Plate Tectonics PDF

**PLATE TECTONICS** Earth\'s surface has been a subject for discovery for the past years, this includes the tectonic plates that have been studied for over 4.5 billion years in the making. It\'s like a **puzzle piece scientists have been working slowly over the years.** The theory of tectonic plate...

**PLATE TECTONICS** Earth\'s surface has been a subject for discovery for the past years, this includes the tectonic plates that have been studied for over 4.5 billion years in the making. It\'s like a **puzzle piece scientists have been working slowly over the years.** The theory of tectonic plates has shifted the entire earth science, it\'s what we call a grand unifying theory. Key terms for the lesson: **Plates** - A thick and rigid object. **Tectonic** - Geological term for processes that change the structure of the earth\'s crust. **Lithosphere** - Earth\'s parts that includes the crust and upper mantle. **Pangea** - All earth (Greek) Alfred Wegener (1912) -He **reproposed** that all of the land masses are linked together. He **used the spatial distribution of fossils, location of rock types and trends of mountain**. He stated that all of the continents are all linked together creating the supercontinent **pangea** that broke due continental drift. However, Wegener **did not have the explanation of what energy causes the movements of the continents.** Bruce Heezen and Marie Tharp (1957) - They published the **first physiographic map** that shows the depth measure of Atlantic Ocean. They discovered that the ocean floor is **not what people think like a flat floor in the ocean, rather it has valleys, mountains and even deep trenches that are the deepest part of the earth.** Harry Hess (1960) - He discovered when he captained the ship equipped with **echo sounder** that there are happenings at the sea floor. He stated that magma sits out from the fracture lines of the mid-oceaning ridges. **New seafloor was formed on the either side which pushed away the old seafloor.** Creating a pattern which makes our seafloor young (for rocks). Robert Dietz (1961) - He proposed the **Spreading Seafloor Theory**. The evidence was recorded at the seafloor and was published two years later by Fred Vine and Drummond Matthews. Through these scientists, **Wegener's point was established**. It was indeed that the world once had a supercontinent pangea and connected to each other. As for the crust being destroyed in the vast ocean trenches. In the early 50's and 60's during the cold war there are nuclear test vans between the US and USSR. They created a **global seismic surveillance** to monitor the underground blasts which gave the geologists some observations about the deep earthquakes 700 metres below the trenches. Later it visualises a **thick slab of Pacific Ocean Floor that was being pushed below another crust of the earth**. This process is called **Subduction**. Thus, another discovery for the geologists and earth science. Years of improvements and discoveries through technologies, they unfolded that the **world is divided into moving plates. Through numerous satellites and even scientists** observing the earth, we are able to discover more and more information about how the plates are moving, hence creating the **Tectonic Plate Theory**. The theory emphasizes that the plates are moving into three different patterns. **Divergent Plate Boundary, Convergent Plate Boundary and Transform Boundary.** **Tectonic Plates** +-----------------------------------+-----------------------------------+ | **Large Plates** | **Small Plates** | +===================================+===================================+ | 1. 2. 3. 4. 5. 6. 7. | 1. 2. 3. 4. 5. 6. 7. 8. | +-----------------------------------+-----------------------------------+  Most geological activity occurs at the Pacific Ring of Fire or Circum Pacific Belt because of the different boundaries it has. Example of Divergent Plate Boundary are from the North American to Nazca Plate called as East Pacific Rise, it is where most of oceanic plate and continental plate move away from each other. Example of Convergent Plate Boundary is from the west of south american plate. It is where the oceanic plate is getting into the bottom of continental plate, hence creating a volcano. Another creation of this boundary is the Himalayas Mountain, it is when a continental plate is converging into another continental plate, hence creating a mountain. Example of Transform Boundary is from the west of North American Plate, the San Andreas fault where in the two plates are moving at the same direction but different speeds that creates massive earthquakes. **Earthquake, Volcanoes, and The Ring of Fire** **EARTHQUAKE** An earthquake is a tremor or **shaking** of the ground caused by rocks shifting beneath the Earth\'s surface. Earthquakes usually start where tectonic plates meet. The point underground where an earthquake begins is called the focus, and the spot on Earth's surface directly above it is the epicenter. We can measure the strength of an earthquake in two ways: magnitude and intensity. Magnitude measures the earthquake\'s power at its source, using a machine called a seismograph. Intensity measures how strong the earthquake felt in a specific area, considering damage to people, things, and the environment. Magnitude is shown with numbers (like 4.8 or 9.0), while intensity is shown with Roman numerals (like II, IV, or IX). In the Philippines, we use the PHIVOLCS Earthquake Intensity Scale (PEIS) to measure intensity. There are two main kinds of earthquakes: tectonic and volcanic. Tectonic earthquakes happen when parts of the Earth\'s crust shift or break. Volcanic earthquakes are caused by magma or lava moving under active volcanoes **VOLCANOES** A volcano is a feature on the earth's surface where molten rock erupts, generally as a mountain. Worldwide, there are a great deal of active volcanoes. The definition, genesis, and varieties of volcanoes are covered in this article. Near the edges of Earth\'s tectonic plates, which are vast stretches of lithosphere that constantly move and collide, most volcanoes in the world form. An area known as a subduction zone is where two colliding tectonic plates frequently descend far below one another. **Types of Volcanoes** While some volcanoes only ever erupt once, lasting only a few days or less between eruptions, others may have periods of