Volcano: Types, Formation, Rocks Formed

Volcano: Types, Formation, Rocks Formed

A volcano is a vent or fissure in Earth's crust through which lava, ash, rock and gases erupt. A volcano is also a mountain formed by the accumulation of these eruptive products. Let's take a look at how volcanoes form:
Earth's crust is 40 to 250 miles (64 to 402 kilometers) thick. It is broken up into 14 major and 38 smaller pieces called tectonic plates. These plates float on a layer of magma — semi-liquid rock and dissolved gases. At the boundaries of these plates — where they move past, are pushed under, or move away from each other — magma, which is lighter than the surrounding solid rock, is often able to force its way up through cracks and fissures. Magma can explode from the vent, or it can flow out of the volcano like an overflowing cup. Magma that has erupted is called lava.

Principal types of volcanoes

1        Cinder cone volcanoes

  Also called scoria cones are the most common type of volcano and are the symmetrical cone shaped volcanoes we typically think of. They may occur as single volcanoes or as secondary volcanoes on the sides of stratovolcanoes or shield volcanoes. Airborne fragments of lava, called tephra, are ejected from a single vent. The lava cools rapidly and builds up around the vent, forming a crater at the summit. Cinder cone volcanoes are fairly small, generally only about 300 feet (91 meters) tall and not rising more than 1,200 feet (366 meters). They can build up over short periods of a few months or years.
2   Stratovolcanoes are also called composite volcanoes because they are built of layers of alternating lava flow, ash and blocks of unmelted stone. They are larger than cinder cones, rising up to 8,000 feet (2,438 meters). Stratovolcanoes result from a conduit system of vents leading from a magma reservoir beneath the surface. When dormant, they typically have steep concave sides that sweep together at the top around a relatively small crater.
Stratovolcanoes erupt with great violence. Pressure builds in the magma chamber as gases, under immense heat and pressure, are dissolved in the liquid rock. When the magma reaches the conduits the pressure is released and the gases explode, like soda spewing out of a soda can that you shook up and opened suddenly. Because they form in a system of underground conduits, stratovolcanoes may blow out the sides of the cone as well as the summit crater.
Stratovolcanoes are considered the most violent eruptions. Mount St. Helens, in Washington state, is a stratovolcano that erupted on May 18, 1980. Approximately 230 square miles (596 square kilometers) of forest was completely obliterated and 57 people were killed. Ash was blown up into the atmosphere and fell over 11 states.
3  Shield volcanoes are huge, gently sloping volcanoes built of very thin lava spreading out in all directions from a central vent. They have wide bases several miles in diameter with steeper middle slopes and a flatter summit. The gentle convex slopes give them an outline like a medieval knight’s shield. Eruptions are not generally explosive, more like liquid overflowing around the edges of a container. The world’s largest volcano, Mauna Loa in Hawaii, is a shield volcano. Mauna Loa is about 55,770 feet (17,000 meters) from its base beneath the ocean to the summit, which is 13,681 feet (4,170 meters) above sea level. It is also one of the Earth’s most active volcanoes and is carefully monitored. The most recent eruption was in 1984.
4  Lava domes are built up when the lava is too viscous to flow. A bubble or plug of cooling rock forms over a fissure. This cooler, thick lava usually rises near the end of an explosive eruption and lava domes often form within the craters of stratovolcanoes. Mount St. Helens has several well-defined lava domes inside the crater.

Cooling takes place in the crust and not over the surface. E.g. Granite, Gabbro, Diorite etc. Intrusive igneous rocks are classed into the following types according to their forms.

Different Rocks Formed By Lava Cooling

1. Batholiths:  magmatic material cools in the deeper depth in the form of a large dome. These are granitic bodies. They sometimes appear on the earth surface when the denudation processes remove the overlying materials.
2. Laccoliths: Large dome shaped intrusive bodies with a level base and pipe-like conduit from below. Resembles a composite volcano structure, but beneath the earth. (Eg: Karnataka Plateau)
3. Lapoliths: They are saucer shaped, concave to the sky.
4. Phacoliths: Wavy materials which have a definite conduit to source beneath.
5. Sheets/ sills: They are the near horizontal bodies of intrusive igneous rocks. Thinner ones are called as sheets and while thick horizontal deposits are called sills.
6. Dykes: When the lava comes out through cracks and fissures, they solidify almost perpendicular to the ground to form wall like structures called dykes. (Eg: Deccan traps in Maharastra region).

Effects of volcanoes

There are many different types of volcanic eruptions and associated activity: phreatic eruptions (steam-generated eruptions), explosive eruption of high-silica lava (e.g., rhyolite), effusive eruption of low-silica lava (e.g., basalt), pyroclastic flows, lahars (debris flow) and carbon dioxide emission. All of these activities can pose a hazard to humans. Earthquakes, hot springs, fumaroles, mud pots and geysers often accompany volcanic activity.

