Volcanoes Essays - Volcanology, Plate Tectonics, Igneous Rocks

Volcanoes By Tricia Severson 2nd hour Science 4/30/98 A volcano is a vent, or opening, in the surface of the Earth through which magma and associated gases and ash erupt. The word also refers to the form or structure, usually conical, produced by accumulations of erupted material. Volcanoes occur mainly near plate tectonic boundaries and are especially common around the Pacific basin, called the Pacific Ring of Fire (see Plate Tectonics). Humanity has long been awed by this powerful force of nature. The Romans attributed volcanic events to Vulcan, the god of fire and metalworking. In AD 79 the eruption of Mount Vesuvius destroyed the Roman cities of Pompeii and Herculaneum. Polynesians believe volcanoes to be ruled by the fire goddess Pele. One of the most spectacular volcanic eruptions in recorded history occurred in 1883 with the explosion of Krakatoa, an island in the Sunda Strait near Java (see Krakatoa). A more recent example is the dramatic 1980 eruption of Mount St. Helens in the Cascade Range in Washington State. Volcano Formation and Eruptions Volcanic eruptions may be violent, even catastrophic, or relatively mild. The most explosive eruptions are essentially blasts of steam that create spectacular displays. Quieter fissure eruptions occur when molten rock pushes through long cracks in the Earth's crust and floods the surrounding landscape. Such repeated outpourings of lava can fill surrounding valleys and bury low hills, creating thick lava sequences that eventually become plateaus (see Plateau). The origin of molten rock, referred to by geologists as magma, is not clearly understood. About 80 percent of all magma is composed of basalt rock. Geophysical research suggests that volcanic magma forms near the base of the Earth's crust and moves upward to a shallow magma chamber before erupting at the surface. Magmas rise because they are less dense than the rocks at lower depths, and their heat probably weakens surrounding rocks. The upward movement of magma may also be due to expanding gases within the molten rock or to chemical reactions that dissolve rocks above the magma. Volcanic material moves toward the surface through channelways, or volcanic conduits, and is extruded through vents at the Earth's surface. (See also Lava and Magma.) Eruptions take different forms depending on the composition of the magma when it reaches the surface. Sudden eruptions are often associated with low-viscosity (more fluid) magma where the expanding gases form a froth that becomes a light, glassy rock called pumice. In eruptions of high-viscosity (thicker) magmas, the gas pressure shatters the rock into fragments. Pyroclastic rocks, formed by volcanic explosion, are named according to size: volcanic ash if sand-sized or smaller, volcanic bombs if larger. Consolidated ash is called tuff. Quieter, more passive eruptions release fluid basalt lava from dikes or dike swarms (magma intrusions that cut across layers of rock). These eruptions cover large areas and often produce ropy, or pahoehoe, lava flows. Thicker basalt lava breaks into chunks or blocks, forming blocky lava flows, called aa. The products of volcanism may be classified into two groups: lava and pyroclastics. Lava is the fluid phase of volcanic activity. Pyroclastics (also called tephra) are various-sized particles of hot debris thrown out of a volcano. Whether lava or pyroclastics are being ejected, the eruption is normally accompanied by the expulsion of water and gases, many of which are poisonous. Lava usually forms long, narrow rivers of molten rock that flow down the slopes of a volcano. Explosive eruptions tend to be spectacular events best observed from a safe distance. Earthquakes, high columns of vapors, lightning, and strong whirlwinds often accompany the explosions. The eruption of Krakatoa unleashed a tsunami, a large seismic sea wave, that swept the coasts of Java and Sumatra and drowned more than 36,000 people. A volcano can grow with frightening speed and often affects territory far beyond the area on which the cone forms. When volcanoes are born in the sea, the eruptions may be more violent than those on land because the contact between molten rock and seawater produces steam. Volcanoes also create craters and calderas. Craters are formed either by the massive collapse of material during volcanic activity, by unusually violent explosions, or later by erosion during dormancy. Calderas are large, basin-shaped depressions. Most of them are formed after a magma chamber drains and no longer supports the overlying cone, which then collapses inward to create the basin. One of the most famous examples is the still-active Kilauea caldera in Hawaii. Types of Volcanoes Volcanoes are usually classified by shape and size. These are determined by such

