Structural geology is the systematic study of the deformed rocks which constitute the planet Earth’s upper layers of geological materials. Thus, it is the study of the deformation of the Earth from a planetary perspective as the major structural features are described. It also describes the situation and processes by which the upper layers of the planet undergo horizontal and vertical displacement.
In the universe, each planet or moon exhibits its own distinctive process and style of deformation. This reflects the degree of movement of the planetary interior as well as its ratio of volume. As a planet radius increases, the rate of cooling of the planet drops, since there is less surface area to cool across. Thus, larger planets are hotter and more mobile, due to the dependence of rock strength on temperature. This causes a planet interior to be able to flow plastically.
While the bed of rock lying on the surface of a planet is brittle and relatively weak, the rocks that lie deeper underneath are stronger, due to pressure. However, when we reach some depth, the effect of increasing temperature causes the rock strength to drop as it become weaker the deeper we go. Hence, the a layer of high rock strength is found near the surface of a planet. This geological layer is called lithosphere, with ‘litho’ meaning rock. The most fundamental structural property of the Earth is the distinction between ocean basins and continents, which are the most obvious features of its surface. The boundary that divides continent from ocean is found at 2000 m below sea level.
The continents of the planet consists largely of 100/3000 million years old rocks, which have been repeatedly deformed. They are rich in quartz and feldspar.
Lower Mantle
The lower mantle is one of the five geological layers of Earth. It is different from the other geological layers of the Earth, being the site of molten rocks that are ejected to the surface through volcanoes. Although it is also molten rocks, it is more solid than the upper mantle as it flows very slowly, like a very dense liquid.
The main process that helps shape the planet take place in the lower mantle, playing an important role in creating volcanoes. Hot convection forces in this layer cause molten rocks and mineral to boil so intensely that they explode through the Earth’s crust, giving birth to volcanoes and the formation of rock islands in the oceans (Pacific).
Characteristics
The lower mantle is the thickest continuous layer of the Earth’s as it constitutes more than 50% of its size and the 70% of the planet’s mass. It measures about 1,550 miles (2,500 km) thick, having an estimated temperature of 4,000° F (2,204° C). It is believed that this layer is made mostly of magnesium, silicon, and oxygen, with smaller amount of iron, calcium, and aluminum. Combined together, these elements form a rare mineral called perovskite.
The age of the lower mantle is hard to figure out, simply because its molten rocks cannot be reached to take a sample and study it. However, since this layer was formed very early in the geological history of the Earth, it is probably billions of years old. At the same time, the lower mantle’s rocks change their form slowly and regularly as the layer convects and boils, with older rocks changing into new, younger ones.
You must remember that convection is the propagation of heat in a liquid. Hot melted rock is less dense and lighter than cooler molten rock, which is more dense and heavier. As the hotter lighter rock rises up to the top, the cooler and dense one sinks down.
Below, diagram of the Earth geological layers, showing the upper and lower mantle.
Upper Mantle
The upper mantle of the planet Earth is the geological layer which is located right below the crust. It is not made up of solid materials but it is rather a very thick, slow-moving liquid of molten rocks. The crust has been formed by these molten rocks that have been ejected from deep below over hundreds of millions of years. Layers upon layers of sediment that derive from once upon-a-time living creatures and vegetation lie on top of the crust. Consisting of the lithosphere and the asthenophere, it is estimated that the upper mantle measures about 217 miles (350 km) thick. The lithosphere in turn is also a part of the deep part of the crust, overlapping both.
As the upper mantle drifts slowly around the Earth surface, so does the crust lying on top of it. This geological process is called plate tectonics. According to the theory, plate tectonics have shaped the continents, islands, mountains, causing the strongest earthquake on the planet. The upper mantle and the crust move so slowly that it cannot be observed on a day to day, or a week to week, basis, for it takes millions upon millions of years to shape huge mountain ranges, such as the Andes or the Himalaya.
Composition
The top section of the upper mantle (the lithosphere) is rigid, almost solid, and it is 40-mile deep. It is composed of peridotites. A peridotite is a plutonic igneous rock, which consists of olivine. Olivine is in turn a yellowish green mineral made up of silicate containing iron and magnesium, mainly (Mg, Fe)2SiO4. Since peridotites are heavier than most of the rocks found in the Earth crust, they have a tendency to sink down deep into the bottom of the crust and the upper mantle.
