For those of us who live in Indonesia, the threat of natural disasters in the form of earthquakes and volcanic eruptions can become a reality at any time. Because, as Sinaumed’s already knows, Indonesia is located at the confluence of three major tectonic plates, namely the Eurasian Plate, the Pacific Plate, and the Indo-Australian Plate.
According to historical records, Indonesia was devastated by the eruption of Mount Krakatau in 1883 which erupted 4 times in 4.5 hours and the sound of the eruption was heard as far as Sri Lanka and Australia. Not only that, this eruption caused a large tsunami as high as 36 meters which claimed 36,417 lives.
In 2004, Aceh was rocked by a massive earthquake measuring 9.3 on the Richter scale which generated a 30 meter high tsunami whose waves bounced off several other countries such as Sri Lanka, Thailand, Maldives, India, Malaysia, Myanmar, Tanzania, Somalia, Bangladesh, Seychelles, to Kenya.
It was so great that the natural disaster that occurred on December 26, 2004 also had an impact on the Earth’s rotation and shortened the duration of one day by 2.68 microseconds; and shifting the North Pole a few centimeters.
So, talking about earthquakes and volcanic eruptions, it’s incomplete without discussing plate tectonics. You see, these two natural disasters are closely related to the movement of tectonic plates.
Plate Tectonics, The Most Advanced Theory of the Formation of the Earth’s Surface
As we know, planet earth and its present form were not created just like that. It took billions of years for the earth to “form” itself to be habitable by humans.
In geography, there are several theories that explain the process of formation of the earth’s surface. Starting from the theory of contraction (Descrates, 1596-1650); The theory of two continents (Edward Zuess, 1884); the theory of Continental Shift (Lothar Wagener, 1915); Ocean Floor Expansion Theory (Harry H. Hess, 1962); and finally the theory of plate tectonics (Tozo Wilso, 1968).
The birth of the theory of plate tectonics brought changes to the human perspective in viewing the structure of the earth, natural wealth, and natural disasters. In fact, some say this theory is as powerful as Einstein’s theory of relativity because of its benefits to earth science.
In the theory of plate tectonics, it is stated that the planet Earth consists of plates that are constantly moving. These plates can be in the form of oceanic crust, continental crust, or a combination of the two. Well, this movement is caused by convection currents or the transfer of heat energy in the asthenosphere layer (the Earth’s mantle which is a very hot liquid).
Because all the plates are constantly moving, there is interaction between one plate and another. These interactions occur along plate boundaries. The forms of interaction are divided into three, there are those that collide, move away from each other, and shift. Well, the surface of the earth that exists today is the result of interactions between these plates.
According to the theory of plate tectonics, there are 13 plates that make up the earth’s crust which are divided into large plates and small plates, namely:
|North American Plate
|South American Plate
If compared, the 13 plates are exactly like puzzle pieces that are fused together but the puzzle pieces are “placed” on top of the liquid. So if there is movement in the liquid, the puzzle above it will automatically move too. Well, this is what is called the movement of the earth’s crust plates.
You can read other explanations of the theory of the formation of the earth’s surface in the book Ips: Geography of SMA/Ma Kls.10/Km , compiled by Yasinto Sindhu Priastomo. This book is designed to help you understand the causal relationship of geosphere phenomena or phenomena on the earth’s surface and events that occur on the earth’s surface.
In this article, we will discuss one of the major plates on earth, namely the Eurasian Plate. The Eurasian plate is the third largest plate which is slightly smaller than the Pacific plate and the North American plate.
The Eurasian Plate includes parts of the Atlantic Ocean, Arctic Ocean, most of mainland Europe, Russia, Asia, and several sub-oceanic basins, such as the Norwegian, Lofoten, South China, Aleut, Western European basins).
On the east side, the Eurasian plate is bounded by the North American plate and the Philippine Sea plate. While on the south west side, it is bordered by the African plate, in the middle by the Arabian plate, and on the south side east by the Indo-Australian plate.
