PALEOLITHIC AGE

Paleolithic Age roughly corresponds with the geological stratographic age, Pleistocene. It was spread over the Indian sub-continent between two lakh fifty thousand to one lakh BC. Paleolithic Age is divided into three phases on the basis of the types of stone tools and implements and techniques used to make them:

1. Lower Paleolithic Age: 2.5 to 1.0 Lakh BC

2. Middle Paleolithic Age: 1.0 lakh to 40 thousand BC

3. Upper Paleolithic Age: 40 thousand to 10 thousand BC

Following are the sources to know about the Paleolithic man:

1. Old river course

2. Water bodies: Stationary water bodies

3. Tools recovered from river basins and other places

4. Paleolithic fossils

5. Sketches/ lines drawn on the walls of the caves

Implements or tools of the Paleolithic Age are as follows:

· All the implements and tools of the Paleolithic age were made of stones only

· On the basis of the quality of stones, these implements can be divided into three types:

1. Quartzite

2. Chalcedonic

3. Sandstone

· All of them were hard stone and could not have been broken into smaller fragments for the purpose of tool making. That is why the tools of Paleolithic age were larger in shape and size.

· On the basis of their shapes, the implements and tools of Paleolithic age could be divided into following types:

1. Hand Axe: This was the oldest tool developed by the humans. It was used to cut something into smaller parts. It was broad at base and tapered towards the end. It was held in hand from the broader end.

2. Cleaver: It was double edged implement used to cut trees and make pieces of huge trunks.

3. Discoid core: It was big rounded stone used to kill an animal either in defence or for food.
 

4. Chopper: It was also a big stone sharpened along at least one edge. It was also used to cut objects. (Gandasa)

These were the four basic implements used by the Paleolithic men first, and all were big stone tools. It seems that all these tools were made of naturally found large stones, which were put to use by Paleolithic people. This technique of tool making is known as Conglomerate Boulder Technique. All the four above mentioned implements were made of using this technique. Later on, humans developed techniques to make specific implements by cutting or breaking large boulders according to their needs and wishes. This technique of cutting boulders to make implements is known as flaking technology, which saw use of brains in cutting and shaping implements according to humans’ needs and imagination.

· The flaking technology produced two types of implements: Flake tools, which were smaller in size as they were cut or broken from the large boulders. They were simply called flakes. Second was the core implement, which was the main part of the original large boulder. It is called core tool. Owing to this technological development humans went to make better implements and tools using these flakes.

5. (Side) Scrapper: It was the first improved implement made by using flake technique. It had a sharp edge while the other side was developed as such to make a comfortable grip to hold on. Scrapper might have been used to fleece animals or remove bark of tree trunks. Scrappers stamp the first evidence of use of improved technology by Paleolithic man. (Khurachani)

6. Burins: (It is equivalent to Randa/ Takshini of modern days’ carpenters). It was used to draw lines or sketches on the walls of the caves and to make holes in tree trunks. It was a quality implement.

Of the six implements basic four were used during Lower Paleolithic age. Flaking technique came into use during Middle Paleolithic age. Flakes were being used this time around along with core tools. During Upper Paleolithic age improved flake tools like side scrappers and burins were developed.

· Technological development: Conglomerate Boulder Technique was employed in Lower Paleolithic age. Flaking technology was used in middle Paleolithic age while during Upper Paleolithic age technology further developed and free flaking, step on flaking, block on block flaking and di-polar flaking techniques were employed to make tools.

· On the basis of the nature of the stone tools, one can have an idea about the needs of the Paleolithic man.

1. They needed protection against wild animals and gathered food from forests.

2. Initially they used implements which were defensive in nature. Later on, they developed aggressive/offensive implements.

3. There were two sources to meet food related requirements: meat from animals and fruits from forests. So, the humans developed such implements that can meet their requirements. They developed implements to cut dead animals, fleece them and mash their flesh.

4. Their implements and tools were large in size. This might have been a case of meeting necessities. Large boulders were naturally available and big animals were large in number making easy availability of food for humans, who just had to kill those animals to feed on. Further, killing a big animal could fulfill their food requirements for more days, they became their primary targets. And, to kill big animals only large implements could have been the need of the hour.

5. Later on, when number of big animals dwindled a bit and humans found it easier to kill small animals, which were much more in numbers making meeting of food requirements easy on daily basis, the later middle and upper Paleolithic man developed small implements using flake technology.

6. The fossils that have been found from the earlier ages prove that most of the animals killed or devoured by humans were big in size. This proves that humans were food gatherers and passing though a barbaric phase of their evolution. But, they were progressing rapidly.

7. All the sources of information on Paleolithic man point to one thing that the humans were totally dependent on the nature for all their needs. They were striving to adapt to the vagaries of the nature, which was very harsh as most of the earth was covered by ice during Pleistocene, which was the age of Paleolithic man. Humans were struggling for survival. Fresh water ponds were hard to find, during ice age smaller animals were not in great numbers, forests were not easily accessible due to ice coverage and also, better quality of rocks were not exposed to them for making improved tools. But, they survived using their fast evolving brain. The entire age was the age of food gatherers, who were yet to be introduced to any form of agriculture.

8. Evidence show that humans were not yet aware of the significance of fire. Though there is slight possibility that they might have seen some kind of fire. However, most of the scholar rule out this possibility saying that during ice age wild fire due to friction among the branches could not have occurred as the temperature could not have gone much above the freezing point. Whatever may be the case, it is a fact that humans ate uncooked food, both vegetarian and non-vegetarian. They ate fruits, some roots and some other produces of forests. They consumed raw meat of the animals, killed during hunting. They were essentially barbaric in nature.

