Category: Geography Notes PPT

Let’s talk about the Halide mineral before we get into Carnallite. Any of a group of naturally occurring inorganic compounds that are salts of the halogen acids is known as a halide mineral (e.g., hydrochloric acid). With the notable exceptions of halite (rock salt), sylvite, and fluorite, such compounds are uncommon and only found in small quantities. The simple halides, halide complexes, and oxyhydroxy-halides are known as three broad groups of halide minerals in terms of composition and structure. These categories are also distinguishable in terms of their modes of occurrence.

Alkali salts, alkaline earth, and transition metals are examples of basic halides. The transition-metal halides are unstable when exposed to air and are soluble in water. The most well-known evaporite mineral is halite, sodium chloride (NaCl); it is found in large beds with other evaporite minerals as a result of the deposition of brines and trapped oceanic water in impermeable basins and their evaporation. Sylvite, potassium chloride (KCl), is also present in small quantities in such beds. Among the simple halides, a few double salts such as carnallite and tachyhydrite formed under conditions close to the formation of halite. Carnallite is also a halide mineral.

Carnallite

Carnallite is a soft, white halide mineral that contains hydrated potassium and magnesium chloride and is used to make fertilisers. Carnallite is found in the upper layers of marine salt deposits, where it tends to be an alteration result of pre-existing salts, along with other chloride minerals. The mineral can be found mostly in salt deposits in northern Germany, as well as in Spain, Tunisia, and the southwestern United States.

Carnallite Formula

Chemical Formula of Carnallite is KMgCl₃·6(H₂O). Slow crystallisation at 25°C will yield synthetic carnallite crystal specimens from 1.5 mole percent KCl and 98.5 mole percent MgCl₂·6H₂O. It has a density of 1.602 g/cm³. Grinding a mixture of hydrated magnesium chloride and potassium chloride can also yield carnallite.

Structure of Carnallite

We discussed the Chemical Formula of Carnallite. Now let’s look in detail about the Structure of Carnallite. 

• Carnallite basic structure has corner- and face-sharing. A network of KCl₆ octahedra exists, with two-thirds of them having the same faces.

• The open spaces within the KCl octahedra are occupied by Mg(H₂O)₆ octahedra.

• The interatomic distance between Mg and H₂O varies between 0.204 and 0.209 nanometers, with an average of 0.2045 nanometers. 

• K and Cl have an interatomic distance of 0.317 to 0.331 nm, with an average of 0.324 nm.

• The estimated density of the resulting structure is 1.587 g/cm³, which is very similar to the measured value of 1.602 g/cm³.

Structure of Carnallite [Carnallite Formula is KMgCl3·6(H2O)]

According to the third of Pauling’s law, sharing one’s face increases the chances of instability. The magnesium ions are encased in water molecules in carnallite. The water molecules serve as charge transmitters, preventing the magnesium and chloride from interacting directly. Each of the five chloride anions is paired with two potassium cations and four water molecules. This means that each of the two potassium ions gives each chloride anion 1/6 of a +1 charge. Each of the four water molecules gives the chloride 1/6 of a +1 charge. The charges add up to six 1/6 positive charges, which offset the chloride’s negative charge. Because of these two factors, the rare face sharing mentioned in Pauling’s second and third rules is appropriate in the carnallite structure.

Physical Properties of Carnallite

The refractive index of carnallite varies from 1.467 to 1.494. Hematite (Fe₂O₃) inclusions in carnallite can cause it to be red. In the thin laminae of hematite, broken shards of iron oxide create red tints. In high humidity, carnallite also deliquesces. This indicates that it is highly soluble in water. Individual crystals are tabular and pseudo-hexagonal, but they are exceedingly uncommon. The forming environment, the lack of cleavage, and fracture are all field indicators of carnallite. Other factors to consider include density, taste, associations with local minerals, and luminescence. Carnallite has a sour flavour. Carnallite has the potential to be both fluorescent and phosphorescent. The potassium in carnallite readily fuses in a blaze, resulting in a violet hue. Carnallite can be distinguished from other evaporate minerals very easily. It has a bitter taste and, unlike halite, no cleavage. Carnallite has a specific gravity of just 1.6 and, unlike kieserite and other non-potassium salts, produces a violet flame when placed in a gas flame. Environment of formation, lack of cleavage, associations, density, deliquescence, fracture, and taste are the best Field Indicators.

