Category: Geography Notes PPT

Grasslands are defined as areas where grasses predominate over large shrubs or trees. Mountains rose in western North America during the Miocene and Pliocene Epochs, which lasted about 25 million years and created a continental climate favourable to Grasslands. Ancient forests dwindled, and Grasslands proliferated. Following the Pleistocene Ice Ages, Grasslands spread across the globe as hotter and drier climates prevailed. Grasslands can be called multiple names, for example Grasslands in the USA midwest known as “prairies’ ‘. In South America, they are called “Pampas”. 

Grasslands are found on all the continents except for Antarctica as the land there is covered with thick snow, leaving no scope for any vegetation to break out from the soil. Human beings alter the natural vegetation and give birth to artificial vegetation of crops and pastures.

Grasslands are Classified into Two Types:

1. Savannas or Tropical Grasslands

2. Temperate Grasslands

Examples of tropical grassland include the hot savannas of sub-Saharan Africa and northern Australia.

 

Savanna Tropical Grassland

Savanna is Grassland with a few scattered trees. Savannas of one kind or another cover nearly half of Africa’s surface (about five million square miles, mostly in central Africa) as well as large areas of Australia, South America, and India. 

Savanna is a mix of different trees and grass, their proportion depends directly on the rain in that area. Some may range below 0.3 m while some can outgrow this and grow upto 2.1 m that is approximately 7 feet. It is also spelled as “Savannah”. 

 

Tropical Grassland Climate

• The most important factor in the formation of a savanna is the Climate. 

• Savannas are always found in warm or hot climates with annual rainfall ranging from 50.8 to 127 cm (20-50 inches). 

• It is critical that rainfall be concentrated in six to eight months of the year, followed by a long period of drought during which fires can occur. Many of these areas would become Tropical forests if rain fell evenly throughout the year.

• Climatic savannas are savannas formed as a result of climatic conditions. 

• Edaphic savannas are savannas that are caused by soil conditions and are not entirely maintained by fire. These can occur on steep hills or ridges with shallow soil, or in valleys with clay soils that become waterlogged in wet weather. 

• People clearing forest land for cultivation creates a third type of savanna, known as derived savanna. 

• Farmers cut down a forest, burn the dead trees, and plant crops in the ashes for as long as the soil is fertile. The field is then abandoned, and, while forest trees may recolonize, grass (succession) takes over on the bare ground, becoming luxuriant enough to burn within a year or so. 

• In Africa, elephants have created a savanna by eating leaves and twigs and breaking off branches, smashing trunks, and stripping the bark of trees in protected parkland. Elephants can quickly transform dense woodland into open grassland. Annual fires keep the area as a savanna.

 

Rainfall/Season:

• The average annual Rainfall in savannas is 76.2-101.6 cm (30-40 inches).

• The savanna has both a dry and wet Season. Seasonal fires are critical to the biodiversity of the savanna. 

• The start of the dry Season is signalled in October by a series of violent thunderstorms followed by a strong drying wind. 

• During the dry Season, fires are common around January. Poachers who want to clear away dead grass to make it easier to see their prey often start fires in savannas. The fires do not completely destroy the community. The majority of the animals killed in the fires are insects with short lives. 

• Some animals, such as birds, come to fire sites to eat grasshoppers, stick insects, beetles, mice, and lizards that are killed or driven away.

• Small creatures can find refuge in underground holes and crevices. 

• Larger animals can usually run fast enough to avoid the fire. Although fire consumes the dry stems and leaves of grasses, the grasses’ deep roots are unharmed. When the soil becomes moisture, these roots, with all of their starch reserves, are ready to send up new growth. 

• The scattered shrubs can also survive on food reserves stored in their roots until the time comes for them to rise above the soil again. 

• Trees, unlike grasses and shrubs, can withstand fire by retaining moisture in all of their above-ground parts throughout the dry season.

 

Tropical Grasslands Location

• Tropical Grasslands of the world near the equator produce plants that can withstand hot weather for the majority of the year, as well as drought and fires. 

• The African savannas are probably the most well-known, but Tropical Grasslands can also be found in South America, India, and Australia. 

• There are llanos in Colombia and Venezuela, Campos in the Brazilian highlands, Pantanals in Upper Paraguay, plains in Australia, and India’s Deccan Plateau. 

