Volcanoes

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. alifornia, Mt. Hood in Oregon, and Mt. St. Helens and Mt. Rainier in Washington (e.g. USGS/Cascades Volcano Observatory, Vancouver, Washington) (see figure 4).

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Cinder and scoria cones are the simplest type of volcanoes. They are built from particles and blobs of congealed lava ejected from a single vent. When gas-charged lava is blown violently in the air, it breaks into small fragments that solidify and fall as cinders around the vent to form a circular or oval cone. Cinder cones are numerous in western North America as well as throughout other volcanic terrains of the world. Calderas are among the most spectacular and active volcanic features on Earth. When a large volume of magma is removed from beneath a volcano, the ground subsides or collapses into the emptied space, to form a huge depression called a caldera (see figure 5).Most calderas very active, but this does not always lead to an eruption.

The possibility of violent explosive eruptions forces detailed scientific study and monitoring of some active calderas. The Five Types of Volcanic Eruptions The five types of volcanic eruptions are Pelean, Vulcanian, Strombolian, Hawaiian, and Icelandic. The Pelean type of eruption, which is the most explosive, is represented by many volcanoes in Central America and the West Indies. A Pelean eruption has violent and destructive activity that takes place during the opening stages when glowing avalanches of magma are produced. Airfall material is much less widespread than those of most Vulcanian eruptions.The eruptive cycle generally lasts only a few years, but there are exceptional cases such as in Santiaguito, Guatemala, where the cycle lasts more than 50 years (McBirney 240). The second type of volcanic eruption is referred to as the Vulcanian type.

In a Vulcanian volcano the crater crusts over solidly between eruptions. When gases accumulate beneath the crust, the upper part of the magma column becomes thoroughly gas-saturated. Strong eruptions sometimes disrupt the cone, followed by a cauliflower-shaped cloud, dark in color because of high ash content, as the obstruction is blown out. As the pressure is suddenly reduced, the gas-charged magma is disrupted by the explosively expanding gases into pumice and ash (Bullard 185).Lava flows may flow from the crater or from fissures on the sides of the cone.

Vulcano, in the Lipari Islands off the coast of Sicily, was the example used by Mercalli (1891), Lacroix (1908), and other scientists for the Vulcanian type of eruption. However, many others consider Vesuvius to be an even better example (Bullard 185). The prime characteristics of a Strombolian eruption are the throwing out of incandescent fragments of lava accompanied by a white eruption cloud (Bullard 242).

The Strombolian eruption is named after a volcano named Stromboli.Stromboli is one of the few volcanoes in the world, which is in a state of permanent moderate activity. In contrast with the Vulcanian eruption cloud, which is heavily charged with ash, the Strombolian cloud contains little ash. The lava column crusts over lightly, and at frequent intervals mild explosions break the crust, hurling the pasty, incandescent fragments into the air (Bullard 242). The Mauna Loa and Kilauea volcanoes are examples of Hawaiian type eruptions, in which basaltic lava issues more or less quietly from a fissure that may extend for a number of miles.

Earthquakes usually proceed these eruptions, as the fissure opens to allow the magma to reach the surface.The lava is quite fluid, and the gases escape readily without the disruption of the lava into ash or cinders which occurs in the Pelean type of eruption (Bullard 263). Less than 0.5 percent of the portion of the Hawaiian Islands exposed above sea level consists of fragmental material, thus attesting to the great predominance of the outpourings of lava at these vents (Bullard 263). The Icelandic type of eruption has many features in common with the Hawaiian type. The lava in both cases is primarily basalt, and the eruptions are quite similar (Bullard 99). During Hawaiian type eruptions the lava piles up in dome-shaped masses, while in the Icelandic type the lava forms plateaus with flat-laying layers.

The volume of lava involved in individual plateau building and in dome making is similar.Volcanoes Are Disasters A volcanic hazard is a destructive natural process that has occurred previously at a particular volcano; therefore, there is the probability that it could occur again during a future eruption (Fisher, Heiken, and Hulen 268). Risk is the potential loss from a hazard; losses include people’s lives, property, livestock, and the productive capacity of the area. The magnitude of the risk increases as population increases near a volcano. The number of human fatalities due to volcanic eruptions between 1900 and 1986 was a total of 76,000. That’s an average of 880 people per year (Fisher, Heiken, and Hulen 269).

There are many factors that affect the prediction of future volcanic activity.Some of the factors are: the longer a volcano is inactive the chances increase for it to become active, eruptive behavior may change with time, and some hazards are indirectly related to an eruption making it difficult to forecast. As you can see, volcanoes can cause horrible disasters.

To prevent some of these disasters, here is a list of caution steps and facts provided by the USGS / Cascade Volcano Observatory. Stay indoors. If you are outside, seek shelter such as a car or a building. If you cannot find shelter, breathe through a cloth, such as a handkerchief, preferably a damp cloth to filter out the ash. When the air is full of ash, keep your eyes closed as much as possible.

Heavy falls of ash seldom last more than a few hours-only rarely do they last a day or more. Heavy fall of ash may cause darkness during daylight hours and may temporarily interfere with telephone, radio, and television communications. Do not try to drive a car during a heavy fall of ash-the chance of an accident will be increased by poor visibility. The thick accumulation of ash could increase the load on roofs, and saturation of ash by rain would be an additional load. Ash should be removed from flat or low-pitched roofs to prevent thick accumulation. During an eruption move away from a volcano-NOT TOWARD IT! Most important-DON’T PANIC-KEEP CALM.

Conclusion In conclusion I would like to remind you that there are three main components that erupt out of a volcano: lava, ash, and bombs. The seven different types of volcanoes are: Submarine volcanoes; Ridges and Vents; Shield Volcanoes; Lava Plateaus and Flood Basalts; Lava Domes; Composite Volcanoes; Cinder and Scoria Cones; and Calderas. The five volcanic eruptions are Pelean, Vulcanian, Strombolian, Hawaiian, and Icelandic.

Volcanoes are disasters that cause losses such as: people’s lives, property, livestock, and the productive capacity of an area. The factors that affect the prediction of future eruptions are: the longer a volcano is inactive the chances increase for it to become active, eruptive behavior may change with time, and some hazards are indirectly related to an eruption making it difficult to forecast. Volcanoes are disasters that cause devastation, so please take caution if you live near a volcano. Science.