Geologic Occurrence

Halite, anhydrite, dolomite, gypsum, kainite, kieserite, polyhalite, and sylvite are examples of mineral associations dependent on physical properties. Evaporites are mineral sediments that contain carnallite minerals. Evaporation of seawater concentrates evaporites. The water inflow must be less than the evaporation or usage levels. This results in a longer evaporation period. When 10%–20% of the original water sample remains after controlled environment experiments, the halides shape. Sylvite makes up about 10% of the total, followed by Carnallite. Carnallite is mainly present in marine deposits that are saline.

Uses

Carnallite is a mineral that is often used in fertilisers. It is a significant potash source. Only sylvite is more important in potash production than carnallite. They’re both rare because they’re among the last evaporites to form. The primary sources of fertiliser are soluble potassium salts. This is due to the difficulty of separating potassium from insoluble potassium feldspar. Carnallite is a minor magnesium source found all over the world. 

Conclusion

Carnallite is a valuable fertiliser since it contains a lot of potash. Potash is mostly obtained from sylvite, but carnallite also contributes significantly. The magnesium production of carnallite is much less important globally, but it is still Russia’s most important source. Potassium is a common element, but it is unfortunately wrapped up in insoluble silicate minerals like potassium feldspars. Since potassium must be in a soluble state to be effective as a fertiliser, soluble potassium salts are the preferred source. Evaporite minerals like carnallite and sylvite, for example, are some of the last minerals to evaporate from sea water, making them difficult to form. In approximately that order, minerals including calcite, dolomite, gypsum, anhydrite, and halite crystallise first. The conditions required for potassium and magnesium salts to form include seawater contained in a cut-off, but not fully isolated basin, similar to the Black Sea. The Black Sea, on the other hand, does not form carnallite because it does not have a warm enough environment to allow for intensive evaporation (this is an evaporite mineral after all). The concentrated brine must not be allowed to leave the basin in order for the salinity to continue to rise. The brine will fall to the basin’s bottom, allowing fresher water to join, bringing more magnesium into the basin. This has the effect of delaying the crystallisation of the salts and increasing the brine’s salinity. If evaporation does not continue in this direction, the minerals mentioned above will fill the basin before the potassium salts crystallise.

India shows a wide variation in the climatic conditions ranging from snowfall in the Himalayan arch to burning heat in the south. The Himalayas and the Thar Desert have a great influence on the overall climatic conditions of the country. The Indian subcontinent is warmer than the other areas of the same altitude because the Himalayan Mountains block the central Asian katabatic winds. On the other hand, the Thar Desert attracts the southwest summer monsoon winds that are moist and provide the required rainfall in the months from June to October. There are four principal weather and climate of India, winter, summer, monsoon, and post-monsoon.

 

What are the Factors Affecting the Climate of India?

1. Location

The Indian subcontinent stretches from 8°N to 37°N and is located to the north of the equator. Tropic of Cancer passes over the center of the country hence the southern areas are closer to the equator and experience higher temperatures. While the northern parts of the country experience lower temperatures comparatively. The temperatures are quite low during the winters. The presence of the Arabian Sea and the Bay of Bengal, cause the right and left coasts of the country to be humid and mild. The Indian subcontinent is located north of the equator and stretches from 8°N to 37°N. Because the Tropic of Cancer passes through the center of the country, the southern areas are closer to the equator and have higher temperatures. The northern parts of the country, on the other hand, have lower temperatures. During the winter, temperatures are quite low. Because of the presence of the Arabian Sea and the Bay of Bengal, the country’s right and left coasts are humid and mild.

