Category: Geography Notes PPT

Noctilucent clouds or night-shining clouds are the highest clouds found in the Earth’s atmosphere located in the mesosphere at an altitude around 76 to 85 km (249,000 to 279,000 ft). The cloud consists of ice crystals and is only visible during astronomical twilight. In Latin, the term Noctilucent means “night-shining”. The clouds are most visible during the summer month and when the Sun is below the horizon from latitude between ±50° and ±70°.

The clouds are too faint to be observed during daylight and are visible only when illuminated by sunlight from below the horizon while lower levels of the atmosphere are in Earth’s shadow.

Noctilucent Meaning

The term Noctilucent means “night-shining” and is an indicator as to what makes them special.  Most clouds are dark at night, but night-shining clouds appear to glow a brilliant white or electric blue. Nlc clouds can reflect the light of the sun as shown in the figure given below as they are the highest clouds in the Earth’s atmosphere. The Nlc clouds are located in the mesosphere at an altitude of around 76 to 85 km (249,000 to 279,000 ft).

Noctilucent Clouds Definition

Noctilucent clouds, also known as polar mesospheric clouds, are very thin clouds of water ice crystals located in the Mesosphere at a height of about 75 km to 90 km.

Noctilucent Cloud Discovery 

Noctilucent or night-shining clouds were first observed in 1885, two years after the 1883 eruption of Krakatoa in the straits of Java. 

It is not confirmed whether their appearance had anything to do with the volcanic eruptions or whether their occurrence was due to more people observing the incredibly vibrant sunset caused by volcanic debris into the upper atmosphere by eruptions and contributing to their formation.  

Subsequent studies have shown that noctilucent clouds are not solely caused by volcanic activity, although dust and water vapour could be inserted in the Earth’s atmosphere by a volcanic eruption and contributed to their formation.

The assumption was made by the scientist at that time that clouds were another phenomenon of volcanic ash, but the cloud persisted after the ash liquidated out of the atmosphere.

In 1972, Nlc clouds were first observed from space by an instrument on the OGO – satellite. 

Noctilucent Cloud Formation

The night-shining clouds are made up of small crystals of water ice up to 10 mm in diameter and exist at a height of about 76 to 85 km, higher than any other cloud in the Earth’s atmosphere. Similar to the other clouds. Clouds in the Earth’s lower atmosphere form when water collects on particles, but mesospheric clouds or clouds in the mesosphere may come directly from the water vapour as well as forming on dust particles. 

Nlc clouds required water vapour dust, and very cold temperature to form. The source of both dust and water vapour in Earth’s atmosphere is not known with certainty. The dust was expected to come from micrometres, although particles from volcanoes and dust from the troposphere are also possibilities. Scientists believe that moisture could be lifted through the gas in the tropopause, as well as forming the reaction of methane with hydroxyl radicals in the stratosphere. Noctilucent clouds form mostly in the polar regions because the mesosphere is the coldest in that region. 

Noctilucent Cloud Observation

Nlc clouds are mostly found colourless or pale blue, but occasionally other colours such as red and green are also observed. The attributes of blue colour come from absorption by ozone in the path of sunlight brightening the Nlc clouds. The Nlc clouds appear as featureless bands, but frequently show different patterns such as streaks,  waves, and wavelike undulations.

The Noctilucent occurs during summer from mid-May to mid-August in the northern hemisphere and between mid-November to mid-February in the southern hemisphere. The clouds are very faint and tenuous and may be observed only in twilight around sunrise and sunset when the clouds of the lower atmosphere are in the shadow, but the Nlc clouds are brightened by the Sun.  The clouds are best observed when the Sun is between 6° and 16° below the horizon.

Although night-shining clouds are found in both the hemisphere, they have been observed thousands of times during the northern hemisphere and fewer than 100 times during the southern hemisphere. 

Also, Nlc clouds are made up of small crystals which are not noticeable to the viewer on the ground because they cannot disperse enough light. The size of the crystals may be 30 mm or less.