9. There was settled habitation. Humans lived in caves and rock shelters. But, they lived in groups. There are enough evidence to prove this point. Scholars are unanimous in believing that humans lived in congregation out of safety concerns. They had learnt by now that only by living in groups they can fight with wild animals. This group habitation or congregation led to evolution of society.

10. No metal was being used during Paleolithic age. Pottery making has not come to the fore yet.

11. There was no specific pattern of disposal of dead bodies. This proves that the humans were yet to develop the emotional feelings for fellow beings and that there was no respect yet for those who died.

12. There has been no evidence of cloth making or use of cloth to protect their bodies against a very hostile nature. It is possible that the humans might have used the skin and hides of animal to guard themselves against icy winds. But, this can not be said conclusively for the lack of evidence.

13. Cave paintings are available. The evidence can be found on the inner walls of the caves at Bhimbetka, nearly 40 kilometres from Bhopal in Madhya Pradesh, at Machchhutavi in Andhra Pradesh, Patne in Maharashtra and Mirzapur in Uttar Pradesh. It is possible that these sketches were made using burins developed in the upper Paleolithic age. In Mirzapur, a cave sketch shows an animal and a man with large boulder lifted above head behind that animal. This shows as if the man is getting ready to strike the animal with the boulder.

14. There are evidence in sketches that depict humans breaking and tearing fishes, fruits and other things. All such cave paintings belong to a period around thirty thousand BC. So, even the initial cave paintings of Bhimbetka belong to the upper Paleolithic age. This is an evidence of humans’ natural inclination towards arts.

· The evidence of Paleolithic habitation has been found all over the Indian sub-continent. The main river valleys which have thrown proof of Paleolithic habitation are as follows:

1. Sohan valley in Pakistan

2. Beas-Wainganga valley in Punjab (India)

3. Luni-Jojri valley in Rajasthan

4. Sirsa valley in Punjab and Haryana

5. Sabarmati-Mahe valley in Gujarat

6. Chambal-Betwa valley in Madhya Pradesh

7. Narmada valley in Madhya Pradesh

8. Belan valley in Uttar Pradesh

9. Godawari valley in Maharashtra and Andhra Pradesh

10. Krishna-Vibha valley in Karnataka and Andhra Pradesh

11. Malprabha-Ghatprabha valleys in Karnataka

12. River valleys in Singhbhum region of Jharkhand

13. Damodar-Mahanadi valleys in West Bengal and Odisha

14. Kaveri valley in Tamil Nadu

· Following are the important sites of Paleolithic habitation:

1. Sohan: Adiyal, Balwaaland Chandal.

2. Punjab: Derda

3. Kashmir: Chauntara and Pahalgam

4. Rajasthan: Chittorgarh, Mysoregarh and Didwana

5. Gujarat: Medhamali and Visadi

6. Madhya Pradesh: Bhimbetka, Hathnala, Baghor and Maihar

7. Uttar Pradesh: Belan region, Mirzapur hills, Chakia Tahasil of Varanasi

8. Jharkhand: Hazaribagh

9. West Bengal: Bankura and Purulia

10. Odisha: Budha Valang, Mayurbhanj and Kyonjhar

11. Maharashtra: Naivasa, Bori, Inamgaon and Patne

12. Karnataka: Hungsi. This might have been an industrial site.

13. Andhra Pradesh: Kurnool, Nagarjunakonda, Renigunta, Machchhutavi Hill and Chintamanigaavi hill region

14. Tamil Nadu: Pallavaram, Attirampakkam, Budia Maim, Vanka and Gudiyan caves near Chennai. They exhibit a transition from lower to upper Paleolithic phases.

15. Only Kerala and the states of the northeast do not have any evidence of Paleolithic habitation in India. Assam has thrown some evidence but those are negligible.

16. Clearly, the Indian sub-continent has evidence of humans’ activities for over one lakh years.

Volcanoes, Activities and Volcanic Landscape

A landscape is the collection of landforms. Volcanic landforms consist of Extrusive and Intrusive landforms.

A. Extrusive Landforms: In this case lava solidifies in contact with air. Here the rate of cooling or solidification is faster and hence mineral grains are fine and not distinguishably visible to naked human eyes.
B. Intrusive Landforms: They are formed due to solidification of lava within the crust In this case lava cools or solidifies slowly, that is why the grains are bigger in size.

Volcanic materials are of two types:
A. Pyroclasts
B. Lava

In general, lava dominates the volcanic scenery. However, a volcanic landform containing no lava is possible, it would have only pyroclast. This is seen in two cases. First, when there is a closure of vent after the pyroclasts have come out, here lava gets solidified in the vent and later converts into the crust.

Second, when a thin layer of lava gets deposited over the pyroclasts and after some time the layer of lava is eroded leading to the exposure of the pyroclasts.

Pyroclasts materials are collectively called Tephra.
A large sized angular pyroclastic material or rock is called Block or Brecia.
A large oval sized lava rocks are called volcanic bombs.
Pea shaped lava rock is called Lapili. They are as small as glass marble.
Bombs and lapili solidify before they fall on the ground. This explains their round shape.
Sometimes, lava acquire vesicular shape and the lava crusts hold gases inside. Such rocks are referred to as Pumice, Scoriae or Cinders. Escaping gases make vesicles and holes in the upper solidified lava crust. Lower lava has not solidified in such structures.
The rock which is composed of a mixture of ash, dust, lapili and cinder is called Tuffs.
Hornitos are small mounds of spatter or driblets.