To make it easier, try to pay attention to the position of each plate in the following image:
Based on the picture of the Eurasian plate above, the location of the Eurasian plate in Indonesia includes Sumatra, Java, Bali, Nusa Tenggara, Kalimantan, Sulawesi and Maluku. Indonesia is indeed located at the confluence of three plates, namely the Indo-Australian Plate, the Eurasian Plate, and the Pacific Plate.
The Movement of the Eurasian Plate And Its Effects
In general, the Eurasian plate is moving about ¼ to ½ inch per year on average. More specifically, this plate is moving northward by 2 cm each year. Compared to other plates, the Eurasian plate is the third slowest moving plate after the North American and South American plates.
The movement of the Eurasian plate occurs due to the flow of magma that is under the earth’s surface. When the magma heats up and boils. The hot magma then rises to the top and cools when it comes in contact with seawater so that it creates new rock.
One of the effects of the movement of the Eurasian plate that we can see clearly today is a series of mountains along the islands of Sumatra, Java and Nusa Tenggara, then the Himalayas and the Tibetan Plateau.
The series of mountains in Sumatra, Java and Nusa Tenggara emerged as a result of the Pacific plate colliding with the Eurasian plate. Meanwhile, the Himalayas and the Tibetan Plateau emerged after the landmasses of India and Asia collided about 50 million years ago. This phenomenon then causes the Eurasian plate to fold over the Indian plate.
Tectonic Plate Boundaries
Because the shape is similar to a puzzle, of course each plate has its own limits. Well, these boundaries can be divided into three, Divergent, Convergent, and Conservative boundaries.
1. Divergent Boundary
Divergent movement is the movement of tectonic plates that move away from each other and move slowly and cause cracks. These cracks then become a way out for magma that continues to flow.
The magma flow will gradually appear a little to the surface of the earth which can cause new volcanic islands to emerge. Meanwhile, if it occurs on the seabed, this will cause what is called the Sea Floor Spreading or the expanse of the seabed.
It is estimated that the spreading rate in these ocean ridge areas is 2 to 10 cm per year, and averages 6 cm (2 inches) per year. Because the amount of newly formed rock is equal on both sides of the plate that is moving away from each other, the growth rate of the ocean floor is twice the value of the spreading rate.
One of the most famous examples of divergent boundaries is the Mid Oceanic Ridges which are at the bottom of the Atlantic ocean. Apart from that, there are also other examples such as rifting that occurred between the African continent and the Arabian mainland which then created the red sea.
2. Convergent Limits
This is the boundary between plates that collide with each other. This collision can occur between two oceanic plates, one oceanic plate and one continental plate, or two continental plates. Convergent boundaries are divided into two based on their shape, the first is Subduction and the second is Obduction.
Subduction boundaries are plate boundaries in the form of plate collisions. This means that one plate sinks into the bowels of the earth while the other plate rises to the surface.
subduction boundary image
One example of a subduction-type convergent boundary is the Indonesian Archipelago which is part of the Southeast Asian continental plate with the Indian-Australian oceanic plate. The boundary of these two plates is in the form of a subduction zone in the sea with a trough shape that extends from the islands of Sumatra, Java, to East Nusa Tenggara.
Another example is the Philippine archipelago which is the result of subduction between the Philippine oceanic plate and the Pacific oceanic plate.
Meanwhile, obduction boundaries are plate boundaries caused by collisions between continental plates and other continents. The results of this collision then form a series of mountains. Like the Himalayan mountain range that emerged as a result of the collision between the Indian continental plate and the Eurasian continent.
obduction limit image
3. Transform Boundary
Finally, there is a transform limit. This is a boundary between plates that pass each other and slide over each other without causing destruction of the lithosphere. This interaction then produces a horizontal fault of the Strike Slip Fault type.
Most of the transform faults occur in the oceanic crust, but a few occur in continental crust such as the San Andreas fault in the United States. This fault appears due to a shift in the Pacific Ocean plate with the North American continental plate.