2. Span from the Sea

The closer the regions are to the sea, the more humid is the climate. They experience moderate summers and mild winters. However, areas situated far away from the coastline, don’t have any influence on the huge water body and hence experience extreme climatic conditions. Delhi for example has an annual temperature of 20° C whereas Kochi has about an average temperature of about  30°C. The climate becomes more humid as one gets closer to the sea. Summers are pleasant, and winters are mild. However, areas located far from the coastline do not influence the vast body of water and thus experience extreme climatic conditions. For example, Delhi has an annual temperature of 20° C, whereas Kochi has an average temperature of around 30° C.

3. The Himalayan Mountains

These mountains are a climatic divider between Central Asia and the Indian subcontinent. They do not allow the cold Central Asian winds to enter the continent, hence keeping it warmer than other regions. They also block south-west monsoon winds from entering the country’s atmosphere. These mountains serve as a climatic barrier between Central Asia and India. They prevent cold Central Asian winds from entering the continent, keeping it warmer than other regions. They also keep the southwest monsoon winds out of the country’s atmosphere.

4. Pressure and Winds 

India has northeasterly winds flowing from the subtropical high-pressure belt of North towards the equatorial low-pressure areas. These winds carry very little moisture since they flow only over land. Hence they do not bring any rain to the county. On the other hand, during winters, from the high-pressure region of the northern Himalayas, cold dry winds flow into the continent towards the South. In summers this reverses and low pressure is created in interior Asia. Hence the southwest monsoon winds are originated and because these winds flow over the warm oceans they collect moisture and bring the majority of rainfall in the country. Northeasterly winds blow across India from the subtropical high-pressure belt to the equatorial low-pressure areas. Because they only blow over the land, these winds carry very little moisture. As a result, they do not bring rain to the county. During the winter, however, cold dry winds from the high-pressure region of the northern Himalayas flow into the continent from the south. This is reversed in the summer, resulting in low pressure in the interior of Asia. As a result, the southwest monsoon winds are formed, and because these winds blow over warm oceans, they collect moisture and bring the majority of the country’s rainfall.

 

What do you mean by Climatic Controls? 

The factors that influence or control the contrast of weather in a particular region are called climatic controls. Climate controls are the factors that influence or control the contrast of weather in a specific region.

 

The following are India’s climate controls-

• The dominant temperature of the region is determined by the country’s geographical location on the latitude. Temperatures gradually decrease as we move from the equator to the poles, as we all know. Because the southern states are closer to the equator, they have higher temperatures, while the northern states have lower temperatures.

• Temperature variations are caused by altitude, just as they are by distance from the equator. As a result, higher altitude regions in India have cooler climatic conditions.

• The major factors that influence the climate of any region are pressure and winds. The northeasterly and southwest monsoon winds, for example, are responsible for the monsoon in India.

• The temperature of a region is determined by the ocean currents that flow over it; warmer ocean currents warm the region, while moist ocean currents cool it.

• The Himalayan Range is the country’s most important relief barrier. It restricts the inflow of Central Asian winds to the peninsula’s northern tip, keeping temperatures warmer than in other parts of Asia.

• The geographical location on the latitude of the country decides the dominant temperature of the region. As we know, the temperatures gradually reduce when we move from the equator to the poles. Since the southern states are located closer to the equator they have high temperatures and the northern states have comparatively lower temperatures. 

• Just like the distance from the equator causes variations in temperatures, the altitude also does. Hence regions at higher altitudes in India experience cooler climatic conditions. 

• Pressure and Wind are the major factors that influence the climate of any region. For example, the northeasterly winds and southwest monsoon winds are responsible for the monsoon in India.

• The ocean currents flowing over a region determine the Temperature of that region, warmer ocean currents make the region warmer, whereas moist ocean currents make it cooler. 

• The Himalayan Range is the most important relief barrier of the country. It restricts the inflow of Central Asian winds to the northern part of the peninsula,  hence keeping the temperatures warmer than other regions of Asia.

