Category: Geography Notes PPT

Fringing reef meaning can be defined as a coral reef that lies close to the shore. The fringing reef is the most common of the three main forms of coral reefs, with examples found in all major coral reef growth regions. The New Hebrides Society islands off the coast of Australia and the southern coast of Florida have fringing reefs.

One of the three major forms of coral reef is a fringing reef. It differs from the other major groups, fringing barrier, and atoll reefs, in that it either has a completely shallow back reef zone (lagoon) or none at all. Barrier reef fringing reef and atoll can be explained as An atoll is created when a fringing reef continues to expand upward from a volcanic island that has sunk completely below sea level. Atolls are usually circular or oval, with a central open lagoon. The coral flat stretches to the beach when a fringing reef rises directly from the shoreline, and there is no backref. Fringing reef barrier reefs and atoll are widely spread and having large importance. In other cases (for example, the majority of the Bahamas), fringing reefs may develop hundreds of yards from the shore and include extensive backreef areas with numerous seagrass meadows and patch reefs. This is the most common form of fringing coral reef found in the Caribbean and the Red Sea. Fringing reefs, according to Charles Darwin, are the first type of reef to form around a landmass in a long-term reef growth phase.

Structure of Fringing Reef:

There are two main components that makeup of fringing reef which is mentioned below:

Reef Flat ( Back Reef)

The reef flat is the reef’s most shoreward, flat, and broadest location. The reef flat is located in relatively shallow water and is exposed at low tide. The reef is only slightly slanted towards the open ocean in this location. The reef flat does the most damage from runoff and sediments because it is adjacent or nearby adjacent to the shore. Usually, only a few of the corals on the flat are alive. There are also seagrasses, seaweeds, and soft corals to be found there.

Reef Slope (Fore Reef)

The coral slope is located on the fringing reef’s outer side, nearest to the open ocean. This section of the reef is often very steep, descending either to a shallow sand bottom or to depths too great for coral development. Coral is much more common on this slope, both in terms of numbers and the diversity of organisms. This is mostly due to the lower concentration of runoff and sediments here. Pollutants are dispersed and nutrients are transported to this environment as a result of increased wave action. Spur and groove formations, which carry sediment downslope in the groove, are a common feature on the fore reef.

Formation of Fringing Reefs

The availability of space, as determined by sea-level changes, is the most important determinant of fringing reef development. Glaciers and plate tectonics are the main causes of sea-level changes. Tectonic activity may have a negative effect. An earthquake on Ranongga, in the Solomon Islands, raised 80 percent of the island’s fringing reef above sea level permanently. Northern reefs rose 1 meter above the high tide water level, while reefs on the south side rose 2 to 3 meters above the water level. Reefs that keep up with the rising sea level are known as keep-up reefs. Catch-up reefs expand slower than sea level rises at first, but gradually catch up as the rise slows or stops. Reefs that have given up are unable to develop quickly enough and are “drowned out.” 

The reef crest is the uppermost part of this slope. Since the crest has the best combination of sunlight and waves, coral grows here the fastest. Out of the entire slope, the base receives the least sunlight and has the least development.

Distribution of Fringing Reef

Fringing reefs are the most common reef form in the tropics, and they are found near the shore in many places. Coral reefs are located in the tropics, where the water temperature is between 18 and 30 degrees Celsius (64 and 86 degrees Fahrenheit). Many of the sections of the Great Barrier Reef are simply fringing reefs. Just 760 of the nearly 3,400 individual reefs are fringing reefs. The reef near Msambweni, Kenya, is the world’s largest continuous fringing reef, stretching from Msambweni to Malindi in the north. Coral reefs that develop on the continental margins or on the island’s area unit referred to as fringing reefs. Such reefs are found close to Rameshwaram within the Gulf of Mannar. Sometimes the fringing reef is separated from the shore by a shallow lake brought up as a “Boat Channel” as found in Madagascar and the Red Sea.