The asthenosphere, on the other hand, consists of about 150 miles of molten rocks, which are made up mostly of silicon and magnesium, but it also contains smaller amount of magnesium, iron, aluminum, and calcium. Diamonds and other rocks also erupt onto the surface of the Earth from deep in the upper mantle in some places of the planet.
Below, Diagram/Drawing of Earth Geological Layers, Showing the Upper Mantle.
Hydrothermal Circulation
Hydrothermal circulation is the circulation of hot water underneath the earth. It is located most often in the vicinity of sources of heat within the Earth’s crust. It usually occurs near volcanic activity, but can also occur in the deep crust related to the intrusion of granite, or as the result of orogeny or metamorphism. The word “hydrothermal” derives from Greek: “Hydros” means water and “thermos” means heat.
Hydrothermal circulation in the oceans is the passage of the water through mid-oceanic ridge systems. The term includes both the circulation of the well known, high temperature vent waters near the ridge crests, and the much lower temperature, diffuse flow of water through sediments and buried basalts further from the ridge crests.
Hydrothermal circulation is not limited to ocean ridge environments. The source water for geysers and hot springs is heated groundwater convecting below and lateral to the hot water vent. Hydrothermal circulating convection cells exist any place an anomalous source of heat, such as an intruding magma or volcanic vent, comes into contact with the groundwater system.
Origin of The Andes
The origin of the Andes Mountains Range goes back to 50 million years ago, to the Tertiary period of the Cenozoic Era. This long chain of massive geological elevation originated by the collision of the Nazca tectonic plate against the South American plate about 50 million years ago. The portion of the Andes with highest peaks in the American continent makes the border between Argentina and Chile. Aconcagua is 6,959 m high.
This geological phenomenon of collision of plates, which gave rise to all mountain ranges in the world, is called subduction movement, which occurs at a convergent boundary between two tectonic plates of the lithosphere. To sum up, the origin of the Andes mountains is the result of a collision of plates, with the Nazca plate sliding underneath the South American one, lifting geological materials up to great heights and folding them up amid intense volcanic activities.
This slow geological process that formed the Andes range is still going on, causing strong earthquakes and sunamis in the Chilean and Peruvian coastal regions. During the orogenesis of the Tertiary, igneous rocks, such as granite, basalt, and quartz which are part of the western edge of the South American crystalline basement rock, were raised above 6,000 m of altitude. The Tertiary is a geological period of Cenozoic Era.
Below, a picture of the Andes Mountains in Patagonia, Argentina, near the Chilean border.
Below, a map showing the world’s tectonic plates, with the convergent movement of the Nazca against the South American Plate marked with a red line.
Geographical Features
Geographical features are all those natural formations of the planet Earth’s surface which form the landscapes of a country. All these formations, which are characteristics of any given region of the world, have names in geography; they are the mountains, plains, plateau, valleys, rivers, lakes, seas, oceans, etc. All these features have been shaped by natural phenomena, such as rain, winds, volcanoes, and especially geological movement of tectonic plates of the Earth over millions of years.
Mountains can be geologically new or old as they are usually arranged in chains, which are called range, like the Andes mountain range in South America. If the system of mountains is new, they can be very high and the mountains have snow-capped peaks, with the tallest ones being called mounts, which are abbreviated “Mt.”, such as Mt Everest in Asia, or Mt Aconcagua in South America. A chain of mountains usually constitute a divide or water shed, determining the direction in which water streams flow, sometimes being the natural boundaries or borders between countries.
Valleys are limited open spaces, often with grassy land, surrounded by chains of mountains. They are usually wide enough to be inhabited by human beings and ruminants. A valley is emptied by a main river and its creek-like tributaries, whose water originates from melting snow on top of mountain peaks. It is usually communicated with a wide open plain through a ravine or gorge.
Rivers can be large and small, flowing into oceans, seas or large hollow areas called depressions, forming lakes. Large rivers are fed by other important water streams, which are called tributaries. A large region drained by a big river and its tributaries is called basin. Rivers can be created by rain water or by the melting of snow in the mountains, or by both. The largest river in the world is the Amazon, which originates from the union of snow-melting streams in the Andes, in Peru.
Plains are large areas of flat land, usually covered by rich, black sediments where grass grow and large herds of ruminants thrive. The black sediment, the top layer of plains, are geologically new in the Earth history. They can be referred to as savannas, prairies, steppes, or grasslands. There are famous plains, such as the Pampas (Argentina), the Great Plains (USA), and the Aquitaine (France).