A coral reef is a marine ecosystem characterized by corals that create reefs. Reefs are made up of coral polyp colonies bound together by calcium carbonate. The majority of coral reefs are made up of stony corals, which have polyps that crowd together.

Shallow coral reefs, also known as sea rainforests, are home to some of the most diverse species on the planet. They cover less than 0.1 per cent of the world’s ocean surface or about half the size of France, but they are home to at least 25% of all marine animals, including fish, molluscs, worms, crustaceans, echinoderms, sponges, tunicates, and other cnidarians. Coral reefs thrive in nutrient-depleted coastal waters. Coral reefs are most often seen at deeper depths in tropical oceans, although deep water and cold water coral reefs can be found on smaller scales in other regions. Let us take a look at different types of reefs.

Types of Reefs

It is classified into three types of coral: fringing, barrier, and atoll.

1. Fringing Coral Reefs

2. Barrier Coral Reefs

3. Atoll Coral Reefs

Let us take a look at them in detail.

1. Fringing Coral Reefs: One of the three major types of coral reef is a fringing reef. It differs from the other major groups, barrier reefs and atolls, in that it has either a completely shallow backreef zone (lagoon) or none at all. If a fringing coral rises straight from the shoreline, the reef flat stretches all the way to the beach, with no backreef. This is the most widespread kind of coral reef found in the Caribbean and the Red Sea. In a long-term reef development pattern, fringing reefs, according to Charles Darwin, are the first kind of reefs to develop around a landmass.

2. Barrier Coral Reefs: Barrier reefs are isolated from the shores of a peninsula or island by a deep channel or lagoon.  Formal paraphrase They are similar to the later stages of a fringing reef with its lagoon, but they vary mostly in size and origin. Their lagoons can span many kilometres and range in depth from 30 to 70 meters. Over everything, the offshore outer reef edge formed in the open sea rather than along a shoreline. These reefs, including atolls, are thought to have evolved when the seabed lowered or the sea level rises. Barrier reefs are much rarer than fringing reefs and they take much longer to form.

3. Atoll Coral Reefs: It is a ring-shaped coral reef with a coral surface that partly or entirely encircles a lagoon. Around the bottom, there may be coral reefs or cays. The creation of an atoll reef is described by Charles Darwin’s subsidence model as the subsidence of a volcanic island around which a coral fringing reef has formed. The volcanic island became extinct and eroded over geologic time, eventually sinking entirely under the ocean’s crust. When the volcanic island subsides, the coral fringing reef separates from the island, becoming a barrier reef. There are around 440 coral atolls on the planet.

Zones of Coral Reefs

Coral reef environments are divided into zones that house various types of habitats. 

The three main areas are usually recognized: 

• Fore coral,

• Reef crest, and

• Back reef 

The three zones are connected both physically and ecologically. Oceanic cycles and reef life facilitate the exchange of seawater, sediments, nutrients, and aquatic life. The majority of coral reefs live in seas less than 50 meters deep. Some live on tropical continental shelves, such as the Great Barrier Reef, where cool, nutrient-rich upwelling does not occur. Others, such as the Maldives, are located in the deep ocean around islands or as atolls. Reefs form around islands as they sink into the water, and atolls form when an island sinks below the sea’s level.

Reproduction in Coral Reefs

Corals reproduce sexually as well as asexually. During the course of its life, a polyp can use all reproductive types. Internal or external fertilization is used by corals to replicate sexually. The reproductive cells are located on the mesenteries, which are membranes that radiate inward from the stomach cavity’s layer of tissue. Any mature adult corals are hermaphroditic, while others are either male or female. Only a few, change sexes as they mature.

Spawning happens like a mass orchestrated process along several reefs, where all coral species in an environment release their eggs and sperm at about the same time. Since male and female corals cannot come into reproductive interaction with each other, the timing of a broadcast spawning event is critical. Since colonies can be separated by large distances, this release must be specifically and widely timed, and it typically occurs in response to several environmental cues.

The less water that moves, the greater the chance of fertilization. The best time is in the spring. The release of eggs or planula is normally at night and is often in sync with the lunar cycle (three to six days after a full moon). The time between release and settlement is just a few days, but some planulae will float for several weeks.

