Category: Geography Notes PPT

Alluvium is a loose soil, or sediment, not fused into a rock, formed by erosion, reshaped by water in some form, and redeposited in a riverside setting or by a river. This is suitably represented by the name Alluvium meaning “to wash against”. In simple terms, the soil or sediment deposited or redeposited by continuous erosion from water (for example of a running river) and solidifying but not completely fused into a rock is generally called Alluvium. It is typically made up of many various materials which include fine particles such as silt, clay and large sand and gravel particles. When such alluvium is over time deposited and solidified or lithified, into a rock, it is called an alluvial deposit.

Characteristics of the Alluvium

Alluvium occurs in deposits of a variety of landforms. The recent alluvium or the new alluvium is deposited on all level floodplains which are near to a stream or a river. Whereas the older alluvium is found on alluvial terrace landforms which are higher than any of the river-associated floodplains and are not subject to frequent erosion or washing away due to flooding. An important point to note is that sediment forms and deposits in a perennial river system are not typically referred to as alluvial. Thus, if any of the sediment formations can be credited to another very well-described geological event, then it is not referred to as alluvial. 

As is clear from the alluvium meaning – “wash against” in Latin, alluvium is the subaerial deposition of sediments due to river currents in the flood plains. The typical composition of alluvium or alluvial soil includes clays, silts, sands, gravels and occasional cobbles. Many times the composition is a mixture of all these particles along with some organic matter. This type of deposition of a landform is poorly sorted and the variations in particle shape are of different degrees. But in very general forms they all are rounded to some extent. 

Alluvium is associated with all the channels where water is present or was present in the past. The term “alluvial channels” based on alluvium is a very general term for all the channels that derive their deposition or form in some part because of flowing water irrespective of their time duration i.e. either perennial or short-lived. A variety of landforms are associated with alluvium which includes alluvial fans, braided channels, deltas, meander cutoffs, levees, point bars and terraces.

The soil of alluvium landforms is generally rich in potash and poor in phosphorus. The colour of the alluvial soils varies from light grey to ash grey. The shades depend on different factors namely, the texture of the materials and the time taken for attaining certain maturity after deposition. Due to various factors such as their location around the floodplains and the deposited particles with organic matter and mineral content, alluvial soils are one of the highly used soils for cultivation.

How Old or New is Alluvium?

Alluvium is the most recent form of a deposition. Geologically it comes in the Quaternary, which is the most recent of the three periods of the geologic Cenozoic era of the most recent Phanerozoic Eon. It is mostly referred to as the “cover” simply because it covers or hides the underlying lithified rock under it. 

Most of the sediments that are present in a given basin, but are not lithified into rocks are typically lumped together as alluvium. Depending on the time passed from their deposition, the alluvium is categorized into two types: Khadar and Bangar. They are explained below:

• Khadar: The new alluvium is known as Khadar. It is formed by the deposition brought by the annual floods in a given flood plain. It contains the newly deposited fine silts which aid in enriching the soil. 

• Bhangar: As the new alluvium is known as Khadar, the old alluvium is known as Bhangar. It is a system of older deposition which are found away from the flood plains and were probably deposited by flowing water in the past.

Both the Khadar and Bhangar contain calcareous concretions (called Kankars). In India, both types of Alluvium are found in the upper and middle Ganga plain. Some of the alluvium is also found in the Brahmaputra valley. In the composition of the alluvium, the sand content decreases while one goes from west to east. 

Alluvium is also distributed in different parts of the world. For example, the alluvium of the Pliocene age occurs in parts of Idaho. Alluvium from the late Miocene age is found in the valley of San Joaquin River, California. An example of alluvium deposition is shown in the given picture:

The Alluvium Conclusion 

From the given article it is quite clear that Alluvium is a type of geological deposition (yet to be lithified into a rock) of sands, silts and other particles including organic matter by flowing water. It is rich in minerals such as potash and is widely used for cultivation. 

An Equinox is an astronomical phenomenon that occurs twice a year, once in the spring and once in the fall, when the Earth’s axis is turned neither away from nor towards the Sun. The inclination of the Earth (with respect to the Sun) is 0° at Equinoxes, and the day and night are almost equal in length on Equinox day, i.e. 12 hours. 

