Category: Geography Notes PPT

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. 

Clay is a fine-grained natural material of soil and contains many clay minerals. The size of the soil particles of clay is usually less than 0.005 mm. There are also rocks that are composed of clay particles. The rock here means a composition of soils, ceramic clays, clay shales, mudstones, glacial clays, and deep-sea clays. Characterised by the presence of clay minerals in varying amounts of organic and detrital materials, such as quartz, the clay geology is formed. The clay geology is also defined by plasticity which is developed when there is a molecular film surrounding the clay particles making it flexible and when in dried form it becomes hard and brittle and non-plastic. Most of the clay is formed as the result of weathering.

Features of Clay Geology

As mentioned above, the defining characteristic of clay is the plasticity when it is wet and the hard nature in dried form. Clay geology shows a huge variety and broad range of water content holding in between the minimum when it moist enough to be moulded and the maximum when the moulded clay is just dry enough for holding on to a shape. For example, the plasticity limit of kaolinite clay, from the kaolinite geology, ranges from about 36% to 40% and the liquid limit ranges between 58% and 72%.

The characteristics of the plasticity of clay geology are attributed to the mineral content such as hydrous aluminium phyllosilicate minerals. There are thin plates formed by interconnecting oxygen and hydroxyl ions which are part of the mineral content. These plates are tough and flexible thus providing the inherent characteristics of the clay. 

The chemistry of the clay minerals and their ability to retain nutritional content such as the cations like potassium and ammonium are important for soil fertility. Some clay minerals are known as the swelling clay minerals as they can take up water to great extent. They increase in volume with the absorption of water and when dried they shrink back to their original volume which can produce cracks and other distinctive textures such as “popcorn” texture in clay deposits. Examples include clay from the smectite geology site and bentonite geology site which is also known as the blue clay. Especially, the clay from the bentonite geology (or blue clay geology) isn’t favourable for civil engineering projects because of this property. 

Varieties of Clay Geology

The main kinds of clays are obtained from the kaolinite geology, montmorillonite-smectite geology, illite geology and bentonite geology (or blue clay geology). There are a wide variety of clays, approximately, 30 different types of “pure” clays with a variety of mineral content. But the most naturally available clay deposits consist of the different types of clay along with other weathered minerals. The easiest way to identify clay minerals is X-ray diffraction rather than any other chemical or physical tests. Another kind of clay geology from which a type of clay is obtained is the fire clay geology. The fire clay geology, from which the fire clay is obtained, consists of mineral aggregates of hydrous silicates of aluminium with the presence or absence of free silica. 

Chlorite, vermiculite, talc and pyrophyllite are the types of minerals obtained from metamorphic rocks. The particles of such clay metamorphic rocks are very high in nutritional value and thus provide a significant amount of nutrition nurturing life. Thus, the plant life throws on the mineral content derived from the clay metamorphic rocks. 

Concluding with the Importance of Clay

Clay is one of the most important of the various soil components. It has a wide variety of usage and essential material in various industries. As a component of the soil, they are responsible for providing the plants with the environment for growth and by extension nearly all life on the surface of the Earth. Their porous nature aids them in providing aeration, and in water retention. Clay is also a reservoir of nutrient material such as potassium oxide, calcium oxide, and nitrogen as well. 

Furthermore, they are used in pottery. This culture of pottery making surpasses many centuries of human history. Clay pottery also serves as a record of past civilizations. They are used as building materials in bricks either in baked form or even in raw form for ages. Fire clay is another type of clay that is used for the manufacture of ceramics such as fire brick which is used for making furnaces, fireplace, kilns, fireboxes, etc.

Along with bricks clay is also used for making tiles, the cruder types of pottery, as china clay or kaolin for the finer grades of ceramic materials. Another major usage of the china clay is paper coating and filler giving the paper a glossy appearance and increases the opacity of the paper. It is also used in refractory materials including fire brick, chemical ware, and melting pots for glass and also in heat insulators as it increases the resistance to heat. Wool scouring is another example of usage of a certain type of clay known as fuller’s earth. In the process of rubber compounding, the addition of clay increases the resistance for wear and eliminates the moulding troubles. 

Even in engineering, clay materials serve vital purposes. In the construction of the dams, clay provides water impermeability characteristic when added with porous soil. It serves the same purpose of controlling water loss in canals. Along with the limestone, clay either in pure or impure form is utilized as the raw material of portland cement. After treating it with acid, clay can be used as a water softener. Clay also helps in removing calcium and magnesium from the solution and substitutes sodium. One of the other major usages of clay is drilling mud i.e. heavy suspension consisting of chemical additives and weighting materials when employed in rotary drilling. 