• Even though they are all hot, the annual rainfall varies. The Australian plains may only receive 18 inches (45.72 centimetres) of rain per year, but African savannas receive more than 50 inches (127 centimetres). 

• South America’s llanos and Pantanal are frequently flooded during a portion of the year.

 

Tropical Grassland Animals

• Although it may appear that Animal life is scarce on the savanna, it is actually thriving. Elephants, zebras, wildebeest, giraffes, and other browsers eat the grasses on Africa’s savannas, which are then eaten by cheetahs, lions, and other predators. 

• Emus and other foragers in Australia rely on hot Grasslands. Insects, on the other hand, constitute the majority of Animal life in the savannas. There are billions of locusts, termites, and flies here. 

• Zebras prefer fibrous grass, whereas hartebeest eat plant stalks left by previous foragers. Giraffes and elephants eat the trees, and carnivorous Animals hide in the tall grasses before pouncing.

 

Tropical Grassland Vegetation

The natural vegetation of Tropical Grasslands

• The savanna soil is porous, allowing water to drain quickly.

• It only has a thin layer of humus (the organic portion of the soil formed by the partial decomposition of plant or animal matter), which provides nutrients to vegetation. Savannas are sometimes referred to as forests. 

• Grass and forbs are the most common types of vegetation (small broad-leaved plants that grow with grasses). Because of differences in rainfall and soil conditions, different savannas support different grasses. 

• Because the savanna supports so many species competing for living space, only one or a few types of grass are usually more successful than the others in a given area.

• For example, in drier savannas such as the Serengeti plains or Kenya’s Laikipia plateau, the dominant grasses on well-drained soils are Rhodes grass and red oat grass; star grasses are dominant throughout East African savannas, and lemon grasses are common in many western Uganda savannas. The open landscape is dotted with deciduous trees and shrubs. 

• One type of savanna, known as grouped-tree grassland, is found in southwestern Kenya, Tanzania, and Uganda, and features trees that grow only on termite mounds, with the intervening soil being too thin or poorly drained to support tree growth at all. 

• Frequent fires and large grazing mammals kill seedlings, keeping tree and shrub density low. 

Threats to Savanna Grassland – 

• Fire – managing fire is very typical because it can be very dangerous and fatal to the lives of every breathing being. Fire in a forest is way more troublesome than compared to the cities and villages. Though everything is connected and closely attached, even a small spark can turn the whole forest in ashes very quickly. Savannas are known for fire occurring on a regular basis. 

• Animal grazing – animals don’t graze on closely structured forest as the trees and grass doesn’t provide much opportunity to them to even enter in them. Savanna on the other hand is open structured and considered as a hub for the grazing animals to enter and graze on the vast fields. Animal grazing affects the soil because when these animals graze, they disturb the soil with their tongue. 

• Change in the climate – there is evidently said by the researchers that Savanna is expanding its range in reaction to the visible variation in the climate there and it is possible that the Grasslands are shifting dramatically and the distribution of vegetation changing. 

• Clearing of trees – the Savannas of Australia and South America are clear of trees now and still going on in a continuous manner. The vegetation in these areas are disturbed by the process of thinning down the trees.  There are many techniques used in clearing or cutting down woody plants. Heavy machinery was also used for this process. 

Volcanic Ashfall can be defined as the minerals, rock fragments and glasses that are exposed violently during a volcanic eruption in the form of ashes into the atmosphere.

The force created by the gases present in the magma propels the ashes to solidify in the atmosphere in the form of volcanic rock fragments and glass. On this page, students will get an idea about the formation and properties of volcanic ashes. We have also provided information about different types of Valcano.

These ashes also commonly known as tephra includes all the erupted volcanic particles, even the one larger than 2 mm in size. The explosion of this ash in the air has a negative impact on the health of humans as well as animals. As the disruption takes place in a wider aspect, it also greatly affects the infrastructures, buildings, industries, vegetations and cultivations of the nearby areas. 

Formation of Volcanic Ash Falls 

The formation of volcanic ashes or ashfall is an outcome of a volcanic eruption that takes place due to the expansion of the magma. Magma is the hot molten form of rocks present under the Earth’s surface. On exertion of high pressure, these magma comes out violently in the form of hot bubbling lava which leads to a volcanic eruption. On coming in contact with the air, the magma solidifies in the form of rock fragments and glass known as volcanic ashes. These ashes are minute particle-like which have a diameter less than 2 millimetres.