What are volcanoes:

The English word volcano is derived from a Greek word Vulcan who was a Roman god. According to greek mythology he was believed to be living in the interior of the earth. Going by the mythological sense of the people, volcano can be defined as the fire place of gods. No wonder in Japan, Fujiyama is still worshipped. Pele is the Hawaiian goddess of volcanoes. The term Pele’s Tears, though derived from the goddess Pele, in volcanic jargon it means teardrop shaped pyroclastic $ glassy lava thrown out in volcanic explosions, which have fused and solidified in air. In India too the land of myths, Jwalamukhi festival is related to the nature’s peculiar phenomenon in Himachal Pradesh.

The volcanic explosion, a devastating and terrible phenomenon was considered in ancient times as the expression of the anger of a god or goddess.

Coming to the science of volcano, the Penguin’s Dictionary of Geography defines volcano as a vent in the earth’s crust caused by magma forcing its way to the surface, molten rock or lava is finally , sometimes with explosive force rock fragments and ashes being thrown into the air. The emission of lava or eruptions often cause the volcano to take the form of a conical hill or mountain, the latter is gradually built up of ejected material, which is deposited most thickly round the outlet.

In other words, volcanoes are built by the eruption of molten rock and heated gases under pressure from a relatively small pipe or vent, leading from a magma reservoir at depth. Eruption may take place from the top or sides of the cone.

Structure of Volcano

A volcano is a vent or a group of closely spaced vents through which molten rocks, magma and not gases are ejected out of a deep seated source.

A volcano has three important parts:

Vent: An opening or conduit in the surface of the earth through which volcano material is ejected. A series of vents may form along a major fracture creating a fissure volcano. Volcanoes also develop with central vents and subsidiary vents on the sides of the cone.

Cone: The ejected rock material rushing out of the vent creates a cone like formation at the upper end of the vent. The cone has a steep slope and sometimes takes the form of a mountain.

Crater: A funnel shaped depression at the top or on the sides of a volcanic cone. It may be produced by an explosive eruption or by the collapse of the cone following the withdrawal of underlying lava. Its walls are almost vertical.

Volcanoes are of three types:

Extinct: Such volcanoes that don’t have any realistic possibility of magma upwelling in future are called extinct volcanoes. These volcanoes were active in the geological past. Examples are the Popa mountains in Myanmar, Mt Kilimanjaro in Africa, Mauritius, Madagascar, Malagasy and several other islands in the Indian Ocean. There are thousands of extinct volcanoes which are undergoing erosion by running water and wind and therefore look really extinct.

Dormant: Such volcanoes that have exploded in the recent past and may explode in future are known as dormant volcanoes. It is not easy to differentiate between the extinct and the dormant types of volcanoes. The Vesuvius was considered to be an extinct volcano. But it becomes dangerously active after hundreds of years. Examples are, Fujiyama and Krakatoa.

Active: Such volcanoes that have exploded recently and whose explosions may still be vivid in the public memory. Some of them emit lava after every 15 or twenty minutes. Stromboli is most well known among them. There are almost 300 active volcanoes in the the world. Examples are Mauna Loa, Mt Etna, Mt Vesuvius, Cotopaxi of Ecuador—world’s highest active volcano at 19, 600 feet.

Volcanic landscape is conical. The axis of the formation goes along the vent. Magma or lava particles solidify around the vent of a volcano. After solidification, the magma materials become igneous rocks.

Lava is of two types:
A. Felsic or Acidic
B. Mafic or Basic

Mafic lava has greater fluidity than the felsic lava and its melting point is also lower. Presence of high silica content in the Felsic lava increases its meting point. Acidic lava is of two types: Andesitic and Ignimbrite or rhyolitic lava. Andesitic lava has medium silica content while Ignimbrite lava has high silica content. Ignimbrite rocks are highly acidic. Nuee ardente is an andesitic lava flow. Lahar is also a form of andisitic lava flow. It is volcanic mud flow. Lahars cause accumulations of large quantities of sandy and rocky debris on lower slopes and surrounding areas and may form extensive plains. The plains west of central volcanic mountains of North Island of New Zealand is a good example of Lahar. A mixture of fine debris and water, derived generally from a crater lake of a dormant volcano, bursts out when eruption is resumed forming mud that rushes down the mountain side.

A vent is essentially required for the upwelling of felsic lava while the basic lava can come out through a crack or fracture, the only requirement is that the crack should have continuity with the magma chamber. Latur region in Maharashtra has such cracks.

Silica or acid lava builds high steep sided cones while basic or basaltic lava produces a flatter cone of great diameter. Sometimes the surface of the solidified lava may be smooth but usually it is quite rugged. In the case of both acid and basic lava, the escaping gases make the surface of the lava vesicular and full of small holes.
Besides, the upper surface cools early and forms a crust while lava continues to flow beneath the surface for quite some time. This results into the opening up cracks in the crust and the parts thus broken are transported downward by the moving lava.

Thus, the surface formed by the lava deposits is normally rough and irregular and full of cracks and holes into which rainwater can easily penetrate. The two contrasting surface features or structures may develop owing to differential lava flow at different levels of the volcanic materials in motion. They are known by their Hawaiian names, Aa for angular vesucular scoriaceous surface and Pahoehoe or Ropy for smoothly twisted, convolute surface which develosps on hotter and more fluid lava.