Oceans and seas are large masses of salt water covering the the lowest parts of the Earth surface. They account for about 70% of the planet’s surface. Life began in the oceans as primitive prokaryotic cells, most of them being cyanobacteria.
Below, on of many geographical features, a grassy plain; here a Central Asia grassy steppe, which is very fit for animal husbandry. The nomadic tribes have been its main inhabitants.
Types of Deformation
There are two types of deformation in the lithosphere, according to the morphology of the Earth’s continents. They are orogeny and epeirogeny. The former has taken place recently, between 45 and 50 million years ago, and it is still going on, while the latter dates back to the Proterozoic era, having begun about 4 billion years ago.
Orogeny is the deformation of the Earth crust through the mountain-building process, which involves the violent collision of two tectonic plates and the ejection of molten rocks that are uplifted as they get solidified. This dynamic geological process comprises faulting, folding, strong seismicity, and a linear mountain chain of high-altitude sharp peaks. It is relatively new, from the Tertiary period of the Cenezoic era. An example of orogeny is the Andes mountain range in South America, which is the product of the South American plate and the Nazca plate collision as it is 47 million years old. The word orogeny derives from Greek, with oros meaning ‘mountain’, and –geny, ‘genesis’ (creation, development).
Epeirogeny is the broad and slow warping of the lithosphere. It does not involve local intense folding, faulting; nor is there seismicity. This type of deformation has given way to plains (due to erosion), to the emergence of plateaus, as well as large areas of depression. Sometimes these geographical features are surrounded by very old, low mountains. The cratons are examples of this process, such as the Guayana’s Highlands in Venezuela and Brazil. Granite and basalt rock outcrops and the absence of seismicity are two common features of epeirogeny. Thus, it only occurs in stable and solidified portions of the Earth’s crust. Also from Greek, with epeiros meaning ‘continent’, and -geny, ‘genesis’.
CO2 Levels in Geologic History
The charts of CO2 levels in geologic history show you clearly that today’s carbon dioxide levels are some of the lowest, with 400 ppm (parts per million), especially if you compare it with those of the Paleozoic and Mesozoic Era. Today’s levels might be higher than the 1980s but they are still very low. You can see that during the Cambrian period of the Paleozoic Era, it was at the highest, with almost 7,000 ppm. When the CO2 levels were between 4,500 and 4,000, there was a massive proliferation of terrestrial plants and animal lives, with the appearance of the amphibians and primitive reptiles during the Devonian and Carboniferous period, respectively.
Not only did the quantity of carbon dioxide was much higher during the Paleozoic and Mesozoic than today’s levels but also the amount of nitrogen in the atmosphere was much, much higher than it is today, yet animals could still breathe, live, and thrive as there was enough oxygen for every living creature and enough CO2 for every plant. In the geological history of the Earth, CO2, oxygen, and nitrogen levels rose and fell without the existence of human beings and human industry.
During the Permian, the last period of the Paleozoic, the CO2 levels dropped sharply to about 700 ppm. However, the amount of carbon dioxide rose up steeply to about 2,100 and 2,500 ppm as animal and tropical plants flourished again, with the emergence and abundance of the dinosaurs during the Triassic and Jurassic respectively; also the first mammals appeared during the Cretaceous period. During the first part of the Cenozoic Era, they still remain high between the Paleocene and Eocene epoch at 2,200 and 1,700 ppm. Yet, at these high levels of carbon dioxide, mammals thrived and scattered to every corner of the planet. Then CO2 dropped sharply at the end of the Eocene and the beginning of the Oligocene. This coincided with a general cooling of the Earth temperatures and the disappearance of large tracts of rain forests, giving way to the emergence of the huge grassy plains, such as the African savanna, and the Caucasian, Russian, and Mongolian steppes. Abundant grass (Gramineae) boosted the thrive of ruminants (cattle, deer, sheep, buffalo, etc.) and equines; and with them carnivores flourished.
Below, the CO2 levels during the Cenozoic.
Jura Mountains
The Jura Mountains are a chain of geological elevations, whose highest peak reaches 1,723 m (5654 ft). They run from northeast to southwest for about 250 km, forming a wide open arch that constitutes the natural border between France and Switzerland. Thus, they are located in west-central Europe, between the Rhine and Rhône River. Le Crêt de la Neige, the highest peak, is situated in the department of Ain, France.