Noctilucent Cloud  Forms

The noctilucent cloud comes in different forms and patterns. As per the identification scheme introduced by Fogle in 1970, the clouds are classified in five different terms. This classification is further modified and subdivided. In view of the recent research, the World Meteorological Organization now observed four major forms that can be subdivided. The four major forms are:

• Type 1 veils are very fragile and lack definite structure, similar to cirrostratus or inadequately defined cirrus.  

• Type 2 bands are long streaks that rarely appear in roughly parallel groups, usually more widely spaced than the bands or elements seen with cirrocumulus clouds. 

• Type 3 billows are arranged in a closed-space, roughly parallel short streaks that most often look like cirrus. 

• Type 4 whorls are more partial, or more often complete rings of cloud with dark centres. 

Did You Know?

• NLC clouds are the highest cloud in the sky, growing at the edge of space 50 miles above the Earth’s surface.

• Nlc clouds exist in the atmosphere mesosphere layer.

• Nlc clouds are the newest clouds that we all have observed. Scientists first observed the Nlc clouds in 1885 after the same famous explosion of the Krakatoa volcano.

• Nlc clouds occur during summer from mid-May to mid-August in the northern hemisphere and between mid-November and mid – February in the southern hemisphere.

Our country is the most diverse country in the world whether in terms of its culture and heritage or geographical features. Here in this article, you will get a chance to know your country India. This article will help the students of Class 6 and higher classes to get a brief understanding about our country. Read the notes and observe the maps and diagrams properly to retain the information.

Know Your Country India

To know about our country you need to check the world map and map of India (which are given below). These maps will help you to observe where our country lies. Once you know about its location, then you can predict its temperature, rainfall, vegetation, crops, and a lot of things. The important concepts and information about our country are written below:

Location

 

From the maps given above, it can be observed that India has its place in the Northern-Eastern Hemisphere of the globe. The tropic of cancer which lies at 23 1/2° N passes through the country through its center and the standard meridian which is 82°30′ E of the country passes through Mirzapur, Uttar Pradesh. From the map, it can be seen that it lies in the Asia continent and that too in South-Asia.

Climate

From the map, you must have observed that the tropic of cancer passes through India. Thus, it is a tropical country. The climate of the country is not the same at all places and depends upon the topography and the location of the region. The monsoon is a special feature of India’s climate.

Neighbourhood

India is a South Asian country and has a number of neighbouring countries that are connected with India through land or water. Countries near India are also shown on the map below.

Names of Countries that Shared Maritime Border With India:

• Bangladesh

• Bhutan

• China

• Nepal

• Pakistan

• Afghanistan

• Myanmar

• Sri Lanka

Name of Countries that Shared Maritime Border With India:

• Bangladesh

• Indonesia

• Myanmar

• Pakistan

• Sri Lanka

• Maldives

• Thailand

Administration

India is divided into various states and union territories for administrative purposes. Our country was reorganized in 1956 as per the State Reorganization Act and then the country was divided into 14 states and 6 union territories. This division was done on the basis of language. After that, a lot of States and Union territories have been formed. The number of states and union territories is not fixed and keeps on changing as per the requirement of the country. States and UTs can be formed or demolished or merged etc. as per Part 1 of the Constitution of India. The number of States and UTs in different years is shown in the table below:

So, How many states are there in our country right now? (as of 2021)

After the Jammu and Kashmir reorganization Act, 2019, India has 28 states (excluding Jammu and Kashmir).

Number of Union Territories

After Jammu and Kashmir Reorganization Act, 2019 and Dadar and Nagar Haveli and Daman and Diu (Merger of Union Territories) Act, 2020, India has 9 Union Territories (as of 2021).

Physical Division of India

India is gifted with a number of physical features like mountains, plateaus, plains, etc. The physical features of India are listed below and can also be seen on the map:

Himalayas

These mountains are called young fold mountains which lie in the north. These can be divided into the Himalayas, the trans-Himalayas, and the Purvanchal. The Himalayas are further divided into three parts ie. the Great Himalayas or Himadri, the Lesser Himalayas or Himachal and the outer Himalayas and Shiwalik. Trans Himalayas include the Karakoram range, the Zaskar and Ladakh ranges and these lie North of the Himalayas whereas the Purvanchal mountains lie in the North-Eastern side of the country.

