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GEOGRAPHY : MOUNTAINS, WEATHERING, DRAINAGE SYSTEM
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Friday, 07 September 2012 04:07

 

MOUNTAINS, WEATHERING, DRAINAGE SYSTEM


MOUNTAINS

Mountains come under the second order of relief features. This is a portion of land surface rising considerably above the surrounding country, either as a single eminence or in a range or chain.

 

TYPES OF MOUNTAINS

 

(1)   Folded Mountains (Geosynclines)

  • Most of the Fold Mountains are the youngest mountains in the world.

 

  • The main examples are the Himalayas, the Alps, Rockies, and the Andes.

 

  • The fold mountains are formed by compression when two horizontal forces act towards a common point that compresses the intervening rock strata to produce fold mountains.

 

  • The fold consists of two inclined arts called limbs, the upper portion is called anticlines, while the lower portion is called synclines.

 

On the basis of the period of origin folded mountains are divided into:

 

(i) Old Folded Mountains:

All the folded mountains originating before the tertiary period come under the category of old folded mountains, e.g. the old folded mountains of Calledonian and Hercynian periods, such as the Aravalis, Appalachians etc.

(ii) New Folded Mountains:

In this category come the Alpine folded mountains of the tertiary period, e.g. the Alps, Himalayas, Rockies, Andes etc.

  • These are gigantic mountains characterized by glacier-capped high peaks, intense erosion, complex folding and faulting, volcanism etc.

 

(2)   Volcanic Mountains:

Volcanic mountains are formed by the extrusion of lavas and pyroclastic materials, which, if continued long enough, produces gigantic volcanic piles.

  • The Kilimanjaro (Africa), Cotapaxi (Andes), Mount Acancagua (the highest volcanic mountain), etc., are some of examples.

 

(3)   Block Mountains:

These are the result of faulting caused by tensile and compressive forces.

  • Examples are Vosges and Black forest mountains bordering the Rhine Rift Valley, Salt Range of Pakistan, Siera Nevada (USA) etc.

 

  • Siera Nevada mountains of California is considered to be the most extensive block mountain of the world.

 

(4)   Relict Mountains:

When mountains, plateau, or high plains take the form of mountains by continued erosion over a long period of time they are known as Relict Mountains.

  • Examles are Aravali, Satpura, Vindhyachal in India, mountains of Scotland and Penine range of Europe.

 

OTHER IMPORTANT FACTS

Nilgiri Hills of India are an example of Block Mountain.

Ojas Del Saldo, situated in the Andes, is the highest active volcanic mountain of the world.

The Western Ghats of India is not a true mountain range. It is, in fact, a fault scrap whose western part has been displaced and has subsided to the west.

Andes, the folded mountains of South America, is the longest (7,000 km) range in the world.

Folded Mountains are made up chiefly of the sedimentary rocks, but their core is characterized by massive granitic intrusions.

Folded Mountains are generally found in arc sphere and they extend for greater lengths but their widths are far smaller.

Great Dividng Range of Australia is an old folded mountain.

Folded mountains are generally found along the margins of the continents either in north-south direction, such as Rockies & Andes, or in east-west Direction such as the Alps in Europe, Atlas in Africa, Himalayas, etc.

 

PLATEAUX

  • Plateau is an elevated tract of relatively flat land, usually limited on at least one side by a steep slope falling abruptly to lower land.

 

  • This second order relief feature covers about 33 per cent of the land surface of the globe.

 

TYPES OF PLATEAU BASED ON MODE OF ORIGIN

 

1. Plateaux Formed by Exogenetic Processes:

(a) Glacial Plateaux:

Garhwal Plateau, Plateau of Greenland are formed by erosion, whereas, Plateaux formed by deposition are the Russian Plateau, Marg of Kashmir.

 

(b) Fluvial Plateaux: Bhander Plateau of Central India, Brazilian plateau.

 

(c) Aeolian Plateaux: Loess Plateau of China, Potwar Plateau of Pakistan.

 

2. Tectonic Plateaus:

(a) Intermontane Plateaux:

Tibetan Plateau is the largest and highest plateau situated between Mt. Kunlun in the north and Himalayas in the South. Bolivian Plateau in the Andes mountain range, Mexican plateau between the eastern and western Sierra Madre mountain range, are other examples.

 

(b) Piedmont Plateaux:

Plateau formed at the foothill zone of extensive mountains e.g. Piedmont plateau at the eastern margin of Appalachian mountain range and Patagonian Plateau in the east of Andes.