Geology
The Jura Mountains gave the name to a period of the Mesozoic Era; the Jurassic, which followed the Triassic and preceded the Cretaceous. Hence, these low mountain range is about 160 million years old. Lime is the main rock that makes up the bulk of the system.
The Jura Mountains originated from the thin-skinned tectonic that deformed a calcareous Mesozoic cover. Although the Mesozoic Jura shelf emerged at the end of the Cretaceous, the rock structure, which is lime, was formed and compressed during the Jurassic. Later, during the Cenozoic Era, it underwent Paleogene subtropical weathering and erosion. During the late Miocene epoch (Tertiary period of Cenozoic), it was invaded by a perialpine sea. Then the internal part of the Jura Mountain would be reached by Alpine compression.
The intense folding of the internal Jura was responsible for a thickened cover, which in turn induced the uplift of this zone. Most of the fold belt of the Jura is no longer active today, according to present day stress field pattern; this was suggested by Becker in 1999.
Below, map of Europe, showing the exact location of the Juran Mountains.
Pacific Ring of Fire
The Pacific ring of fire is the geological boundary line which surrounds the Pacific tectonic plate. Its the limit is where it meets other plates, or drifts apart from them. Thus, on its southern border the line divides it from the Antarctic plate; on its eastern side, the line separates it from the Nazca, Cocos and North American plate; on the north, this geological fissure divides it also from the North American plate, while on its western border, the Pacific plate runs into the Philippine and Australian plate; here the fissure shows intense geological activities, causing strong earthquakes and tsunamis. This is due to the collision of these tectonic plates.
The coastal regions of California are on the Pacific ring of fire. So is Japan, the Philippine islands, New Guinea, and New Zealand. When the Pacific plate edge suddenly and violently slips under the Philippine or the Australian plate, powerful earthquakes hit cities lying near this geological boundary line. The strong earthquake that struck Japan on March 11, 2011, caused an apocalyptic tsunami that killed thousands of people and affected a nuclear power plant. Thus, these violent natural phenomena are caused by what is known as the Pacific ring of fire. In other places, the volcanic activities spew out lava deep on the bottom of the ocean as the molten rocks pile up and forms islets, which over the millions of years they become islands.
Below, the different tectonic plates whose boundaries form the Pacific Ring of Fire.
South Africa Topography
South Africa topography basically consists of a broad central plateau, which is surrounded by a series of escarpments on its west, south, and east side. These surrounding high, steep slopes are called the Great Escarpment. Inland from the crest of the Great Escarpment, the landscape is composed of rolling grassy plains, which gradually descend to an average altitude of about 900 m (2,952 ft) in the center. The Highveld is the highest and largest grassland region of the central plateau.
The outside the central plateau, the periphery of the escarpment consists of overlooking slopes, which pitch to the eastern, southern, and western coasts. To the east of the central plateau, there is the Drakensberg Mountain Range. To the south, there is a series of three chains of mountains; the Great Karroo Range, the Groote-Swartberge, and the Little Karroo Range, which extends along near the southern coast of the country.
South Africa features a rugged coastline, with rocky shores, sheltering a few bays and harbors. There are coral reefs off the eastern coast that surround Sodwana Bay, which attracts divers from all over the world. Meanwhile, the country is crisscrossed by three main rivers; the Orange, the Vaal, and the Limpopo River. The Vaal is the most important tributary of the Orange River, which is 2,100-km-long, flowing in eastern-western direction as it empties into the Atlantic Ocean.
On the east, South Africa is bordered by the Indian Ocean; on the west by the Atlantic, and on the south by both the Indian and the Atlantic Ocean. The coastal belt of the west and south ranges in elevation between 150 and 180 m (500 to 600 ft). This strip of land is very fertile. In the East, on the other hand, there is very little coastal plain, where the Great Escarpment borders the central plateau as it reaches almost to the sea.
Below, a physical map of South Africa, showing the different geographical features of its topography.
Continental and Oceanic Crust
The continental and oceanic crust constitute the external surface of our planet. They are the outermost layer of the Earth as they are parts of the lithosphere. The crust is constantly being formed, destroyed and rebuilt by geological processes happening inside the mantle. It consists of volcanic rocks on top of which layers of softer sedimentary rock and organic sediment rest. On average, it is estimated that it is 22 miles (35 km) deep and it gets slightly thicker every year as more molten rocks constantly come out from within the Earth.