Benefits of Coral Reefs

• Coral reefs shield coastlines from hurricanes and flooding, provide employment for local residents and provide recreational opportunities.

• They are source medicines and food. Reefs provide fuel, jobs, and security to over half a billion people.

• On and around beaches, fishing, swimming, and snorkelling generate hundreds of millions of dollars for local companies. The annual net economic value of the world’s coral reefs is estimated to be in the tens of billions of dollars.

Did You Know?

• Coral reefs make up a small percentage of the ocean – less than 1% – but they are home to about 25% of all aquatic animals on the planet. Coral reefs are home to over 4,000 different species of fish!

• Corals and algae have a symbiotic bond, so as the ocean temperature rises, corals remove their algae, causing them to white in colour and this process is bleaching and the coral is known as bleached coral. Many corals have been seen to emit bright colours in a vain effort to withstand rising ocean temperatures.

• The Great Barrier Reef is the largest coral reef which is the only animal structure visible from space, stretching for 2300 kilometres.

The economy of a country shows up its overall financial condition and denotes the country itself as an economic unit. There are various elements on which a country’s economy depends upon. Some of them are demography, infrastructure and natural resources, and the average lifestyle of the people This is the reason why geography is prominently related to a country’s economy. If you are at the school level, you have to know the economy of your country. The best way to know about the economy of the country is by going through the chapters and understanding the sources of finances. You can visit the site to get in-depth knowledge. 

Lifelines of National Economy

There are several factors on which the economy of a country can depend. Here is a shortlist with some details about the economical lifelines of any developing country in the world. 

1. Demography: 

The primary lifeline of a nation’s economy is demography. If the ratio of the working-class population and the scopes of jobs are in balance, you can expect the economy of a country is well balanced. 

2. Natural Resources: 

Several businesses depend on the abundance of some natural resources. A country with several natural resources might not have a weak economy. 

3. Population: 

Population is one of the lifelines of a country’s economy but an instance of overpopulation can be harmful in the same way. The economy can never be in equilibrium in an overpopulated country as the per head finances will never be constant. Overpopulation leads to unemployment which is one of the prominent curses for the economy. 

4. Infrastructure: 

Infrastructure plays a crucial role in maintaining a balance in the economy of a country. A country must have the proper infrastructure in the field of industries, agriculture,  transport, health, social service, defense, and entertainment to ensure that the economy remains at a satisfactory stage. 

5. Government Rules: 

In many leading countries, the ruling government plays a vital role as a determinant of the economic condition of the country. If the government of the country follows an administrative blueprint that is constructive, it can be the most secured economic lifeline for a country. In the same way, if the government is reluctant towards properly running the country, the economy of the country can crash. 

In a condition, the cash flow in the country can get hampered. Moreover, corruption can destroy the financial sector of the country.

Lifeline of Indian Economy: Details

Lifeline of the Indian economy is a chapter of CBSE class 10 Geography that contains the details of the main sector that helps the nation to gain finances. It is transportation. India has a huge landmass and the transport network in the country is excellent. The other factor that helps boost up the economy of India is communication.

Here are the Details that you Need to Learn in the Chapter:

Importance of Transport in India

Transport is important in India as both goods and people frequently move from one place to another. As the importance of finished products is high in the case of saving the economy of a country, the transport sector in the Indian landmass has high importance. 

Roadways in India: The roadways in India and their importance is high. At present, the total road network in the country is 2.3 million. Roadways are important for transporting such goods that cannot be taken by rail. Moreover, it helps people to move from one city or state to another comfortably. 

Railways: Railways in India is fully government property. India has an enriched railway network o0n which both frights and passengers move from one point of the country to another. It is surely one of the prominent economic lifelines of India.

Airways: Airways in India is another way the Indian administration can earn finances. This improves the economy of the country and the country can make an effort to enhance the economical equilibrium. 

