Geography: Our Changing Earth, Grade 7 CBSE

1. OUR CHANGING
EARTH
KICKSTARTER
TUTORIALS
STD VII

2. KICKSTARTER TUTORIALSKICKSTARTER TUTORIALS

3. CHANGES IN THE EARTH SURFACE
Mountains Volcano Mushroom Rock
Delta Sea Arches Sand Dunes

4. The changes on the Earth surface
is due to two types of forces.
1. ENDOGENIC (Endogenous) FORCE
2. EXOGENIC (Exogenous) FORCE

5. ENDOGENIC (Endogenous)
FORCES

6. It refers to the forces that occur beneath the
surface of the Earth.
• Deep inside the earth’s core, heat is generated.
• The heat is transferred upward to the mantle causing
it to slowly circulate.
• This movement of the lava applies force on the
lithospheric plates above. These plates keep shifting
and sliding at a very slow speed of a few mm in a year in
different directions. The movement of these plates is
called Tectonic Activity or Plate Tectonics.
ENDOGENIC (Endogenous) FORCE

7. ENDOGENIC (Endogenous) FORCE
Endogenic Force causes -
Earthquake, Tsunami, Volcano and
change in the earth’s landscape.
There are 20 lithospheric plates of different sizes.
These are commonly known as Tectonic plates.

8. The earth's crust is cracked and the pieces of the Earth's
crust formed by the cracks are called tectonic plates.
The plates are continually moving (albeit very slowly, a few
millimetres a year) and this movement helps to form
volcanoes.
These tectonic plates can be seen in this map.

9. An earthquake is a sudden tremor or movement of the
earth’s crust, which originates naturally at or below the
surface.
What causes earthquakes ?
Sudden movement of tectonic plates.
Earth surface is subjected to endogenic forces
occurring from beneath the earth’s surface. This
force makes the plates move at a very slow speed.
However a sudden movement of tectonic plates
triggers an earthquake.
Seismometer or Seismograph records earth movements.
1. EARTHQUAKE

10. KICKSTARTER TUTORIALS
Focus or Hypocentre
EARTHQUAKE – Focus & Epicentre
It is the point of origin of
the earthquake. Sudden
movement occur deep
below the crust or mantle
causing tectonic plates to
move vigorously.
Concentric shock waves
generated from this point
determines the extent of
damage caused.
(Since the Focus point is often
deep below the surface, it is
difficult to map.)

11. KICKSTARTER TUTORIALS
Epicentre
• It is the point on the earth surface which is
directly above the focus.
• It is most commonly used to describe the
point of concentration of an earthquake.
The strength and magnitude of an earthquake is
measured on the Richter Scale. An earthquake whose
measurement is above 7 on the Richter Scale can cause
major damages.
Earthquakes are now measured using the Moment
Magnitude Scale (or simply Magnitude scale). This
measures the size of the seismic waves during the
earthquake.

12. Tsunami
When the epicentre of earthquake
is in sea bed, it cause huge tidal
waves which could have
devastating effect on sea shores.
Such phenomenon is known as
Tsunami.

13. Tsunami

14. 2. VOLCANO
A volcano is an
opening, or
rapture, in a
planet’s surface,
which allows
hot, molten rock,
ash and gases to
escape from
below the
surface.
Volcanoes are most commonly
found along plate boundaries.

15. Mountain ranges & trenches –
Slow movement of lithospheric plates causes
change on the earth’s surface. Collision of plates
3. Change on the earth’s surface
creates mountain
systems of earth
like the Himalayas
and huge
trenches on the
ocean floor.

16. KICKSTARTER TUTORIALS

17. SUMMARY
ENDOGENIC (Endogenous)
FORCE
1.It occurs beneath the
surface of the Earth.
2.It causes natural
devastation & physical
change in the earth’s
surface , like
earthquake, volcanoes &
formation of mountains
or valleys.