Equinoxes occur every year on the 20th or 21st of March and the 22nd or 23rd of September, and all days have the same duration of day and night. In the Northern Hemisphere, March Equinox is known as Vernal Equinox and Spring Equinox, while it is known as Autumnal Equinox and Fall Equinox in the Southern Hemisphere. In other words, it is springtime in the United Kingdom, the United States, Canada, Russia, India, and China on March Equinox, while it is autumn in Australia, Argentina, Chile, New Zealand, and South Africa.

Equinoxes are preferably referred to as March Equinox (Northern Equinox) and September Equinox (Southern Equinox).  

This only occurs twice a year, on the spring and autumn equinoxes. This means that on these days, the day period is the same (12 hours) at all points on the earth’s surface (except right at each pole, where it will be about to change from permanent light to dark, or vice versa). In several parts of the world, especially in the northern hemisphere, the autumnal equinox marks the start of autumn. This is the first day of spring in the southern hemisphere.

 

Types of Equinoxes

Equinoxes are classified into two groups. The equinoxes in March and September are each assigned their own names.

Spring Equinox

The Spring Equinox is the first day of spring. The Spring Equinox happens as the sun reaches the equator from the southern to the northern hemisphere, marking the start of the spring season. The North Pole continues to lean back against the sun. The day and night are nearly similar in time. Spring Equinox is near 20 March.

Autumn Equinox

The Autumn Equinox occurs as the sun reaches the equator from the northern to the southern hemisphere, marking the beginning of the autumn season. The North Pole tilts away from the sun. The day and night are nearly similar in time. The autumnal equinox is near September 22nd.

Equinox and Culture

For thousands of years, equinoxes have been a part of many cultures and rituals. Equinoxes, for example, signifies the start of important days such as the new year. Planting and harvesting seasons are determined by the equinoxes. Both equinoxes are designated as national holidays in Japan as a day to honor ancestors. During the equinox, the Hindu temple Angkor Wat in Cambodia is said to be constructed in such a way that the sun rises directly above its central temple. Between 1113 and 1150, the temple was founded. There are many examples of this in various religious and cultural cultures.

Fun Facts

• Equinoxes do not always occur on the same day each year.

• Saturn has equinoxes as well, but they only happen every 15 years because it takes about 30 years for Saturn to orbit the Sun.

• Equinoxes generally occur about 6 hours later each year, with a jump of a day (backward) on leap years.

• The Mid-Autumn Festival, also known as the Moon Festival, is held in China to mark the autumnal equinox.

Canyon geography is very simple. A canyon is a huge valley, with tremendously deep, steep sides and perhaps a river flowing along the bottom. The term “Canyon” is derived from the Spanish word cañon, which implies “pipe” or “tube”. The word “gorge” is also most commonly used to refer to “canyon,” but a gorge is relatively steeper and narrower than a canyon almost always. That said gorges and canyons are almost similar except for steepness and narrowness.

 

How are Canyons Formed?

The natural processes of weathering and erosion, the movement of rivers, and activity in tectonic creates canyons. Canyons are most commonly developed by erosion.

 

Have you ever thought how old the Canyons would be? Any guesses, you might think it is around a few months or some years. Not exactly! Canyons have been formed long back millions of years. Canyons are formed with erosion. This happens when the land has started to be worn away within the time due to some sort of force, this might be bodies of water or due to the impact of weather. In terms of Canyons, the river is the primary player that is responsible for creating erosion. Rivers start carving within the land with the flowing water, and the land is worn away and then Canyons formation happens in millions of years. 

 

You must have heard of a Grand Canyons that is available in the United States (western part). This canyon is tremendous so it earns the tag of its grand shape. The size of these Canyons is measured as 250 miles long and a mile deep. It has been formed after millions of years via the famous Colorado River. Similarly, Colca Canyons in Peru, and from Tibet to China Yarlung Tsangpo Canyons is famous for its deep and grand area. The next type of Canyons formation is due to the rifts that occur between the peaks of two mountains. We can give an example of the Himalayas and Alps rocky mountains. In such a situation, a stream or river helps in chalking out a split between two mountains that are towering. And, when Canyons are formed with this process then they are known as box canyons. 

 

What is the Real Role of Weathering in Canyon Formation? 