Fringing Reefs Around the World

The Ningaloo Reef is the world’s largest fringing reef, extending 260 kilometers along Australia’s western coast. Because of its proximity to the sea, it is a popular snorkeling and scuba diving spot.

Granite is a type of igneous rock which forms when the magma cools down slowly underground. It comprises mainly the minerals like quartz, feldspar and mica. Some granites contain hornblende and augite, although in small amounts, along with the main ingredients. Accessory ingredients of apatite, hematite, rutile, tourmaline and zircon are also constituents of granite rock. Biotite and other ferromagnesian minerals are also present sometimes in granite. Granite igneous rock usually is pale grey, white or pink in colour which depends on the colour of their constituent feldspars. For example, in the presence of pink microcline feldspar, the granite looks pink. Granite mainly occurs in the form of huge batholiths, stock and sometimes laccoliths.

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Constituents of Granite

Granite igneous rock consists of minerals like K-feldspar (orthoclase, microcline and perthite) about 50 to 80 per cent, quartz about 20 to 40 per cent, Na-plagioclase and mica(s) such as biotite and muscovite. The intergrowth of albite or oligoclase with a microcline or orthoclase host results in the formation of mineral perthite.

The feldspars are the dominant components of granite. They can easily be identified on the basis of the appearance, colour and cleavage properties of granite. Quartz is generally anhedral and is usually present as fillings at interstices between the other mineral constituents while overriding its own characteristic crystal shape. In general, quartz is colourless or smoky. It is identified by its hardness, glass-like appearance, conchoidal fracture and lack of cleavage property. The constituents like biotite, hornblende and muscovite in granite can be distinguished by flaky black or silver colour, black dark green grains or prism characteristics.

Various igneous rocks especially the granodiorite, gabbro and diorite are often wrongly designated as granites by architects and builders. However, they are petrologically defined and cannot be considered commonly as granites. Granites are used commonly in buildings, as decorative stones, for kitchen stall surfaces, tiles, modern sculptures, engineering, rock climbing etc.

Granite Composition

Granite consists of minerals and rocks, dominantly quartz, potassium feldspar, mica, amphiboles and small traces of some other minerals. Granite comprises 20-60 per cent quartz, 10-65 percent feldspar and 5-15 per cent mica(s). The presence of different minerals in different proportions gives the granite different colours and textures.

The variation in proportions of differently coloured minerals in granite comes from the original source of molten rock that was cooled to form the granite. For instance, if we consider a molten rock that was abundant in potassium feldspar, it will be more likely to set into granite with salmon pink colour. While, if it was rich in quartz and minerals that make up amphibole, it would be a black and white speckled granite which we often see on the kitchen stalls and countertops.

Following are the typical effects of different constituents on the granite colour and appearance:

• Quartz – milky white colour

• Feldspar – off-white colour

• Potassium Feldspar – salmon pink colour

• Biotite – black or dark brown colour

• Muscovite – metallic gold or yellow colour

• Amphibole – black or dark green colour

The minerals listed above are responsible for the colours we see in granites generally. In the next section, we will talk about the structural features of granite.

Granite Structure

The term Granite is derived from the Latin word ‘granum’ which means grain. This is related to the coarse-grain-like structure of the rock. As the granite rocks consist mainly of feldspar, quartz, mica and amphibole minerals, they form interlocking between them. The equigranular matrix of feldspar and quartz usually form the lighter portions in the granite structure while minerals like biotite and amphibole (or/and hornblende) form the scattered darker portions. Sometimes, few individual crystals become larger than the groundmass. The texture formed in this case is known as porphyritic and such rocks with the porphyritic structure are known as a granite porphyry. Light-coloured and coarse-grained igneous rocks are often called Granitoid in general and descriptive fields. Granitoids are classified for their specific types through petrographic examination. The mineralogy of the granitic rocks is the deciding factor for their colours which can be predominantly white, pink or grey typically. 