A contour line can also be called an isoline, isopleth, or isarithm. The lines are the function of two variables, a curve. Here the function has a constant value, here the curve joins the points of an equal value. Contour lines are plane sections of the dimensional graph.

In cartography, a contour line is normally called a ‘contour’. These lines join points having equal elevated heights, above a predetermined level, normally the sea level. 

These contour lines often illustrate a contour map, which is the main topic of discussion in this specific content. For example, a topographic map, showing valleys and hills, its steepness or gentleness of the slopes is represented by the contour lines. We will vividly discuss Contour Mapping in our subsequent sections. 

Contour Mapping

First and foremost, we will answer ‘what is a contour map?’ 

A contour map is a type of map where the shape of the land surface is shown by the contour lines, the relative spacing done between these lines indicates the relative slope of the particular surface.

Contour map meaning is quite clear to us, if we further deduce this definition it means – this is the delineation of any property in the map which is formed by constructing lines. The lines are carved based on the equal values of that property which is available as data points. 

In the contour map meaning, it can be said that contour mapping is a type of topography mapping, but to distinctly study the concept we will find there is an acute difference between the two, so we cannot use each other as synonyms. A topographic map is an accurate map that displays natural terrain and also man-made objects like buildings, roads, or bridges. While Contour maps represent changes in the elevation with the help of contour lines. 

Each of the contour lines being marked on a map joins the points having an equal height. The method of contouring cannot be totally relied on because two investigators can produce different types of maps whenever interpolation between two data takes place. 

Contour Mapping According to the Crustal Thickness

A contour map of global having the crustal thickness represents the bimodal division of the earth’s crustal thickness. The ocean basins have 6 to 7 km thick crust (excluding 4 to 5 km of water). The continents have an average thickness measuring 39.7 km. The crust is generally 30 km measured for thickness in the ocean-continent margin and this gradually increases towards the continental interior towards 40 to 45 km. The crust which is thicker than 50 km is only to few regions, which includes the Tibetan Plateau located in western China, the Andes in western South America. The contour map shows merely the large-scale crustal features, hence the regions with locally thick crust are not visible in this map. The crust does not display the pattern of increased thickness with the increase in age, as this would be the case if the same were to be repeatedly subjected to the igneous intrusions which are from the underlying mantle. For example, the crust located in western Australia is older compared to that in central Australia, yet the crust is a minimum of 10 km thinner in western Australia. This crust has a thickness which is in excess of 50 km, this is almost a young and active mountain belt. These regions consist of high topography and are vulnerable to rapid erosion. 

Contours Geography 

What is a Contour?

Contours are imaginary lines. These lines connect points of the same value. A contour map generally shows different contours such as the elevation or even the temperature contours.

Contours are the lines on a map that join the same height. The Contour interval refers to the variation in height, example the contours are drawn at every meter. 

 Contour lines on a map basically illustrate the height of a distinct place. This also helps us to obtain information regarding the steepness of the slopes, which is along the direction of the land that is sloping.

The contours here form patterns representing how steep the slopes actually are. The closer the contour lines are stuck together; the steeper is the slope.

With this result, we can study the relief of the land; whether this is a valley, a mountain, a valley which has a flat floor, also we can study if the valley has a stream, or not, or is it around the cone-shaped hill or a hilltop.

Uses of Contour Mapping

The Contours provide important information which can help us to study the nature of the terrain. This proves to be useful for the selection of sites, to determine the catchment area of a drainage basin, or to find intervisibility between two or more stations, etc. Some of the uses of contours are described below.

Nature of Ground

To study the nature of the ground which catches interest.

To Locate Route

To identify the route, a contour map provides worthy information on how to locate a route.

Intervisibility Between Stations

When the intervisibility between the two points cannot be easily ascertained by inspecting the area, then the contour map comes to the rescue. 

 

To Determine Catchment Area or Drainage Area

The catchment area of a particular river can be well determined by using the contour map. The watershed line very well indicates the drainage basin of the river which passes through the ridges and then saddles of the terrain that turns around the river. It is always perpendicular to the contour lines. The catchment area which is contained between this watershed line and the river outlet is measured with a planimeter.

Alexandra Cousteau, an emerging explorer of National Geographic Channel, initiated a nonprofit ‘Blue Legacy’ in order to raise water issues concerns around the globe. Water problems like droughts, storms, floods, and degraded water conditions made her believe that this is a rising crucial issue of the century. Like this initiation, other people across continents have started to work accordingly to save water and to avoid fatal scenarios such as droughts.

Unlike other natural disasters, the starting time or the ending time of drought cannot be pinpointed, hence this causes a lot more disastrous situation for the people facing it. We will in this section learn about droughts and how we can manage to surpass such a problem. 

What is Drought? 