As a result, the volcanic ash in the air can be carried to a larger area by the winds and falls eventually on the ground creating a layer of a thick dust-like particle around the area of eruption. 

The formation of volcanic ashes also occurs as a result of phreatomagmatic eruptions. This kind of eruption takes place due to the contact of the magma with the water bodies, or even snow. This, as a result, forms an insulating vapour film as the boiling point of magma is higher than that of water. The reaction of cold water with hot magma increases the amount of heat transferred, thus, leading to expansion of water and fragmentation of the magma, which later comes out violently through the vents of the Volcano. 

Unlike burnt wood ashes, these volcanic ashfalls can be dangerous as they have sharp edges containing very small particles of glass and hardened rocks. There are several harmful effects of volcanic ashes on humans as well as animals. It can lead to breathing problems and irritation of the eyes, lungs and nose. 

Composition of Volcanic Ashfalls

Volcanic ashfalls are the hardened form of magma in the form of rock fragments and volcanic glasses after coming in contact with the exposed air. The elements found in the volcanic ashes depends upon the thickness of the ashes along with the chemistry of the erupted magma. But as per the reports, the abundantly found elements in these volcanic ashes includes silicon and oxygen. The dark coloured ashes formed after eruptions mainly consist of 45-55% of silica. This silica is rich in iron (Fe) and magnesium (Mg) content. These ashes are sharp-edged particles that have a thickness ranging from 1-5mm which even goes up to 100-300 mm in adverse conditions. 

Apart from the volcanic ashes, volcanic eruption also releases harmful gases into the atmosphere which causes severe breathing problems and irritation to the human eyes and nose. These gases are mainly sulfur dioxide, carbon monoxide and dioxide, hydrogen, hydrogen sulfide and hydrogen chloride. 

Effects of Volcano Ashfalls 

The effects caused by the ashfalls depends upon the thickness of the volcanic ashes. The thickness of the ashes may range from 1-5 millimetres and in adverse conditions it may be over 100-300 millimetres. Since volcanic eruptions cover a wider area, it greatly affects the nearby area. 

Some of the Impacts of Volcanic Ashfalls on the Ecosystem are Given Below:

• Volcanic Ashfalls can greatly affect the crop fields and can cause damage to the crops and vegetation. 

• They also contaminate the nearby water bodies, which as a result affects the marine ecosystem.

• Due to its expansion in a large area, it causes damage to the infrastructure including roads, buildings and breakage of telephone and electric polls, thus affecting the normal living of human beings.

• As volcanic eruptions release harmful gases such as carbon dioxide, sulfur dioxide and hydrogen sulfide into the atmosphere, it gives rise to breathing inability and irritation of the skin, eyes and nose.

• Ashfalls of higher thickness ranging from 100-300 millimetres can lead to collapsing of building, the burial of low plants and severe damage to plantation and trees.

• Livestock and other animals are killed every year due to this complete burial of land and soil horizon.

White Mica Powder is a pearlescent powder pigment that yields a satin white colour, ideal for backgrounds and seascapes. We can also use a little amount of mica powder in order to lighten darker micas. Mica Powder in different forms is acquired by grinding and exfoliating mica flakes, which is a slow, expensive and extremely complicated process. The process of mica powder formation is tough mainly because it is having a plate-like structure and delamination of flakes.

           

Facts About Mica Powder

Mica powders are:

• Composed from muscovite flakes coated with ultramarines, iron oxides and organic dyes

• Cosmetic grade natural mineral pigments that contain a wonderful shimmer and metallic-like appearance.

• Completely non-toxic, ethically sourced, vegan ( NO crushed beetles) and are cruelty-free,

• Contains millions of light-reflecting particles that form appealing shiny effects in all kinds of arts, crafts and cosmetics.

• Pure white mica powder is free from “fillers” and thus have pure pearly colour

• Is also available in delicate pastels to vibrant and bold shades

• Is a raw material which is perfectly safe to use in cosmetics (skin, lips, eyes)

What is a White Mica?

White mica is a finely-grained (coarse) version of any of the silicate minerals i.e.— muscovite, paragonite, or talc. White mica denotes a group of dioctahedral sheet silicates that are usually formed in low-grade metamorphic and hydrothermally reworked rocks. This substitution results in white mica in addition to compositions transitional from muscovite to celadonite, which is often referred to as phengite or phengitic white mica.

