Rocks:
The solid part of the earth crust is called rocks.
Rocks may not always necessarily be hard.
Minerals are obtained from rocks.
Types of Rocks:
Igneous Rocks:
Igneous rocks are crystalline solids which form directly from the cooling of magma.
This is an exothermic process (it loses heat) and involves a phase change from the liquid(magma) to the solid state.
The earth is made of igneous rock - at least at the surface where our planet is exposed to the coldness of space.
Igneous rocks are given names based upon two things: composition (what they are made of) and texture (how big the crystals are).
These rocks are harder and granular.
There is no layer in igneous rocks and fossils are not found in igneous rocks.
Rocks formed by the cooling of the molten matter beneath the earth surface are called intrusiveigneous rocks and are crystalline rocks.
Sometimes the molten mater comes out on the earth surface and forming extrusive igneous rocks e.g. Obsidian, basalt.
Sedimentary rocks:
They are formed by deposition and sedimentation ofsediments over a long period.
Sedimentary rocks are called secondary, because they are often the result of the accumulation of small pieces broken off of pre-existing rocks.
Sandstone, limestone, shale are some example of sedimentary rocks.
Metamorphic rocks:
The metamorphic get their name from "meta" (change) and "morph" (form).
The nature of igneous and sedimentary rocks changes due the effects of tremendous heat or pressure and the new transformed rocks are called metamorphic rocks.
Earthquake:
The sudden tremors or shaking or the earth’s crust is called an earthquake.earthquakes:
The earth surface is made up of several plates.
When these moves plates moves, it will leads to earthquake.
Seismology is the branch of Geology which deals with the study of earthquake.
Richter scale is used to measure the magnitude of the earthquake.
Mercalli Scale is used to measure the intensity of the earthquake.
Seismic wave an elastic waves produced in the earth due to the earthquake.
The place where these seismic waves originate beneath the earth’s surface is called the focus the earthquake.
The epicentre is that point on the earth surface which is near to the focus.
Seismic waves are of three types i.e. Secondary waves, primary waves and Surface or long waves.
Volcano:
A volcano is a vent or fissure in Earth's crust through which lava, ash, rock and gases erupt.
The pouring out of the magma or molten rock through ground surface is called volcanic activities.
The opening at the earth surface through which these molten materials comes out with a large force is called Vent.
Types of Volcanic eruptions:
Central eruption:
This type of eruption is sometimes very explosive because the molten material or other materials are ejected through a narrow pipe with greater intensity.
This type of eruption leads to the formation of the conical or dome shaped hills.
Central eruption poured acidic lava.
Mt. kilimanjarao in Africa, Fujiyama in Japan and Vesuvius and mount Etna in Italy are some example of mountains formed due to central eruptions.
Fissure Eruption:
When a large crack or fissure is developed in the ground surface then the hot lava and other material pour out with small speed and slowly.
Lava spread over a large distance.
The poured lava cools down over a period of time and leads to the formation of Basalt Plateau.
In Maharashtra the fertile black regur soil has been formed from basalt rocks.
Mountains:
A mountain is a large landform that stretches above the surrounding land in a limited area, usually in the form of a peak.
A mountain is generally steeper than a hill.
Mountains are formed through tectonic forces or volcanism.
The height of the mountains is greater than 600m.
Types of mountains:
Block Mountains:
Block mountains are created when faults or cracks in the Earth’s crust force materials upward.
Block Mountains usually have a steep front side and then a sloping back side.
Black forest(Germany), Vindhyanchal and Satpura in India, salt range of Pakistan are some example of block mountains.
Fold Mountains:
Fold Mountains are formed when two of the Earth’s tectonic plates collide head on.
Fold mountains are wave like mountains which have numerous peaks and low.
Himalayas, Ural, Alps, Rockies, Andes etc.
Residual Mountains:
Such mountains are formed as a result of weathering. E.g. Aravali, Nilgari, Parsnath Hills.
Accumulated Mountains:
These are formed due to accumulation of sand, soil, rocks, lava etc. on the earth crust, e.g. Sand Dunes.
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