Continental Crust
It is the geological layer which is constituted by dry land. It is made up largely of rocks called granite, which is not only igneous (volcanic) but also plutonic rock. Granite is the pink, black, and grey rock that came out of active volcanoes hundreds of millions of years ago, cooling off and solidifying under the earth surface. It is characterized by being the hardest rock on Earth. Today, melted rocks from beneath this crust still rise to the surface through volcanic activities and tectonic plates movement as they solidify into granite rocks.
Oceanic Crust
It is the layer of geological material located under the oceans. It consists of rocks called basalts. They are black, dense heavy rocks, which were spewed out of underwater volcanoes. Although they are not easily spotted, there is a lot of them in the ocean floors. Oceanic crust is much younger than continental crust, because the former is constantly being destroyed and reshaped anew by these volcanoes, adding new rocks to it. Continental crust rocks are about 3.7 billion years old, whereas oceanic crust basalt is about 100 million years of age.
Tectonic Plates
The tectonic plates are rigid blocks of lithosphere which drift over the surface of the Earth. They move in different directions, separating from one plate to collide against another. The planet Earth’s crust is not one indivisible layer of rocks but it is broken up into large pieces, which are called plates. The movement of each one of these plates causes what is known as the continental drift. Their existence is based on the theory of plate tectonics, which dates back to the 1920s, when the German geophysicist, Alfred Wegener, first explained how a large original supercontinent broke up into smaller ones that drifted apart to take today’s present positions. If you take a look at the diagram/map below this article, you will have a clear picture of them.
Cause
The breaking up of the lithosphere into several drifting plates is caused by the immense inner pressure exerted by the mantle’s molten rocks that are squeezed upwards by convection currents. It means that the molten rocks flows in streams between the lower mantle and the upper mantle in a circulatory pattern. This, in turn, caused the formation of the different continents from a primeval continental mass. The molten rocks are ejected up in the form of lava onto the planet’s surface through what is known as subduction zone, which is the place where two tectonic plates meet, with one pushing against the other. This gives birth to mountain ranges and volcanoes.
Number of plates
Although the tectonic plates are separated from one another, they are held together by the upper mantle. When they move, each plate carries land mass and the ocean floor. The planet Earth has more than twelve different plates, with the exact number of them depends on where the geologists establish the plate boundaries. Most of the scientists agree that there are the following tectonic blocks: South American, Nazca, Cocos, Caribbean, North American, Pacific (the largest plate), Juan de Fuca, Australian, Eurosian, African, Somali, Anatolian, Aegean, Indian, Philippine, and Antarctic Plate. The Nazca Plate moves and pushes against the South American Plate, with a long subduction zone being the boundary, as this geological collision caused the folding and elevation of rocks and geological materials that shaped the Andes Mountain Range. African Plate collides against the Eurasian, the Aegean, and the Anatolian Plate.
Below, you can see a map of the Earth that show the different tectonic plates
Ocean Currents
Ocean currents are moving masses of sea water, which flows in all oceans, determining the weather patterns in coastal regions. Each one of them have a characteristic direction, length, depth, speed, and temperature. They move like great flow of global conveyor belts.
Ocean currents are caused by the planet rotation, the gravitation of the moon, the wind, temperature, and salinity differences. Warm ocean currents are corridors of warm water moving from the tropics towards poles where they release energy to the air. Cold ocean currents are corridors of cold water moving from higher latitudes toward the equator where they absorb the energy received in the tropics as they cool the air above.
Although some ocean currents result from density and salinity variations of water, the major ocean currents are wind-driven currents. Surface currents make up about 10% of all the water in the ocean. These waters are the upper 400 meters of the ocean. Deep water currents make up the other 90% of the ocean; these waters move around the ocean basins by density driven forces and gravity. Density difference is a function of different temperatures and salinity.
Ocean currents can flow for thousands of kilometers. They are very important in determining the climates of the continents, especially those regions bordering on the ocean. Perhaps the most striking example is the Gulf Stream, which makes northwest Europe much more temperate than any other region at the same latitude. Another example is the Hawaiian Islands, where the climate is cooler than the tropical latitudes in which they are located because of the California Current.
Below, a world map showing the cold and war ocean currents.