Volcanic gases

The concentrations of different volcanic gases can vary considerably from one volcano to the next. Water vapor is typically the most abundant volcanic gas, followed by carbon dioxide and sulfur dioxide. Other principal volcanic gases include hydrogen sulfide, hydrogen chloride, and hydrogen fluoride. A large number of minor and trace gases are also found in volcanic emissions, for example hydrogen, carbon monoxide, halocarbons, organic compounds, and volatile metal chlorides.
Large, explosive volcanic eruptions inject water vapor (H₂O), carbon dioxide (CO₂), sulfur dioxide (SO₂), hydrogen chloride (HCl), hydrogen fluoride (HF) and ash (pulverized rock and pumice) into the stratosphere to heights of 16–32 kilometres (10–20 mi) above the Earth's surface. The most significant impacts from these injections come from the conversion of sulfur dioxide to sulfuric acid (H₂SO₄), which condenses rapidly in the stratosphere to form fine sulfate aerosols. The SO₂ emissions alone of two different eruptions are sufficient to compare their potential climatic impact.The aerosols increase the Earth's albedo—its reflection of radiation from the Sun back into space—and thus cool the Earth's lower atmosphere or troposphere; however, they also absorb heat radiated up from the Earth, thereby warming the stratosphere. Several eruptions during the past century have caused a decline in the average temperature at the Earth's surface of up to half a degree (Fahrenheit scale) for periods of one to three years; sulfur dioxide from the eruption of Huaynaputina probably caused the Russian famine of 1601–1603.

India – Size And Location

 India – Size And Location 

 

1 Introduction

India is one of the oldest civilizations in the world.It moved towards remarkable progress in the field of agriculture, industry, technology , and overall economic development.

2 Location

The main land of India extends between latitudes 8°4'N and 37°6'N and longitudes 68°7'E and 97°25'E. The Tropic of Cancer (23° 30'N) passes almost through the middle of the country. Apart from the mainland, the Andaman and Nicobar Islands (Indian Ocean) and the Lakshadweep (Arabian Sea) are also parts of India.

3  Size

# India has an area of 3.28 million (3.28 lakh) square km.
# About 2.4% of the total geographical area of the world.
# India is the seventh largest country in the world.
# The land boundary of India is 15,200 km.
# The coastline of the country is 7,516.6 km;which includes the Andaman and Nicobar
     and Lakshadweep.

4 Standard Time

The latitudinal and longitudinal extent of India is about 30°. The time along the Standard Meridian is taken as the Indian Standard Time. The Standard Meridian of India passes through Mirzapur in UP which is located at 82°30’ east. The time lag between Arunachal Pradesh (in the east) and Gujarat (in the west) is about 2 hours. When one moves from south to north, the latitudinal extent influences the duration of day and night.

5 India And The World

India is centrally located between the East and the West Asia. India is strategically located at the centre of the trans-Indian Ocean routes which connect the European countries in the west and the countries of East Asia. Thus, India could establish close contact with West Asia, Africa and Europe from the western coast. Moreover, it could establish close contact with Southeast and East Asia from the eastern coast.

6  Nieghbours

In the northwest, India shares its boundaries with Pakistan and Afghanistan. China and Nepal are its northern neighbours. Its eastern neighbours are Bangladesh and Myanmar. Maldives and Sri Lanka are its southern neighbours.

Natural Vegetation And Wild Life

Natural  Vegetation  And Wild Life

Natural Vegetation -  The growth of vegetation depends on temperature and moisture.     

-          With the change in height ,  climate  change that change the vegetation.

-          Growth also depends on slope and thickness of soil.

Categories:-      1. Forests           2. Grassland              3. Shrubs  

1       . Forest:-  Grows where temperature and rain are plentyful 

-          May be open and dense forest.

    #  Types of forests:- 

   A   Tropical Forests:-

a)      Also called rainforests

b)      Found near equator and close to tropical

c)        Region are hot with heavy rainfall and trees remain green      

d)       Dense trees do not allow sunlight to penetrate.      

e)      Trees – Hardwood trees like rosewood,  ebony, mahagany

f)       Rainforests are populated with insects (like butterflies and beetles), arachnids (like spiders and ticks), worms, reptiles (like snakes and lizards), amphibians (like frogs and toads), birds (like parrots and toucans) and mammals (like sloths and jaguars). Different animals live in different strata of the rainforest.

g)      Countris-Bolivia, Cameroon, Central African Republic, Ecuador, Gabon, Guyana, India, Laos, Malaysia, Mexico, Myanmar, Papua New Guinea, Republic of Congo, Suriname, and Venezuela.