activity spanning several million years or longer. Every kind of volcano has a distinct size and shape, style and kind of eruption, duration and duration of eruption, type(s) of rock, and collections of volcanic features. The physical characteristics of a volcano interact with the compositions of erupting magmas. The physical properties of magma are determined by its chemistry, which also controls the dynamics of eruptions and the ease with which lava can flow. Explosivity is also dependent on the gas quantity and the pace of eruption. Some types of volcanoes tend to erupt only once (and are called monogenetic), and others erupt multiple times over their lifespan (and are called polygenetic). Each volcano is somewhat unique, but most volcanoes can be classified into one of several types. The most well-known types of volcanoes are cinder cones, composite volcanoes (stratovolcanoes), and shield volcanoes. The illustration below provides an example of the difference in size between shield, composite, and cinder cone volcanoes. **Cinder Cones** The most basic type of volcanoes are cinder cones. Their small size, steep slopes, and cone-like form define them. These are the most frequent volcanoes as well. The buildup of ejected igneous rocks, or cinders, that form the slopes is what creates cinder cones. These cinders are known scientifically as scoria, a black igneous rock with numerous round cavities. These kinds of volcanoes are also known as scoria cones since scoria and cinders are identical. Cinder cone volcanoes have rocky steep slopes covered in scoria cinders.  Scoria is a type of ejected igneous rock formed by cinder cone volcanoes **Composite Volcanoes (Stratovolcanoes)** Composite volcanoes can be the most picturesque of all volcanoes. A classic composite volcano is conical with a concave shape that is steeper near the top. These mountains commonly have snow-covered peaks standing high above the surrounding mountainous terrain. Typically made up of mudflow (lahar) deposits, pyroclastic deposits, and lava domes, composite cones are massive volcanoes that reach heights of hundreds of feet or meters. Tens to hundreds of thousands of years are active times for composite volcanoes, which also occasionally erupt. Given that they can erupt lava of varying compositions, many times, and with a variety of eruption forms, composite volcanoes are likely the most complex sort of volcanic structure. The majority of composite cones have a main vent at the summit, though they may have several. The magma chamber of active composite volcanoes is typically shallow, ranging from 3 to 6 miles (5 to 10 km) deep. **Shield Volcanoes** Since a shield volcano is made up of several lava flows, it has a broad shape. Lava flows over a period of time to build this kind of volcano. There are several places where the lava can flow, creating a surface that slopes gently. They are called shield volcanoes because of the way this surface resembles a warrior's shield. The diameter of large shield volcanoes can range from three to four miles. Unlike composite volcanoes, which generate towering mountains with conical peaks, shield volcanoes are the largest volcanoes on Earth. Rather, they resemble a warrior's shield resting flat on the ground and are large volcanoes with mild slopes. Shield volcanoes are flatter at the summit, giving them a convex shape. Shield volcanoes are usually constructed almost entirely of basaltic and/or andesitic lava flows which were very fluid when erupted. They are built by repeated eruptions that occurred intermittently over vast periods of time (up to a million years or longer). **THE RING OF FIRE** Less frequently than at random, most earthquakes and volcanic eruptions occur in specific locations, such as at plate borders. One example of this is the circum-Pacific Ring of Fire, which is the area where the Pacific Plate meets other nearby tectonic plates. The Ring of Fire has the highest seismic and volcanic activity in the globe. This Pacific Ocean stretch known as the Ring of Fire, or Circum-Pacific Belt, is characterized by active volcanoes and frequent earthquakes. That\'s almost forty thousand kilometers, or 24,900 miles long. It traces, among other boundaries, those between the Pacific, Juan de Fuca, Cocos, Indian-Australian, Nazca, North American, and Philippine plates. The quantity of tectonic plate movement in the Ring of Fire is what causes the region's profusion of earthquakes and volcanoes. Subduction zones are places where plates converge around a large portion of the Ring of Fire. In other words, the plate above subducts, or pushes down, the plate underneath. Rock melts and turns into magma as it is subducted. The availability of magma at such close proximity to the Earth's surface creates ideal circumstances for volcanic eruptions. The boundary separating the Pacific and North American Plates is a notable exception. This portion of the Ring of Fire is a transform boundary, meaning that plates pass one another sideways. As tension in the earth\'s crust accumulates and releases, this kind of boundary causes a lot of earthquakes. The Ring of Fire Is home to around 450 volcanoes, or 75% of all volcanoes on Earth. The path of 90% of Earth's earthquakes, including the most powerful and spectacular ones on the planet, is where they happen.  *References:* CK-12 Foundation. (n.d.). Ocean-Continent Convergent Plate Boundaries ( ReAd ) \| Earth Science.https://www.ck12.org/earth-science/ocean-continent-convergent-plate-boundaries/lesson/Ocean-Continent-Convergent-Plate-Boundaries-HS-ES/ Coburn, H. C., & Coburn, H. C. (2022, October 14). Earth as seen from space 500 million years ago \| EarthSky. EarthSky \| Updates on Your Cosmos and World. https://earthsky.org/space/earth-as-seen-from-space-500-million-years-ago DOST. (n.d.). Introduction to Earthquake. Philippine Institute of Volcanology and Seismology. [[https://www.phivolcs.dost.gov.ph/index.php/earthquake/introduction-to-earthquake]](https://www.phivolcs.dost.gov.ph/index.php/earthquake/introduction-to-earthquake) Ring of fire. (n.d.). https://education.nationalgeographic.org/resource/ring-fire/ Writer, S., & Writer, S. (2015, August 4). What is an Oceanic-Oceanic collision? Reference.com. [[https://www.reference.com/science-technology/oceanic-oceanic-collision-8f54388c339a8]](https://www.reference.com/science-technology/oceanic-oceanic-collision-8f54388c339a8525)5.