Importance of Communication In India

Communication in a huge country like India can also be a prominent economic lifeline. You can learn about the best ways of communication like the post, media, telecom, and internet and their details in the chapter. Even the film industry of India falls under the communication lifeline in the country. 

Solved Examples 

Q1. Are Underdeveloped Economies Generally Cursed with Unemployment?

Answer: Yes, the underdeveloped economies generally are cursed with unemployment. The main reason being the lack of scopes for employment. Some examples of such countries are Afghanistan, Madagascar, etc. 

Q2.  Which is the Main Occupation of People in India?

Answer: Agriculture is the main occupation of the people in India. This is another lifeline of the country in terms of economy. However, a huge chunk of youth is shifting towards urban-based jobs right now. 

Ferrous metals are pure iron or an alloy which typically consists of iron. The term ‘ferrous’ has been derived from the Latin term ‘ferrum’ meaning iron. The most common ferrous alloys are steel. Ferrous metals contain little amounts of other metals or components added, to render it the requisite properties. These metals are magnetic and offer only slight resistance to corrosion.

All commercial forms of iron and steel bear carbon, which has become an integral part of the metallurgy of iron and steel. The preference for ferrous metals is quite strong, thus also making scrap metals highly merchantable. Most recycling companies pay fairly for scrap metals.

Types of Ferrous Metals and Features

Currently, There are Different Forms of Ferrous Metals Available in the Market. Some of the Major Types and Their Characteristics are Stated below:

1. Stainless Steel – Resistance to Corrosion

2. Cast Iron – Hard, brittle, strong, self-lubricating, economical

3. Mild Steel – Ductile, tough, high tensile strength. Due to low carbon content, it cannot be toughened and tempered. It should only be case hardened.

4. High Carbon Steel – The hardest of the carbon steels. Tough and malleable but less ductile.

Other available types of ferrous alloys and ferrous material include free cutting steel, construction steel, high temperature steel, low temperature steel, high strain steel, and spring steel

Manufacturing Process of Ferrous Metals

Ferrous metals need to be extracted from basic iron ore. The original source for iron ore is the earth’s crust, which bears metals and metal compounds such as iron oxide. However, the ore is commonly mingled with other materials. For the purpose of optimizing the usage of the metal, it has to be derived from the mixture.

The method principally used to derive metals from the ore depends on their reactivity. With respect to iron, a less-reactive metal, it can be derived by reduction with carbon or carbon monoxide. Iron is then extracted from iron ore in a big container known as a blast furnace. Oxygen should be eliminated from the iron oxide to leave the iron behind.

Applications of Ferrous Metals

Ferrous metals are used in a variety of applications. Listed below are its some major uses:

• Sturdy crushing machinery

• nuts, bolts girders and plates

• Car cylinder blocks and gear wheels

• machine tool parts, machine handle and engine parts

• vices, brake drums, and plumbing fittings

• Gears and shafts

• Cutting equipments for lathes

• Kitchen draining boards and cutlery

• Aircraft and pipes

• Chisels, files and lathe tools

• garden tools, hammers, drills, dies and taps

• Metal ropes, springs and wire

Environmental Impacts of Ferrous Metals

Recycling of ferrous metals enables in decreasing the quantities of solid waste accumulated in landfills, which have become costlier. As these metals are magnetic, scrap can be gathered with the help of a magnet and sent to a recycling unit.

Source of Ferrous Minerals

One of the massive sources of scrap steel is the reprocessing old automobile bodies. The automobile body is crushed and compressed, and is then macerated into small pieces using hammer mills. Ferrous metals are isolated from the shredder residue by heavy magnets while other substances are sorted manually or with high-pressure air flows and liquid floating systems.

Applications of Recycled Ferrous Metals

Studies reveal that recycled steel contains the same strength as new steel. Now, a large variety of appliances contain about 75% recycled steel.

Properties of Ferrous Metals

Ferrous metals may include a variety of alloying elements. Some examples are nickel, chromium, vanadium, molybdenum, and manganese. Those provide ferrous steels properties that make them extensively used in engineering.

