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GEOMORPHOLOGY

Making of Earth

Following theories have been proposed:

1. Continental Drift Theory

It was given by Alfred Wegner in 1912.

Approach:

The terrestrial land found on this Earth in the form of different continents was earlier a single land mass called as Pangea while the ocean was called as Panthla Sea. Pangea started breaking up due to gravitational force and tidal force and led to the formation of various continents.

Evidence to support this theory:

• Jigsaw fit – South America and Africa continent show similarity on its pacific coast
• Similarity of geographical features of Appalachian mountains and Britney peninsula
• Similarities of fossil species belonging to same biological group were found in different continents. For e.g. Same fossil was found in Australia, South America, and Africa
• Grooves study  – The features of grooves were similar in Antarctica and South America

Limitations:

• The forces mentioned by Alfred Wegner were extremely weak as these forces cannot bring such a big drift
• The jigsaw fit was not applicable to all the parts of the continents especially to North America and North Europe

 

2. Convection Current Theory

This theory was given by Arthur Holumes.

Approach:

According to this theory the various relief features on the surface of the earth are being made due to the movement of thermal current in the Mantle part due to the temperature difference which led to the moving of the plates.

Limitations:

It was unable to explain the formation of various features like Himalayan Mountain, Ocean, and Rift Valley

 

3. Sea Floor Spreading Theory

This theory was given by Robert Diat and Hess.

Approach:

The volcanic eruptions took place in marine ecosystem (ridges). The ruptured lava extended which led to the spread of the ocean while the ocean boundary got consumed in the subduction zone.

Evidence to support this theory:

• Mid Ocean Ridges found in the Ocean
• The study of mid oceanic ridge of Atlantic Ocean in which the edge of the ocean floor on both sides of ridge have a similar pattern
• Magnetic Polarity was found similar on both sides of the ridge

Limitations:

It was only able to explain the sea bed topography while the terrestrial topography remains unexplained.

 

4. Plate Tectonic Theory

This theory was given by W.J.Morgan and Mechansy

Approach:

According to this theory there are 2 types of plates called as continental plate and oceanic plate. These plates float over ‘esthinosphere’ (upper part of mantle and lower part of crust). These plates have movement either parallel or against each other which led to the formation of various relief features on the surface of the earth and sea floor.

Evidence to support this theory:

It explained the formation of Mid Oceanic Ridge, Rift Valley, Block Mountain, Young fold Mountain, Volcanic Mountain

Limitations:

• The folded mountain of Australia was not being explained by this theory
• It could not explain why spreading of ridges occur generally in Atlantic Ocean while subduction was confined to Pacific Region
• It could not explain the double trench concept

Major Plates in the World

1. Antarctica plate
2. North American plate
3. South American plate
4. Pacific plate
5. Indo-Australian-New Zealand plate
6. African plate
7. Eurasian plate

Geomorphic Process

Due to the continuous influence of external and internal forces, the formation and deformation of landforms on the surface of the earth are continuous processes. The internal and external forces causing stresses and chemical action on earth materials and bringing about changes in the configuration of the surface of the earth are known as geomorphic processes.

The energy emanating from within the earth is the main force behind endogenic geomorphic processes. This energy is mostly generated by radioactivity, rotational and tidal friction and primordial heat from the origin of the earth.

Geomorphic Agents

Glciers, Groundwater, running water, the wind, waves, currents are called geomorphic agents

Types of Movement

1. Diastrophic Movement (slow in nature)

Diastrophic forces refer to forces generated by the movement of the solid material of the earth’s crust. All the processes that move, elevate or build portions of the earth’s crust come under diastrophism.

• Orogenic processes involving mountain building through severe folding and affecting long and narrow belts of the earth’s crust.
• Epeirogenic processes involving uplift or warping of large parts of the earth’s crust.
• Earthquakes involving local relatively minor movements.
• Plate tectonics involving horizontal movements of crustal plates.

2. Sudden Movement

Examples are Earthquakes and Volcanoes

Movement of Plates

Continental Plate is made up of Granite while Oceanic Plate is made up of Basalt. Therefore Oceanic Plates are heavier or have higher density than Continental Plates.

INTER PLATE MOVEMENT

Converging Plate Boundaries

source: www.cotf.edu

In this, plate moves opposite in direction to each other

1. Continental-Continental Plate Convergence

Folded Mountains are formed

E.g. Alps Mountain, Caucasian Mountain, Zagros Mountain, Hindukush Range, Himalayan Mountain,  Arakayoma Range.

Features:

• No Volcanic activity takes place
• High intensity of earthquake occur in this region having a deep foci

 

2. Continental-Oceanic Plate Convergence

Formation of Volcanic Mountain

E.g. Rocky Mountain, Andes Mountain

Features:

• Low intensity of earthquake
• High volcanic activity takes place

 

3. Oceanic-Oceanic Plate Convergence

Leads to the formation of Trenches (since oceanic plates are of higher density than continental plates)

E.g. Mariana Trench

 

Hotspot Island

When continental plate moves over volcano of an ocean and due to the eruption of that volcano small island is formed. Those islands are being called as the hotspot island. E.g. Islands of Pacific Ocean

 

Diverging Plate Boundaries

In this, plate moves away from each other

1. Oceanic-Oceanic Plate divergence

Formation of mid oceanic ridge

E.g. Mid Atlantic Ridge

 

2. Continental-Continental Plate divergence

Formation of nascent sea

E.g. Red Sea

 

Transforming Plate Boundaries

In this, two plates move parallel to each other therefore it doesn’t form any landform but this area becomes prone to earthquakes. E.g. Californian Plate

 

INTRA PLATE MOVEMENT

Movement occur within the plate

1. Formation of Block Mountain

When certain part of plate gets subducted, the remaining part that stands as it is forms Block Mountain.

E.g. Vindhyas and Satpura Range, Drakensberg Mountain

The subducted part in intra plate is called rift valley.

E.g. East Rift Valley and West Rift Valley in Africa

 

2. Formation of Nascent Sea

E.g. Caspian Sea