Top Tips To Use Mica Powder

• Intermix: With mica powders, you can create any colour under the sun

• Quantity in Resin: Mica powder being inert allows you to pretty much use as much as you like. It doesn’t affect the chemicals that induce resin and hardener to cure.

• Dust into Moulds: Use a soft-bristled craft brush in order to dust mica powder inside silicone moulds before making resin candles and castings. This will provide a more balanced shimmer effect.

• Soap & Bath: The mineral is just perfect for CP & M&P soap makers. However it is not soluble in water, therefore to make bath bombs you will need to add Polysorbate 80.

Refer to the table below for complete information on mica and white mica powder.

Physical and Chemical Composition and Properties of White Mica

Mica Reserves in India

India is the foremost supplier of mica mineral to the world with major reserves in:-

• Andhra Pradesh (41%)

• Rajasthan (21%)

• Odisha (20%)

• Maharashtra (15%)

• Bihar (2%)

• Jharkhand (Below 1%)

Mica Production and Distribution in India

India bears a near monopoly when it comes to the production of mica [60 % of the world’s total] With

• Andhra Pradesh (1st in production [93 %]).

• Rajasthan (2nd in production [6.3 %]).

• Jharkhand (3rd in production).

Mica Exports

India is by far the largest exporter of mica. Certain grades of Indian mica are and will continue to be vital to the world’s electrical industries. Major exports of white mica are executed through Kolkata and Visakhapatnam ports.

Fun Facts

• White mica and most Mica have a high refractive index (higher than sparkle) and even excellent chemical, mechanical and thermal stability.

• Made from natural minerals, mica powder contains a small micron size (giving great cover and diffusion, and the all-significant shimmer)

• you only require a little amount of mica powder in order to create lustrous effects.

• Can be used in art, resin, nail polish, car paint card-making, calligraphy, body butter/wax, oil, face products and cosmetics such as eye shadow, blushers and lip products.

• You can mix micas to create new shades

• India is one of the top suppliers of mica to the world.

• Mica-carrying igneous rocks form in Maharashtra, Andhra Pradesh, Bihar, Jharkhand, and Rajasthan.

• Significant imports of Indian mica are Japan (19%), United States (17%), and the United Kingdom etc.

In Meteorology, the air mass is the large body of air having nearly uniform characteristics of temperature and humidity at any given level of altitude. Such a mass has a distinct borderline and may outstretch hundreds or thousands of kilometers horizontally and sometimes as high as the troposphere ( about 10-18 km [ 6 -11] miles above the Earth’s surface. An air mass is formed whenever an atmosphere gets in touch with a large, relatively stable land or sea surface for long enough periods to receive the temperature and moisture of that surface. 

Air masses are commonly classified concerning the latitudes, and their continent or maritime source regions. Colder or freezing air masses are termed polar or arctic, whereas warmer air masses are deemed tropical. Maritime and monsoon air masses are moist whereas continental and superior air masses are dry. 

Air Mass Definition

“An air mass is defined as the large mass of air whose physical features such as moisture, temperature, lapse rate, and content are approximately uniform horizontally for hundreds of kilometers”.

According to A.N, Straheler, and A.H. Straheler (1978), a large body of air in which an upward rise of temperature and moisture are fairly uniform over a large area is known as an air mass. 

Types of Air Masses

The most common types of air masses are maritime polar(mP), maritime tropical (mT), continental tropical (cT), continental polar (cP), and continental arctic (cA).  

• Maritime Polar (mP) Air Mass– The maritime polar air mass is cold and humid originating from the oceans in the polar latitudes.

• Maritime Tropical (mT) – The maritime tropical air mass is warm and humid originating from the oceans in the tropics.

• Continental Polar (cP) – The continental polar air mass is cold and dry originating from land regions in the polar latitudes. 

• Continental Tropical (cT) – The continental tropical air mass is hot and dry originating from land in the tropics. 

• Continental Arctic (cA) – The continental arctic air  mass is dry originating from the North pole.

• Continental Antarctica (cAA) – The continental antarctic air mass is extremely cold and dry originating from land at the south pole.

Look at the image given below to observe from where these different types of air masses typically originate. 