Uses of Granite

Being one of the world’s toughest substances, granite has been in use in various ways for a long time. Apart from its use in the construction of monuments and buildings, granite is also useful in curling balls and gym walls for the training of mountain climbing.

Let’s see the different uses of granite in detail:

• Building Monuments: In order to live long lives and create beautiful designs to the structures like temples, gravestones and monuments, they are usually made from granite. Although, in early times, the unavailability of advanced equipment made the carving process of granite quite difficult and laborious. Hence, such stones were used only in important structures.

• Jewellery: Some granites are quite rare and exceptionally beautiful. Hence, they are used as gemstones in jewellery. An example of such granite is the K2 Azurite which is found in the Himalayas, has a blue tint and is a rare stone.

• Fireplace Mantle and Floor: Granite makes an ordinary fireplace mantle more attractive and suitable for being used as a place of gathering with friends and family. Also, granite tiles are preferably better than other options for perfect, smooth and nice-looking flooring. The availability of granites in different colours and textures is an add-on for suiting the different preferences of people. As it is really hard, it is exceptionally wear-resistant. Also, it is bacteria resistant and easy to clean. One could easily keep such flooring neat and clean with regular sweeping and mopping.

• Bathrooms, Shelves, Tabletops, Basins: Kitchen tops, tabletops and shelves look more elegant while maintaining strength when made up of granite. They are also cleaned very easily and look really stylish in appearance. Also, granite is completely water-resistant. Granite sinks, angular basins and modern or pedestal sinks are some more applications of granite in kitchens and bathrooms.

Do You Know?

• At ambient pressure, dry granite melts at around 1215 to 1260°C. However, in the presence of water content, it gets melted around 650°C at a few hundred megapascals of pressure.

• The primary permeability of granite is poor overall. However, the secondary permeability due to the presence of cracks and fractures is very strong.

Conclusion

We get to know all the information related to granite rock such as what is granite and its usage. Granite is an igneous rock that has grains large enough to be easily visible to naked eyes. The two main constituents of granite are feldspar and quartz. Apart from these, granite also consists of other compounds such as amphiboles, mica, etc. in small and different proportions. Granite is mainly used in flooring, decorating purposes and in jewellery also.

Human settlement in that place, particularly where the people live their livelihood. Human settlement refers to the totality of the human community which involves the social, material, organizational, spiritual, and cultural elements that sustain within it. Any form of human dwelling, be it the smallest house to the largest city, the group of people that reside and pursue their life goals, are to be understood as settlement. Human settlements are of different forms, which can be permanent or temporary, rural or urban, mobile or sedentary, disseminated or in agglomerated form. 

Human Environment Settlement Transport and Communication 

Settlements are those places where people build their own homes. A human can settle in those places on a permanent or temporary basis. With settling in the places, the people are required to move from one place to another for trade here comes the definition of Transport. 

Transport is the means of traveling which is made convenient for the people to move from one place to another. The four main means of transport are – the roadways, the railways, the waterways, and the airways. 

After the transport comes the communication system which is another important facet of a settlement. Communication is the streamlined process of conveying any message to others. Mass media means communicating with the mass of people through newspapers, radio, or television.

Settlement Definition Geography 

In geographical definition, a settlement is a place where people live and conduct their livelihood. Settlements may be small as a single house in a remote or a distant location or it can be an area as large as a megacity (where over 10 million residents reside together).

A settlement can be both permanent or temporary settlement. An example of a temporary settlement is a refugee camp, used by armies. However, a temporary settlement may also become a permanent settlement over time. This has happened to many refugee camps which have been built in conflict zones.

Temporary Settlement examples can be cities and towns, where the families can stay for years with their families. 

Settlements are usually developed to perform a specific function. For example, the settlement in  Southampton is for conducting port functions.