By this time you are aware of the term erosion so weathering is another word for erosion. And, erosions can be of varied types including win, freezing water, flowing water, and thawing water. This is associated with varied factors such as you collect a few stones on a bach that are powerful and large waves. The shape of these stones is well-rounded. Have you ever thought about how they got this round shape? Similarly, you can notice some sand particles having pointed edges now you are getting that weathering is also there in the sand. So, these are examples of water and wind erosion. With such erosion, they have got jagged edges. 

 

These are a few popular examples, you can explore Geography for more such examples. 

 

Canyon Landform

A canyon is a deep valley that is also narrow and cut by a river through rock. Canyons differ in size from narrow cuts to mega trenches. They consist of very steep sides and maybe thousands of feet deep. Smaller valleys of identical appearance are known as gorges. Over thousands of years, a river’s flowing water erodes or wears down rocks and soil to create a valley. The largest and most popular canyons have had slit through dry areas by swift streams sustained by rain or melting snow from wetter areas. The walls remain rough and steep since there is little rainfall or surface water to wear them off. An example is the Grand Canyon, in the U.S. state of Arizona.

 

Weathering and Erosion

Weathering and erosion also lead to the creation of canyons. In the winter season, water seeps into cracks in the rock and then this water. As this water freezes, it enlarges and converts into ice. Ice compels the cracks to get bigger and bigger, eroding bits of stone in the process. During short, heavy rainfalls, water gushes down the cracks, wearing off even more rocks and stone. As more rocks fragment and fall, the canyon grows wider at the top than at the bottom.

 

When this process takes place in soft rock, like the sandstone, it can result in the formation of slot canyons. Slot canyons are observed to be very deep and narrow. At times, a slot canyon can even be less than a meter (3 feet) wide, but hundreds of meters deep. Slot canyons can be threatening since their sides are generally very smooth and difficult to climb.

 

Canyon Ledges

Some canyons with hard, underlying rock may grow ledges and cliffs after crumbling their softer, surface rock. These ledges have the appearance of giant steps.

 

It is in fact quite amazing to know that sometimes an entire civilization can develop on and around these canyon ledges. Native US nations, such as the Sinagua and the Hopi created cliff dwellings. Cliff dwellings look like apartment-style shelters that accommodated hundreds of people. The shaded, lofted canyon ledges in Walnut Canyon and Canyon de Chelly, in Arizona, rendered protection from antagonist locales and the burning desert sun.

 

Box Canyons

Hard-rock canyons open at one end are known as box canyons. The Navajo and Hopi people usually used box canyons as natural corrals for sheep and cattle. They simply established a gate on the open side of the box canyon and closed it when the animals were inside.

 

Limestone is a kind of hard rock that is most commonly found in canyons. Sometimes, limestone erodes and develops caves underneath the earth. As the ceilings of these caves crumble, canyons form. The Yorkshire Dales, a region in northern England, is an assemblage of canyons and river valleys developed by limestone cave collapses.

 

Grand Canyon Geology

The Grand Canyon is one of America’s treasure troves and a World Heritage Site of UNESCO. In the Grand Canyon, there are clear horizontal layers of different rocks that are themselves a telltale of when, where, and how they have been deposited, long before the canyon was even carved. The Law of Superposition implies that sediment is accumulated in layers in order, with the youngest rocks on the top, while the oldest rocks on the bottom just the way sand piles up in an hourglass.

 

Conclusion 

Thus, this was all about canyons. For the ease of the student’s definition, ways of canyon formation and their different types have been explained thoroughly. The topic is really interesting if it is studied from scratch and understood with examples. Here, the best tip for the students who are preparing it for examination is that they should prepare their own notes along with this so that their practice starts right from the time of learning. And, once they are versed with the historical background then it is going to be easy for them to learn and remember the concepts. 

According to the terminology of geography and geology, a vertical or nearly vertical exposure of a surface of a rock or a hill or a mountain is known as a Cliff. They are generally formed because of the erosion of landforms by the weathering forces of nature. For example, a cliff near the water body such as a sea or an ocean is caused by the erosion of the rocks by the water waves over a period of years. Aside from the sea-shores or coasts, a cliff edge is most commonly found in mountainous areas, escarpments, and along the rivers. If a rock is resistant to weathering and erosion, it generally results in the emergence of a cliff. 