Air Mass Creation

Air masses are developed when air is present to the surface over an extended period. This generally occurs at high temperatures with light winds. The area where air masses develop is known as the source area. Air masses over the warmer surface develop much faster than the colder surface because there is a weaker disturbance in the stable air over the cold surface. When the air masses get shifted from their source region, they change over time due to the surface and the area over which the air masses flow. 

Air Masses Movement

Air masses do not stay over their source location for a long period. As the weather pattern changes slightly, air mass gets shifted to a new location. Two things occur as the air mass moves towards a new location. First, as the air mass shifts over different surface characteristics, it begins changing. This process is known as air modification. For example, a maritime polar air mass that moves from the Pacific oceans over the mountains in the western continental US will sometimes dry as it crosses over the mountains, wash away its moisture, and warm over the land surface until it becomes the continental tropical air mass. The second thing that occurs when air mass moves is that they can hit the other air masses. When two air masses hit, a boundary known as the front is developed.

Did You Know?

• Maritime tropical air masses are often referred to as the trade air mass.

• Continental Polar masses are dry and cold because of their continental source regions. 

• The continental polar mass that affects North America develops over interior Canada.

• Colder air masses are known as polar or arctic whereas warmer air masses are known as tropical. 

• Five air masses that affect the United States around the time of a typical year are maritime polar, maritime tropical, continental polar, continental tropical, and continental arctic. 

• The stability of air mass can be represented using the third letter either ‘k’ ( air mass colder than the surface below it ) or ‘w’ ( air mass warmer than the surface below it).  An example of this can be a polar air mass blowing over the Gulf airstream, represented as cPk.

In the ionosphere, the ions out of the solar wind collide with the oxygen atoms and also with the nitrogen from the Earth’s atmosphere. Here the energy which is released during the collisions causes a colourful glowing type halo around the poles, this is known as an aurora. Studies say the most active auroras occur, at the time when the solar wind is the strongest.

Aurora is a light show that is caused when the electrically charged particles from the sun come in collision with the particles of gases such as oxygen and nitrogen that are present in the Earth’s atmosphere. An aurora is usually caused by the streams of electrified particles (that is emitted by the sun) which is bounded in the magnetic field of the earth.

Aurora 

Aurora is a luminous phenomenon that occurs in the Earth’s atmosphere, this occurs mainly in the higher latitudes of both hemispheres. Auroras occurring in the Northern Hemisphere are known as the Aurora Borealis, Aurora Polaris, also they are commonly known as the northern lights. While, in the Southern Hemisphere it is known as aurora australis, also known as southern lights.   

Auroras are generally caused by the interrelated action of the energetic particles which are mainly the electrons and the protons located in the solar wind with other atoms of the upper atmosphere. This interaction remains confined to the higher latitude regions. They are located in the oval-shaped zones which surround the Earth’s magnetic poles and also maintain an orientation that is according to the sun. During the time of low solar activity, this auroral zones shift towards the pole. While, during the periods of solar activity, these auroras occasionally extend towards the middle latitudes, like for example, the aurora borealis which has been seen as far as in the south which is 40° latitude in the US. The Auroral emissions generally occur at altitudes of about 100 km (approximately 60 miles). Though, they may occur anywhere which is between 80 and 250 km (that is about 50 to 155 miles) above the Earth’s surface.

Aurora Atmospheric Phenomenon 

Aurora is at times referred to as the ‘polar light’ which is predominantly seen in the regions of higher altitudes like in the Arctic and the Antarctic regions. This aurora is caused by the gush of electrified particles, they are emitted by the sun. 

Auroras are commonly seen in the latitudes which are around 70 degrees. They normally occur in a band which is known as the ‘auroral zone’. The auroral zone is about 3 to 6 degrees measured in terms of width in latitude. It lies between 10 to 20 degrees from the geomagnetic poles. 

Aurora Borealis 

The northern lights, or the aurora borealis which offers an entrancing or dramatic, magical presentation that fascinates all those who see are a sight to cherish. 

In the centre of this solar system, the sun is located which is a yellow star and this sustains life on our planet. The sun got many magnetic fields that distort and twist within itself as our parent star rotates around on its axis. While, when these fields become knotted together, they quite burst and create sunspots. They occur in pairs the largest sunspot can be quite almost several times the size of the planet Earth’s diameter.