Drought is such a period of time when an area or a region is exposed to below-normal precipitation conditions. Drought condition, also known as the Water Drought condition means the lack of necessary precipitation, which is either in the form of rain or snow. This causes the soil to reduce its moisture. This loss of moisture also causes reduced groundwater, less streamflow, crop damage, and all over a general water shortage. 

Discussing further drought conditions, firstly to mention this disaster affects people in many ways. People do not have access to clean drinking water which is undoubtedly essential to live. Other sources of water also diminish during a drought. In this condition, people are seen travelling miles after miles to fetch water from elsewhere. Drought condition also prevents the growth of the crops. As there is a lack of precipitation, naturally then the water crops must be watered by irrigation, but irrigation is also not possible as there is not enough water in nearby rivers, lakes, or streams, or from the groundwater. Some places also might face severe drought-like situations. Severe droughts are described as a long period of abnormally low rainfall, a low amount of rain adversely affects the growing cultivation including the living conditions. This is a prolonged dearth or shortage of water. 

Types of Drought

There are different types of drought conditions on many bases in this section. We will know the basis of classification and the types of droughts under them. In our next section, we will explain the typical types of drought conditions. 

Drought is being classified- 

On the basis of Source of Water availability 

Under this we have three types of drought:

1. Meteorological Drought. 

Meteorological Drought is again classified as:

• Slight Drought – When the rainfall is 11 to 25%

• Moderate Drought – Rainfall here is 26 to 50%

• Severe Drought – In this, the rainfall is more than 50%.

2. Hydrological Drought

3. Agricultural Drought

On the basis of Occurrence

1. Permanent Drought Area

2. Seasonal Drought Area

3. Contingent Drought

On the basis of medium

1. Soil Drought

2. Atmospheric Drought

 

Meteorological Drought 

Meteorological droughts abbreviated as MD are the water shortages that are caused by the imbalance in precipitation and the rate of evaporation. 

Hydrological Drought

Hydrological drought refers to the lack of water that is contained in the hydrological system. Hydrological drought also gives rise to abnormally low streamflow in the rivers and low levels in the lakes, reservoirs water. This is a part of the bigger drought phenomenon with a natural hazard.

Agricultural Drought 

Agricultural drought is marked with the set in when the soil moisture requirement to plants has totally dropped to such a level which adversely affects the crop cultivation and thus decreases the agricultural profitability. Agricultural Drought is the soil moisture being deficient compared to the meteorological droughts and climatic factors with their impacts on agricultural production and in economic profitability. 

Socioeconomic Drought 

Socioeconomic definitions of drought are related to the supply and demand of some economic goods. Socioeconomic drought is very much different from the already mentioned types of drought. Socioeconomic drought occurrence depends on the time and the space processes for the supply and demand to identify or to classify the types of droughts. Economic goods, such as water, food grains, fish, and power supply, depending on the weather conditions. Thus, these goods face scarcity of production. 

 

Floods and Droughts 

We, human beings, do require water to survive. Water is used for washing, drinking, and for watering crops. Thus, the amount of water that is available depends on the rain or snowfall. 

Unfortunately, precipitation is not equally distributed around the world. Some areas rarely see rainfall, the acute drought condition which we are discussing in this content. While others get more water than required, the acute flood problem.  These problems occur when they are least expected to happen. 

Equally, humans are responsible for this disaster to happen. If we have paid attention to the soil condition, its loosing of moisture, also if minimum attention was paid to the dry weather conditions, and thus, if we planted vegetation droughts could be resolved. 

Also, floods could be prevented, by proper sewage and draining systems and unnecessary clogging of water. If we emitted less pollution and stopped the glaciers from melting rapidly, maybe it would aid for floods. 

Management of Drought

Managers are available who are responsible to supply water, preparing for and responding to drought-like events. Apart from this, below are the management techniques that one must follow if drought hits. They are:

• Starting public information and education campaigns.

• Initiating emergency conservation programs.

• The water service is to be under restrictions.

• Stoppage of nonessential uses of water.

• Drought emergency pricing is to be done.

• Water rationing programs are to be started.

• Augmentation is required.

• Improvements in the water systems, like leak detection and lining of transmission canals.

• Emergency sources of supply are to be found out. 

• Managing the available water sources.

• Searching for new supplies of the water system.

Mafic and Felsic Both are made-up terms used to indicate the chemical composition of silicate minerals, magmas, and igneous rocks.