18. EXOGENIC (Exogenous)
FORCES

19. EXOGENIC (Exogenous) FORCES
It refers to the external phenomena
that occur on or above the earth’s
surface.
The main elements of exogenic forces are
–
AIR & WATER

20. Waterfall are often formed where a layer of harder
rock overlays a layer of softer rock.
WATERFALL
Harder rock
Softer rock

21. As the river passes over the softer rock, it is able to
erode it at a faster rate, forming a step in the river
bed.
WATERFALL
Harder rock
Softer rock

22. The force of hydraulic action does two things:
Further erosion makes the plunge pool and notch
bigger over time.
WATERFALL
Harder rock
Softer rock

23. As the notch grows, eventually there isn’t enough
support under the harder rock and so it collapses
into the plunge pool.
WATERFALL
Harder rock
Softer rock

24. WATERFALL
The processes of erosion continue, further eroding
out the notch and plunge pool. Eventually the
harder rock above will collapse again, meaning that
the waterfall will retreat upstream over time.
As it retreats,
it leaves
behind a
steep sided
gorge.

25. Why do river curves

26. • Rivers cause change on the surface over
which it flows.
RIVER
> Meanders – It is a
snaking pattern of
water stream formed
by alternatively
eroding sediments
from the outside of a
bend and depositing
them on the inside.

27. > Ox-bow lake –
An oxbow lake is a U-shaped
body of water that forms
when a wide meander from
the main stem of a river is cut
off, creating a free-standing
body of water.
This landform is so named for
its distinctive curved shape,
resembling the bow pin of
an oxbow.
bow pin of an oxbow

28. Floodplain – A floodplain is a generally flat area of
land next to a river or stream. It stretches from the
banks of the river to the outer edges of the valley.
Flood plains are natural flooding outlets for rivers.

29. Agriculture remains a critical industry for flood plains
today. The silty sediment is rich in nutrients that support
plant growth. (This farmer is harvesting on the fertile
flood plain of the Omo River in Ethiopia)

30. As it takes more energy
to carry large particles,
these are deposited first
and therefore build up
along the banks of the
river to form a natural
embankment which are
called levees. The levee
will become higher
every time the river
floods.
> Levees - In times of flood a river may overflow its banks
and spread over the flood plain. As it does so it loses
energy and deposits its material across the flood plain.

31. Levees

32. Delta
Deltas are formed at the mouth of a river where the river
flows into the ocean or other water body. When a river
carrying sediments reaches a body of standing water,
it reduces its velocity
causing it to deposits the
sediments at the mouth.
Over time these sediments
builds up to rise above the
surface of water. The river
then cuts across the land
and forms different
branches. These branches
are called distributaries.

33. Bay of Bengal Delta

34. EXOGENIC (Exogenous) FORCES
 Sea caves – continuous wave action of
the sea erodes the rocky faces on the sea
shore to form caves.
 Sea arches – over a period of time a sea
cave convert into sea arch with increased
erosion in the rock.
 Stack – Stacks are formed when part of a
main landform is eroded by water action,
like water crashing against the rock.
 Sea Beaches – Sea waves leave behind
sediments in the form of fine sand at these
places are called beaches.
Sea waves also create various changes in landforms.

35. GLACIER
• Glacier are
accumulation of snow
that are formed in areas
where the amount of
snow that falls exceeds
the amount that melts.
• Glacier form distinct
landforms that looks like
frozen river moving
slowly over some land
surface or down a valley.

36. Glacial Moraines
Moraine is
sediment
deposited
by a glacier.

37. Wind flowing over a long period create
different forms.
AIR (WIND)

38. Mushroom Rocks –
Usually found in deserts
areas. The wind blowing at
high speed takes with it sand
particles. The particles being
heavier remain close to the
surface and as wind passes
along the rocks the sand
particles erodes the portion
of rock closer to the surface
without affecting the upper
portion. This gives the rocks
a mushroom like shape.

39. Wind can create landforms when it
deposits its sediments, especially in
deserts and along coasts.
Sand dunes & Loess
are landscape features deposited by wind.