As the temperature at the centre rises and falls, the sun boils and turns into bubbles. These particles escape from the star and then escape from the sunspot, hurtling the particles of plasma, known as the solar wind, into space. It thus takes these winds which are around 40 hours to reach the Earth. After they reach the earth, they can cause dramatic displays which are known as the aurora borealis. 

Aurora Polaris

The northern lights are considered one of the several astronomical phenomena, they are called the polar lights (also known as the aurora Polaris), they act as shafts or as the curtains of the coloured light which is visible on an occasion in the night sky.

Polar lights (or the Aurora Polaris) are a natural phenomenon that is found in both the northern and southern hemispheres. This streak of light is truly awe-inspiring. These northern lights are also known by their scientific name, which is known as aurora borealis, and the southern lights are also called the aurora australis.

Fun Facts

This is a picture of Aurora Australis. It is a display of the southern lights, which are quite manifesting by itself and as a glowing loop, this is an image of a part of Earth’s Southern Hemisphere, which is taken from space by the astronauts. 

Natural processes take time to occur and have various stages. Volcanic eruptions are one such type. During the eruption, magma present underneath comes out, the volcano explodes, and hence there is no boundary support left behind. Thus there are no sides and top of the volcano anymore as they fall inward with no support between. This depression formed due to magma eruption forms caldera. As a result, we either get steep cliffs around or lakes formation. These are huge-ranging up to 100 km in diameter. These are generally oval or circular. These have different depths, sizes, and shapes. 

Caldera Volcano

The word ‘caldera’ is associated with a volcano’s huge eruption, which can eventually have different sizes, depths, and shapes. As a result of the eruption, we get a large amount of magma expelled out on the earth’s crust. This hollow cavity on the earth’s surface is sometimes referred to as a crater. However, the two are not the same. It is because a crater is formed with the subsequent collapse. 

In the entire world, there have been seven known caldera volcanoes since the 1900s. The word is taken from the Spanish language, which means cooking pot. Also, this circular fracture is called a ring fault. 

Caldera Volcano Examples

A significant depression on the earth’s surface, let ground above the hollow part, is the caldera Volcano. However, different types vary according to size and shapes. Let us study some of them. 

Stratovolcanoes are the most explosive types which form crater-lake calderas as a result. These are caused by Plinian eruptions, which cause colossal lava, rocks, and ash to move out of the earth. One such example is Crater Lake in the US, Oregon which is not a crater that took 7000 years to form. 

Shield Volcanoes do not explode at one time. They undergo several stages and take a lot of time to pull magma out. Usually, these are characterised as lava fountaining and are less explosive. Unlike Crater-lake types, these produce nested depression on the earth’s surface. These are generally small and less than 5 km in diameter. The islands of Hawaii have good examples of shield volcano calderas. 

These are the largest depressions running from 15 to 100 km in diameter. These are not formed by a single volcano but result from different volcanic eruptions that collapse several magma chambers. These are the most destructive types that take thousands of years to form. Toba Caldera on the Indonesian is the best example of resurgent calderas with a rough figure of 74,000 years of formation. 

Some Other Caldera Volcano Examples

• The Yellowstone Caldera: 

It is named after its location- Yellowstone National Park, the US, where Yellowstone SuperVolcano erupted. It is a complex type that took 64,000 years to form.

It is a crater-lake type located at Antarctica’s off coast with a rough figure of 10,000 years formation. It has resulted in lake formation after seawater flooded inside it. 

This island has a series of shield volcanoes that finally resulted in the most profound hole formation. 

It has an elliptical-shaped oval depression known for the largest collapsing with magma eruption. 

Crater and Caldera

Usually, people mix the two terms, Crater and Caldera, with each other. When a crater is formed, you cannot get to the largest part. Thus the change from the deepest depression to crater is irreversible. 

What is a Crater in a Volcano?

When a volcano erupts, it brings different shapes and sizes. If it is a bowl-shaped depression on the earth’s surface, it is called a crater. These volcanic eruptions have steep and deep sides. As a result, a crater is formed. Craters are formed when magma or rocks from a volcano moves out and leaves behind hollow inside. There are generally Summit craters and Flank craters formed as a result of the eruption.

Difference Between Crater and Caldera

People usually confuse between a crater and caldera, but both of them are opposite. The crater is caused when volcanic eruptions cause hollow inside, letting magma out. On the other hand, the deep hollow collapses to form large craters. Craters are generally small and have small features, but giant holes are referred to as calderas.