Formation of a Cliff

The formation of a cliff happens mostly with sedimentary rocks. Sedimentary rocks such as sandstone, limestone, chalk, and dolomite are most likely to form a cliff. Sometimes, if there is a landslide formed because of a geologic activity then it can also lead to the emergence of a cliff edge. In old mountains, a mountain cliff can appear because of landslides caused due to the differential erosion of rock layers of differing hardness.  

In arid areas, a cliff edge can be determined by the jumbles of fallen rock. It means that in such areas, a rock that has fallen because of erosion, can give rise to the emergence of a cliff side. Opposite to that in areas of high moisture, a soil slope alongside an elevated portion of the earth can give rise to a cliff side. Certain mountain cliffs are part of the tributary waterfalls or rock shelters as well. Sometimes the edge of a cliff is created at the end of a ridge with different types of rock columns such as mushroom rocks. And as already stated before, coastal erosion by the waves can lead to the creation of the edge of a cliff which is the sea-cliffs on the receding coastline. 

The Ordnance Survey – a national mapping agency of Great Britain differentiates between cliffs and outcrops. According to them, a vertical exposure can be called a cliff only when it forms a continuous line along the top edge of the exposure (top edge of a cliff) with downward projections towards the land surface. They call the continuous lines along the lower edges as outcrops.

Large and Famous Cliffs

As per the above definition of a cliff, there is confusion in the extent of vertical exposure that is to be considered. There are various questions such as how much of the vertical slope be counted as a cliff. One can totally consider the combination of a vertical rock wall with a very steep slope as the cliff in terms of vertical exposure or only consider the rock wall as the cliff. Setting apart these doubts, one can find ascertaining qualities in some of the cliffs that are found around the world. 

Some of the largest cliffs on Earth are actually found underwater. A glistening example of such a cliffy feature is the ridge found sitting inside the Kermadec Trench. It has an 8000 m drop with a 4250 m width.

Another example of the highest cliffs is the steep non-vertical cliffs of Nanga Parbat: The Rupal Face and Gyala Peri. Both of them rise approximately 4600 meters or 15000 feet high above their base. 

The east face of the Great Tango in the Karakoram range of mountains of northern Pakistan is said to be one of the highest cliffs with a height of 1340 meters steep face. This height of this mountain cliff is considered by referring to the nearly vertical headwall of two stacked pillars which adds a very steep approach bringing the total drop from this cliff top of the east face to the nearby Dunge Glacier making it to 2000 meters.

One of the highest sea-cliffs stated by the Guinness World Records is Kalupapa in Hawaii. The height of this cliff from the cliff top is measured to be 1010 meters. The north face of Mitre Peak in New Zealand is also one of the competitors for the title of the world’s highest sea-cliff in the world. The north face of the Mitre peak has a height of 1683 meters. But these cliffs are taken into consideration by referring to the less stringent definition of the cliff as they also include it even though they have average slopes of 1.7 corresponding to 60° angle. A more stringent view of the definition is accepted for the vertical cliff found at Maujit Qaqarssuasia situated in the Torssukátak fjord area located at the tip of South Greenland having a vertical height of 1560 meters.

Mount Thor on Baffin Island in Arctic Canada is often referred to as the highest cliff with a height of 1370 meters. This height is inclusive of the cliff hanging part which does not form part of the 1250 meter which is said to be the longest vertical drop on Earth. But there is a possibility that the Polar Sun Spire in Sam Ford Fjord, in the Baffin Island may be higher than this. 

One interesting fact is that the highest cliff in the Solar System is said to be Verona Rupes which is approximately 20 kilometers of height found on the fault scarp on Miranda, a moon of Uranus.

Life Forms and Folklore

Clifftops and surrounding areas provide a unique ecosystem that is part of diverse habitat niches of a variety of plants and animals. An interesting fact is that many birds have decided preferences for choosing cliff locations for nesting and are often chosen because of their defensibility and absence of certain predators. 

The word ‘cliffhanger’ or cliff hanging became popular because the character in the novel To Kill a Mockingbird is hanging on the edge of a cliff. Thus, apart from being a source of scenic beauty cliffs form an integral part of the ecosystem and habitats with cultural values as well. 

