EARTHQUAKES: are violent tremors of Earth’s crust.
CHIEF CAUSE: slipping of rock formation along faults and fractures in the earth’s crust. This happens due to constant change in volume and density of rocks due to intense temperature & pressure in the earth’s interior.
FOCUS/HYPOCENTER: place of origin of an Earthquake inside the earth
EPICENTRE: point on the Earth’s surface vertically above the focus is called epicenter. On the earth’s surface, the maximum damage is caused at the Epicentre.
Generally, the greater the intensity of the shocks, the longer they last.
ISOSEISMIC LINE: an imaginary line connecting all points on the surface of the earth where the intensity of shaking produced by earthquake waves is the same.
MAGNITUDE: a measure that depends on the seismic energy radiated by the quake as recorded on seismographs; measured in terms of Richter scale.
INTENSITY: depends on the damage caused by the quake; does not have mathematical basis but the Modified Mercalli Intensity Scale is used.
AFTERSHOCKS: earthquakes that often occur during the days and months that follow some larger quake.
SEISMIC WAVES: spread out from the seismic focus. These waves are of three main types.
The two main areas of earthquakes in the world are
- Around the Pacific ocean along a belt of volcanoes known as the RING OF FIRE .(more active)
- From the middle Asia through the Mediterranean Sea to West Indies
The term ‘landslides encompasses falling, toppling, sliding, flowing and subsidence of soil and rock materials under the influence of gravity and other factors.
Slope instability may be caused by removal of lateral or underlying support mainly by river erosion and road cuts, landfill dumping, faulting, tectonic movements or the creation of artificial slopes by constructional activities.
Large Landslides of India
( Tamil Nadu)
Rocks below the crust have very high temperature, but the great pressure upon these keeps them in a semi –solid state. If the pressure weakens then some of the rocks become liquid – called MAGMA. Within crust, volcanic features are BATHOLITHS: a large mass of magma, which often forms the root of mountain and is made of granite; SILI: a sheet of magma lying along the bedding plane – same may give rise to waterfalls and rapids when a mass of magma cuts across the bedding planes. Some dykes when exposed on the surface resist erosion and stand up as ridges or escarpments.
Sometimes magma reaches the surface through a VENT (hole) or FISSURE (crack). When magma reaches the surface, it is called LAVA. If lava comes through a vent, it builds up a volcano and if it emerges through a fissure. It builds up a LAVA PLATFORM OR LAVA FLOW.
Volcanoes pass through three stages:
In the active stage, eruptions are frequent: Mt Etna (Italy), Cotopaxi (Ecuador)
In dormant stage, eruptions become infrequent: Mt. Vesuvius (Italy)
Volcanoes, which have not erupted in historic times, are called extinct: Mt Aconcagua (Argentine Andes)
Distribution of Volcanoes in the World
They occur along coastal mountain ranges, as off- shore islands and in the midst of ocean, but there are few in the interiors of continents. The greatest concentration is probably that in the Circum –Pacific Region (Pacific Ring of Fire)- accounts for 2/3 of the world’s Volcanoes ; active Volcanoes in; Philippines- 100 , Andes-40, Japan- 35 , Indonesia – 70.
Atlantic Coasts- has many dormant or extinct volcanoes. Mediterranean region – associates with the Alpine Folds e.g. Vesuvius, Etna, Stromboli.
The Himalayas have no active volcano at all.
In Africa- Mt Kilimanjaro & Mt Kenya (both Extinct); Mt Cameroon (active volcano)
Landforms formed by Internal Forces
|MOUNTAINS||They are formed in the process of orogenesis.|
formed relatively recently & higher than old fold mountain; pointer peaks e.g. The Andes , The Rockies , the Alps, The Himalayas
formed long ago, rounded peaks
e.g. The Appalachians, The Urals and The Aravalis
| ||Land betn the two parallel faults either rises, forming block mountains or horsts , or subsides into depression termed as a rift valley . |
e.g. Arabian Peninsula, the Sinai Peninsula, the Vosgus( France)
Black Forest Mountains( Germany) , Salt Range(Pak) , The Vindyas & The Satpuras (India)
| ||called mountains of accumulation as formed by the accumulation of volcanic material. |
e.g. Mt Fuji( Japan) , Mt Mayon( the Philippine) , Mt Merapi (Sumatra) Mt Agung( Indonesia ) & Mt Catopaxi( Ecuador)
| ||form due to erosion by different agencies, known as relict mountain/ mountain of circumdenudation |
e.g. Mt Manodnock( USA) , the Niligiri , the Parasnath, the Girnar & the Rajmahal( all in India)
| ||also called continental plateaus |
e.g. Plateaus of Brazil, SOUTH Africa , West Australia, Chhota Nagpur & Shillong
| ||when plateaus are enclosed by fold mountains they are known as Intermontane Plateaus e.g. Tibetan plateaus , Bolivian plateaus|
| ||situated at the foot of mountains |
e.g. plateau of Malwa (India ) , plateau of Patagonia(Argentina) , plateau of Appalachian (USA)
| ||structurally depressed areas |
e.g. Russian Platform, the Great Plains of USA , central lowlands of Australia
| ||e.g. Northern Canada , . Northern Europe & Western Africa (all ice-eroded plains) & parts of Sahara in Africa(wind eroded plains)|
| ||e.g. Indo-Ganga (India), the Hwang Ho Plains (N.China) , the Po River Plains/Lombardy ( N.Italy) , Nile River- all great alluvial plain |
plains of north-western Eurasia 7 PLAIN OF Ladakh – are plains made by glacial deposition