Agenda - 05-06-2010 - 4m - Laserfiche WebLink

Browse Search

Volcanoes Volcanic eruptions are one of the most dramatic and violent agents of environmental change. Not only can powerful explosive eruptions drastically alter land and water for tens of kilometers around a volcano,but tiny liquid droplets of sulfuric acid erupted into the stratosphere can temporarily change the climate of the planet. Eruptions often force people living near volcanoes to abandon land and homes, sometimes forever. Those living farther away are likely to avoid complete destruction,but cities and towns,crops,industrial plants, transportation systems, and electrical grids can still be damaged by tephra, lahars, and flooding caused by volcanic eruptions. Worldwide volcanic activity since 1700 A.D. has killed more than 260,000 people, destroyed entire cities and forests, and severely disrupted local economies for months or years.Even with the improved ability to identify hazardous areas and warn of impending r cientists have estimated that eruptions,increasing numbers of people face certain dange . S the total population at risk from volcanoes in 2000 is at least 500 milhon, which is comparable to the entire population of the world at the beginning of the seventeenth century. Volcano Hazard Areas Around the Globe Active volcanoes are not randomly distributed over the earth surface. Instead, they tend to be located in linear volcanic mountain chains thousands of kilometers long on the edges of continents, in the middle of oceans, or as island chains. The locations of these volcanic chains are closely related to the way in which the earth crust is divided into more than a dozen enormous sections or"plates" and how the plates move relative to one another. According to the theory of plate tectonics,rigid plates averaging 80 kilometers in thickness, move in slow motion on top of the hot,pliable interior of the earth. Most active volcanoes are located along the boundaries where these massive plates spread apart or collide. But some of the most active volcanoes, like Kilauea Volcano on the Island of Hawaii, aze found in the middle of these massive plates above hot spots in the interior of the earth.More than fifty volcanoes in the United States have erupted one or more times in the past few hundred years. The United States Geological Survey(USGS)is charged with the responsibility to issue warnings of hazardous volcanic activity in the United States. The USGS has identified volcano-hazazd zones around active and potentially active volcanoes. Volcano-hazard assessments are based on the assumption that the same general area around a volcano is likely to be affected by future volcanic activity of the same type and at about the same average frequency as in the past. Through detailed geologic mapping of the type and size of past eruptions,the USGS has estimated the area most likely to be affected by similar events in the future. Volcanoes generate a wide range of activity that can affect the surrounding land,river valleys, and communities in different ways. Depending on the type, size, and duration of the eruptive activity,hazardous areas might exist within a few kilometers of a volcano or extend to areas hundreds of kilometers from an active vent. By studying the natural history 25