Volcanoes can affect the health of the populations of two ways: directly as a result of the explosions, lava flows, ash, and other effects, and indirectly by causing tsunamis, population displacement and adverse effects on agriculture.
Two variables determine the characteristics of a volcanic eruption: the fluidity or viscosity of the lava, and the magnitude of the pressure of the gases. In short, the more viscous is the largest lava and gas pressure that builds up before the eruption, the greater the potential dangers. Volcanic activity ranges from quiet lava output, even violent explosions that throw bulky masses of rock at high altitudes in the atmosphere. This last activity can be classified into 6 categories:
1) lava flows
The extent, thickness and speed with which advances a lava flow varies with its volume, its fluidity and topography del terreno. La velocidad con que avanza la corriente varia de unos cuantos metros al día. hasta 40 km por hora o más en laderas muy inclinadas. Sin embargo, dado que la rapidez de avance es pequeña, las corrientes mencionadas conllevan poco riesgo para la vida. No obstante, dado que pueden dañar extensamente las propiedades, se han intentado diversos métodos para controlar la dirección del flujo y la velocidad, incluidos el empleo de explosivos detonados desde el aire, la erección de barreras de desviación y el enfriamiento del frente de lava, con chorros de agua.
2) domos
La viscous lava may collect in the vent holes to form domes grow by internal expansion and its size varies by several meters in width and depth, can reach 2 000 m wide and 600 meters deep. The expansion of a dome breaks makes the solid outer shell or "shell" and the continued displacement of blocks, rolling, could present danger for the inhabitants of the surrounding area. In some cases, cooling of viscous magma that protrudes from the shell fractures of the dome as "thorns", which sometimes are 100 m in height, they are unstable and can cause avalanches.
3) tephra
The term denotes the material ejected during volcanic eruptions, varying in size from dust to boulders several meters thick. The older tephra tend to settle near the exit, while dust and ash injected at the top of the atmosphere can be carried thousands of miles away.
direct effects of tephra. Large stones fall can trigger a fire or injure people or animals. Once deposited the ashes, it is rarely hot enough to cause fires. However, her weight may make them collapse the roofs of houses.
ash eruptions that generate a continuous and long may force people to evacuate the danger zone, but few examples of these situations. Two other types of eruption of ash would be the lifting of the base and ash flow. The first is formed at the base of some columns is a volcanic ash cloud hanging ring that is sold very quickly, and erode the surface near the crater. In the inner zone may break off or uprooted trees and high buildings at greater distances is likely to have crushed objects because of the severe sandstorm. In some eruptions, much of the ash suspended in a cloud and moving closer to the ground, an effect known as "ash flow." Friction removes the dispensed gas within the cloud, which makes the particles are kept separate ash. The flow is driven by gravity, and follow the anfractuocidades ground, the ash flow often exceeds 200 km / hour.
Effects of ash on the respiratory tract and eyes. To assess the risks that have the rain of ash on the health of people are important five factors: the concentration of total suspended particles that travel through the air, the particle size, frequency and duration of exposure, additional factors such as preexisting diseases of the respiratory tract, and the presence of crystalline silica (SiO2) in the ashes. Humans can suffer
suffocation by volcanic ash. In Pompeii, buried by the eruption of Vesuvius, 79 AD, it was noted that some victims found in the excavations, covered their faces with their hands or clothes, perhaps smothered by the ashes. The
silicon crystals travel through the air and have size "breathable", ie less than 10mm in diameter and particles when they penetrate the alveoli can irritate lung airways and cause obstruction symptoms in them. If exposure is to a large enough concentration for a long time, could cause silicosis, a disabling lung fibrosis and sometimes fatal.
4) Avalanches of incandescent material (glowing avalanches or pyroclastic flows)
three are recognized avalanche types identified by the name of the volcanoes in which each is first observed, these are the effects (Sofrière, Merapi and Pelee). Although the mechanisms by which they form are different but their effects are similar: a turbulent mass of superheated gases in which no dust, hot ash and lava fragments that travel, even to 160 km / hour which destroys everything in its path. The avalanche of incandescent material that devastated the population of St. Pierre, Martinique, in 1902, killing the 28 000 inhabitants.
volcano Pele
5) lahars
This term applies to many types of volcanic mud flows and whose temperature ranges from very low to the boil. The gravity-driven mud can proceed even at 100 km per hour, travel considerable distances and still cover areas of several hundred square kilometers. The lahars are common and are the leading cause of death and destruction by volcanoes. They may arise from the expulsion of water from a lake in the crater, melting snow, by the movement of ash or water saturated land on the slopes of a volcano, and other forms of volcanic activity that interacts with water. Because they are able to travel with extraordinary rapidity can cause many deaths. For example, in Kelud, Java, in 1919 a lahar killed 5 000 people and lost hundreds of square miles of land.
On rare occasions, a lahar may contain sulfuric acid or hydrochloric acid in sufficient concentrations to cause chemical burns to exposed skin is known of a case of this type resulted the explosion of a lake in the crater of Kawah Idjen in Java, in 1917.
lahar
6)
volcanic gases gases expelled by volcanic action contain varying amounts of water vapor, carbon dioxide and carbon monoxide dioxide and sulfur trioxide, sulfuric acid, hydrochloric, hydrofluoric, methane and more complex hydrocarbons, and nitrogen, argon and other inert gases affect people in different ways. Carbon dioxide and sulfur dioxide can cause asphyxiation, the first, to build "mass" in areas very low, and the second by the direct effect that causes the respiratory tract.
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