DON BOSCO SCHOOL, BERHAMPORE

SUB: GEOGRAPHY

CH-5II. Structure of the Earth

Landforms of the Earth

❑A landform is a natural

or artificial feature of the

solid surface of the Earth

or other planetary body.

❑Landforms together

make up a given terrain,

and their arrangement in

the landscape is known

as topography.

MOUNTAINS

The Three Most Recent Orogenics Are :

The Caledonian period-

▪ Period- about 350 million years ago.

▪ Raised the mountains of Scotland and Scandinavia.

▪ At one times these were very striking & now worn down.

The Hercynian period-

• Period- about 240 million years.

• Characterized by ranges (Ural Mountains, the Pennines and Welsh Highlands of Britain,

the Harz Mountains in Germany and the Appalachians of America)

The Alpine period: ▪ Major orogenic and recent period (30 million yrs ago)

▪ These young fold mountains buckled up and consist of the Alps, Himalayas, Rockies and Andes (Alpine System)

▪ Thrust on a gigantic scale.

▪ Peaks are several thousand metres high.

Three broad categories of mountains:

❑ Mountains of Elevation or Upliftment: 1. fold mountains

2. mountains caused by faulting

or the Block mountains.

❑ Mountains of Accumulation.

❑ Mountains of Erosion or Residential Mountains.

(For details follow page-35)

Types of Mountains

Fold Mountains

Block Mountains

(Horsts)

Residual

Mountains

1. Fold mountains:

• They have a great thickness of sedimentary rocks compared to rocks of the same age in adjacent regions.

• Massive granitic intrusion occur up to several km in length and with the direction along the trend of the

mountain ranges.

• They have a great thickness of sedimentary rocks compared to rocks of the same age in adjacent regions.

The maximum thickness of Mesozoic and Cenozoic rocks is over 10km in the Alps ,barely 2km to the north

of young fold mountain zone.

• Massive granitic intrusion occur up to several km in length and with the direction along the trend of the

mountain ranges.

• Structural features are related to conditions of intense pressure and include large scale recumbent fault

,nappes and Thurs, w high causes great wedges of rock to travel over the top of younger rocks

• Recurrent seismicity is the most prominent phenomenon experienced by orogenic belts. These earthquakes

are expression of the release of stresses building up in the orogenic

• High heat flow ,which is manifested in the volcanic activity ,which it nested in the Zagreb, Malian, Central

Burma ,Indonesian arc and Circum-Pacific Rockies, Andes and Japanese,Philippines and New Zealand

mountain belts.

FOLD MOUNTAINS:

FEATURES OF YOUNG FOLD MOUNTAIN:

❑Himalayas are called young fold mountains because they began

forming in the late Cretaceous - Tertiary period and continue to

increase in elevation even today.

❑They are called fold mountains due to the compressive

forces involved in the collision of the two continental plates - the

Asian and the Indian / Australian.

❑It is the northern most and continuous range.

❑It consists of lofty peaks like Nanda Devi and Kanchenjunga.

❑It is snow-bound and consists of glaciers.

❑It is symmetrical in nature and is composed of granite.

Young Fold Mountains

The Himalayas

Young fold mountains Old fold mountains

• They are of recent origin. • They have been formed long ago.

• They are higher than the old fold

mountains.

• They are lower than the young fold

mountains.

• Most of the young fold mountains

have pointed peaks.

• These mountains generally do not have

pointed peaks due to erosional activities of

exogenic forces. They have rounded peaks.

• These have steeper slopes and

deeper valleys.

• Due to the erosional activities of the exogenic

forces, these mountains have gentle slopes.

• The Himalayas, the Andes and the

Rockies mountains are some

examples of young fold mountains.

• The Aravali Range, the Appalachian and the

Ural Mountains are some examples of old

fold mountains.

Difference between Young Fold Mountain & old Fold Mountain

Circum-Pacific Mountain Belt

* Found along the margins of the Pacific Ocean.

* Includes the Andes ranges of S.A., the Rockies of N.A. &a series of eastern Asia.

* Rich in mineral resources.

Mid-World Mountain Belt:

* Includes the Alps, associated ranges in Europe, etc.

* Continued by the Himalayas & the associated ranges Indonesian islands.

* Relatively unstable portions of the earth’s crust.

(For details follow page-37)

1I. BLOCK MOUNTAINS OR HORSTS

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•

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•

(For details follow page-38)

111. RESIDUAL MOUNTAINS:

❑ Residual mountains are those mountains which

have been eroded by the agents of degradation

such as winds, rain, frost and running water.

❑ The hard rocks that are left behind are called

residual mountains.

❑ The Sierras of central Spain and Mesas of USA

are some examples of residual mountains.

❑In India the Aravalli Mountain

and the Parasnath mountain of Bihar belong to this

type.

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❖ Now turn to page no.-34 and have a thorough reading till page no.-39 (before types of plateaus start).

❖While reading, mark the new words and important sentences with a pencil.

❖ Go through the slides given today attentively.

❖ After completing your reading nicely do the assignments that follow below:

ASSIGNMENTS:

1. Give the definition of:

a) Normal fault b) Intermontane plateau c) Peak d) Geomorphology

2. How many types of mountains are there? Explain each of them giving examples.

3. How can you define Young Fold mountain?

4. Show the difference between Block mountains & Residual Mountains with examples.

✓

✓ Rimi Ghosh

Shreya Saha