Orinoco River
The Orinoco River is the longest and most important river of Venezuela. It is 1,550-mile (2,500 km) long. It rises on the western slopes of the Parima mountains in the southwestern Guiana Highlands. Then it flows down in a southeast-northwest direction, to the green lowlands of Venezuela. Next, it turns right to run eastward across the savannas, making a large arc. It contains more than 1,000 species of fish, which include piranha. Giant otters and crocodiles are also found in its waters.
The Orinoco River empties into the Atlantic Ocean, forming a delta. Along its way, it receives fresh water from important tributaries, such as the Ventuari, Caura, and Caroni river from the right, and the Guaviari, Meta, Apure, and Arauca river from the left. Thus, the Orinoco becomes very wide, between 1 and 1.5 km in width. It is formed by 90% of rain water and only 10% of melting snow. The melting snow water flows from the Andes Mountain Range through the Apure and Guaviare river.
Below, a map of Venezuela, exhibiting the Orinoco River, which runs across the South American country.
Appalachian Mountains Orogeny
The Appalachian mountains orogeny dates back to the beginning of the Paleozoic era, about 530 million years ago. Today, these mountains are only a fragment of what used to be a much larger orogenic system, which had a direct northern continuation in the Caledonian mountain belt of Great Britain, east Greenland, and northwestern Scandinavia. This old mountain chain of North America extends some 3,200 km, from Newfoundland to Alabama, with an exposed width which ranges from 150 to 650 km. The narrowest part is in New York.
Orogenic Periods of the Appalachians
There are four major periods in the orogeny of the Appalachian mountain system.The Avalonian, which began in the Cambrian (520 million years ago); the Taconic, at the end of the Ordovician (445 million years ago); the Acadian, at the end of the Devonian (360 million years ago); and the Carboniferous-Permian (300 millions years). The first three orogenic periods can be seen in the northern Appalachians and Newfoundland, and the last orogenic period are exposed in the southern Appalachians and it is characterized by an intermontaine sag which was filled with intercontinental coal deposits. Therefore, the southern Appalachians consist of upper Paleozoic deposits, which are linked to important deposits of coal, gas, and oil, with its external wider zone comprising folds pointing northwest and accumulation of Lower and Middle Paleozoic granite and other rocks.
The last uplift and folding the southern Appalachians took place toward the end of the Paleozoic era. In the late Triassic period (Mesozoic era), however, the structure of the Appalachians was altered by grabens, which are elongated depressions of land between two faults. These grabens were then filled with red continental deposits and basalt extrusions. The western edge of the Appalachian mountain belt is a fold-and-thrust belt that impinges on the stable North American craton (a geologically stable portion of the continental crust that has not been deformed or altered significantly for millions of years). Along the western edge of the Appalachian mountains, sedimentary rocks span virtually the entire Paleozoic era, providing an extensive indirect record of nearby mountain building.
Geological Faults
Geological faults are breaks in the Earth’s crust. They can be caused by tension, compression or shearing forces, which the outermost layer of the planet constantly undergoes. Thus, there are three types of faults: normal fault, thrust fault, and strike/slip fault. Earthquake is associated by these geological features.
Normal fault
It is created when tension forces stretch the crust, which is constituted by either basalt or granite rocks. When the fault stretches to its breaking point, the rocks are moved along the direction of this force, causing an earthquake. A normal fault rips the crust at an angle; thus, a large piece of rock slides up as the other piece of geological material slides down, with the rocks that slides up becoming either mountains or plateau, while the rocks that slides down turning into rifts or river valleys. The Franklin Mountains of Texas, and Rio Grande rift is examples of this, respectively.
Thrust fault
Also called reverse fault, it is formed when compression forces smash the crust together. When the rock layer get ripped, it breaks at angle similar to a normal fault. This type of fault also creates mountains and rifts. Most mountains in Southern California are the consequences of thrust fault movements. The San Gabriel mountains, for example, are constantly being pushed up and over the rocks of the San Fernando and San Gabriel Valley by a thrust fault.
Strike/slip fault
It arises when shearing forces push two blocks of rocks sideways (horizontally) in opposite directions. Contrary to the above-mentioned faults, in this case there is very little up and down motion. Instead, when the layer of rock breaks, the two pieces of broken land slide past each other in a side by side motion. Although it does not form mountains and valleys, this type of fault causes very strong earthquake. The San Andreas fault is an example of strike/slip one.
