Earthquakes
The sudden tremors or shaking of the earths crust is known as earthquake.when a part of earths surface moves backward and forward or up and down,the earth surface quakes and these are called the earthquake.
TABLE OF CONTENTS
The earths crust is made up of different parts of various sizes.they are called plates.
Most of the earthquake in the world are caused by the movements of the plates.
Seismology the special branch of Geology.its deals with the study of earthquake.
Richter scale is the instrument to measure or record the intensity of an earthquake.
SEISMIC WAVES
The place where the seismic waves originate beneath the earths surface is called the focus of the earthquake.
The epicenter is that point on the ground surface which is closest to the focus.
Seismic waves are recorded on seismograph.Seismic waves are mainly of three types-a) Primary waves b) secondary waves c) surface or long waves
THE EARTHQUAKES ZONES IN INDIA
The Indian plate is moving from south to north.that is reason there are earthquake in the himalayan region.
Earthquake occurs in indian plates are following:
Assam
Arunachal pradesh
Nagaland
Tripura
Manipur
Mizoram
Andaman and nicobar island
Jammu and kashmir
North-western region of uttar pradesh
Northern region of Bihar etc.
During the last few years,there have several earthquakes of varying intensities in
Maharashtra
Gujrat
VOLCANIC ACTIVITY
Magma or molten rock is formed beneath the ground surface due to various reason.
This molten rock ruptures the ground and pours out. sometimes,it cools down beneath the ground surface instead of pouring out.
All these activities are called volcanic activities.
Volcanic activities have been taking place since times immemorial.
There are three types of volcanoes:
1) Active volcanoes
2) Dormant volcanoes
3) Extinct volcanoes
VOLCANIC ERUPTIONS
The pouring out of the magma or molten rock through ground surface is called a volcanic eruption.
At the time of eruption,the magma,steam,fragments of rock,dust and gaseous substances are ejected with great force from under the ground surface through a pipe like passage.
The opening of the pipe on earths surface is known as vent which forms a crater.
The lava which is thrown into the sky during an eruption,falls to the ground in the form of solid fragments.Dark clouds gather in the sky and it begins to rain heavily.
The volcanic ash and dust mixes with the rainwater giving rise to hot mud flows.
TYPES OF VOLCANIC ERUPTIONS
Volcanic eruptions are classified into two types depend in the manner of ejection of the magma:
1) central eruption
2) Fissure eruption
CENTRAL ERUPTION
This type of eruption is sometimes very explosive, because,lava,steam,gas,dust,smoke,stone,fragmentare ejected from a narrow pipe from under the ground with greater intensity.This type of eruption gives rise to conical or dome-shape hills.
Some examples of volcanic mountains formed due to central eruptions are Mt. Kilimanjaro in Africa, the Fuji yama in japan and the Vesuvius and mount Etna Italy.
It is basically poured acidic lava.
FISSURE ERUPTIONS
A very long fissure (cracks) develops in the ground surface and so,the molten rock,rock fragments,steam and gases within,pour out slowly.
These eruptions take place at very slow speed.Since this lava is more fluid,it spreads over longer distances.
The lava cools down on the ground over a period of time,increasing the thickness of the surface in that areas.Basalt plateaus are formed due to these eruptions.
Basalt plateaus are also found in area such as
Brazil in south America
Saudi Arabic in west Asia and
Deccan plateau in India.
In maharshtra,the fertile black regur soil has been formed from basalt rocks.Its also called black cotton soil.
VARIOUS LANDFORMS
Mainly there are three type of landforms
Mountains
Plateaus
Plains
MOUNTAINS
The height of mountains are over 600m and have conical peaks.On the basis of origin there are four types of mountains.
Block mountains
Residual mountains
Accumulated mountains
Fold mountains
BLOCK MOUNTAINS
The middle part of such mountains is lower and the parts on both the sides are higher.The middle lower portion is called as Rift valley.The longest rift valley is the valley of the Jordan river.
Examples of block mountains:
Black forest-Germany
Vindhyachal and Satpura-India
Salt range-Pakistan
RESIDUAL MOUNTAINS
Such mountains are formed as result of weathering.
Examples:
Aravalli mountain
Nilgiri mountain
Parasnath mountain
Hills of Rajmahal(india)
Sidra(spain)
ACCUMULATED MOUNTAINS
These are formed due to accumulation of sand,soil,rock,lava etc. on the earths crust.
Example: Sand Dunes
FOLD MOUNTAINS
These are formed because of the fold in rocks due to internal motions of the earth.These are wave like mountains which have numerous peaks and lows.
Examples:
Himalayas
Ural
Alps
Rockies and
Andes etc.
PLATEAUS
These are extensive upland areas characterised by flat and rough top surfaces and steep walls which rises above the neighbouring ground surfaceat least for 300m.
Generally the height of plateau ranges from 300 to 500 ft.
Some plateaus having more than average height:
TIBETAN PLATEAU -16000FT.
BOLIVIAN PLATEAU -11800FT.
COLUMBIAN PLATEAU -7800FT.
PLAINS
Plains can be defined as flat areas with low height (below 500feet).
1)Weathered plains
2)Loess plains
3)Karst plains
4)Erosional plains
5)Glacial plains
6)Desert plains
7)Depositions plains
Comments
Post a Comment
Hello everyone