What Are the Essential Skills to Be Possessed by a Manager Essay Example

What Are the Essential Skills to Be Possessed by a Manager Essay Example What Are the Essential Skills to Be Possessed by a Manager Essay What Are the Essential Skills to Be Possessed by a Manager Essay What are the essential skills to be possessed by a manager? A:- In order to perform your role as a good manager, you need to possess and exhibit a range of skills to plan, control, organize, lead and take decisions of an organization. In this article I am giving a brief idea of those unique set of skills needed for a professional manager. Planning skills It’s often needed to define the future of an organization. Managers must be able to ensure that his company does exist in the future. Hence his planning skills include ability to Forecast future environment Think ahead Plot organizational objectivesChoose strategies to attain these objectives Reach their performance standards When an organization increases its complexity, it needs its managers to acquire skills as needed to fit the present needs of the system. Organizing skills Organizing process follows the planning process. Its skills can be broadly spelled as the ability to Analyze and describe various tasks Select, train a nd appoint people Define roles, authority and controls Change these working links whenever necessary and make these changes flexible It depends upon the managerial skills to achieve the best you can, with the limited resources available.Leading skills A leader must be able to know the values, personality, attitudes and perceptions of his subordinates. Value is an opinion or belief a person holds about something while personality is a sum up of personal traits of an individual. It’s determined by our physical constitution, beliefs and values he holds. Perception is how a person interprets something from what he see, smell or feel while attitude is a person’s behaviour to a particular event, situation or person. Though we can’t observe it directly, we can observe its consequences.Attitudes can be learned and have three aspects – cognitive, affective and behaviourial. manageskills2 Controlling skills It consists of actions and decisions which managers undert ake to ensure that outputs obtained are consistent with desired ones. Any difference between the actual and planned results must be corrected by management by taking appropriate actions. So, a management has a pre-determined standard according to which outputs are needed to be checked. manageskills1 Decision making skills They are related to planning process and pervade all other modules of managerial skills.A manager’s skills and effectiveness lies in making appropriate and timely decisions most suited to that particular situation. Sometimes repetitive or routine problems are involved which are to be verified periodically. So, at the end of all the above managerial skills, you may be able to know the overall skills of a manager. Also, there are different levels of managers – first level managers, having the direct contact with the employees, middle level managers to whom the first level managers report, comparatively less in number than first level managers and top le vel managers who are the overall decision makers of the company.Managerial skills at various levels These skills refer to the ability of managers at different managerial levels of the system hierarchy. Katz in 1974 categorized managerial skills into three types. Technical skill It’s the ability to work with resources in a particular area of expertise. For example, a lab assistant must know his subject well, to help the project students. An accountant should know everything about accounts and balance sheet and a surgeon should be well expert in surgery.In a small manufacturing organization, top boss should have a clear idea of technology skills. Very often, training programs can help employees to expertise in technical skills. Human skill It deals with the ability of a manager to work effectively among his group of members, interact well and take suitable decisions to lead them from front. Communication skill of a manager is very important. Also, to provide a better working at mosphere for his subordinates, a manager is needed to possess certain human skills and it can be developed without any formal training. Conceptual skillIt’s the ability to see organization as a whole and recognizing relationships or links of different modules within the system. Also, it identifies the impact of changes of one module affecting other modules, it may be one or two or a group. As a manager you need to view situations and determine the inter-related factors. Also, his ability to co-ordinate and integrate a variety of factors is very important. Top management skills No doubt, top management has to run the organization as a whole and hence they need some special, distinct management skills to control the whole organization.Most important of them include Building a strong and efficient team of people at the middle management level and should encourage his subordinates to learn some of his management skills as well. Need to monitor and review the functioning of an org anization at different time intervals and check if the outputs are matching the already set targets. Keep in touch and share ideas with planners, policy makers and intellectual and skilled people of the organization. To find competent human resources to fit their organization and encourage and appreciate them in the form of rewards if needed.Develop a distinct and special skill to make you different from others and prompt others to follow you. You can even guide your subordinates by sharing your experiences and piece of knowledge. Thus skills of a manager is essentially two ways – functional, which involves planning, organizing, leading, controlling and decision making and skills of managers involving technical, human and conceptual. Through this article, I have given a brief description of managerial skills needed for an organization.