevationSnowfall Exceeds Melting & Evaporation Excess Snow Turns to Ice & Flows Out. Zone of Melting or Ablation (Melting + evaporation)Lower part of the glacierMelting & Evaporation Exceeds Snowfall Melting Excess Made up by Ice Flowing in. Equilibrium LineLine between accumulation and ablation zonesThis is a conceptual line assuming that around this line ablation equals accumulation in a year.Terminus of GlacierIt is the part from where the melt water emerges out. ANATOMY OF GLACIERS

ICE SHEET (over 50,000 sq km).(GREENLAND)

Vatnajvkull, Iceland's largest ice cap ICE CAPS (less than 50,000 sq km): (ICELAND)

VALLEY GLACIERS (up to 100 km in length): (Himalaya, Alpine)

PIEDMONT GLACIERS(e.g. Malaspina Glacier, Alaska).At the foot of steeper slopesPIEDMONT GLACIERSPIEDMONT GLACIERSPIEDMONT GLACIERS

EROSIONAL LANDFORMS

DEPOSITION LANDFORMS (Contd.)Moraine: An accumulation of unconsolidated material deposited by glaciers. These accumulations tend to be unsorted.Medial Moraine

SIGNIFICANCE OF GLACIER STUDIESMapping and monitoring of glaciers is important and justified by their significance for:Management and planning of water resources,Delineating the major climatic trends and forecastingSnow and glacial hazard assessment and Sea- level changes.

Himalaya means the abode of Snow. True to its name, the Himalaya encompasses the worlds 3rd largest glacier systems after Antarctica and Greenland.

The Himalayan glaciers feed three major rivers, the Indus, Ganges and Brahmaputra.

But most of the Himalayan glaciers have been thinning and retreating over the past 3-4 decades.

In India, there are more than 5,000 glaciers on the southern slope of Himalayas covering an area of nearly 38,000 Km2.

The distributions of these glacier are higher in North-West than in the North-Eastern part of the Indian.GLACIER RETREAT - AN INDIAN SCENARIO

RETREAT OF IMPORTANT GLACIERS IN HIMALAYAS

EXAMPLES OF GLACIER RETREAT IN HIMALAYASCHANGE IN THE GLACIER BOUNDARY FROM 1780 TO 2001

Atolls are roughly circular (or occasionally horseshoe-shaped) oceanic reef complexes surrounding a large, deep central lagoon.Barrier reefs are reef systems that parallel the shore and are separated from it by a wide lagoon that contain at least some deep portions.Fringing reef is a reef system growing fairly close to or directly from shore with an entirely shallow (less than about 10m) lagoon, or no lagoon at all.CORAL REEFS:

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Depending on the magnitude of water flow, stream system is sub-classified into a number of units, as given below: Creek is smaller than a Stream, Brook is smaller Creek, Rivulet is smaller that Brook. Gully is the 1st order stream Creek, Brook & Rivulet terms are applied interchangeably to any small river.

Consequent Stream:

A stream following the slope. Development of slope may be due to sudden tectonic uplift.Subsequent Stream:

A stream that develops later on, carving the softer rocks and flow at almost right angle to the original slope of the landStream Types

Levees

Oxbow lakes

Some Important Aeolian landforms (contd.)Inselberg : island mountains rise abruptly out of desert landscapes

Bornhardt : highly resistant rock landform; a type of inselberg.

GroundwaterGroundwater: The zone of subsurface water in which all pore spaces or fractures in the rock are filled with water (saturated).

Water table: The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called the water table.

Aquifer: A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water.

Travertine is a terrestrial sedimentary rock, formed by the precipitation of carbonate minerals from solution in ground and surface waters

ANATOMY OF GLACIERSEQUILIBRIUM LINE or TERMINUS

TYPES OF GLACIERS Ice Sheets are enormous continental masses of glacial ice and snow expanding over 50,000 sq km. E.g.- Antarctic and Greenland ice sheets.

Ice Caps are miniature ice sheets, covering less than 50,000 sq km. E.g.-Iceland.

Valley Glaciers these glaciers spill down valleys, looking like giant tongues. They may be quite long, up to 100 km in length, but those having a length of 10-20 km are more common. E.g.- Himalayan and Alpine glaciers.

Piedmont Glaciers occur when steep valley glaciers spill into relatively flat plains, where they spill into bulb like lobes. E.g. Malaspina Glacier, Alaska.

GLACIAL PLUMBING

EROSIONAL LANDFORMSMoulins:

Holes in glaciers that water flows through Connect surface streams to subsurface streams

Cirque :

A semicircular or amphitheater-shaped bedrock feature created as glaciers scour back into the mountain. This is where the snow and ice forming the glacier first accumulates; it is the "headwatersof a glacier.Cirque Moulins

EROSIONAL LANDFORMS (Contd.) Steep-sided, sharp-edged bedrock ridge formed by two glaciers eroding away on opposite sides of the ridge. A pyramid-shaped mountain peak created by several glaciers eroding away at different sides of the same mountain.Arete:Horn:Arete

EROSIONAL LANDFORMS (Contd.)Col:

A low spot or pass along a cirque or an arete.

Striations :

Lines etched in bedrock underlying glaciers as individual particlesembedded in the glacier scratch the underlying bedrock. These lines indicate the orientation of Glacial flow.

Striations

EROSIONAL LANDFORMS (Contd.)Peak surrounded by glaciers but not itself glaciated.Nunatak :Tarn :A glacial lake produced by scouring. These are often found in cirques. Nunatak Tarn

DEPOSITION LANDFORMS (Contd.) Fine unconsolidated glacial deposits that compose moraines.Till : Debris deposited in front of glaciers. Often sorted.Outwash plain :

DEPOSITION LANDFORMS (Contd.)Long-sinuous ridge formed by sediment deposition in sub-glacial streams.Esker :Formed by melting ice chunks in glacial debris.Kettle lake :

Esker

DEPOSITION LANDFORMS (Contd.)

Large boulders left by glaciers in areas where they obviously dont belong.

Erratics :Can be transported from 10s to 100s of kilometers form point of origin.

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