Earthquake and volcanoes cause effect and distribution

1. Volcanoes & Earthquake
Mr. Toradmal Agastirishi B.
Asst. Professor
Department of Geography
Dada Patil Mahavidyalaya, karjat, Dist- Ahmednagar

2. SUDDEN MOVEMENT-
Tectonic movements like earthquakes and
volcanoes abruptly bring about changes in
the features of the earth's surface.
● Earthquake
● Volcanoes

3. ● Earthquake
Vibrations or tremors produced in the rocks of the earth's
crust are known earthquakes. As a pond of water
generates waves in all directions when struck by a stone,
similarly the elastic earth's crust also experiences tremors
due to sudden disturbance below the surface. Vibrations
or waves produced in the rocks travel outward from the
center of disturbance.

4. Types of Earthquake wave-
A) Primary waves
B) Secondary Waves
C) Surface wave

5. Causes of Earthquakes:
Earthquakes occur due to the following reasons :
1.Majority of the earthquakes occur along the fracture line
where slipping and settling down of rock masses takes place.
Stresses on the two sides of the fault accumulate and cause
bending of the rocks. When rocks can bear no more stress,
breaking with sudden displacement of the rocks on two sides
of the fault takes place. It produces a blow to the upper rocks
on one side of the fault-plane and to the lower rocks on the
other side. This theory is put forward by Prof. Reid and is
known £
as the elastic rebound hypothesis.

6. 2.According to some geologists, earthquakes
originate mainly in the mantle. In this zone,
continuous changes are taking place in the
crystalline structure of the silicate minerals due to
which localized energy increases. It is of an
explosive nature and causes earthquakes .
3.Earthquakes may also be caused by volcanic
eruption.

7. 4. Earthquakes also occur due to large scale
accumulation of sediments in the delta' regions,
e.g. the Mississippi delta.
An earthquake usually originates some kilometres
beneath the surface. The point in the crust at which an
earthquake occurs is known as the focus of the
earthquake. The point on the earth's surface situated
above the point of origin is known as the epicentre,
Vibrations spread in all directions from the focus of an
earthquake. They first reach the epicentre.

9. Earthquakes are recorded with the help of an instrument known
as a Seismograph. Seismographs are stationed on the flanks of
the volcano. These record the frequency, duration and intensity
of the earthquakes and report it back to the volcano observatory

10. Distribution of Earthquake
The Cir cum-Pacific Belt

11. Distribution of Earthquake
The Mid-world
Mountain Belt

12. No place on the earth's surface is totally free from
earthquakes but the earthquakes occur more frequently in
certain areas. These areas are the weak and unstable parts
of the earth's crust. These belts are as follows-
☺ The Cir cum-Pacific Belt :
This belt encircles the Pacific Ocean and follows the
western coast of North and South America, the Aleutian
Islands and the islands of the eastern coast of Asia like
Japan and Philippines. Nearly 68% of the 1
earthquakes of the world originate in this belt.

13. The Mid-world Mountain Belt :
This belt is associated with the young
fold mountain ranges of the Alps, the
Himalayas, and their continuation in the
South. East Asian islands. Nearly 21% of the
earthquakes of the world originate in this belt.

14. The Effects of Earthquakes
Apart from the immediate destruction of life and property,
earthquakes bring about several changes in the earth's
crust .
1. Cracks and fissures develop in the surface rock strata
due to which new spring may appear on the surface or old
may disappear.
2. If these cracks develop in hilly areas, they result in land
slides which may block , the river courses and form a
temporary lake. Such cracks may damage the dams
constructed on the rivers and are responsible for disastrous
floods.

15. 3. Due to uplift or subsidence of a small area, some wells
may become dry while others get more water.
4. The rivers may change their courses, if fissures develop
in their beds.
5. When an earthquake affects the ocean-floor, great waves
which are known as • tsunamis (a Japanese name) spread
outwards. They spread with a speed of 500 to 800 kms per
hour and causes great damage to coastal areas. The
earthquake of karnataka in 1883 caused enormous tsunamis
which were responsible for generating 36.5 mts high sea
waves.

16. ●Contraction of the rock strata takes place,
which is evident from the bending of railway
lines and pipelines.
●Earthquakes may form depressions
forming lakes.

17. Volcanoes

18. The term vulcanicity includes all the
processes through which solid, liquid and
gaseous material from the interior of the
earth is forced into the earth's crust or is
ejected on to the surface. The term
'volcanoes' is generally applied to the
extrusive type of vulcanicity in which the
magma reaches the surface of the earth.

19. Origin of Volcanoes –
The temperature-of the earth increases
with an increase in the depth. The interior of
the earth experiences tremendous
temperatures, but' due to the enormous
pressure of the overlying rocks, the material
in the interior of the earth is not found in a
liquid state. It is in a solid state. .

20. Any release of pressure caused by
diastropic movements melts the rocks below
and hence pockets of liquid material, known
as magma occurs in the subcrustal zone of
the earth. The magma thus formed tries to
find its way through the joints and fissures
of the earth's crust and reaches the surface
of the earth.

21. ●Types Of Volcanoes
On the basis of the mode of eruption of
lava, volcanoes are classified into two
types
● Central Type : When the Volcanic
eruption occurs through a single vent or a
group of closely related vents, it is known
as a central type of volcano. Such
eruption gives rise to volcanic mountains.