Great Indian Desert

It lies in the western side of the country and the Aravalli Hills called the Thar Desert which is the 9th largest desert in the world. It is the Aravalli Hills which are old fold mountains that save the country from the desert sand and arid region.

Northern Plains

These plains are formed because of the sediments brought by the major rivers like Indus, Ganga, Brahmaputra, and their tributaries. These plains are the most fertile land in the country and also densely populated. These can be divided into four parts i.e. Bhabar, Terai, Bhangar and Khadar. 

Deccan Plateau

It is a part of the peninsular plateau of India and the black soil found here is called the Deccan Trap which is formed because of volcanic eruptions. This plateau can be further divided into the Western Ghats and the Eastern Ghats.

Coastal Plains

It runs along the coastal regions of the peninsular plateau and it can also be divided into two parts i.e the eastern coastal plains which run along the Bay of Bengal and the western coastal plains which run along the Arabian Sea.

Islands

Our country has a group of islands as well which are a great source of tourism. There lie 204 islands on the eastern side in the Bay of Bengal called the Andaman and Nicobar Islands which is also a Union Territory and 43 groups of islands are situated on the western side in the Arabian Sea called Lakshadweep Islands which is also a Union Territory of India.

Did You Know?

India is called the land of rivers because of the presence of a number of rivers here and in terms of the geographical area it is the seventh-largest country in the world and the second country in terms of population.

When we talk about placer deposits meaning, it is a natural concentration of heavy minerals induced by the effect of gravity on moving particles. When heavy, stable minerals are liberated from their matrix by the mechanism of weathering, they are slowly washed downslope into streams which rapidly winnow the lighter matrix. Therefore, the heavy minerals become concentrated in river, stream, beach, and lag (debris) gravels and include workable ore deposits. Minerals which form placer deposits constitute high particular gravity, are durable and chemically impervious to weathering.

Mineral Found in Placer Deposits

Minerals that form placer deposits include precious deposits like gold, platinum, copper, zircon and various gemstones apart from magnetite, ilmenite, chromite, cassiterite, rutile, and native monazite.

Factors Influencing Placer Development

Placer development is activated by a combination of tectonic activity and oscillations in climate and sea level. Besides that various other factors are responsible for placer developments that are as follows;-

• Chemical and Physical weathering that eases all forms of erosion

• Release of minerals into sediments that are transported, deposited, sorted, and often reworked.

• Placer deposits occupy quite a huge range of geomorphological features, by which they are more simply categorized.

• Mineral sands, and in places diamonds, prefer coastal surroundings, whereas the other placer minerals are concentrated often in fluvial deposits.

How to Identify the Type of Placer Formed?

Alterations in energy levels and the associative physical attributes of the minerals and sediments identify the style of placer formed. Lag placers outcomes from an increase of energy that culls out the hydraulically lighter particles (lights) close to Earth’s ground surface. Accumulation placers are created by selective settling of hydraulically heavier particles because of reduction in energy. Both styles are seen in all placer types. Multiphase accumulation, repetition of supply, and reworking are common and generally advantageous. Minerals are favorably concentrated and depleted at different scales, particularly in a fluvial environment, by external physical conditions that form localized energy change. Beach deposits of mineral sands are a type of lag deposit.

Based on the nature of its source, some situations should coincide and events take place to develop a significant placer. The most significant economic characteristics are size and grade (from parts per billion for diamonds to wt percent for minerals), all together with bedrock qualities, sediment particle sizes, and mineral size and morphology. Post depositional alterations, particularly the upgrading of ilmenite by alteration, are significant. The maximum distance isolating a placer from its source varies extensively; from less than a kilometer to thousands of kilometers. Diamond, zircon and rutile placers have formed over hundred to thousand kilometers from their sources. Transport distance is increased by high-energy flow in constricted fluvial channels. An understanding of how placers develop, together with the study of gold particle composition and morphology, aids in the search for primary deposits.

Where to Find Placers?

Placers can be found in virtually any area where gold takes place in hard rock (lode) sediments. The gold is released by weathering and glacier or stream action, transported by gravity and hydraulic action to some preferable point of deposition, and concentrated in the process. Generally, the gold does not travel far from the source, so familiarity with the location of the lode sediments is useful. Gold can also be linked with copper and may form placers in the surrounding area of copper deposits, although this happens less frequently.