Early Man Communication

Early Man uses the following to communicate better: 

Ancient Means of Transport Pictures

House Boat

Tonga

Trams 

Hath Rickshaw

Gauge Trains

Palki

Types of Settlement in Geography

Classification of the settlements in Geography:

Settlements can be classified according to their pattern, size, and housing density. They are also to be classified according to the functions which they perform.

• Classified according to the pattern: There are 5 types of settlement classified according to their pattern – isolated, dispersed, nucleated, and linear.

• Classification according to size and housing density: According to Size and Housing density:

Rural settlements are small houses and have low housing and population densities.
Urban settlements are the larger houses and have many houses built close to each other.

• A farmstead is the two or more homesteads that usually are dispersed in farmland.

• A hamlet is made up of several dispersed, nucleated, or linear homesteads with local shops, schools, or other service centers that are occupied by few hundreds of persons.

• A village, which is like a hamlet, may be dispersed, nucleated, or both.

• Towns are urban settlements are of up to several thousand persons. Houses are built together and the emphasis is more on secondary and tertiary rather than on the primary occupation. 

• Cities are the major towns of a country, where the major state capitals have administrative functions. 

• A conurbation that grows when two or more towns or parts of those towns have grown and joined together to form a big urban area of 1 million persons or its whereabouts. 

• Megapolis is the several cities or conurbations which have grown around the years and which have joined together to form a large sprawling urban settlement. 

We usually see the Earth from the outside. We see different types of landscape structures, plains, plateaus, grasslands, deserts, beaches, islands, forests or wildlife, etc. but have you ever wondered what can be found inside the Earth? All the things we see outside or use in our daily lives are formed because of the internal processes of the earth along with external factors. Here, we will be focusing on the inside of our Earth. We will learn about the rocks and minerals found inside our Earth, their uses, the classification of rocks, and various other related concepts. 

These rocks and minerals are very useful for us and are used in various processes and products. These notes will serve the needs of students who are looking for Class 7 Geography Chapter 3 notes. 

Rocks and Minerals

These are said to be building blocks of Earth which forms various kinds of landscapes on Earth as well as provide a number of resources as well. Rocks consist of minerals and these rocks are mined to extract minerals because these have Important properties and commercial value. There is no specific structure or chemical composition of rocks but minerals do have definite structure or other properties. Each rock can consist of one or more minerals. Rocks can be formed because of various geological processes and during these processes, various minerals get collected in one rock. When rocks are mined, these are called ores and the remaining rock after extraction of minerals is called tailing.

Uses of Rocks and Minerals

• These are used in everyday life around us.

• Rocks are used for making roads, buildings, and other construction purposes.

• Some rocks which are precious are used as gemstones and some small rocks are also used in games as well.

• Minerals are used for energy purposes such as coal, petroleum, etc. whereas others like fluorite, copper, talc, kaolinite, zinc, gold, diamond, etc. are used for making different kinds of products in the manufacturing industries from paper to jewellery products, minerals are used.

Difference Between Rocks and Minerals

Classification of Rocks

The various types of rocks are mentioned below. 

Igneous Rocks

The rocks formed because of the solidification or cooling of the lava from the volcano are known as Igneous rocks. These are said to be the first and earliest rocks to be formed and other rocks are made from these rocks, thus these are also known as the primary rocks. These rocks are also considered magmatic rocks because of their formation from the magma or also called volcanic rocks because of the relationship with a volcano. These can be divided into the following two types:

These are those rocks that solidify under the crust of the Earth along with the presence of other existing rocks and it cools slowly and rocks become coarse-grained. The rocks which form deep in the crust and are coarse-grained are termed plutonic or abyssal rocks whereas the rocks which form under the crust but near the surface and are medium-grained are termed subvolcanic rocks or hypabyssal rocks.

The types of rocks which solidify above the crust of the Earth or on the surface outside are called extrusive Igneous rocks. Here, the process of cooking is not slow as compared to the intrusive one. They follow a quick solidification process because of the outside temperature present in the region thus, they are of fine quality and glassy texture.