Following are Ferrous Metal Properties:

• Durable with Great tensile strength

• Generally magnetic

• Very Low resistance to corrosion

• Recyclable

• Silverish color

• Excellent conductors of electricity

These properties make them workable in constructions of long-lasting skyscrapers. Besides, they are utilized in manufacturing tools, containers, pipelines, automobiles, vehicle engines, cutlery etc.

Non-Ferrous Metals and Their Uses

Non ferrous metals include every metal and alloy which do not contain iron. Examples of a few common non-ferrous metals will include:

• Precious metals like gold, silver and platinum

• Copper and its alloys such as brass and bronze

• Nickel, Platinum, Titanium, Palladium

• Tin, Lead, Zinc

With such a huge array of materials in this grouping, many of the mechanical properties which suggest iron can be unearthed in non-ferrous metals. For example, alloys of aluminum or titanium could be alternated for steel in different cases, if it were not cost-restrictive to do so. Iron’s magnetic abilities could be parallelized with cobalt, nickel, or rare earth elements alloyed with other metals.

However, since non-ferrous alloys are often expensive, they tend to be chosen for their distinctive attributes, instead for the ways they can act like steel.

Properties of Non- Ferrous Metals

• Light weight

• Good conductivity

• Corrosion resistant

• Non-magnetic

• Traditionally valued

• Decorative value

These properties also make the metal to be more prefered. Some metals are prized exactly as they are rare: before extensive aluminum manufacturing was possible, aluminum has been a luxe metal employed in high-end tableware.

Difference Between Ferrous and Non Ferrous Metals

In reference to ferrous (ferrum=iron) metals, the base metal is iron. They take into account a huge part of the overall metals in use today. This has become possible by their properties that are suitable for various industries and use-cases.

On the contrary, Non-ferrous metals do not include iron. This differentiation is made because it brings along a certain characteristic change which non-ferrous metals do not offer.

Many of us love visiting hill stations for vacations. It is a balm for the tired soul and does wonders for the mind. Some of us might love trekking up mountains and settling down on the top to either view sunrise or sunset or just stare in awe at the magnificent landscape all around. 

 

Have we ever looked at those fascinating mountains or the green plains and wondered how they might have been formed? Certainly, the process would not be simple! 

 

Set by William M. Davis, the theory of the geomorphic cycle tries to tell us how terrains are developed across landscapes. The model involves explanations for many different structures such as hilltops, valleys, mountains, and rivers. Because it describes the processes of erosion and deposition which eventually lead to relief or terrain formation, it is also known as the cycle of erosion or the theory of land evolution. 

 

Meaning of Geomorphic Cycle

The geomorphic cycle is any cycle of events that leads to the formation of any relief (terrain) development in landscapes. It is a model explaining the formation of many different terrain structures such as hilltops, valleys, mountains, and river drainage systems. It is also known as the geographic cycle or the cycle of erosion for the development of various landscapes. Hence, a geomorphic cycle is the theory of evolution of landforms that includes many distinct events of erosion and deposition due to a variety of reasons that will be discussed below in this article. 

 

The Geomorphic Cycle

William M. Davis first set the theory of the geomorphic cycle and laid down some concepts of geomorphic cycles and landscape development. According to the theory, there are commonly three stages of the cycle of erosion and the development of any landforms. The three periods are classified from youth to maturity and old age. 

 

These stages were considered to be gradually transitioning from one period to another. This model that explains the concepts of geomorphic cycles and landscape development is known as the Davis geomorphic cycle. Although certain aspects of the Davis geomorphic cycle are not currently accepted, it is still the primary and widely proclaimed theory of the geomorphic cycle that describes the various events leading to the formation of landscapes. 

 

Stages of the Geomorphic Cycle 

The Youthful Stage

The initial stage as put forward by the Davis geomorphic cycle is the youthful stage of landscape development. This stage of terrain development begins with the upliftment of the landform. It includes either the uplifted or to-be-uplifted periods of the development process. During this stage due to the processes that favour the uplifting of the landform, significant folds are produced in the crust of the Earth. These folds are generally the mountains or the block mountains. 