 

(c) Dome Plateaux:

Ozark Plateau of U.S.A., Chhotanagpur Plateau of Jharkhand.

 

(d) Lava Plateaux:

Deccan Plateau, Columbia Plateau (USA).

 

TYPES OF PLATEAUX ACCORDING TO GEOGRAPHICAL LOCATION

1. Intermontane Plateaux:

Tibetan Plateau, Mexican Plateau, Iranian Plateau (between Zagros and Elburz), Anatolian Plateau (between Pontic and Taurus).

 

2. Border Plateaux:

Pedimont Plateau (USA), Patagonian Plateau (Argentina).

 

3. Continental Plateaux:

Arabian Plateau, Peninsular Indian Plateau, Australian Plateau, South African Plateau, Mexican Plateau, etc.

 

4. Coastal Plateaux: Coromandel coastal upland of India.

 

TYPES OF PLATEAUX BASED ON STAGES OF EROSION

1. Young Plateau:

Colorado Plateaux (USA),

Idaho Plateaux (USA),

Khandala upland (India), etc. In these plateaux rivers form deep and narrow valleys through vertical erosion.

 

2. Mature Plateaux:

Ranchi Plateau, Appalachian Plateau.

 

3. Old Plateaux:

Agents of denundation erode it to their base level and the plateau appears as a featureless plain, except for some Monadnocks which are steep-sided resistant rocks surviving the onslaught of erosion. Precise examples are difficult to find.

 

4. Rejuvenated Plateaux:

These are formed due to the upliftment of an old plateau, e.g. Missouri Plateau (USA).

 

PLAINS

  • Plain is an extensive tract of flat land or a gently undulating terrain without prominent hills or depressions.
  • Plains are major centres of population concentration in the world.
  • They are categorized as:

 

1. DIASTROPHIC PLAINS

  • Plains are seldom formed by a single process.

 

  • Diastrophic forces have played a dominant role in the evolution of the Great Plains of USA; hence they are called diastrophic plains.

 

2. EROSIONAL PLAINS

(i)   River Eroded Plains:

  • Peneplains are regarded as the end-product of normal cycle of erosion (Fluvial cycle or erosion).

 

(ii)  Glaciatic Plains:

  • Plains of the northern part of North America and Western Europe are dominated by the imprints of glacial features.

 

  • The Ladakh plain of India in the east of Shyok river is also a glacial-eroded plain.

 

(iii) Wind-Eroded Plain: Wind-eroded plains of Sahara (Africa).

 

(iv) Karst Plains: Plains of Yugoslavia (Karst region), Chitrakoot (India).

 

3. DEPOSITONAL PLAINS

 

(i) River-Deposited Plains:

These include the Piedmont Alluvial Plains formed in the foothill zones (e.g. Bhabar and Terai of Ganga – Yamuna plain), flood plains formed due to deposition of fine sediments in the flood affected areas and Delta plains at the end of the river course (e.g. Ganga-Brahmaputra delta).

 

(ii) Lacustrine Plains: Formed by the filling up of lakes with sediments. Kashmir valley is regarded as a lacustrine plain.

 

(iii) Lava Plains: Formed of thin sheets of lava coming through fissure eruption, e.g. lava plains of Iceland, Argentina, New        Zealand, etc.

(iv) Wind-Deposited Plains: They include sandy desert plains and loess plains, e.g. the Thar desert plain, Sahara desert, Loess plain of China.

 

(v) Glacially-Deposited Plains:

Plains of North Germany, N.W. Russia, etc.

  • Imphal Basin is an example of Lacustrine plain.

 

  • Uplifted Peneplains are found in the Appalachian region (USA) and Chhotanagapur region of Jharkhand (India).

EXOGENETIC OR GEOMORPHIC PROCESSES

Major geomorphic processes include weathering, mass wasting and erosion.

WEATHERING

The process of disintegration and decomposition of rocks in-situ (at their places, involving no transportation) due to mechanical and chemical processes is called weathering.

 

TWO TYPES OF WEATHERING

The work of weathering can be grouped into two broad categories:

 

1. Physical or Mechanical Weahering

When rock is broken and disintegrated without any chemical alteration, it is called physical weathering. It can take place in several ways:

(a) Thermal Expansion and Contraction.

 

(b) Frost Action.

 

(c) Biotic Action.