Examples of Igneous Rocks

The first image is of Basalt which is an example of extrusive Igneous rocks and is dark in colour and finely grained whereas the other image is of coarse-grained rock i.e Diorite which is an example of intrusive igneous rocks. Other examples are Dacite, Diabase, Gabbro, Obsidian, Granite, Peridotite, etc.

Sedimentary Rocks

These are the rocks that formed on or near the surface of the Earth because of geological processes such as erosion, weathering, dissolution, precipitation or lithification, etc. And usually have distinctive layers of bedding. They can be divided into three types:

These sediments are carried in rivers or deposited in oceans or lakes and with time when the water disappears, the rock forms. Examples: sandstone, limestone, shale, etc.

• Clastic Sedimentary Rocks

They are made up of clasts of the pre-existing rocks and the names of such rocks depend upon the size of the clast or grain.

• Biologic Sedimentary Rocks

When a large number of living species die then such kinds of rocks form. Chert or limestone are formed in this way.

Examples of Sedimentary Rocks

 

The first image is of limestone and another black one shale. Breccia, Chalk, Caliche, Chert, Conglomerate, Coal, Diatomite, Flint, limestone, etc. Are the other examples.

Metamorphic Rocks

These are the rocks that are formed from igneous or sedimentary rocks or even earlier metamorphic rocks which are formed due to high pressure, high heat, or other factors. The metamorphism process leads to the transformation of the existing rocks into another form. They are of three types:

These include phyllite, schist, gneiss, quartzite, or marble.

• Foliated Metamorphic Rocks

These are the rocks formed because of the parallel arrangement of certain minerals under pressure and are of platy or sheet-like structure.

• Non- Foliated Metamorphic Rocks

They do not have platy or sheet-like structure and grains do not align even after having so much pressure.

Examples of Metamorphic Rocks

The first image is of Gneiss and the other one is Anthracite. Other examples are Amphibolite, Hornfels, Marble, Lapis Lazuli, Novaculite, Quartzite, Soapstone, etc.

Rock Cycle

It is a cycle of various processes that lead to the formation and transformation of various types of rocks inside or outside the crust of the Earth. The three types of rocks which are formed are called igneous, sedimentary, and metamorphic due to various geological factors such as melting, cooling, heat or pressure, erosion, weathering, compacting and cementing, etc. When the heat and temperature inside the crust of the Earthrise, the magma forms which comes on the surface in the form of lava. When this lava hardened inside or outside the surface of the Earth becomes igneous rocks and when these igneous rocks erode into sediments because of various processes leads to the formation of sedimentary rocks and when these two rocks go under extreme pressure or other processes lead to the formation of metamorphic rocks which eventually are a transformation of already existing rocks.  These metamorphic rocks can be eroded further to form sedimentary rocks or can be melted into magma. Thus this cycle continues and these rocks go on the interchange from one type of rock to another. Our earth has several favourable conditions which lead to the formation or interchangeability of these rocks such as wind, water, tectonic plates, and their movements, heat or pressure, subduction, etc.

So, now we have covered the facts about Earth and have seen what does happen inside it. 

Conclusion

Thus, here in this article, we have covered Chapter 3 of Class 7 Geography i.e. Inside our Earth. These notes will be useful for those who are in Class 7 or even the students of upper classes to understand the basic concepts. These will be helpful for those who find it difficult to read the chapter in the book and make notes out of it. has eased your work by providing you with these crisp as well as comprehensive notes which will surely help you to understand the concepts properly as well as in revising the whole chapter quickly. You can check out notes of all other chapters or topics and other subjects as well on our website. These are created and prepared by the subject matter experts of after thorough research to help you in your studies. We believe that these notes will surely help you to grow.

