Class 11 Geography chapter 3 Interior of the Earth notes

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🌍 Interior of the Earth 🌎

Sources of information about the earth 

• Earth's radius is 6,370 km 
• Most of our knowledge about the interior of the Earth is based on estimates
• Yet , a part of information is obtained through direct observation and analysis of material

Direct source

• Things which are part of earth and analysed to get information about earth
• This includes surface rocks or rocks available from mining
• Scientist over world are working on two major projects . Deep ocean drilling project and Integrated ocean drilling project.
• The second source is through volcanic eruption.As the molten magma thrown into surface
• However, it is difficult to ascertain the depth of sources of such magma

Indirect sources

• Analysis of properties of matter indirectly provides information about the interior
• Like Temperature, pressure and density increases with depth
• Another are meteors which are believed to be made of same material as earth
• Other are gravitation, magnatic field and seismic activity
• The reading of gravity differ due to various factors . The difference is called gravity anomaly

Earthquake

• It is caused by release of energy in simple terms it is defined as the sudden shaking of earth

• Why does earth shake? 
• When the blocks gets deformed and slide past each other. This causes a release of energy and the waves travel in all directions causing earthquake
• The point where energy is released is called hypocentre or focus.
• The point on the surface perpendicular to the focus is called epicenter
  
  
  

• Earthquake waves 
• Earthquake waves are basically of two types 1. Body waves and 2. Surface waves
• As suggested by name body waves are generated at the focus and travel in all directions in the body of earth
• While when body waves reach to the surface they become surface waves
• The surface waves move along surface
• The denser the material the higher the velocity. The direction changes as well with different densities
• Body waves are further divided into two P waves and S waves
• Difference between p waves and S waves
• P waves are called as primary waves while S waves are called secondary waves
• P waves are first to arrive at surface while S waves arrive with time lag
• P waves can travel in all materials while S waves can only travel through solid
• P waves vibrate parallel to direction of waves while S waves vibrate perpendicular to the direction of wave 
• Surface waves
• They are last to be seen on seismograph 
• They are most destructive 

Emergence of shadow zone

• There are some specific areas where waves are not reported on seismograph. The zone is known as shadow zone
• Seismograph at any distance within 105 ° from epicenter will not record S waves
• Seismograph at any distance within 105 ° -145° from epicenter will not record P waves

Types of earthquakes

• (i) The most common ones are the tectonic earthquakes. These are generated due to sliding of rocks along a fault plane.
• (ii) A special class of tectonic earthquake is sometimes recognised as volcanic earthquake. However, these are confined to areas of active volcanoes.
• (iii) In the areas of intense mining activity. sometimes the roofs of underground mines collapse causing minor tremors. These are called collapse earthquakes.
• (iv) Ground shaking may also occur due to the explosion of chemical or nuclear devices. Such tremors are called explosion earthquakes.
• (v) The earthquakes that occur in the areas of large reservoirs are referred to as reservoir induced earthquakes.

Measuring earthquake

• Earthquake is measured by a device called as seismograph
• There are two scale for measuring earthquake
• 1. Richter scale it is numbered from 1-10 and earthquake is measured depending on the density of it
• 2. Mercalli scale it's numbered from 1-12 and earthquake is measured depending on the visible damage caused by it 

Effect of earthquakes

• (i) Ground Shaking
• (ii) Differential ground settlement
• (iii) Land and mud slides
• (iv) Soil liquefaction
• (v) Ground lurching
• (vi) Avalanches
• (vii) Ground displacement
• (viii) Floods from dam and levee failures
• (ix) Fires
• (x) Structural collapse
• (xi) Falling objects
• (xii) Tsunami
• Earthquake of high magnitude are quite rare and tiny ones occurs every minute

Structure of earth 

Earth has three layers

1. Crust

• Outermost solid layer
• Somewhere it is as thin as 5 km and somewhere it is as thick as 50 km 

     2. Mantle

• The portion from moho' s discontinuity to 2,900 km is mantle
• The upper portion of mantle called asthenosphere ( astheno meaning weak ) it is main source of magma
• The layer below asthenosphere is solid
• Lithosphere is made up of crust and upper mantle

    3. Core 

• The outer core is of liquid state while inner core is of solid state
• It is made of heavy metal like iron and nickel
• Which is referred to as nife layer
  

   
  
  

Volcanoes 

Shield volcanoes

• Largest of all volcanoes
• Hawaiian volcanoes are perfect example
• These volcanoes are made of basalt for this reason this volcanoes are not steep 
• They become explosive when water entre in them 
• They may develop in cinder cone

Composite volcanoes

• They have cooler eruption and more viscous lava than basalt
• The material accumulates and lead to formation of layers

Caldera

• They are most explosive volcanoes in the world
• When they erupt they collapse on themselves
• The depression are called caldera

Flood basalt

• They have highly fluid lava that travel long distances
• The Deccan trap of India are much larger basalt provinces 

Mid Oceanic ridge

• This volcanoes occur in ocean 
• They have frequent eruptions
• There is a system of mid oceanic ridge more than 70,000 km long

Volcanic landforms

 Intrusive forms

• Depending on the location of the cooling of the lava, igneous rocks are classified as volcanic rocks (cooling at the surface)
•  plutonic rocks (cooling in the crust).
•  The lava that cools within the crustal portions assumes different forms. These forms are called intrusive forms.
  
  
  

Batholiths

• A large body of magmatic material that cools in the deeper depth of the crust develops in the form of large domes.
• Batholiths are the cooled portion of magma chambers.

Lacoliths

• These are large dome-shaped intrusive bodies with a level base and connected by a pipe-likeconduit from below.
•  It resembles the surface volcanic domes of composite volcano
• The Karnataka. plateau is spotted with domal hills of granite rocks.

Lapolith

• When the laws forms a saucer shape concave to the sky it's called lapolith

Sill or sheet

• The horizontal deposit of Rocks are called sills or sheet
• Thinner one's are called sheets and thicker ones are called sills

Dykes 

• When lawa makes its way towards surface
• It cools down perpendicular forming structure called as dykes 
• This are found in western Maharashtra area 

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