Causes of Placer Development

Following are the Causes of Placer Formation:

• Geological instances such as subsidence and uplift may cause repeated and prolonged cycles of erosion and concentration, and where these processes have been undergone placer deposits may be enriched.

• Antiquated river channels and several river bench deposits are examples of gold-bearing gravels which have been disposed to a number of such events, subsequent to minimum partial concealment by other deposits, including volcanic substances.

• Residual placer deposits developed in the immediate vicinity of source rocks are generally not the most productive, though exceptions take place where veins supplying the gold were extraordinarily rich.

• Reworking of gold-bearing substances by stream action results in the concentrations required for exploitation.

• In desert areas sediments may result from unexpected flooding and outwash of sporadic streams.

The Quaternary is a subdivision of geologic time. It is the Quaternary Period that covers almost the last 2.6 million years up to the present day of the earth. The Quaternary, as well as the Tertiary Periods both together, form the Cenozoic Era.

The quaternary meaning can be understood by the below-given image:

Quaternary Geography

The Quaternary is further subdivided into two epochs, the first is the Pleistocene which is up to about 11,700 years ago and the second is Holocene which is about 11,700 years ago to the present day. The Quaternary Period is one of the very extraordinary changes that took place in the global environment and also the period during which much of human evolution had taken place.

The Quaternary Period has also involved many dramatic climate changes in the planet, which has affected food resources and led to the extinction of many species. The period also saw the rise of a new predator that is known as man.

Climatic Conditions During the Quaternary Period 

Scientists from all over the world have evidence of more than 60 periods of glacial expansion that was interspersed with briefer intervals of warmer temperatures. The entire Quaternary Period which also includes the present is referred to as an ice age because of the presence of at least one permanent ice sheet i.e. Antarctica. However, studies say that the Pleistocene Epoch was much drier and also colder as compared to the present time.

The glacial advancement varied between continents,  but approximately 22,000 years ago, glaciers covered about 30 percent of the surface of the earth. In areas that are now Europe and North America, there existed huge grasslands known as the “mammoth steppes” and had a higher productivity rate with greater biomass than the modern grassland. The grasses were very dense and also highly nutritious. Whereas, winter snow cover was quite shallow.

Ascent of Man During the Quaternary Period

Homo erectus was the first-ever hominid species that widely used fire. There are two hypotheses about the species’ origin. The first hypothesis is that the species were initially originated in Africa and later dispersed throughout Eurasia, with the ability to exploit the colder regions using fire and tools. The second hypothesis claims that the Homo erectus migrated to Africa from the region of Eurasia. Excavations in Dmanisi, Republic of Georgia, have uncovered fossil evidence that Homo erectus species were successful hunters.

The existence of the Homo neanderthalensis was from about 200,000 years ago to about 30,000 years ago. Fossil evidence showed that the species lived in western Europe which also includes southern Great Britain, throughout central Europe and Ukraine, and as far south as Gibraltar and the Levant. However, Neanderthal fossils have not been found in Africa. Neanderthals were shorter as well as stockier than modern humans with longer, stronger hands and arms. They lived in shelters, made and wore clothing, and also used diverse tools made up of stone and bone.

According to the climatic conditions, there was a requirement for a heavy diet in animal protein so they were sophisticated hunters. A recent discovery indicates that they also cooked and ate plants. They buried their dead and made ornamental or symbolic objects. No earlier hominid species have been shown to practice any kind of behaviour that indicates the usage of language.

Evidence suggests that Homo sapiens originated in the continent of Africa and the oldest fossils of anatomically modern humans, found in Ethiopia which are approximately 195,000 years old. By 100,000 years ago they had dispersed as far north which is now known as modern Israel, but the oldest fossils of modern humans are also found farther north are only 40,000 to 60,000 years old. By this discovery, it is clear that Homo sapiens, as well as Homo neanderthalensis, were contemporaries for a time. Few dental evidence claims that H. sapiens matured later than Neanderthals. This suggests that a longer childhood led to more time for social development as well as transmission of knowledge and technology to new generations. 