Coral islands are kinds of islands, and they are formed from coral detritus as well as connected organic materials. A coral island happens in subtropical and tropical areas, commonly in the form of a portion of a coral reef. Coral islands begin in the form of the volcanic island on a hot spot. When the volcano does emerge from the sea, then a fringing reef enlarges on the volcano’s outskirts. Eventually, the volcano shifts to the hot spot via a process that is called plate tectonics. When this happens, the volcano finds it incapable of keeping up with the erosion of the wave, and so, it undergoes subsidence.

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What is a Coral Island in India?

A coral island in India is considered one of the most dynamic and earlier ecosystems of India. A coral reef does not only propose a sanctuary to countless marine life but turns important for shielding the coastline from wearing away. In India, there is nearly 7517km of coastline, and it includes islands though the mainland coast happens to be 6100 km.

Some popular Indian coral reefs remain confined to the Gulf of Manner, Andaman & Nicobar Islands, Palk Strait, the Lakshadweep Islands, and the Gulf of Kutch. All these reefs happen to be Fringing reefs, excluding Lakshadweep as they are Atolls. You will also come across some Patchy corals that remain present all along the inter-tidal zones. 

Some Features of Coral Islands

Though many people know what is coral island, they aren’t aware of its features. A coral island is acknowledged as a tropical island that is built of some organic materials that are derived from the corals’ skeletons and various other plants and animals connected with corals. The coral islands comprise low land but only some metres above sea level, commonly with coconut palms. They remain surrounded by many white coral sand beaches.

The coral islands extend to many kilometres, and they comprise nearly all the tropical limestone islands whose structures are a portion of the living coral reefs. The building of reef takes place below the level of high tide, and a common coral island surmounts the comparatively flat peak of the entire reef system. 

The coral island examples are The American territories of Baker, Jarvis, and Howland Islands etc. Some Indian examples are-

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Gulf of Mannar

The Gulf of Mannar happens to be a huge shallow bay that forms a portion of the Laccadive Sea and it has an average depth of 19 feet or 5.8 meters. This part lies between the Sri Lankan west coast and India’s southeastern tips. The chain of some low islands, as well as reefs, is called Adam’s Bridge or Ram Sethu and it comprises Mannar Island.

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Palk Bay

This is a fifteen thousand square kilometer biodiversity conglomeration that is nestled between India’s South East Peninsula and Sri Lankan. It has a coastal length of two hundred and fifty kilometers. 

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Gulf of Kutch

The Gulf of Kutch happens to be the bay of the Arabian Sea besides the Indian west coast located in Gujarat. It is well-known for its huge daily tides.

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How are Coral Islands Formed?

The formation of coral islands happens to be a dynamic process, and it takes many thousands of years to form a coral island. A coral island is formed with a freshly-formed volcanic island, and it rises above the ocean’s surface. When the island stabilises and magma no longer flows into the ocean, a coral begins to grow. This process happens in the shallow water all across the volcanic island.

Coral reef islands comprise rocks, and they emerge from coral skeletons. They are biologically formed calcium carbonate compounds that are the derivatives of the adjacent coral reefs. The sizes of coral reef islands range from some sq. metres to many sq. km. Again, you will find them in all proportions and shapes. The soils of a coral reef island comprise calcareous algae, coral fragments, various other limestone detritus, and guano that is found from sea birds, various amounts of humus, drifted pumice, and volcanic ash.

Coral reef islands become capable of developing only when ideal conditions maintain coral growth with passing the time. These conditions comprise some favourable physical factors, like high salinity, high temperature, low nutrients, and excellent penetration of light, besides some biological factors in a tropical region. 

Types of Coral Islands 

Coral Atoll

An atoll is acknowledged as a coral reef that is ring-shaped. At times, it emerges as a series of islets and sometimes islands too. The atolls surround bodies of water known as lagoons. Most of the time, lagoons and atolls shield a core island. A channel between islets connects a lagoon to a sea or an open ocean. Atolls form with underwater volcanoes, known as seamounts. At first, a volcano erupts, and it piles up lava. When the volcanoes continue to erupt, then the elevation of the seamount becomes higher, and it finally breaks the water surface. This way, the topmost part of the volcano turns into an oceanic island.

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Fringing Reef

A fringing reef is considered one of the different kinds of coral reefs. These reefs grow closer to the shore on a high island or mainland coasts. Commonly, a fringing reef is shore-attached. Some examples of fringing reefs are Timor-Leste, Indonesia, Philippines, Red Sea, East Africa, The Caribbean and the Australian western coast.