 

2. Chemical Weathering

In chemical weathering, rocks decompose and disintegrate due to chemical reaction. The main chemical weathering processes are:

(i) Solution

(ii) Oxidation

(iii) Hydration

(iv) Hydrolysis

(v) Carbonation

 

EFFECT OF CLIMATE ON WEATHERING

  • Physical weathering is more important in hot and dry climatic regions because of high diurnal range of temperature found here.

 

  • Intensive chemical weathering occurs in hot and humid regions.

 

  • Chemical weathering is minimal in deserts and polar regions.

 

  • Weathering is at its minimum in the polar regions due to permanent ice-cover.

 

  • Both physical and chemical weathering are prevalent in the Monsoonal regions (e.g. India).

 

  • Carbonate rocks having more soluble minerals are easily affected by chemical weathering.

 

  • Rocks having horizontal beds are more compact and less vulnerable to weathering.

 

  • Climate is thus, the single most important factor influencing weathering.

EROSION

  • Erosion refers to those processes of denundation which wear away the land surface by mechanical action of the debris which is being transported by the various agents of erosion (glaciers, winds, rivers, marine waves and currents).

 

  • Running water is the most important agent of erosion. The processes involved in the erosional activities are:

 

(i) The acquisition of weathered material.

(ii) Wearing away of the surface through impact of rock materials in transit and in some cases by solution.

(iii) The breaking down of rock particles by mutual wear and tear.

(iv) Transportation of the acquired rock debris by moving medium.

 

DRAINAGE SYSTEM AND PATTERNS

DRAINAGE SYSTEM

 

Drainage Systems are divided into two broad categories:

 

1. SEQUENT DRAINAGE SYSTEM

System of streams which follow the regional slope and are well adjusted to the geological structure is called sequent drainage system.

 

(i) Consequent Streams:

The initial streams that originate in a particular region in accordance with the initial slope of the land are called consequent streams.

 

(ii) Subsequent Streams:

The streams originated after the consequent stream and joining the master consequent at right angles are called subsequent streams.

 

(iii) Resequent Streams:

Streams which flow in the direction of the initial consequent stream but join the subsequent streams, thereby developing in response to a new base level.

 

(iv) Obsequent Streams:

Streams flowing in a direction opposite to that of the dip of the rock strata, i.e. opposite to the master consequent stream.

 

2. INSEQUENT DRAINAGE SYSTEM:

The streams which do not follow the regional slope and are not adjusted to geological structure are called insequent streams.

 

(i) Antecedent Drainage:

A river that has been able to maintain its direction of flow despite the tectonic uplift of land across its course is known as antecedent river.

(ii) Superimposed Drainage:

When the nature and characteristics of the valley and flow direction of a consequent stream developed on the upper geological formation and structure are super imposed on the lower geological formation of entirely characteristics, it is called superimposed drainage.


  • The Son river flowing across the Rewa Plateau (M.P.) is a typical example of superimposed drainage.

 

DRAINAGE PATTERNS:

(i) Dendritic Pattern:

In this, the network of streams resembles the shape of a tree with its branches.

 

(ii) Trellis Pattern:

In this pattern, the rivers form a net like system and the tributary stream of each class flows roughly parallel to each other, e.g. Appalachian reason of U.S.A.

 

(iii) Rectangular Pattern: Though resembles trellis pattern, it differs from the trellis in that confluence of the tributaries is determined by faults and joints of the underlying rocks and streams are widely spaced and are more irregular than the trellis.

 

(iv) Radial Pattern: It is a pattern of outflowing rivers away from a central higher point. Some structures, volcanic cones and isolated upland tend to develop this pattern, e.g. Sri Lanka, Hazaribagh plateau, Kathiwar peninsula, Mikir range, etc.

 

(v) Annular Pattern: This pattern, also known as circular pattern, is formed over a mature and directed dome characterized by a series of alternate bunds of hard and soft rocks, guiding the tributaries to take a circular path.

 

(vi) Parallel Pattern: Here the master and tributary streams are parallel to each other, guided by the pronounced slopes, parallel faults or parallel topographic features, e.g. streams of western coastal plain of India.

 

(vii) Barbed Pattern: Generally developed due to river capture, this pattern comprises tributaries flowing in the opposite direction to the master stream.

 

MAJOR LANDFORMS AND ATMOSPHERE

FLUVIAL LANDFORMS (RIVER ACTION)

Erosion by the river involves the processes of:

(i) Attrition:

Rock fragments carried by the river strike and roll against each other.

 

(ii) Corrosion/Abrasion:

River, along with the bed wears its bed & banks.

 

(iii) Corrosion:

The river water dissolves the minerals in soluble rocks.

