The magnitude relates to the energy released during the quake.
It expressed in absolute numbers, 0-10.
The intensityscale is named after Mercalli
Intensity scale takes into account the visible damage caused by the event.
The range of intensity scale is from 1-12.
Effects of Earthquake
Differential ground settlement
Land and mud slides
Floods from dam and levee failures
The effect of tsunami would occur only if the epicentre of the tremor is below oceanic waters and the magnitude is sufficiently high.
Tsunamis are waves generated by the tremors and not an earthquake in itself.
Volcanoes are classified on the basis of nature of eruption and the form developed at the surface.
Shield volcanoes are the largestof all the volcanoes on the earth.
The Hawaiian volcanoes are the most famous
It madeofBasalt, a type of lava that is very fluid when erupted
For this reason, these volcanoes are not steep
Basalt is characterised by low–explosive
Upcoming lava moves in the form of a fountain and throws out the cone at the top of the vent and develops into cinder cone
These volcanoes are characterised by eruptions of cooler and more viscous lavas than basalt.
These volcanoes often result in explosive eruptions.
Along with lava, large quantities of pyroclastic material and ashes find their way to the ground.
These are the mostexplosive of the earth’s volcanoes.
They are usually so explosive that when they erupt they tend to collapse on themselves rather than building any tall structure.
The collapsed depressions are called calderas and it form Crater–lake.
Their explosiveness indicates that the magma chamber supplying the lava is not only huge but is also in close vicinity.
Flood Basalt Provinces
These volcanoes outpour highly fluid lava that flows for long distances.
There can be a series of flows with some flows attaining thickness of more than 50 m.
Individual flows may extend for hundreds of km.
The Deccan Traps from India, presently covering most of the Maharashtra plateau, are a much larger flood basalt province.
Mid-Ocean Ridge Volcanoes
These volcanoes occur in the oceanic areas.
There is a system of mid-ocean ridges more than 70,000 km long that stretches through all the ocean basins.
The central portion of this ridge experiences frequent eruptions.
Depending on the location of the cooling of the lava, igneous rocks are classified as
Volcanic rocks – cooling at the surface
Plutonic rocks – cooling in the crust
The lava that cools within the crustal portions assumes intrusive forms.
A large body of magmatic material that cools in the deeper depth of the crust develops in the form of large domes.
Batholiths are the cooled portion of magma chambers.
A laccolith is a sheet intrusion that has been injected between two layers of sedimentary rock.
The pressure of the magma is high enough that the overlying strata are forced upward, giving the laccolith a dome or mushroom-like form with a generally planar base
It can be regarded as the localised source of lava that finds its way to the surface.
The Karnataka plateau is spotted with domal hills of granite rocks.
Lapolith, Phacolith & Sills
As and when the lava moves upwards, a portion of the same may tend to move in a horizontal direction wherever it finds a weak plane.
It may get rested in different forms. In case it develops into a saucer shape, concave to the sky body, it is called lapolith.
A wavy mass of intrusive rocks, at times, is found at the base of synclines or at the top of anticline in folded igneous country.
Such wavy materials have a definite conduit to source beneath in the form of magma chambers (subsequently developed as batholiths). These are called the phacoliths.
The near horizontal bodies of the intrusive igneous rocks are called sill or sheet, depending on the thickness of the material. The thinner ones are called sheets while the thick horizontal deposits are called sills.
When the lava makes its way through cracks and the fissures developed in the land
It solidifies almost perpendicular to the ground.
It gets cooled in the same position to develop a wall-like structure.
Such structures are called dykes.
These are the most commonly found intrusive forms in the western Maharashtraarea.
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