A landform is a natural or artificial feature of the solid surface of the Earth or other planetary body. The terrain landscape formed due to the landform is topography. The characteristic physical attributes like slope, stratification, elevation, orientation, rock exposure, and soil type categorize landforms. Landform includes hills, mounds, ridges, berms, cliffs, rivers, valleys, volcanoes, peninsulas, and various other structures. Minor landforms include canyons, valleys, basins, and buttes, whereas major landforms are hills, mountains, plateaux, and plains. 

Coastal Landforms Definition

Coastal landforms mean any of the relief features remaining on the coast because of the combination of processes, sediments, and the geology of the coast itself. The development and persistence of landforms are the results of a combination of processes acting on sediments and rocks present on the coast. The power and current of waves play a major role in these processes. 

Beach, delta, coastal dune, wave-cut platform, a sea stack, sea cliff, and sea arch are some of the famous coastal landforms.

Erosional and Depositional Landforms 

There are two major types of coastal landforms – erosion and deposition. The erosional and depositional landforms, though they contain some similar features, show distinct different types of landforms. Erosional landforms show high relief and rugged topography. They can be seen on the leading edge of lithospheric plates, the west coasts of North and South America. The erosional coasts also occur due to glacial activity, which is seen in New England and the Scandinavian countries.

The erosional features are dominated by exposed bedrocks with steep slopes and high elevations near the shore. The bedrocks resist the erosion leading to its slow rate of shoreline retreat. The type of rocks and their lithification play a major role in the rate of erosion.

 

Features of Sea Erosion  

Seacliff Formation

The sea bedrock cliffs range from a few meters to hundreds of meters above sea level. The sea cliff landforms are the most widespread of erosion coasts. The wave-induced erosion near sea level and collapse of rocks at higher elevation lead to vertical nature. One can observe a notch in cliffs when they are extended to the shoreline where waves batter the bedrock.

At the base of the sea cliffs, one can find many veneers of sediment that form a beach. The sediment might be of sand, but it is more of cobbles or boulders, a coarse material. These types of beaches might get demolished with the strong waves during the stormy seasons as they are made in low wave-energy conditions. Some beaches of California and Oregon are its example. 

Coastal erosion means breaking down and carrying away materials by the sea, and deposition means the material carried away by sea is deposited or left behind on the coast. Coastal erosion happens due to ‘destructive waves’. We know that in the stormy season, the waves are very powerful and can destroy material into pieces. The strong backwash of waves pulls the material away in the sea.

Destructive Waves  

Erodes through four main processes as –

It is a force against the coastline that leads to dislodging and carrying the material away by the sea.

This can be seen in rocky areas when the water burst against the crack of rocks. These cracks keep on spreading as the air gets compressed and decompressed because of the waves crashes. The creation of caves is the result of compression as the rocks go on breaking off.

Abrasion means when the material is thrown to the coast with the swashes, they tend to break and spread, and this leads to more material backwashing into the sea. 

Attrition means the crashing of rocks and stones against each other while they are carried away by the sea. The attrition gives result formation of sand and rounded pebbles on the beach. 

When the cracks in the rock at the base are eroded and expanded by the continuous crashing of waves, the sea caves are formed. It is the result of constant compression and hydraulic action.

Sea arch is formed when the headland is broken through while waves continue to erode and expand to cut through.

Sea stack means the sea arch is no more capable of supporting till the root and falls broken in the sea. The remaining pillar-like rock is called a sea stack.

The sea stump means a broken pillar is remaining just above sea level. It is a sea stuck almost completely eroded.

Constructive Waves  

Are of low energy and high swashes. Swashes mean the waves deposit or drop the material on the coast. They have stronger swashes than backwashes. This leads to a build-up of material washed away during backwashes. This results in the formation of beaches. 

Magma is described as the extremely hot liquid or the semi-liquid rock which is situated under the Earth’s surface. This magma can easily push through the holes or the cracks in the crust surface which causes a volcanic eruption. When the magma flows or it erupts onto the Earth’s surface, this is given a new name called lava. Like a solid rock that has many constituents, magma is also a mixture of many minerals.

