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Volcanoes Since the beginning of times, volcanoes were something that attracted human attention. Our ancestors often thought of volcanoes as places that powerful gods chose to make their home and they werent far from the truth. Volcano is a powerful exhibition of the might possessed by natural forces and the results of awakening such forces are often devastating. Today, volcanoes are a well-explored natural occurrence and theres even a science, called volcanology, which investigates this phenomenon and attempts to predict the eruptions. But even though volcanoes are well learned, most people dont know anything about them apart from the fact that they usually have a mountain-like appearance and that they erupt once in a while.
This paper is aimed at providing some deeper insights on what volcanoes actually are, how they are formed and what happens when they actually do erupt. In order to understand what volcanoes are and how they are formed we need to have at least a rudimentary knowledge of what our planet is like from the geological point of view. Earth has multiple layers, which are the outer crust, the mantle, the outer core and the inner core. The crust, which is the topmost layer of our planet, can be of two types the oceanic crust, which is about seven kilometers thick and the continental crust, which is significantly thicker - about thirty five kilometers thick. Together with the upper layer of the mantle, which is another stratum, it forms the lithosphere. Lithosphere is supported by asthenosphere, which is a mass of hot, molten rocks that has the ability to flow (Camp).
Lithosphere is divided into tectonic plates that float on this mass of liquid rock. The movement of tectonic plates arises due to currents in the underlying asthenosphere. The region where two different plates meet is called the plate boundary, and there can be three types of plate boundaries divergent, convergent and transform. Divergent plate boundaries are located in places where hot magma is moving upward and two plates are moving away from each other. This are the places where the oceanic crust is formed. Convergent plate boundaries are regions where the oceanic crust meets the continental crust and the oceanic crust is pushed downwards, being denser.
Transform plate boundaries are regions where two plates are sliding past each other. Most of the currently active volcanoes are located along the convergent and divergent plate boundaries, and there are some good reasons for this. Volcanoes are formed when hot liquid magma moves into the crust and breaks through the surface. There can be various reasons for this upward movement of magma, for example, magma generally rises at mid-oceanic ridges (correspond to divergent plate boundaries) and descends at oceanic trenches (correspond to convergent plate boundaries) (Camp). When hot magma breaks through the surface of the oceanic crust it forms underwater volcanoes. The products of the eruption are quickly cooled down by water and form new oceanic crust.
This type of eruptions is called spreading center volcanism. Similar story happens at convergent plate boundaries. When oceanic crust meets continental crust, it is pushed under it, being denser. From friction and high pressure oceanic crust melts and forms magma. This newly formed magma breaks through the surface and forms volcanoes on land. This type of volcanism is classified as subduction zone volcanism.
Theres also another type of volcanism, which is not dependent on the movement of tectonic plates the intra plate volcanism. It occurs at so called hot spots - places that are underlain by unusually hot magma that rises from deeper layers of the mantle. Unfortunately, the process that underlies the formation of such hot spots is not known. In order to distinguish between different types of volcanoes, a classification system was invented. Volcanoes are classified by the eruption products, their location and landform, all of which are connected.
Although volcanoes can be quite different in appearance, they all have a similar basic structure. The main features of any volcano are the summit crater, the central and a magma chamber. Magma chamber is the main storage space for various eruptive materials, and it is connected with the surface by a number of vents, although there is always one main vent, which is the largest of all. Other vents may serve as additional routes for magma or gases that are produced during the eruption. Small vents that provide the escape routes for gases are called fumaroles. There are three main types of volcanoes scoria cones, shield volcanoes and strato volcanoes.
They are different in appearance and they have different eruption production. Shield volcanoes are very broad and usually have low profiles, with their height often being just 1 / 20 th of their width (Camp), although some of these volcanoes still manage to reach significant stature. The lower slopes are gentle, middle slopes are a little bit steeper and the summit is flattened ("Volcano World"). This shape results from the type of magma, which is erupted from these volcanoes.
Usually it is basaltic lava of very low viscosity, which allows it to spread over great areas as opposed to being accumulated around the crater. A good example of shield volcanoes is Mauna Loa, which is located on Hawaiian island and is over one hundred km wide. Another type of volcanoes that are very different from shield volcanoes is strato volcanoes. These are the volcanoes that really fulfill the general stereotype of what volcano should look like. Their slopes are quite gentle at the bottom, but become almost vertical near the summit. The composition of these volcanoes may be very different, but two main components are andesite and basalt ("Volcanic Rock").
Examples of such are Mt. St. Helens or Mt. Agua. Finally, the third main type of volcanoes scoria cones. Being the smallest type of volcano, they are also the most common one.
They can exist in various forms, either being a part of the shield and strato volcanoes or appearing as a separate formation. These volcanoes usually have very straight, steep slopes, formed predominantly by basaltic tephra ("Volcanic Rock"). Another feature that can be seen on various volcanoes is caldera (Alden). Caldera is a large crater-like depression in the volcano that is formed when the magma chamber is emptied and volcano walls collapse inward it. Sometimes calderas fill up with water and form lakes.
Volcanic activity is common not only to Earth, but also to other planets and satellites of our solar system, although it may be caused by different factors. For example, on Mars there is no evident tectonic movement and all volcanic events are thought to be caused by hot spots (Camp). Venus can be considered one of the most interesting and rewarding planets for volcanologist's because of the numerous volcanic events that took place on that planet. Another positive issue is the absence of water on Venus, which limits the erosion and preserved the results of various volcanic events for further investigation. One of such events that bear great interest for science was the massive resurfacing event that was caused by flood basalt volcanism. Why is this knowledge about volcanoes so important to us?
Apart from providing us with better understanding of the dynamics of our planet, it also gives us other important bonuses, such as prediction of eruptions. The consequences of some eruptions may be devastating, as we can see from the history. A great example of an eruption that became a historical event is the eruption of Mt. Vesuvius in seventy nine AD (Camp). The eruption produced a cloud of ash that could have rose as high as forty-five kilometers and buried roman cities of Pompeii and Herculaneum. Other eruptions of equal or greater power may have reshaped the history of the humanity by destroying some nations completely.
For example, there is a legend of the powerful civilization Atlantis, which was destroyed by a cataclysm that reminds of the volcanic eruption. Even during the last two hundred years nineteen major eruptions resulted in death of more than a thousand people. This clearly shows that more research is needed in the area of volcanology, the research that may broaden our view on exactly how do volcano systems works and allow us to predict eruptions and avoid losses of human life. Bibliography "Volcanic Rock." (2004): Online dictionary / encyclopedia . 01 December 2004. < web >. "Volcano World." 01 December 2004. < web >. Alden, Andrew. "Recipes for Calderas." 2004. Primedia Company. 01 December 2004. < web >.
Camp, Vic. "How Volcanoes Work." (10. 25. 2004). 01 December 2004. < web >.
Free research essays on topics related to: shield volcanoes, plate boundaries, hot spots, oceanic crust, tectonic plates
Research essay sample on Oceanic Crust Shield Volcanoes