 

This uplifting process of mountain formation is widely known and an accepted phenomenon. The folding or uplifting can occur due to a variety of phenomena such as the movement and clashing of the tectonic plates of which the Himalayan mountain range is an example. During the youthful stage, the rivers flowing through the uplifted landform would create another distinction between the uplands and valley bottoms. The differences between the uplands and the valley bottoms increase rapidly throughout this stage and even during the height of the youthful stage. 

 

The Mature Stage

Following the youthful or the youth stage, comes the mature stage of the geographical landscape development. During this stage, due to the dissection of the streams or rivers, the ever-increasing difference in-between the valley bottoms and the uplands or the mountains reaches its height. These height differences are the greatest in the mature stage of relief development. 

 

Another factor that plays a significant role in the mature stage is the slope decline. When the height difference between the uplands and the valley bottoms reaches the maximum, slope decline becomes an important phenomenon. The slope of the upland begins to decline faster than the incision or dissection by any river stream. This effectively leads to the decrease in the relief features of height and the difference between the uplands and the bottom of valleys starts to lessen and diminish gradually.

 

The Old Age Stage

The stage following the mature stage is the ‘old age’ stage of relief development. In old age, the initially uplifted terrain feature gradually diminishes or reduces to a surface known as the peneplain. During the old age, which is the latest stage in the process, the erosion has been acting upon the terrain so long that although the terrain was at a significant height when uplifted, it is now reduced to a lowland which is known as the peneplain. 

 

The peneplain is usually at sea level and sometimes is reduced so much that it drowns around the nearest water bodies. Although some of the peneplains may be submerged, some may maintain the residual height from the initial upliftment.

 

The Second Geomorphic Cycle

Following old age, the second geomorphic cycle starts again with the upliftment of the terrain. One of the important factors according to this theory of Davis geomorphic cycle which explains the concepts of geomorphic cycles and landscape development, is the contribution of time in the process of erosion. Time plays an important role according to the theory in the entire cycle of erosion. 

 

But, there are certain cases when during any of the stages of the geomorphic cycle the upliftment can start before completion of old age. This event when it occurs is known as rejuvenation. It may or may not be a common phenomenon for a particular relief structure. This is because according to Davis, the full geomorphic cycle was a rare or special case as there are continuous geological changes taking place throughout the world which can cause changes in the stages of the geomorphic cycle. 

 

This theory of the evolution of landscapes applies to hilltops, valleys, mountains, and river drainage systems. Based on this theory, it is assumed that once the stage of any landform is known, the history of the landform development can be known according to the established principles.

 

Drawbacks of the Common Theories of the Geomorphic Cycle

Although Davis had been able to acknowledge the factors affecting the geomorphic cycle as rock type, structure, and processes of erosion, he emphasised the importance of time. But it is currently believed that time does play a significant role as Davis suggested and the contribution by it is the same as other factors in relief development. 

 

This theory of the cycle of erosion has been widely accepted although there is accumulating evidence that refutes the theory of the Geomorphic cycle. It is now usually considered that the initial conditions or the conditions surrounding the upliftment of the landform may not significantly guide the stages towards the end products. Instead of a gradual transition of the landforms through various stages, there is a dynamic equilibrium reached in-between the landforms and the processes that act upon them, which in turn leads to erasing of the physiographic history of the region. 

 

Another drawback of the theory is that originally the theory intended to provide explanations for the development of temperate landscapes as the major focus was put on the erosive activities by the river streams on the uplands or uplifted regions. Also, the nature of surface processes was poorly represented by the model. It was mostly theoretical and deductive and did not take into account the complexity of tectonic movements and climate change. Nevertheless, the cycle of erosion has been accepted by extending and including certain modifications that involve the arid, glacial, karst, coastal and periglacial areas. 

Conclusion

This is all about the different types, stages, and drawbacks of the geomorphic cycle. Learn the important features of this theory with the aspects defined and explained in this article.