Magma, the word has originated from ancient Greek which means ‘thick unguent’. This is a molten or semi-molten material that is of course naturally produced. They also form the igneous rocks in this process. In another study, it is proved that the magma which is found underneath the earth’s surface has magmatism that is similar to be found on other terrestrial planets and other natural satellites. Apart from molten rock, this magma may also contain suspended crystals and gas bubbles. 

Magma Rock 

Magma is molten or half molten rock that also forms igneous rocks. These magma rocks consist of silicate liquid. The magma tricks at the depth of the earth’s surface which is afterwards ejected in the form of lava. The suspended crystals and the fragments of unmelted rock may also be transported in the magma; this is also dissolved and with high volatility may get separated as bubbles and some liquid may also get crystallized during this movement. Other such intertwined physical properties are also responsible to determine the characteristics of magma. This will also lead to describe the chemical composition of the magma, viscosity of the magma, the dissolved gases in the magma, and its temperature.  

Molten Magma

Molten Magma mostly exists in the lower part of the Earth’s crust and also in the upper portion of the mantle. So, the mantle and the crust are solid, and hence the presence of magma is quite crucial to the understanding of the geology and the morphology of the mantle. 

Magma here forms from the partial melting of the mantle rocks. As these rocks move upward (or they have water as added to them), they begin to melt a little bit. These then melt and migrate upward and form larger volumes that continue to swim upward. They also may collect in the magma chamber. Also, they might just come straight up. 

While they rise, the molecules of gas present in the magma come out of this solution and form bubbles and as these bubbles rise, they gradually expand. After which the pressure of bubbles becomes stronger than the surrounding solid rock and then this surrounding rock fractures, which allows the magma to get to the surface of it. 

Magma and Lava 

We use the term ‘magma’ which means underground molten rock and we also use the term ‘lava’ for the molten rock which breaks through the Earth’s surface.

The accurate distinction between magma and lava is about its location. When we refer to magma, we indicate the molten rock which is being trapped underground. While, when the molten rock comes up to the surface this keeps flowing like a liquid, and then this is called the lava.

Magma is hotter than lava. The hotness actually depends on when the lava has reached the surface and also if the magma and the lava emit from the same magma chamber.

Basaltic Magma 

Basaltic lava, also known as the mafic lava, is the molten rock that is enriched in iron and magnesium with depleted in silica. The basaltic magmas are formed by exceeding the melting point of the mantle that is either by adding the heat or changing its composition or by decreasing its pressure.

Basaltic magma is also formed through the dry partial melting of the mantle. The mantle lies quite below the crust of the earth. The Basalts also make up most of the crust of the ocean, thus the basaltic magma is generally found in the oceanic volcanoes.

Types of Magma 

There are three types of magma: basaltic, andesitic, and rhyolitic. All of these has a different mineral composition. All this type of magma has a significant percentage of silicon dioxide. 

• Basaltic magma is high in iron, magnesium, and calcium but it has deficient or it is low in potassium and sodium. 

• Andesitic magma has adequate amounts of all these minerals.

• Rhyolitic magma is high in potassium and sodium while it is low in iron, magnesium, and calcium. 

Andesitic Magma 

Andesitic magma has moderate amounts of minerals, with a rising temperature that ranges from about 800oC to 1000oC. The Rhyolitic magma is quite high in potassium and sodium but it is low in iron, magnesium, and calcium. 

Magma Volcano 

These are the molten rock inside the earth, they are deeper in the Earth’s surface are hot rocks that slowly melt and this becomes a thick flowing substance which is called magma. Since this is lighter than the solid rock that is around it the magma rises and then collects in magma chambers. Thus, in this process, some of the magma pushes through vents and fissures coming down to the Earth’s surface.