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Barrier Reef

A barrier reef gets featured by a reef and it is separated from the chief coast through a lagoon or deep channel. The initial formation happens on the edge of an open edge. Afterwards, it grows towards the coast or subsequent growth in parallel. The largest and renowned barrier reef example is the Great Barrier Reef of Australia. Some other examples are the New Caledonian Barrier Reef and the Belize Barrier Reef.

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Patch Reefs

These are the isolated little reefs which grow at the bottom of the platform island or even in continental shelf. It is present in between fringing and barrier reefs. They almost never reach the water surface. Patch reefs vary in size.

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Conclusion

A coral island is a low island that is produced in warm waters by very small sea animals known as corals. The corals build up the hard exterior skeletons of calcium carbonate. It is called limestone, and it has huge similarities to the shells of some sea creatures such as mussels and clams.

Earthquake magnitude is the measure of the “size” or amplitude of the seismic waves generated by the sources of the earthquake and recorded by the seismograph. As the magnitude of the earthquake changes tremendously, it is necessary to compare in order to compress the range of amplitude of waves measured on seismograph using the Mathematical device. 

In 1933, the American seismologist Charles. F. Righter introduced the earthquake magnitude scale (known as the Richter magnitude scale) as the logarithm to the base 10 of the maximum seismic waves amplitude reported on a standard seismograph (in thousandths of ml) at a distance of 60 miles or 100 km from the earthquake epicentre. 

Reductions in amplitude are observed at various distances to the expected amplitude at a standard distance of 100 km is formulated based on the empirical tables. Righter earthquake magnitude scales are computed based on the assumption that the ratio of the amplitude of the maximum wave at two given distances is equal for all earthquakes and is different from the azimuth.

Due to the various shortcomings of the Richter scale, most seismologist authorities now use another scale known as the moment magnitude scale to record the magnitude of an earthquake.

What is the Magnitude of Earthquakes?

The earthquake magnitude is a measure of the amount of seismic energy released by it, so it is a quantitative scale. Magnitude is the most commonly used measure to describe the overall strength or size of an earthquake. The magnitude of an earthquake is expressed in decimal fractions and whole numbers. For example, a magnitude of 5.3 is considered a moderate earthquake whereas a magnitude of 6.3 is a strong earthquake. Due to the logarithm basis of scale, each whole number increases in magnitude represents a 10-fold increase in measured amplitude as measured on a seismograph.

In modern times, several different magnitude scales for measuring the relative size of an earthquake are used by scientists and engineers. An earthquake scale for measuring magnitude has no lower or upper bounds. Sensitive seismographs can even record earthquake magnitudes of negative values and have reported magnitude up to about 9.0 (For example, the 1906 San Francisco earthquake had a Richter magnitude of 8.5).

Earthquake Frequency

An earthquake frequently defines how often a given earthquake with a certain magnitude comes about. On average, an earthquake with a magnitude of 2 or less comes about several hundred times a day throughout the world.

However, a major earthquake range with a magnitude of 7.0 – 7.9 occurs more than once per month throughout the world. Whereas, an earthquake ranges to a great extent with a magnitude of 8.0 or greater or comes about only once a year.

Knowing the earthquake frequency is important for engineers as they not only strengthen a building against earthquake shock but also minimize the force a building is subjected to. To minimize the loss, they install a base isolator that helps to isolate the base of the buildings from the earth’s movement. 

Earthquake Range in Magnitude Scale

How Strong is a 3.5 Magnitude Earthquake?

An earthquake of magnitude 3.5 on the scale is considered to be minor. A 3.5 magnitude earthquake is often felt by people, but rarely causes any damage to the buildings. You can even observe the shaking of an object inside the buildings.  

Did You Know?

• The largest-ever earthquake with a magnitude of 9.6 occurred in China in 1916.

• The largest earthquake in the US with a magnitude of 9.2 struck the Prince Willian studio, Alaska on March 28, 1964, UTC.

• An earthquake can occur in any type of weather.

• It is estimated that approximately 500,000 earthquakes are detected in the world each year. 100,000 among those can be felt, and 100 of the earthquakes can cause damage.

• The most deadly earthquake occurred in Shaanxi, China in 1556. It is estimated that 850,000 people were killed in that period.

• Florida and North Dàkota are the places with the least earthquakes.