 

(iv) Hydraulic Action:

The sheer weight of the water itself wears away the bed and banks.

LANDFORM IN THE UPPER COURSE OF THE RIVER

(i) Deep, Narrow V-shaped Valley:

It is formed as the swift flowing river erodes its bed faster than the sides.

 

(ii) Potholes:

The grinding action of the pebbles caused the swirling action of water deeper the circular depressions in the river bed forming potholes.

 

(iii) Inter-locking Spurs:

It is caused by vertical river erosion where spurs alternate on each side of the river as if they are interweaving.

 

(iv) Waterfalls & Rapids:

They are formed when the erosion caused by the river steepens its valley suddenly forcing the water to jump or fall over the steep slope or when river water plunges down the edge of a plateau, e.g. the Angel Falls on River Rio, Caroni Falls in Venezuela (highest in the world), the Niagara Falls (USA) etc.

 

(v) Gorges & Canyons:

These are deep, narrow I-shaped valleys having very steep sides, formed due to vertical corrosion in the upper course of the river. Canyons are usually found in arid areas, and are narrower and deeper than gorges, e.g. Grand Canyon of USA cut by River Colorado.

 

(vi) River Capture or River Piracy:

The river that is more powerful captures the headwaters of a weaker river by headword erosion i.e. towards its source.

 

FETAURES IN THE MIDDLE COURSE OF THE RIVER

(i) V-Shaped Valley:

An open V-Shape valley due to valley widening caused by reduced river gradient and velocity.

 

(ii) Alluvial Fans:

When river descends from the mountains to the plains, steep fall in river gradient forces the river to deposit its sediment in a fan shape, called alluvial fans.

 

(iii) Meanders:

In the middle course, due to reduced slope and increased volume of water, the river resorts to pronounced meanders.

 

(iv) OX-bow Lakes:

It is a crescent shaped lake, once been part of river-meander cut through by lateral erosion of the banks at the meander neck.

 

(v) Floodplains:

A flat tract of land mainly in the middle and lower courses, consists of alluvium deposited by the river.

 

(vi) Natural Levee:

In times of flood, sediment is deposited along the banks and in the channels, elevating the  channel and the bank. These raised banks are known as natural levee.

 

FEATURS IN THE LOWER COURSES

(i) Braided Rivers:

Due to reduced gradient and sediment carrying capacity, large amount of deposited material on the river bed cause the river to divide and move around these barriers, resulting in braiding.

 

(ii) Delta:

It is a deposit of sediments formed at the mouth of the river where it enteres a lake or sea.

TYPES OF DELTA

(i) Arcuate Delta:

Fan shaped, convex towards sea, e.g. Nile, Ganga, Hwang-Ho, Rhine, Meckong, Niger etc.

 

(ii) Digitate/Bird’s Foot Delta:

Finger like pattern reflecting the number of distributary streams, e.g. Mississippi river delta.

 

(iii) Estuarine Delta:

Develops at the mouth of a submerged river, long and narrow, e.g. deltas of Amazon, Congo Ob, Vestula, etc.

 

(iv) Cuspate Delta:

Tooth shaped symmetrical delta formed generally over a straight coastline, e.g. delta of Ebro (Spain), Tiber (Italy), etc.

 

GLACIAL LANDFORMS

EROSIONAL PROCESSES

(i) Abrasion:

In this the glacier scratches, scours & polishes the valley floor through its debies.

 

(ii) Plucking:

Detaching or tearing away of large particles of rocks by the moving glaciers.

 

EROSIONAL LANDFORMS

(i) Cirque / Corrie:

An armchair-shaped depression surrounded by stseep headwall & sidewalls.

 

(ii) Aretes & Horns:

Sharpened peaks resembling saw-teeths and formed due to recession of cirques of both sides called Aretes. A pyramidal or triangular-faceted peak formed due to recession of three or more cirques is called Horn.

 

(iii) Nunatak:

Higher peaks & mounts surrounded by ice from all sides.

 

(iv) Roches Moutonnees (Sheep rocks):

Asymmetrical hillocks having onset side smoothly muolded with gentle slope and steeper, rougher Ice side (Steepened due to plucking).

 

(v) Crag & Tail:

A hill having vertical eroded steep upglacial side and tail like down glacial side.

 

(vi) Glacial Stairways:

Glaciated benches, separated by nearly vertical cliffs. Smaller depressions at the base of a cliff are called paternoster lakes when filled with water.

 

(vii) Hanging Valley:

These are valleys of tributary glaciers which join the main glacial valley of much greater depth.