This might have led to the division of labour allowing all the females as well as the young to forage for more diverse food sources. Diversification in diet could have been a species advantage for the Homo sapiens when the climate cooled again. The most recent Neanderthal remains are approximately 28,000 years old. Homo sapiens weathered the drastic climate changes and continued to disperse throughout the Earth whereas the Neanderthals became extinct.

Salinity means the saltiness or the amount of salt which is dissolved in a water body. The water body which has salt content in it is called the saline water body.

Salinity is considered to be an important factor that determines many aspects of the water. The chemistry of natural waters and that of the biological processes present within it, is a thermodynamic state which is variable along with the temperature and the pressure that governs the physical characteristics of water – density, heat capacity, and other characteristics. 

In this discussion, we will know more about the salinity distribution, the salinity of the ocean, also we will know about the salinity content in the red sea.  

Salinity Distribution

A discussion of salinity that means the salt content of the oceans requires an understanding of these important concepts: 

• The present-day oceans are considered to be in a state where it receives as much salt as they lose

• The salty oceans have been mixed with each other over such a long time period that their composition of sea salt is actually the same everywhere.  

This uniformity of salt content is the reason for the little variation of salinity over space or over the time period. The range of salinity that is being estimated is from 33 to 37 grams of salt per kg. Majorly, the observed departure of this mean value of approximately 35 PSU, is caused by the processes at the earth’s surface which locally add or remove the freshwater content in it. The regions which have high evaporation are of elevated surface salinities, while those regions where there is higher precipitation have depressed surface salinities limit within themselves. Near the shore the regions that are close to large freshwater sources, there the salinity may be lowered by the process of dilution. This is very true in those areas where the region of the ocean which receives the freshwater is isolated from the open ocean by the geographical land.

The Salinity of the Ocean 

Salt in the ocean originates two sources:

The rocks on the land surface are the major source of salts that are dissolved in seawater. The rainwater which falls on the land is a little acidic in concentration, so it erodes the rocks. This erosion of rocks releases the ions which are being carried away to the streams and to the rivers which eventually flow into the ocean. These dissolved ions are used by the organisms living in the ocean and thus they are removed from the water. While, others are not removed, so their concentrations increase over the time period.

There is another source of salts present in the ocean called hydrothermal fluids. This salt comes from the vents on the ocean floor. The ocean water seeps into these cracks in the seafloor and thereby it is heated by magma from the Earth’s core. This heat causes a series of chemical reactions. The water here tends to lose the oxygen, magnesium, and sulfate concentration and it picks up metals like iron, zinc, and copper from the surrounding rocks. The heated water is then released through the vents in the seafloor, thereby carrying the metals with it. The ocean salts which come from underwater volcanic eruptions, directly release the minerals into the ocean water.

Prevalent most ions present in the seawater – chloride, and sodium. Together these ions make up approximately 85 percent of all the dissolved ions in the ocean. While magnesium and sulfate make up for another 10 percent of the total. Other ions are found in very minute concentrations.

Red Sea Salinity 

The Red Sea is actually a sea-water inlet of the Indian Ocean which lies between the continents of Africa and Asia. 

Talking about this sea salinity, the Red Sea is known to be one of the saltiest bodies of water in the world, this owes to higher evaporation and lower precipitation rate, no significant rivers or streams drain into this sea. The southern connection to the Gulf of Aden is an arm of the Indian Ocean, which is quite narrow.

Vertical Distribution of Salinity 

1. The saltiness of ocean water changes with depth, but the way the salinity changes rely on the position of the sea.

2. Salinity which is present at the surface of the sea gets decreased by the input of fresh waters or it gets increased by the loss of water, as it forms ice, or by the process of evaporation.

3. Salinity present at the depth is fixed as neither water nor as salt which can be added to it.

4. There is a major difference in the salinity occurring between the surface zones and between the deep zones of the oceans.

5. The lower saline water saturates quite above the higher saline dense water.

6. The salinity usually increases with the depth and there is a distinct zone known as halocline, where the salinity increases too abruptly.

7. The increase in salinity of seawater causes an increase in the density of the water.

8. High salinity seawater, which usually, sinks below the lower salinity water leads to stratification by the amount of salinity.

What is the Salinity of Seawater?