What Influences Climate?
What influences climate? It is a question that many people ask. Well, the weather patterns of the different regions of the Earth are influenced by several factors, not by only one. These nature's elements, which contribute to the yearly climate of a territory, or country, are the following:
1- The winds. They could bring humid, dry, cold, or warm air. A mass of humid warm air produces rain when it collides with a mass of dry cold air.
2- Ocean currents. They influence the temperature and even the rainfall patterns of coastal regions. There are two types; warm and cold. The Gulf Stream, for example, is a warm current, flowing from the Gulf of Mexico in a southwest-northeast direction. It reaches the northern coast of France and the Southern coast of England and Wales, influencing the weather of these countries. This is the reason why England is not so cold in Winter as it is in central Russia, even though they both lie on approximately the same latitude.
3- Mountain ranges. Chains of mountains influence considerably the climate of a region, because the act as natural barriers that block and hold back the winds. Usually, they determine the formation of two weather patterns, with one side of the mountain range being humid with rain forests, and dry and desert on the other side. One example is the Blue Mountains of Australia, which act as the natural boundary between the rain forests and the Australian Outback, which is very dry, like a desert.
4- Latitude. It determines how far a city or country can lie from the equator. The farther a region lies from the Earth's mid line, the less sunshine it will receives, especially in Winter time. Thus, countries such Finland, Russia, and Sweden are very cold in winter, while Brazil and Ecuador are not cold at all, because the lie on the equator, which is the imaginary line that divides the Earth into a northern and a southern hemisphere.
5- Altitude. Almost everybody knows that temperature starts dropping when we begin climbing up a mountain. For example, on a Summer day, the temperature of Argentinean city of Mendoza, which lies at the foot of the Andes Range, might be 35 degrees Celcius (about 100 F.) but it could be -20 degrees on top of the Aconcagua Mt.
Earth Geological Layers
The Earth geological layers were formed slowly over hundreds of millions of years. This planet is five billion years old. At the beginning, it was a glowing ball of molten rocks and minerals. As it cooled off, the different geological layers were formed amid volcanic eruptions, earthquakes and other natural phenomena. Today, the science of geology has estimated that the Earth has five geological layers:
1) Inner core. It is the innermost layer, which is made up of solid iron. Its thickness (radius) is about 1,300 km (800 miles). The Danish scientist, Inge Lehmann, determined it was solid by studying the seismic waves that are produced by deep earthquake. It has 1.5 % of the planet mass. Although, it is solid, this ball of iron generates heat.
2) Outer core. It consists of liquid iron and has a thickness of 2,200 km (1,367 miles). It is the source of the Earth’s magnetic field, which is vital for man’s orientation when traveling. It constitutes about 30% of the planet mass.
3) Lower mantle. It is composed of silica (quartz, sand, and flint) and a small amount of iron. This layer has a thickness of 2,500 km (1,553 miles). Its main activity is convection, which is the slow movement of subcrustal materials, transferring heat from the outer core to the surface. It has about 55% of the Earth’s mass.
4) Upper mantle. It is formed almost entirely with peridotite, which is a granular, plutonic igneous rock. It has only 13% of the mass of the Earth as it is 350-km thick (217 miles). Its activity is plate tectonics, which cause the continental drift.
5) Crust. It is made up entirely of granite and basalt, which are igneous rocks, which are hundreds of millions of years old. The main geological activity of this layer is earthquake. It is also called lithosphere, with litho– meaning ‘stone’. Different kinds of sediments top off the crust.
Below, a diagram of the Earth layers. From ‘Simple Geology’
Tectonism in Geology
Tectonism in geology is the science which deals with the constant movements of Earth's top structural layer, which is called lithosphere. Earth’s lithosphere is composed of rocks of varying density which drift as relatively rigid plates. Some of these geological plates are continental in origin; some are oceanic, and some, like the South American plate, a mixture of both continental and oceanic rocks.
These plates movements are caused by deep-seated forces, such as convection in the upper mantle, and crustal forces through push and pull mechanics between plates. Crustal displacement, augmented by magmatism, erosion, and deposition, trigger complex three-dimensional patterns.
In the history of Earth, plate architecture has changed over geologic time, but at this moment Earth’s lithosphere consists of seven major plates, including the South American plate, and numerous smaller plates and slivers.
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