 

DEPOSITIONAL LANDFORMS

(i) Moraine:

A ridge like accumulation of material which has been transported and deposited by ice.

 

(ii) Drumlin:

Whaleback hillock of glacial drift looking like an inverted boat or spoon having steeper upglacial slope, also known as ‘basket of egg’ topography.

 

(iii) Eskers:

Long, low, narrow ridges composed of stratified sand, silt & gravel.

 

(iv) Kame:

A steep-sided alluvial cone deposited against an ice front.

 

(v) Erratics:

Large rock fragments transported away from its place of origin and deposited in an area of dissimilar rock type.

 

(vi) Outwash Plain:

Formed from glaciofluvial material carried out from the front of an ice sheet by meltstream, appear as extensive accumulation of gravel, sand and silt.

AEOLIAN LAND FORMS (WIND ACTION)

EROSIONAL PROCESSES

(i) Abrasion: Air currents armed with sand grains scrap, polish or etches away rock surfaces.

 

(ii) Attrition: Mutual wear & tear of rock and sand particles.

 

(iii) Deflation: Lifting and blowing away of loose materials from the ground.

 

LANDFORMS OF WIND EROSION

(i) Rock Pedestals or Mushroom Rocks:

Mushroom shaped rock pillars which have been eroded near their bases.

 

(ii) Zeugen:

Ridge and furrow landscape formed in horizontal layers of hard and soft rocks.

 

(iii) Yardangs:

Here, of the vertically arranged hard and soft rocks, softer rocks are eroded giving rise to long, narrow corridors, separating the steep-sided over hanging ridges called Yardangs.

 

(iv) Mesas and Buttes:

In rocks composed of horizontal layers of hard and soft rocks, hard stratum forms a flat tabular hill of resistant rock, called Mesa. Mesas reduced in area after long period of denundation are called Butte.

 

(v) Deflation Hollow:

Wind erosion excavates the hollow by blowing away the loose material from the surface.

 

(vi) Inselbergs:

An isolated hill rising abruptly from the level ground having steep sides and rounded summits.

 

LANDFORMS OF WIND DEPOSITION

(i) Sand Dunes:

They are formed by the deflation action of wind that deposit sand in ridges. Barchan is a famous dune which is of crescentic shape or moon shape and a special type of transverse dune. Another type, seif is a longitudinal dune.

 

(ii) Loess:

The fine dust blown beyond the desert limit is deposited on neighbouring land as loess. It is a yellow, friable material and is usually very fertile. Noted examples are found in North-west China and parts of Mid-west USA.

 

(iii) Bajada:

It is a depositional feature made up of alluvial material laid down by the intermittent streams in an arid environment. An erosional plain formed at the base of the surrounding mountain scarps is called the Pediment.

 

KARST LANDFORMS (UNDERGROUND WATER)

  • The word Karst is a comprehensive term applied to limestone, chalk or dolomite areas.

 

  • Most of the landforms are produced by underground water and the diversion of surface waters to underground routes, hence the terminology Karst Landforms.

 

EROSIONAL LANDFORMS:

(i) Lapies (Karren):

Highly corrugated and rough surface of limestone rocks, characterized by low ridges & pinnacles & numerous solution holes.

 

(ii) Solution Holes:

Sink holes or swallow holes are small depressions carved out by solution where chemically active rainwater sinks into the limestone at a point of weakness.

 

(iii) Polje:

It is a very large depression with steep sides and flat floor, believed to be formed due to downfaulting of rock strata.

 

(iv) Ponores (Aven):

The vertical pipe like charm or shaft that connects the caves and the swallow holes.

 

(v) Blind Valley:

The valley of that surface stream which disappears in limestone formation through a swallow hole and the valley look dry.

 

(vi) Caverns:

Caverns are voids of large dimension below the ground surface.

 

(vii) Natural Bridge: These are chiefly formed due to collapse of the roofs or the caves.

 

DEPOSITIONAL FEATURES

(i) Stalactites:

A tapering pendant of concretionary material descending from a cave ceiling, formed due to deposition of calcareous solutes which are carried by water dripping through ceiling.

 

(ii) Stalagmites:

The solution that drops on the cave floor is also precipitated and crystallized and forms a columnar concretion ascending from the floor of a cave.

 

(iii) Pillar:

Stalagmites may eventually combine with stalactites to form pillars.


 

Comments   

 
+2 #1 Peter Silungwe 2013-12-17 08:44
excellent stuff
Quote | Report to administrator
 

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