40. Sand Dunes –
A dune is a mound of sand
formed by the wind,
usually along the beach or
in a desert. Dunes
form when wind
blows sand into a
sheltered area behind an
obstacle. Dunes grow as
grains of sand accumulate.
Every dune has a
windward side and a
slipface.

41. Loess –
It is a sedimentary deposit
of mineral particles which
are finer than sand but
coarser than dust or clay,
deposited by the wind.
Loess is a type of silt which
forms fertile topsoil in some
parts of the world. Loess
deposits are usually a few
meters thick. The soil has
few clay particles to hold it
together.

42. EXOGENIC (Exogenous)
FORCE
1.It occurs above the
surface of the Earth.
2.It causes physical
change in the earth’s
surface , like Sea
arches, mushroom
rock, sea shore,
sand dunes, etc.
ENDOGENIC (Endogenous)
FORCE
1.It occurs beneath the
surface of the Earth.
2.It causes natural
devastation & physical
change in the earth’s
surface , like
earthquake, volcanoes
& formation of
mountains or valleys.

43. Question & Answer
1. What cause Tsunami ?
2. List two causes of earthquakes.
3. What is volcano?
4. What are exogenic forces?
5. Where and where is ox-bow lake formed?
6. How are sea arches formed?
7. How are sand dunes formed?
Give Reason.
1. Formation of Mushroom rocks in deserts.
2. Earth surface is not a consistent state.
Answer the following in detail.
1. How is delta formed? Draw a neat and labelled diagram of delta.
2. Explain the depositional work of glacier.
3. Explain the erosional and depositional work of wind.
4. How are sea caves and arches formed?

44. 1. What cause Tsunami ?
A tsunami is a large ocean wave that is caused by sudden
motion on the ocean floor. This sudden motion could be an
earthquake, a powerful volcanic eruption, or an underwater
landslide.
2. List two causes of earthquakes.
An Earthquake is a sudden tremor or movement of the earth's
crust, which originates naturally at or below the surface.
There are two main causes of earthquakes.
1. They can be linked to explosive volcanic eruptions; they are
in fact very common in areas of volcanic activity where they
either proceed or accompany eruptions.
2. They can be triggered by Tectonic activity associated with
plate margins and faults. The majority of earthquakes world
wide are of this type.
Question & Answer

45. 3. What is volcano?
4. What are exogenic forces?
5. Where and where is ox-bow lake formed?
This is formed when a wide meander from the main stem of a
river is cut off to create a lake. This is called ox-bow lake for its
distinctive curved shape that results from this process.
6. How are sea arches formed?
This is formed by the process of erosion
7. How are sand dunes formed?
A dune is a mound of sand formed by the wind, usually along
the beach or in a desert. Dunes form when wind
blows sand into a sheltered area behind an obstacle.
Dunes grow as sediments of sand accumulate.
Question & Answer

46. Answer the following in detail.
1. How is delta formed? Draw a neat and labelled diagram of
delta.
Deltas are formed at the mouth of a river where the river
flows into the ocean or other water body. When a river
carrying sediments reaches a body of standing water, it
reduces its velocity causing it to deposits the sediments at the
mouth. Over time these sediments builds up to rise above the
surface of water. The river then cuts across the land and forms
different branches. These branches are called distributaries.
2. Explain the depositional work of glacier.
Like flowing water, flowing ice carry and deposits the rocks
and sediments. Rock and sediments freeze and stick to the
bottom of the glacier and get carried away by the flowing ice.
Glaciers deposit their sediment when they melt.
Question & Answer

47. Home Work
1. Explain the erosional and depositional work of wind.
2. Earth surface is not a consistent state. Explain

48. Give Reason.
1. Formation of Mushroom rocks in deserts.
2. Agriculture remains a critical industry for flood plains today.
Home Work

49. THANK YOU
KICKSTARTER TUTORIALS
46B, Jaydurga Nagar, Bomikhal, Bhubaneswar, Odisha.
Contact: 9438394565 / 7504193557