Submarine Volcanoes - Essay Example

Submarine Volcanoes Owing to the fact that most of the earth is covered with water, the fact that underwater volcanoes contribute a larger share in the volcanic activity than continental volcanoes do, with 75% of annual magma output, seems obvious. This lava solidifies into the seafloor or is concentrated in the form of seamounts depending on the type of volcano it has come from. It has been estimated that the ocean floors around the world may be home to over a million submarine volcanoes based on the fact that the floor of the Pacific Ocean alone bears 4000 volcanoes per million square mile. (Oregon Space Grant Consortium) However since these volcanoes are hidden underneath the ocean, they do not affect human life directly and thus have been a relatively new study in the field of geology. They do however affect global warming and the formation of islands. (Raine, 2010) “Much like volcanoes on dry land, an underwater volcano is a fissure on the earths surface where lava is produced and can erupt.” (Raine, 2010) The causes of a volcanic eruption cannot be analyzed without an understanding of the earth’s structure. The core of the earth is extremely hot and contains a reservoir of molten rock called the magma. This magma is bounded by cooler layers of rock that form the earth’s crust, including both the ocean floor and land, which increases the internal pressure caused by heat. However when the crust releases the pressure from any opening or when the internal pressure is able to overcome the external pressure, the magma breaks through the earth’s surface and erupts, releasing the magma in the form of molten lava and ash. (Raine, 2010) The basic characteristics of submarine volcanoes are consequences of the fact that the eruptions from the volcanoes are affected by the pressure and temperature of water around them. (Topinka, 2003) “…the volcanic phenomena take place very much in the same manner from the bottom of the sea as from the open surface of a continent, subject only to modifications produced by the lower temperature of the surrounding medium, and the greater external pressure, caused by the weight of the overlying column of water, which in this case becomes one of the elements of the repressive force.” (Scrope, 1862) In shallow waters this lava is cooled so rapidly that it transforms into ‘black sand’ or volcanic debris almost instantaneously or forms volcanic glass. (Palande, 2011)This debris is either piled-up around the volcanic vent or settles down along the seafloor. (Topinka, 2003) Eventually the piling up emerges above the surface of the ocean in the form of volcanic islands, some of which can be seen in the south Pacific and the north Atlantic oceans. (Tufty, 1969.) (Crouse 2012). In the deeper part of the ocean, volcanic activity pretty much resembles the volcanoes on land terms of shape and flows (Topinka, 2003). They are seen to be slightly steeper as the water speeds up the hardening. (Rafferty, 2011.) Furthermore, the pressure of water being 250 times greater than that of air (Palande, 2011), causes a greater explosion when the pressure is relieved. This occurs when the hot molten magma reaching near the oceanic crust causes cracks and provides an outlet to the pressure from within the earth’s crust. The weight of the water above however represses the explosion so that hardly any disturbances are experienced above the surface (Topinka, 2003). The outer crust of the Earth is made up of rigid plates called tectonic plates that are placed over the molten interior. Research into the occurrences of earthquakes and volcanoes has led to the discovery that 12 of these plates are very large and move at a rate of a few centimeters per year. (Rafferty, 2011.) Their movement over the molten magma sometimes leads to them colliding into each other forming convergent boundaries, sometimes drifting apart forming divergent boundaries, and sometimes just sliding against each other creating side-slipping boundaries. (Crouse, 2012) (Martí & Ernst, 2005) (Rafferty, 2011.) Of these three boundary movements, volcanoes occur most frequently at divergent plate boundaries, with lava flowing out from the rift created along the divergent boundary margin. The lava flows out rather than erupting, forming ridges called ‘mid-ocean ridges’ resembling mountain ranges (Oregon Space Grant Consortium), containing mainly basalt (Rafferty, 2011.) which forms most of the seafloor. “Mid-ocean ridges spread out like the seams on a baseball, across the floor of the worlds oceans.” (Crouse, 2012) These seams that apparently provide anchorage to the moving plates, holding them together, add up to make a discontinuous range of nearly 65,000 kilometers in length (Crouse, 2012). Independently however the Atlantic Mid-ocean Ridge, which connects the Arctic Ocean to the Southern tip of Africa, is the longest continuous ridge (Crouse, 2012). The rate at which the plates move away from each other determines the volatility of the volcano formed and thus its character. Ridges that widen at a rate of between one to five centimeters in a year (Oregon Space Grant Consortium) are discontinuous as the smaller quantity of magma under the crust leads to a slower supply, causing the lava to cool and form the oceanic crust. This forms a steeper ridge that didn’t get to spread so wide before setting. The magma itself often