  B   Tropical Deciduous Forest:-

a)      Aiso known as monsoon forest found in India, North Australia and in central America .

b)      Trees shed their leaves in dry season.

c)       Trees found – Sal , Teak, Neem, Sheesham

d)      Wood is used for making furniture, transport and constructional material.

e)      Common Animal- Tiger, Lion, Langoor and Monkeys.             

  C   Temperate Evergreen Forest –

a)      Located in mid latitudinal coastal regions

b)      Commonly found along eastern margin of continents e.g. in South East USA, South China and south East Brazil

c)       Trees found - Oak,  Pine, eukalyptus , Maple, Beech, Birch, Elm, Hickory, Walnut

d)      Common Animals - Red-crowned crane, Owls, Hawks, Squirrels, Sable,  Black bears, Wolves,  Leopard, Lynx, Siberian tiger, Otters,  Red panda, Cougars

  D   Temperate Deciduous Forest-

a)      Found in higher latitudes.

b)      Regions- Northern Hemisphere: eastern North America, East Asia, and  Europe. Smaller areas occur in Australasia and southern South America.

c)       Tress shed their leaves in dry season.

d)      Common Trees - Broadleaf trees (oaks, maples, beeches), shrubs, perennial herbs, and mosses

e)      Common Animals –  In North America, birds like broad-winged hawks, cardinals, snowy owls, and pileated woodpeckers are found in this biome. Mammals in North American temperate deciduous forests include white-tailed deer, raccoons, opossums, porcupines and red foxes.

f)       Receives - 750 to 1,500 mm of rain per year

g)      Trees - Broadleaf trees (oaks, maples, beeches), shrubs, perennial herbs, and mosses

  E.  Mediterranean –

        a)   Mediterranean vegetation, any scrubby, dense vegetation composed of broad-leaved evergreen

              shrubs,  bushes, and small trees usually less than 2.5 m (about 8 feet) tall and growing in regions

               lying between 30° and 40° north and south latitudes.

       b)   Region - Mediterranean Basin, Chilean Matorral, California chaparral and woodlands ecoregion

             of California and the Baja California Peninsula, Western Cape of South Africa, sclerophyll

            forests in Australia found in the southwest, southern and southeast Australia

       c)   Fruits – Oranges, figs, olives, grapes,

       d)  Commonly known as “Orchard of the world”.

      e)  Trees have thick bark and wax coating to reduce transpiration.    

F  Coniferous Forests –

a)      Temperature -  Minus 40°C to 20°C, average summer temperature is 10°C

b)      Receives 300 to 900 millimeters of rain per year

c)       Found -  Canada, Europe, Asia, and the United States

d)      Coniferous forest regions have cold, long, snowy winters, and warm, humid summers; well-defined seasons, at least four to six frost-free months

e)      Tress- Coniferous evergreen – Chir, pine, cedar

f)       Also called as Taiga

g)      Common Animals- Silver fox, mink, Polar bear

2.      Grassland –   

A.     Tropical Grassland-  a)  Tropical grasslands are located near the equator, between the Tropic of

Cancer and the Tropic of Capricorn. They cover much of Africa as well as large areas of Australia, South America, and India.

b)      Tropical grasslands are dominated by grasses, often 3 to 6 feet tall at maturity. They may have some drought-resistant, fire-resistant or browse-resistant trees, or they may have an open shrub layer. They develop in regions where the climax community should be forest, but drought and fire prevent the establishment of many trees.

c)       Common Animals - giraffes, zebras, buffaloes, kangaroos, mice, moles, gophers, ground squirrels, snakes, worms, termites, beetles, lions, leopards, hyenas, and elephants

B.     Temperate Grassland –

a)      Temperate grasslands are located north of the Tropic of Cancer (23.5 degrees North) and south of the Tropic of Capricorn (23.5 degrees South). The major temperate grasslands include the veldts of Africa, the pampas of South America, the steppes of Eurasia, and the plains of North America.

b)       Trees and large shrubs are largely absent. Seasonal drought, occasional fires and grazing by large mammals all prevent woody shrubs and trees from becoming established. A few trees such as cottonwoods, oaks and willows grow in river valleys, and a few hundred species of flowers grow among the grasses. The various species of grasses include purple needlegrass, blue grama, buffalo grass, and galleta. Flowers include asters, blazing stars, coneflowers, goldenrods, sunflowers, clovers, psoraleas, and wild indigos.

c)       Common Animals - bison , pronghorn, pocket gophers , prairie dogs,  wolves, coyotes, swift foxes, badgers , black-footed ferrets,  grouses, meadowlarks, quails, sparrows, hawks and owls.

C.    Thorny Bushes –

a)      Found in Dry desert, western margin of continents.

b)      Vegetation – Scarce because of scanity of rain and scarching heat.

c)       Examples – Mosses, lichen small shrubs

d)      Found in polar region of Europe, Asia, North America

e)      Common Animals – Seal, walruses, musk oxen, Arctic owl, Polar bear and snow foxes.