Consequences of Plate Movement
As previously discussed, the movement of the plates in the earth’s crust can have several consequences, including:
1. Volcanic eruption
Volcanic eruptions can occur when hot magma rises to the surface of the earth. This is caused by the melting of rock into magma due to an increase in temperature, a decrease in pressure, or if water enters it. Usually volcanic eruptions occur at convergent plate boundaries and diverging plates.
At divergent boundaries, the warmer asthenosphere creeps up due to pressure drops which then fill the gaps that appear between two separate plates.
As a result, parts of the asthenosphere will melt and form large amounts of basaltic magma which then spill out onto the earth’s surface.
Meanwhile, at convergent plate boundaries, dense oceanic lithosphere will sink into the asthenosphere along with silt and rocks. Well, the plate that goes into the mantle will change its temperature to heat.
This heat moves water to rise into the hot asthenosphere which is under the opposite plate. After that the water melted the asthenospheric rock and formed magma in large quantities in the subduction zone. Magma that has formed then rises to the lithosphere. Here, some of the hardened magma can enter the lithosphere, some of it is erupted onto the earth’s surface via volcanoes.
Earthquakes generally occur at three tectonic plate boundaries and are quite rare on the inside of tectonic plates. The reason is because plate boundaries are fracture zones in the lithosphere. In this zone, one plate can slip on another plate and this happens continuously.
As explained in the book ( Series of Natural Disasters) Earthquakes compiled by the Atlas & Geography Editorial Team, the fracture can be locked for hundreds of years, then when a plate slips a few centimeters or a few meters on another plate, the surface will also vibrate. This vibration is called an earthquake.
3. The formation of mountains
There are many mountain ranges that form in subduction zones. Usually this happens because a large volume of magma rises into the crust, then triggers the formation of mountains. In addition, volcanic eruptions can also form a series of volcanoes.
4. Oceanic trenches
Trench, briefly, can be defined as the deepest part of the ocean basin. Trenches can appear wherever subduction occurs because they always follow a boundary on the developing ocean floor where subduction feeds into the Earth’s mantle.
5. Transfer of continents and oceans
Continental drift can occur on the surface of the earth because the continents themselves are part of the lithospheric plates that are constantly moving. Now, when a continent moves, it creates ocean basins that open and close during geological time.
About 2 to 1.8 billion years ago, tectonic plate movements brought together the microcontinents and formed the first supercontinent known as Pangea I. This Pangea I then fractured around 1.3 billion years ago. After that, the fragments of the existing continental crust reassembled and formed the second supercontinent known as Pangea II.
Pangea II then broke apart again and the continental fragments reassembled into the third supercontinent or Pingea III 300 million years ago.
Factors That Trigger Tectonic Plate Movement
The movement of tectonic plates on the earth’s surface certainly requires a large amount of energy. This energy is usually drawn from the earth’s membranes – large lumps that are located under tectonic plates.
The Earth’s membrane is up to 2,800 km thick and is composed of rocky material in the form of silicate compounds. The materials within the membrane are arranged in complex ways, some of which even melt together. Even so, this membrane couldn’t be said to have a liquid state.
Experts say the shape of the earth’s membrane is rather soft. very sticky, has a very high temperature and pressure.
The lower the temperature of the earth’s membrane, the hotter the result. Well, because of the temperature difference between the upper earth’s membrane and the lower earth’s membrane, the earth’s membrane continues to move consistently. This movement then causes the tectonic plates to move.
The question is, why did this happen?
The reason is because the earth’s membrane that is at the bottom tries to move its very hot material to the top because the top layer of the earth’s membrane is thicker than the bottom layer. Meanwhile, some parts of the upper membrane layer sink to hotter temperatures. This process continues continuously without ever stopping.
So, if you want to learn more about the plates on the earth’s surface, the book General Geology from Imam Subekti can be the main reference that is right for you. The problem is this book provides a description of the science of geology in general. Arranged chronologically starting from the process of the formation of the earth, the process of forming the earth’s crust or skin, to the evolution of living things that existed and once existed on earth.
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Author: Gilang Oktaviana Putra