An extreme case of pahoehoe lava occurs when the hot fluid lava either erupts under water. In this case, blobs or lobes of lava upto a diameter of one metre is formed, which has tough but flexible skins (upper surface) and is piled up like sandbags or pillows while their interiors are still in molten state. This is called pillow lava. It is an evidence of sub-aqueous eruption and is commonly found on ocean floor.

Volcanic gases are composed of 60- to 90 % of steam. Other components of volcanic gases are carbon di oxide, nitrogen and sulphur di oxide, and small quantities of hydrogen, carbon mono oxide, sulphur and chlorine.

Solfatara: the stage of volcano when it emits only steam and gases is called the solfatar stage even after the eruption of lava and ashes has ceased. Sulphur content is an important feature of Solfatara stage which is named after the Solfatara volcano near Naples.


TYPES OF CENTRAL ERUPTION:

Based on the nature and intensity of eruption and on the composition of the expelled materials, central eruption is classified under six categories:


1. Hawaiian: Eruption is peaceful here. Hawaiian activity is essentially effusive. Lava is of thin basal variety. There is little or no tephra in the Hawaiian type of eruption. Sometimes, fountains of basaltic spray rise up with gases and when the wind is strong. These lava pieces are stretched i8nto long shiny threads known as Pele’s Hair in the Hawaiian islands—named after Pele, the goddess of fire in the islands. Examples are basalt plateau of Columbia and Iceland.

2. Strombolian: Moderate explosive action is found in this type of eruption. Scoriae and bombs are formed in the strombolian type. Normally eruption is intermittent but may be continuous) and fountains of lava are ejected at regular, rhythmic intervals varying from a few minutes to about an hour and flows are unusual. Stromboli is an island in the Lipri group of islands north of Sicily in the Mediterranean Sea. The lava fountain activity of Stromboli, reflected at night as a red glow on the downside of a towering steam plume has caused the volcano to be known as lighthouse of the Mediterranean. This type of eruption took place in Heckila, Iceland in 1947-48.

3. Vulcanian: The type is named after the Vulcano located in Lipri Islands. Vulcnian activity is explosive. In vulcanian type of eruption, lava solidifies and seals the mouth of the crater in between the two explosions or eruptions. Magma materials of all size are thrown with predominance of ash and dust. Eruption gives appearance of a huge cauliflower…as seen from distance. 1883 explosion of Krakatoa is considered Vulcanian type which was also followed by vesuvian type of explosion. But, that Krakatoa explosion is considered a special type of vulcanian explosion called Phreatic Eruption because it was caused by groundwater or sea water entering the magma chamber and flashing into steam.

4. Vesuvian: It is violent in nature. Lava comes out first from lateral cracks and then through main vent as the gases keep on accumulating in the main vent. Example is 1883 Krakatoa explosion. An eruption of this type was first recorded by Pliny in 79 AC during Vesuvius explosion hence sometimes it is also called Plinian type. Some consider the Vesuvian and Vulcanian types essentially the same and Vesuvius explosion of 79 AD is often cited as an example of Vulcanian eruption.

5. Pelean: It is violently explosive eruption. At the time of first eruption, the dense lava solidifies and closes the mouth of the crater and a dome is formed there. After some time it is broken and lava comes out along the hill slope and then an extremely dense mass of highly charged gaseous lava mixed with magma materials and ash flows down the slope like avalanches. These have been called Nuees ardentes or glowing clouds. Nuee ardente is soundless in spite of the fact that it has the velocity of winds in a hurricane. Example is 1902 explosion of Mt Pelee in West Indies. Nuee ardente is an andesitic lava flow.

An explosion of Pelean type differs from that of Vulcanian type in that the very hot gas and lava mixture is not thrown upwards but spreads downslope as nuee ardente.

6. Mud Volcano: In areas where petroleum or gas is found, sand and clay accompanies the gas emitting out in those areas. If water is also there, sand and clay form mud. The sand and clay is deposited at the vent and form a cone. The example is Bog-Boga in Baku area near Caspean Sea.

DISTRIBUTION OF VOLCANIC LANDFORMS IN THE WORLD

There are three well known zones of volcanic landforms:

A. Mid-oceanic Ridge: Upwelling Zone
B. Subduction Zone
C. Intra-plate volcanic/ seismic zone

At the mid-oceanic ridges mafic lava upwells which widely spreads over the sea floor leading to volcanic landform.

At the subduction zone felsic lava upwells which leads to formation of Plutonic, that is, Intrusive landforms. Though there may also be volcanic, that is, extrusive landforms having felsic lava in the same region. Examples are, Mt Etna, Alaska plateau, Columbia plateau, plateau of Peru, Reunion Islands in the Indian Ocean. In the Mediterranean Sea, all islands are made up of acidic lava.

Intra-plate volcanism is found in the interior of a plate. At present a number of active volcanoes are in the intra-plate region. Examples are, Mt Kilimanjaro: the highest volcanic mountain in Africa, Mt Kenya: the second highest in Africa- both are of acidic nature; Deccan Lava plateau (formed due to basic or fissure eruption): it is the highest lava plateau in the world, Parana plateau of Brazil: the second highest lava plateau in the world, Columbia plateau: the third highest lava plateau and it is the youngest lava plateau dating early Pleistocene age. Parana plateau of Brazil and Deccan plateau of India are contemporary in age.

Volcanic Landforms are of two types:

A. Associated to central eruption
B. Associated to fissure eruption


CENTRAL VOLCANIC LANDFORMS:

Central volcanic eruption occurs through the vent and in general acid lava erupts through this and so some typical landforms are produced.