The seawater salinity is about 35 parts per thousand. 35 parts per thousand are the average salinity which can be stated in another way, that is about 3.5 percent of the weight of the seawater comes from the dissolved salts. 

Sedimentation can be described as the tendency for the particles which are in suspension to settle out of the fluid content. Here they are entrained and then they come to rest against a specific barrier. This happens due to their own motion through the fluid which is in the response to all the forces that are acting on them. The forces can be because of the gravitational pull, due to the centrifugal caused by acceleration or electromagnetism.

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In terms of geology, sedimentation is generally described as the opposite process of erosion that is the terminal end where the sediment transport. In this sense, it also includes the termination of the transport by the process of saltation or the true bedload transport.   

What is the Process of Sedimentation? 

Sedimentation is the process that allows the different particles which are in the suspended form in water to settle under the gravitational effect. The particles which settle out from the suspension become the sediment, while in water treatment this is known as sludge. When this thick sediment continues to settle, this is called consolidation. In consolidation, the sediment, or sludge, which is assisted by mechanical means is known as the process of thickening.

Sedimentation for water treatment might be used to reduce the concentration of the particles in suspension before the application of coagulation, in order to reduce the amount of coagulating which the chemicals need, or after the coagulation and, possibly after the flocculation. When the sedimentation is applied after coagulation, this purpose is done mainly to reduce the concentrated number of solids which are in suspension so that the subsequent filtration can function well.

Sedimentation is used as one of the other application methods prior to the process of filtration. While other methods include dissolving in air flotation and some other methods of filtration. The solids-liquid separation processes at times are referred to as clarification processes. While there are different processes of sedimentation like horizontal flow and others which we will discuss in our further section. 

Explain Sedimentation

The Method Involved

The simplest sedimentation method is to fill a jar or a tank with water, leave that jar or tank alone, undisturbed for a longer period of time. This will allow the particles to settle and then pour the resulting water into another can. This practice is rarely viable in treating the water for townships hence, sedimentation tanks are operated continuously.

Another simple method of sedimentation is done with the process of rectangular tanks which have a horizontal flow through them. The water with the particles which are in suspension is then introduced at one end of the tank, and then when the water flows to the other end of the tank the settlement of particles in the water occurs here. The aim is simply to settle the particles and to manage the reach of the tank floor before the water is drawn out of the tank at the end. This kind of horizontal flow tank is generally built with a floor that has slopes that are flowing gently down to the inlet end of a hopper. This tank is then fitted with a mechanism that helps to scrape the sediment from the outlet end back to the inlet end and then into the hopper from where the water can be discharged hydraulically. In this design of tanks, attention has to be given to the inlet and the outlet ends to make sure that the water flows from one end to another end as uniformly as possible.

Deposition Definition Science

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A deposition is moreover a geological process where the sediments, soil, rocks get added to a landform or the landmass. The wind, ice, water, and gravity transport previously get weathered into the surface material, which in the kinetic form of energy in the fluid is being deposited and is built up in layers of sediment.  

Deposition occurs when the forces responsible for sediment transportation are no longer sufficient to overcome the forces of gravity and the process of friction. This creates a resistance to motion which is known as the null-point hypothesis. This deposition can also be referred to as the build-up of the sediment from the organic derivation of matter or via the chemical process. 

Types of Sedimentation Tanks 

Horizontal Flow Tanks

They are rectangular in shape which has more length twice their width. This structure is designed as they need to flow more the distance and then to settle all the suspended particles. 

Radial Flow Tanks

The section which is via a typical type of radial flow circular tank has the water entering this tank through the inlet pipe which is centrally located and is placed inside the deflector box.

Inclined Settling

The inclined setting device is designed to increase the settling capability of the basin. This design principle majorly utilizes the fact which the depth of a gravity settler has very little bearing on the settling capacity. These are of great importance for settling areas which are 140 square feet in each of the inclined plates.

Ballasted Sedimentation

In this type of sedimentation process, the density difference which occurs between the water and its particles produced in the water for the treatment by the coagulation, flocs, in general, is quite small. For this reason, they settle slowly. The methods of plain sedimentation (which are horizontal, radial, and inclined sedimentation) are then preceded by a slow mixing process known as flocculation.