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Wednesday, March 24, 2010

geography short notes -7

KYANITE

the name derived from the greek word kyanos, meaning blue. it is typicaly blue siliacte mineral, comonly found in aluminium-rich metamorphic pegmatites & sedimentary rocks. it is strongly anisotrophic , in that its hardness varies depending on its crystallographic direction. this is used primarily in refractory & ceramic products, including porcelain plumbing fixtures & dinnerware. it is also used in electrical insulators & abrasives. it undergoea an irreverssible expansion when fired at high temperature. this is also been used as gemstone.

ASSOCIATED MINERALS OF KYANITE :
andalusite Ai2SiO5
sillimanite Al2SiO5
Quertz SiO2
staurolite Fe2Al9Si4Onn(OH)2
micas AB2-3(X1Si)4 O10(O, F, OH)2
garnete A3B2(SiO4)3


LAHAR

it is a type of mudflow composed of pyroclastic material & water that flows down from a volcano, typically along a river valley, the term lahar originated in the Javanese language of Indonesia. lahars have the consistency of concrete. fluid where moving then solid when stopped. lahars are be huge, the osceola lahar produced 5600 years ago by mount rainier in washington produced a wall of mud 140 mts 450 feet deep in the white river canyon & extends over an area of over 330 square kilometers. these are extermely dangerous, became of their energy & speed. large lahares can flow several dozen meters per second & can flow for many kilometers , causing catastrophic distruction in their path. lahars possible causes :
- snow & glaciers can be melted by a pyroclastic flow during an eruption.
- a flood caused by a glacier, lake breakout & heavy rainfall can release a lahar also called glacier run. lahars are associated with volcanic activity, can occur even without any current volcanic activity , as long as the conditions are right to cause the collapse & movements of mud originating from exisitng volcanic ash deposits.

LAMPROPHYRE

it is a greek word Lampros meaning "bright", Prophyre meaning "rocks". they are uncommon, small volume ultrapotassic igneous rocks primarily occuring as dikes, lopoliths, laccoliths, stocks & small instrusions. they are alkaline silica-undersaturated , ultramafic rocks with high magnesium oxide, >3% potassium, high sodium oxide & high nickle & chromium. they occur in all geologic eras.

ESSENTIAL COMPONENTS OF LAMPROPHYRE :

- high depth of melting which yields more mafic magmas.
- low degrees of partial melting, which yields magmar rich in the alkalies (potassium mainly)
- lithophile element (K, Ba, Cs, Rb) enrichment , high Ni & Cr.
- high potassium & sodium concentrations.
- some form of volatile enrichment, to provide the biolite (phlogopite) & amphilobole (pargasite) mineralogy.
- lack of fractional crystallisation
- high Mg# (NgO// FeO+Fe2O3).

Lamprophyre are usually associated with voluminous granodiorile intrustive episodes ^. Lamprophyre are also known to be spatially & temporarily associated with gold mineralisatio



MEANDER

it is a bend in a river also known as an oxbow loop. a stream or river flowing through a wide valley or flat plain will tend to form a meanding stream course as it alternatively erodes & deposits sediments along its course . the result is snaking pattern as the stream meander bock & forth across its flood plain . meander is linked to the existance of pool-riffle sequence where meander form hard rock, when the meander meets the hardrock it then bends into another area. on the inside of menader, most of meander occur in the lower course of river . on the inside meander, willows are often far from the bank, whilst on the outside of the bend, the roots of the willows are often exposed & undercut, eventually leading the trees to fall in the river. the term derives from the river known to the ancient greeks Maiandros meander is located in present-day Turkey near the ancient greek town of miletus. Meander is calculated as the length of the stream divided by the length of the valley.


 MERCALLI INTENSITY SCALE

it is a scale used for measuring the intensity of an earthquake. the scale quantifies the effects of an earthquake on the earth's surface , humans, objects of nature & man-made structures on a scale of 1 through 12, with 1 denoting a weak earthquake, 12 denoting : one that causes almost complete destruction.

EVOLUTION

it originated with the widely used simple ten-degree rossi-forel scale, which was revised by Halian volcanologist Giuseppi mercalli in 1883 & 1992. in 1902, ten-degree mercalli intensity scale was expanded to 12 degrees by Italian physicist Adolf cancani. it was later completely re-written by german geophysicist August heinrich sieburg & became known as the mercalli-cancani-scale. then changed the name to mercalli-intensity-scale.

 MESA ROCKS

this is a spanish & portuguese word meaning table. it is a elevated area of land with the flat top & sides that are usually steep cliffs. it is in table top shape. Mesa form in area where horizontally layered rocks are uplifted by tectonic activity. the differences in strength of various rock layers is what gives mesas their distinctive shape. less resistant rocks, are eroded away on the surface into valley. where they collect water drainage from the surrounding area, while they more resistant layers are left standing out. a large area of very resistant rock, such as sill may shield the layers below it from erosion while the softer rock surrounding it is eroded into valley. thus forming caprock. difference in rock type also reflect on the sides of mesa, as instead of smooth slopes, the sides are broken into a staircase pattern calle "cliff &-bench topography".

MOUNTAIN PASSES OF INDIA

Name of Pass = Place

- Banihal pass = doda & anantnag districts, J & K

- shipkila la pass = sutlej enters india from tibet , Himachal pradesh

- Bara Lancha La pass = kyelang & leh, himachal pradesh

- Rohtang = kullu & kyelang, himachal pradesh

- Bomdi La pass = tezpur & tawang, arunachal pradesh

- Thanga La & Niti La pass = uttaranchal

- Lipu = leh, indo-nepal-china, uttaranchal

- Jelepla = india & china (gangtok-lhasa road), sikkim

- Nathu La pass = india & china, sikkim

- Karakoram pass & Aghil pass = j & k

- Palghat = palakkad & coimbatore

- Shenkotta = kollam & madurai

- Thalghat = mumbai & pune

- Bhorghat = mumbai & nasik. 




  

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