1. Cinder cone: These are smallest of the volcanoes, built entirely of pieces (pyroclasts) of solidified lava thrown from a central vent. They form where a high proportion of gas in the molten rock causes it to froth into a bubbly mass and to be ejected from a vent with great violence. The froth breaks up into small gragments which solidify as they are ejected and fall as solid particles near the vent. Finer particles are rained down on the crater, and form a cone in a circle around the crater. The slope of wall ranges from 260 to 300….in other words, cinder cone is a concave structure as a whole and its slope is 30-40 degrees. Cinder cone rarely grow to more than 150 to 300 metres in height. Growth is rapid. Monte Nuovo near Naples grew to a height of 120 metres in the first week of its existence. Puraricutin in Mexico reached a height of 300 metres in three months. Cinder cones usually occur in groups, often many dozens in an area of a few tens of square miles. They sometimes show an alignment parallel with fault lines in the underlying rock. Pushpagiri in Karnataka, Mt Kenya and Mt Kilimanjaro are dominated by pyroclasts. Barren Island in the Indian Ocean is also an example of cinder cone. Pushkar Lake is situated in a cinder cone. Lake Pushkar is an old caldera wherein the conical head has been massively eroded leading to the exposure of pyroclasts. (Image: cinder cone)

2. Acid Dome: In this case pyroclasts are covered by solidified thin layer of rhyolite. Acid domes are also called cumulo-domes or endogenous domes which rise into a crater. Examples are, Reunion Island and also islands in the Auvergne region of France. (image)

3. Basalt Dome: Sometimes basalts came out through the vent when the crustal layer is thin enough. Here concentration of pyroclasts is very low. It is basically a plateau like structure having a raised central portion which is occupied by a lake. Basalt domes and shield volcanoes are essentially the same structure, the difference being that of size only. The basaltic domes grade upwards to become shield volcanoes. Basaltic domes are exogenous domes- piled around a central vent. Examples are, Shield Island in Hawaii, Mauna Loa and Mauna Kea, Tahiti Island and Banks Peninsula in New Zealand.

4. Composite Cone: Composite cones are the characteristics of dormant volcanoes. Composite cone has alternate layers of pyroclasts and solidified lava. These are found in old cone and are known as strato-volcanoes. Most of the world’s great volcanoes are composite cones. The steep sided form is governed by the angle at which the cinder and ash stand, whereas the lava layers provide strength and bulk to the volcano. Height upto several thousand feet and slope of 20 to 30 degrees are characteristics. The slope is less than what is found in the case of cinder cones. The crater may change form rapidly, both from demolition of the upper part and from new accumulation. Examples are Fujiyama- it has three well defined such layers, Vesuvius and Stromboli in Italy, Popokatepatal in Mexico, Mt Hood in Oregon, Mt Shasta and Mt Ranier in USA, Cotopaxy in Ecuador, Mayon in Philippines. (Image)

5. Parasite Cone: Parasite cone is also the characteristics of dormant volcanoes. In this case the lava does not find passage through the main vent or the parent vent due to thick deposition and solidification of lava during erstwhile volcanic activity. Os, the lava tends to move towards subsidiary vents (owing to less pushing gaseous force) along the cracks or the fracture in the crust. Lava come out to the slope side of the parent volcano through some cracks, but at the other cracks may not give route to any amount of lava. The lateral volcano is called parasite or satellite cone. The lateral crack is a heterogeneous layer. Presence of a parent vent is the essential condition for the formation of parasite cone. Also, parasite cones would only develop if the length of the lateral vent is shorter than the main vent and the rocks are brittle. Examples are, Mt Etna- highest in Europe and has 230 satellite cones, Fusiyama has 45 satellite cones, Mt Egmont in New Zealand. Composite and Parasite cones are found on the landforms. (Image)

6. Crater and Caldera: Just above the volcanic vent there is usually a rounded bowl or funnel shaped structure which is called crater. Its diameter is normally small. The following are the causes of crater formation:

A. Violent throw off of the volcanic material
B. Process of solidification of the volcanic materials around the vent or the ring crater and their compactness promote crater formation.
C. Erosion of materials from around the vent.

In the crater depression small lakes are formed which are called maare or maars. Maar is a German word that refers to a small, near circular sheet of water situated in the explosion vent, the result of an eruption that blown a hole in the surface of the rocks, surrounded by a low crater ring of fragments of the country rock but accompanied by no extrusion of igneous rocks.
Craters can be seen in Eiffel volcanic region of Germany due to violent explosion in the western part of the rift valley of Africa. Caldera is an extensive rounded volcanic depression whose diameter is greater than that of a crater. Crater is due to geological process and when it is eroded massively it becomes caldera, that is, for caldera formation erosion is required but it can also be formed by an explosion. A huge caldera with a diameter of four miles was formed at the time of the Krakatoa explosion in 1883, the caldera of Mt Katmai in Alaska, the Crater lake of Oregon is located in the caldera in USA-it has a diameter of six miles and is of Pleistocene origin. On the top of the Barisan Highland in the northwest Sumatra, there is a huge caldera in which Loke Toba is situated. Lonar Lake, lake Nicaragua and Lake Titikaka are the other examples of caldera.