22. Fissure Type :
In this type, volcanic eruption takes place
through fissures, i.e. along a line of considerable
length or at numerous points along it. The lava
wells up quietly and may spread over large areas.
This type of volcano gives rise to volcanic plateaux
or extensive lava sheets. The Deccan Trap region
of Peninsular India has been formed by fissure
eruption.

23. Volcanoes are also classified on the basis of
their degree of activity. On this basis
volcanoes are divided into three groups :
1; Active Volcanoes : Those volcanoes that
erupt fairly frequently are called active
volcanoes. Stromboli and Vesuvius are active
volcanoes.

24. 2.Dormant Volcanoes :
Some volcanoes which were
considered as extinct suddenly start their
activity. Such volcanoes are known as
dormant or sleeping volcanoes. eg. Katmai
in Alaska

25. 3.Extinct Volcanoes :
The volcanoes that have not erupted
during historical times and do not
show any sign of activity are known as
extinct volcanos, e.g. Mount Egmont
volcano in New Zealand.

26. Products of Eruption
The materials thrown out during volcanic
eruption are of three types - solid, liquid
and gases.

27. Solid Material
- When an eruption is in the form of a
series of explosions, solid materials
are ejected. They are known as
.pyroclasts. The finer material
includes scoria, pumice cinders and
volcanic dust.

28. Liquid Material
The most important product of vulcanicity is
lava. Some lavas contain more silica and
thus have a high melting point. It solidifies
rapidly and does not flow over a long
distance. On the other hand, basic lava
which is poor in silica and rich in magnesium
and iron has a lower melting point and it
flows over a considerable distance.

29. Gaseous Material
The gases emitted during an eruption
include gaseous compounds of sulphur
and hydrogen with carbon dioxide. The'
steam comes out from the vent and
gets condensed to form clouds and
then a torrential rainfall.

30. Landforms associated with volcanoes :
Different landforms come into existence due to
vulcanicity.
Volcanic plateau: Extensive plateaus are
formed due to-fissure eruption. The lava
Comes-out from the fissures quietly and
spreads over a large area. The piling up of lava
flows, one after another results in enormous
thickness extending over wide areas. Eg. The

31. Volcanic cones : Volcanic cones are hill-like
masses formed around a pipe by the
accumulation of molten rock materials and
fragments of rocks that are the products of
volcanic material. The height of cone increases
with each successive eruption.
These cones have different shapes and sizes as
they depend on the material that has been
thrown out from the pipe.

32. All of them have conical shape and many
of them have '•craters at the apex of the
cones. Crater
Conical
shape
Volcanic pipe

33. Ash And Cinder Cones-
During explosive eruption, fragmental
material like dust, ash, cinders and bombs
which are thrown out from the volcanic vent,
again fall back to earth around the vent. As
this volcanic material spreads outwards near
the base, the .cones attain a concave shape.
They may rise upto 600 m. Eg. Volcano de
Feugo in Guatemala

35. Shield Volcanoes
These volcanoes come into existence when
there is an absence of explosive activity and
therefore, an absence of fragmentary
material, 'T-he lava is very mobile and flows
over al considerable distance before it
becomes solid. Hence, these volcanoes are
not very high.| and have small angles of
slope. Such volcanoes are found in Hawaii

36. Shield volcano
Composite volcano

37. Caldera – a caldera is a remnant of the
former crater which was destroyed and a second
cone is built by eruption of lesser intensity . Most of
composite cone are surrounded by the calderas.

38. Crater Lake
Sometimes the volcanic eruptions are violent.
The tops of the cones are blow forming' a large
depression on the top of the volcanic cone.
Water may collect in the c: It is funnel shaped.
Such lakes are known as 'crater lakes', e.g.
Lake Toba in Sumatra.

39. Volcanic Plunge
Sometimes solidification of lava takes place in the
vent of a volcano. When the. surrounding rock
material is removed by different agents of erosion,
the vent stands prominently, It is known as a volcanic
plug. The diameter of a plug varies between 300":
"and 600 mts.
Eg. The Devil Tower in Wyoming state of the U.S.A.

40. Distribution of Volcanoes
The total number of active and dormant volcanoes is
nearly 800, They mainly occur in belts or zones.
Thus they occur in three major belts :
1. Circum-Pacific Belt : This belt more or less
surrounds the Pacific Ocean and is known as 'a girdle
of fire'. Nearly 66% of the active volcanoes lie in this
belt. It is
co-incidental with the belt of earthquakes.

41. It runs through the young fold mountains of
the Rockies and Andes in North and South
America and along eastern coastal areas
and islands of East Asia. Mayon, Fuji Yama
and Cotopaxi are some of the well known
volcanoes in this belt.

42. 2. The Alpine-Himalayan or Mid-world Mountain
Belt : The belt starts from the Canary islands and
stretches through the Mediterranean and Middle
East- to South-eastern Asia. The young fold
mountain ranges of the Alps and the Himalayan do
not have a single volcano. Vesuvius, Etna and
Stromboli are the famous volcanoes in this velt.
3. The African Rift-Valley Belt : This belt passes
through the Red Sea and extends
upto Israel in the North, Kilimanjaro in Tanzania

45. ~75% world’s active volcanoes in Ring of Fire

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