solidifies and forms the lower crust. The faster-spreading volcanic ridges are the opposite in terms of magma production, with greater heat content, which continuously flows out of the rift causing a wider spread in less time with a less pronounced topography. They are fed by magma chambers that run all along the axes of the ridge and speed up its widening to around ten to twenty centimeters in a year (Oregon Space Grant Consortium). Near axis-seamounts are also developed near the fast-spreading mid-ocean ridges. Between these two we have the ridges that expand at the rate of five to ten centimeters in a year. (Oregon Space Grant Consortium). The second type of volcanism at the boundaries of tectonic plates is better known as the subduction process, which is described as “…a process of recycling where oceanic crust is returned to the mantle. The size of the Earth has remained relatively constant and therefore the production of new seafloor at the mid ocean ridges must be balanced by subduction of the crust at convergent margins.” (Martí & Ernst, 2005). The convergent boundary movements cause two plates to collide in such a ways that one moves above the other causing the overlapping edge to melt and feed the magma reservoir under the crust, which causes an increase in the internal pressure. This pressure is released in eruptions parallel to the convergent boundary margin. Volcanoes of this nature pose a greater threat to human life as they occur close to human populated regions and are more explosive in nature than the divergent, but they only contribute 15% of the volcanic activity in the whole planet. The volcanoes that make up the “Pacific Ring of Fire” are of this kind and have been studied by geologists because of their danger. The content they erupt constitutes basalt, andesite, dacite and rhyolite (Rafferty, 2011.) which often solidifies around the volcanic vent or on the ocean floor until eventually they rise up above the water level to be called small volcanic islands (Oregon Space Grant Consortium). No lava rises up as a result of the third plate movement and thus no volcanoes are formed as a result if this movement alone. But when these plates slide over certain ‘Hot Spots’ under the earth’s crust which have larger reservoir of lava underneath it, a chain of volcanoes seamounts is formed as a result. (Rafferty, 2011.) (Crouse, 2012) (Oregon Space Grant Consortium). HOT SPOT volcanoes are different from the above two as they do not depend on inter-plate movements; rather they are affected by the movement of the plate with respect to the mantle. Certain “HOT SPOTS, which give these types of volcanoes their name, are situated beneath the crust being themselves characterized by “… voluminous outpourings of basaltic magma, higher than normal heat flow, thinning of the overlying crust, and development of a broad topographic high.” (Martí and Ernst) These are created as a result of the convection of plumes of magma from the core mantle of the earth to magma chambers which break through the ocean floor in the form of volcanoes, when plates move over them. (Cain 2009). When the plate moves away the plate moves away the volcano is no longer supplied with magma and thus it becomes dormant and eventually erodes overtime. (Oregon Space Grant Consortium).The HOT SPOT is now supplying another volcano not far and thus a chain of volcanoes is formed similar to the chain of islands in Hawaii which are formed as a result of Hot Spot volcanism and the chain is still growing (Crouse 2012). There are many known examples of each of these types of volcanoes around the world which characterize them and help geologists understand further the causes and effects of volcanic activity. There are even more that are unknown and waiting to be discovered that might give an insight into the researches being conducted around the world. Meanwhile “The Ring of Fire” in the Pacific being a subduction zone, the Atlantic Mid Ocean Ridge and the Hawaiian islands serve as basic studies for the phenomenon described above. BIBLIOGRAPHY: Cain, F. (2009, May 27). Volcano Hotspot. Retrieved June 7, 2012, from Universe Today. Crouse, R. (2012). Volcanoes, Submarine. Retrieved June 7, 2012, from Water EncyclopediaScience and Issues. Martí, J., & Ernst, G. (2005). Volcanoes and the Environment. Cambridge: Cambridge University Press. Oregon Space Grant Consortium. (n.d.). Volcano World: Submarine Volcanoes. Retrieved June 7, 2012 Palande, L. (2011, July 6). Underwater Volcano Facts. Retrieved June 7, 2012 Rafferty, J. P. (2011.). Plate Tectonics, Volcanoes, and Earthquakes. New York, NY : Britannica Educational Pub. in association with Rosen Educational Services, . Raine, S. (2010, May 14). A Deeper Look into the Underwater Volcano - Facts and Information. Retrieved June 7, 2012 Scrope, G. P. (1862). Volcanos: The character of their phenomena, their share in the structure and composition of the surface of the globe, and their relation to its internal forces. With a descriptive catalogue of all known volcanos and volcanic formations. London: Longman, Green, Longmans, and Robert,. Topinka, L. (2003, May 13). DESCRIPTION: Submarine Volcanoes, Vents, Ridges, and Eruptions. Retrieved June 7, 2012, from USGC Science for a Changing world. Tufty, B. (1969.). 1001 questions answered about earthquakes, avalanches, floods and other natural disasters. New York: Dover. Read More