7. Nested Caldera: Also called Cone in cone. It is also associated with dormant volcano. In this case there are two or more than two calderas situated one above the other and each caldera possesses a lake. Example is Fusiyama which has three such lakes.
8. Plug Dome: Plug refers to a more or less cylindrical mass of acid lava, occupying the vent of a dormant or extinct volcano. Here acid lava is generally exposed by denudation. This landform is produced due to greater erosion within the caldera exposing the dykes which is relatively harder. In this case, the surrounding rocks are removed and the dyke remains stranded. This landform is not precisely a dome but similar to dome topography and hence this is known as plug dome. It is also called tholoid or volcanic neck. It is the intrusive feature of Plutons. Examples are found in Nicaragua in central America, in crater dome of Mount Pelee, Matinique in West Indies, the Arthur’s Seat, the site of Edinburgh in Scotland, the plugs of Auvergne in France, Hopi Buttes in north east Arizona (in Colorado plateau region) and also in the Castle Rock (near Edinburgh).

At times, eruption occurs through cracks and fractures in the rock structure. In this case basic lava is the only material that upwells in huge quantity. Felsic lava does not have enough fluidity to pass through small cracks. The upwelled basic lava spreads over a vast area due to high fluid nature of the moving magma. This process leads to the formation of large basaltic landforms. Deccan plateau of India and Columbia plateau. All the major plateaux of the world are basaltic.

Radial dykes may sometimes be laid bare by deep erosion of a volcanic neck. A classic example is Shiprock in New Mexico where volcanic neck with prominent radiating dykes are seen in north east New Mexico. Radiating dykes are also found in the Glasshouse Mountains of Queensland, north of Brisbane.

Plate Tectonics and Volcanism:

In 1968 Morgan outlined the hypothesis of plate tectonics. He divided the earth’s surface into twenty plates which are moving relative to one another above the weaker semiplastic asthenosphere as a result, it is believed, of thermal convection currents within the mantle. Le Pichon simplified the concepts of plate tectonics by dividing the earth’s surface into six major, and a few minor or small ones.

The phenomenon of volcanism takes place due to destructive plate activities along the margins of the converging plates.As the oceanic crust is forced downwards into the subduction zone, it becomes molten and forced back to the surface of the earth as a chain of volcanoes.

DISTRIBUTION OF VOLCANOES

Volcanoes in Philippines

There are about 200 hundred volcanoes in the Philippines archipelago, 21 of which are active; to name a few, Mt Isarog (1900 metres) situated 280 kilometres southeast of Manila, erupted 600 years ago; Mr Natib 1200 (metres), 40 kilometres south of Mt Pinatubo is supposed to have ejected steam and therefore mild tremors were recorded by the scientists.

Eruption in Japan

Mt Unzen erupted on June 3, in 1991, killing 38 geologists who were studying the invisible activities going on within the heart of the volcano. The evacuation of nearby inhabitants was already accomplished on the warnings issued by the same group of 38 scientists, who themselves fell victims to the fury of the nature.

Eruption in Andaman Islands

A team engaged in routine inspection of light houses in the Andaman Islands sighted thick smoke spewing out of the Barren Island volcano 125 kilometres from port Blair on April 10 in 1991.

The advancing lava front had already covered a sizeable portion of the island, rendering the light houses non functional and making it virtyually impossible to use any of the landing sites.

The volcano had erupted 200 years ago. The lava thrown out on Barren Island is chemically different from the lava spewed during its previous eruption. According to geologists, the volcano activity on Barren Island has been in three phases. Eruption of submarine lava gave birth to the island 50,000 thousand years ago, creating a joint volcanic cone that covered the whole island. In the second phse, the cone was later blown off and the ejected debris was deposited on the cauldron. In the last phase, a large spatter cone has developed at the mouth of the eruption as a result of which, two volcanic cones are now visible.

The eruption on about 30th April in 1991 originated not in the older crater, but in a vent alongside it.

Narcondum Island, the other volcanic island in the region has shown no sign of becoming active. According to the geological survey of India, Nacondum Islands has no recorded history of eruption.

Two volcanic islands in the Andamans are in the Pacific Volcanic belt which extends to Japan and Philippines.

WORLD DISTRIBUTION

The zones along which earthquake, volcanic or mountain building activity is currently taking place coincide with junctions between plates.

1. Island Festoons of the Pacific: Two third of world’s active volcanoes of the world and thousands of inactive volcanoes are found in this belt. The volcanic belt surrounds the pacific ocean. It is also known as the Ring or Circle of Fire. Among the important volcanic areas of this circle of fire are Aleutian Islands, Alaskan sub-continent, Guatemala, northern and southern Andes. The Circle of Fire contacts with the Atlantic belt at two places: A. Lesser Antilles Vocanic belt. B. The one spot situated in the volcanic belt of South Antilles and which joins Patagonia with Grahamland.
2. Alpine Himalayan Belt: The belt starts from Maderia and the Canary Islands and passes through the Vesuvious, Lipri Island, the Etna and the Aegian volcanoes of the Mediterranian Sea. The belt continues further through Caucasus, Armenia, Iran and reaches Balochistan. After crossing the Himalayas the belt crosses Yunan, Myanmar, Andamans and ends in Indonesian Islands.
3. African Rift Valley: It starts from Bay of Guinea to Red Sea passing through the middle of Africa. The most active volcano in this belt is Cameroon. Mt Kilimanjaro and Kenyan volcanic mountains are beyond the rift valley but Algon is within the belt.
4. Other Areas: Mid Atlantic Cape Verde is famous among them. Volcanoes of Indian Ocean are Comoro, Mauritius and Reunion situated close to Madagascar. There are many volcanoes close to Antarctica.

Environmental Aspects of Volcanoes:

Heavy loss of life and property occurs when volcanoes erupt. About 50 active volcanoes erupt each year. About 360 million people live in the shadows of volcanoes that may explode at any time. Geologists watch only mountains they believe to be still active. Some of the world’s worst disasters have resulted from the eruption of volcanoes thought to be extinct, for example, Vesuvius in 79 AD. In 1985 eruption of Nevado del Ruiz in Columbia killed 22,000 people.

