Natural Catastrophic Events
Introduction
The major types of natural calamities are
- Volcanoes
- Earthquakes
- Tsunami
Volcanoes:
Volcanism and causes of volcanism aren’t random. The areas of high volcanic activity are of ocean – ocean convergence and ocean continent convergence.
One of the regions is the Pacific ring of fire located in the pacific ocean and consists of border areas of China, Philippines, Japan, rocky mountains, Mexico , Andes mountains, Indonesia, new Zealand, Tanzania.
The second reason for volcanoes is the ocean – ocean divergence which creates peaceful basaltic eruptions as mid ocean ridges are formed.
The third reason for volcanic eruptions is breaking up of plates into blocks. The andesitic eruptions are seen in this type.
Intrusive land – forms:
1.Sills – Horizontal
2.Dykes – vertical
3.Laccoliths – magma which couldn’t come out
4.Balolith – intrusive granite rock
5.Phacolith – shaped like waves
6.Lopolith – saucer shaped.
Extrusive Landforms:
Lava plateau: The cracks in the continental crust leads to basaltic flows which spread across land creating lava plateau. E.g. Deccan plateau.
Shield / Dome volcano: The magma reservoir creates volcanic islands. These create peaceful basaltic flow with gentle flow. E.g.: Hawaii.
Cinder cones: The ocean continent plates collide and then viscous lava explodes violently.
Composite cones: Volcanic eruptions led to new layers of ash or lava.
Geysers:
Fountains of hot water. Ground water heated by shallow source of magma. They have chambers in interior and water comes out like fountains due to pressure. Silica is dissolved in water.
Hot springs:
Springs: The groundwater stored in rocks comes out of outlets called springs where the water table reaches the surface. The water may seep out gradually out of rocks or gush out as a fountain. Wells are man made for obtaining ground water by digging a hole in the ground till the water table is reached.
Water reaches interior and there it is heated. Water is heated by magma or hot rocks. It is common and is present in many places of the world. Cyano bacteria are present in this water.
Fig 3: Hot springs vs geysers
Chapter Review
Score more than 80% marks and move ahead else stay back and read again!Q1: Pacific ring of fire consists of which countries
1.china
2.phillipines
3.indonesia
4.all
Q2:Cause of volcanism are
1.ocean ocean convergence
2.ocean continent convergence
3.ocean ocean divergence
4.all
Q3:Intrusive volcanic landforms include
1.sills
2.dykes
3.laccoliths
4.all
Q4:Which is a hot water source that comes out with force
1.spring
2.geyser
3.both
4.none
Q5:Extrusive land forms of volcanic activity are
1.caldera
2.dome
3.lava plateau
4.all