Mafic refers to silicate crystals, magmas, and rocks with a high proportion of heavier elements. The name “mafic magma” comes from the combination of the letters MA and FIC, which stand for magnesium and iron in Latin. Mafic magmas are also high in calcium and sodium. Mafic minerals are usually dark in color with high specific gravities (greater than 3.0). Olivine, pyroxene, amphibole, biotite mica, and plagioclase feldspars are common rock-forming mafic minerals. Mafic magmas are typically formed at spreading centers and represent newly differentiated upper mantle material. Basalt and gabbro are examples of mafic rocks. (It should be noted that certain geologists with dubious intentions reverse the magnesium and iron order and coin the name “femag.”) This is not to be confused with Femag, the Diabolical Dr. Saprolite’s dimwitted henchman.)

Felsic rock like the one shown above, on the other hand, refers to silicate crystals, magmas, and rocks with a smaller proportion of heavier elements and a higher concentration of lighter elements including silicon and oxygen, aluminum, and potassium. The word is derived from FEL, which stands for feldspar (in this case, the potassium-rich variety), and SIC, which stands for silica content. Felsic minerals have a light color and a basic gravity of less than 3.0. Quartz, muscovite mica, and orthoclase feldspars are common felsic minerals. Granite, the refined result of the earth’s internal separation process, is the most common felsic rock.

Felsic and mafic rocks are igneous rocks classified according to their silica content. Chemical analysis of the most abundant components in rocks are commonly presented as oxides of the elements; igneous rocks generally contain about 12 major oxides, which account for over 99 percent of the rock. Silica (SiO₂) is normally the most prevalent of the oxides. Due to this abundance and the fact that silicates make up the majority of igneous minerals, silica content was used as a basis for early classifications, and it is still generally accepted today. Rocks are classified as felsic, intermediate, mafic, or ultramafic according to this scheme (in order of decreasing silica content).

Rocks with more than 65 percent silica are felsic; those with 55 to 65 percent silica are intermediate; those with 45 to 55 percent silica are mafic; and those with less than 45 percent are ultramafic, according to a generally recognized silica-content classification scheme. Rhyolite and granite are felsic rocks, with an average silica content of 72 percent; syenite, diorite, and monzonite are intermediate rocks, with an average silica content of 59 percent; gabbro and basalt are mafic rocks, with an average silica content of 48 percent; and peridotite is an ultramafic rock, with an average silica content of 41 percent. Despite the fact that the averages have full gradations, rocks appear to cluster around them. The transition from felsic to mafic is generally accompanied by a rise in the color index (dark-mineral percentage).

Classification of Felsic Rocks

A rock must contain >75 percent felsic minerals, such as quartz, orthoclase, and plagioclase, in order to be categorized as felsic. Rocks that contain more than 90% felsic minerals are known as leucocratic, which means ‘light-colored.’ 

Felsite is a petrologic word for fine-grained or aphanitic light-colored volcanic rocks that may be reclassified after a more thorough microscopic or chemical examination.

Some felsic volcanic rocks contain phenocrysts of mafic minerals, such as hornblende, pyroxene, or a feldspar mineral, and must be named after the phenocryst mineral, such as ‘hornblende-bearing felsite.’ 

The TAS diagram of Le Maitre is used to determine the chemical name of a felsic rock (1975). This, however, is only true of volcanic rocks. If the rock is felsic yet metamorphic and lacks a definite volcanic protolith, it may be appropriate to simply refer to it as a ‘felsic schist.’ Extremely sheared granites that can be mistaken for rhyolites have been discovered.

The QAPF diagram should be used for phaneritic felsic rocks, and a name should be given according to granite nomenclature. Since the term granite already assumes feldspar and quartz, species of mafic minerals are often included in the name, such as hornblende-bearing granite, pyroxene tonalite, or augite megacrystic monzonite.

Mafic vs Felsic 

Two terms are widely used to describe the characteristics of rocks and lava in the concept of mineralogy, or geology in a wider context. The terms mafic and felsic are used to describe these types of rocks. 

1. Sticky or Runny 

Mafic lava is runnier or more viscous than felsic lava when used to characterize its characteristics.

The amount of silica in the lava is the explanation for this. Mafic lavas have less silica than felsic lavas. The volcanic eruption would most likely be less violent than the Hawaiian Island volcanic eruptions due to the runnier lava.

Summary: Mafic vs Felsic 

1. Mafic lava is viscous compared to felsic lava. 

2. Mafic lava dominates mid-ocean ridges, while felsic lava is found mostly at convergent areas. 

3. Mafic lava flows more easily than felsic lava, and the former has a lower risk of exploding. Since felsics tend to cap steam and other gases, explosive eruptions are more likely. 

4. Basalt is formed by mafic lava, while andesitic and rhyolite are formed by felsic lava. 

5. When discussing rocks or lava, mafic means the lava or rock contains less silica, while felsic means the lava or rock contains the most silica. 

6. Mafic rocks are darker than felsic rocks in color.