Volcanic ash may have a beneficial effect upon productivity of soil where the ash fall is relatively light. Eruption of Sunset crater near Flagstaff, Arizona in 1065 AD spread a layer of sandy volcanic ash over Barren reddish soil of the surrounding region and caused it to become highly productive because of the moisture conserving effect of the ash, which acted as mulch in the semi-arid climate.

Steep slopes provide valuable timber resources e.g. San Francisco. A scenic feature of great beauty, attracting a heavy tourist trade, few landforms outranks volcanoes. National Parks have formed due to volcanic activities, e.g. Mt Rainier, Mt Lassen and Crater Lake.

The gas-bubble cavities in some ancient lava have become filled with copper or other ores. The famed Kimberlite rock of South Africa sources of diamonds is the pipe of an ancient Volcano.

As a source of crushed rock for concrete aggregate or railroad ballast and other engineering purposes, lava rock is often extensively used. Thus the ancient layers that make up the watching ridges of northern New Jersey have in places been vertically leveled in quarrying operations continued over several decades.

ORIGIN OF EARTH'S CRUST

Several theories have been put forward regarding the origin of the continents and oceans. Of these theories only the Plate Tectonics Theories have received wide acceptance and rest are generally carry historical and academic value. Kelvin was of the view that higher and lower parts of the earth’s surface were determined quite early in the history of the earth in the process of contraction of rocks. The low and high density rocks solidified to form higher and lower longitudinal columns of earth surface; for example, north and south Americas are low density rocks aligned along Atlantic Ocean of high density rocks followed by Europe and Africa again of low density rocks. But, Kelvin’s hypothesis does not stand the test of science. Since the rotation of the earth has not changed since its origin, Kelvin’s logic would place columns of high and low density rocks on latitudinal axis and not on the longitudinal as these are place and as Kelvin suggested.

Sollas suggested that the distribution of elevations and declivities is related to the original atmosphere so that in areas of high atmospheric pressure the molten material was pushed downward.

Thus Sollas presumed that the original atmospheric pressure belts were distributed longitudinally. But this is not corroborated by geological evidence. The pressure belts have wandered in geological past and that there are evidence showing that the axis of earth deviated in past by 11 to 30 degrees but there no research till date has suggested that earth’s axis deflected by 90 degree at any point of time in the past. Put simply, the rotational axis of the earth has never been horizontal, the essential pre-condition for Sollas’ model to be true. Even if his principles are applied on the earth, the arrangement of the continents and oceans would be along latitudes in relation to pressure belts, with low pressure regions comprising continents and high pressure belts oceans. But the earth’s orientation is markedly different.

There are many other view. The supporters of the Planetesimal Hypothesis attribute the crustal distribution to unequal collection of planetesimals during the formation and solidification of earth. According to Lapworth, the continents and oceans have been formed through of large scale folding on the surface of the earth so that the anticli8nes represent the land and synclines constitutes the sea. However, it does not appear logical to invoke large scale folding merely on the ground of contraction and cooling of the earth. In 1907 Love gave a mathematical grab to the hypothesis of Lapworth and tried to prove that since the gravitational centre and geometrical centre of the earth are not the same, there will be a series of harmonic deformation in the shape of the earth resulting in upwarpings and depressions and thus in the formulation of the continents and oceans.

In the beginning of the 20th century, a new hypothesis was proposed by Jeans later supported by Sollas as well. According to this view, after the earth had given birth to the moon , the earth became pear-shaped in the process of attaining rotational stability. On this pear shaped earth, the neck would form the oceans and the edges would constitute higher land. Jenas postulated that these two hemispheres in the process fo cooling would press against each other due to mutual attraction, resulting in equatorial buldge and the formation of higher land.


Sollas tried to show that it was possible to explain the present distribution of land and sea or water the the help of Jeans’s hypothesis but the idea was not accepted. In this connection, it may be pointed out that recently, Osmond Fisher of Australia has suggested that the depression which was left on the earth after the separation of the moon, gave way to the pacific ocean in due course. This hypothesis has the merit of explaining the principal asymmetry on the earth’s surface and also the difference between the Atlantic and Pacific coasts.

In 1875, Lothian Green proposed his tetrahedral hypothesis. He pointed out that the distribution of land and water shows a tetrahedral arrangement. Green stated that the earth was an inverted tetrahedral which stood on its top. In such a position the four oceans would occupy the four flat faces of the tetrahedron and the upper horizontal face would be occupied by the artic ocean. ON the edges of the upper horizontal face would be found the landmasses which would form a ring around the arctic ocean. On the three vertical edges would be the continents extending from north to south are north and south Americas, Europe and Africa and Asia and Australia respectively. At the bottom would lie the south pole around which would extend landmass of Antarctica. He pointed out that the shape of the earth could not an exact geometrical tetrahedron and its edges which constituted the continents would be convex and not sharp and angular.


In recent years, J W Gregory has tried to present the above theory in a more detailed and systematic manner with reference to the characteristics of the distribution of land and water. But this hypothesis has now been rejected for not standing the test of mathematical principles. According to the laws of mathematics, a big body like the earth can not mountain its tetrahedral shape in gravitational equilibrium.

The continental drift theory of Wegener also tried to explain the present status of the crust but failed to provide scientific reasoning. The major breakthrough was achieved by Harry Hess (1956-60) when he presented Sea Floor Spreading Theory. This theory provided basic, relevant and scientific information regarding evolution of oceanic crust. Thereafter came the Plate Tectonics Theories, mainly by Wilson and Morgan. Now, it was viewed that the initial cooling of the earth solidified the upper layer of the earth body. This solidified upper layer is called the crust. Solidification or the formation of the crust was not a homogenous or regular phenomenon rather it was in the form of crustal blocks, which are known as plates.


But these plates are not irregularly spaced, they are arranged in a way to that two plates have a common boundary known as Rim. This boundary is a space through which internal energy of the earth escapes. The plate margins are defined as tectonic zones because the margins are subjected to folding, fracturing, squeezing, volcanism and passage of seismic waves. The characteristics are related to the functional behaviour of the energy flow as explained under the convectional current theory of Arthur Holmes.

All modern views suggest that boundary planes are characterized by upwelling and sinking of energy matter, that is, magma. Whenever there is upwelling there will be volcanism i.e. it brings crustal accretion- formation of basaltic crust, as explained by Harry Hess. All mid-oceanic ridges are the centres of crust formation. Divergin trend of energy cycle takes crustal columns apart and the vacuum is occupied by the new basaltic rocks or magma forming crust.


But whatever crust is added at or near the mid-oceanic ridge is compensated in the subduction zone where crustal plates are destroyed. Subduction plate margins are found at the place of convergence of two plates generally of varying densities. At the site of collision the low density rocks will go upward and high density rocks downward. The upward column is subjected to up-folding and sinking column undergoes melting in the Benioff Zone. Granitic crust develops on the continents by means of volcanism caused by subduction zone or Benioff zone effect.

Crust formation is compensated by the process of weathering and erosion. There is a rock cycle and whatever continental crust is formed is consumed by the rock cycle.


Crustal evolution is thus a dynamic phenomenon and modern geophysical and geomorphological evidence favour this modern model of origin of the crust. In spite of having gained wide acknowledgement this modern theory of evolution of crust based on sea floor spreading and plate tectonics theory is not beyond the scope of criticism. According to this model there must be equal, parallel and continuous subduction column to compensate the sea floor spreading or crustal accretion but we don’t find equal and continuous subduction column. Secondly, the rate of upliftment or crustal formation exceeds the rate of crustal destruction. However, this model is the best one at our disposal for understanding geomorphological phenomena.

Still There Are Some Thoughts

Still you didn't get me.

Still you got me wrong.

Still you want me,

To feel free.

Still I am cowed down.

I don't know what is better

Love or logic?

Love is blind,

Logic is brutal.

I can't go blind.

I can't become brutal.

I live in perceptions,

But, perception isn't truth

Perception builds new perecepion,

I get farther from truth.

Life is beautiul,

Living it a pain.

In search of freedom,

I tighten my chains.

I can't love it,

I can't leave it.

Reality bites.

Dreams are scary.

Daydreams are brighter.

As night falls, dreams take over.

And as day breaks out, 

Reality bites again.

I don't like the day, 

I don't love dreaming.

I know the pain of torture.

Not because, I have suffered it,

But because, I have inflicted it,

Upon you.

I wanted to save you,

Be your saviour.

But, the fence ate the crop.

Crop the fences, now!

Life is indeed beautiful.

Living it but still a pain.

Shakespeare haunts me again.

Again, I do not know,

What is better? 

To love it or to leave it?

Indai-Australia Face-off

Once again India and Australia are set to lock horns on a cricket field and once again an Australian skipper says that playing India in India is the toughest assignment hitherto in his career. And, once again Team India are preparing or under-preparing to bask in another possible glory of beating the proven champions. Given the recent performances of the Team India, the cricket management and critics, both have had their sharp focus on the domestic cricket hoping that some of the problems of the national team could be solved. Alas! This could happen! 

However, the focus on the domestic cricket season was welcome and well timed. Inclusion of Shikhar Dhawan in the national squad is a positive result of that focus. Though, Wasim Jaffer would consider himself unlucky. He must rue the fact that he is aging with time! (But, who doesn't?) This poses the eternal question once again: Should age be a criterion for national duty? This comes at a time when the team has consistently failed in proving good opening stand exposing the middle order, which has failed more often than not in such situations. India has witnessed many disasters in test arena in past couple of years. 

Rahul Dravid and VVS Laxman are gone and Sachin Tendulkar has played his innings. We can hear those words from the maestro any day. In such a phase of transition Jaffer would not have been a bad option. He is mature. He scores freely. He is dependable and has sound techniques. He may have one or two years of good cricket left in him at 34. His presence at the top may give some breathing experience to the likes of Kohlis, Pujaras and others. However, dropping Gautam Gambhir seems to have worked well and served its purpose. Gambhir hit a good century against the Australians while leading India 'A'. All the players must understand that their place in the national team is not to be taken for granted.

Harbhajan Singh may like to emulate in bowling what Gambhir in batting against the Kangaroos. Ishant Sharma would also sense an urgency to perform. No one can considered raw after playing more than 40 test matches. Virender Sehwag must think that he has been given one last chance to prove that he still has something to offer at the highest level. One hopes that a bespectacled Sehwag would be wiser.

On the other side, the Australians though have a depleted bowling attack, they are capable enough to bowl out India twice over five days. Australian skipper Michael Clarke does not think he is a fresher. Neither does Shane Watson think so. Watson can double up at a world class batsman and an equally good speedster. Mitchell Johnson and Peter Siddle have shown that they are dangerous against Indians. Fans must be waiting for a mouth-watering recipe of cricket February 22 onward.