Composite volcanoes have a principal conduit system through which magma from a reservoir deep in the Earth's crust rises to the surface repeatedly to cause eruptions.Composite volcanoes, sometimes called stratovolcanoes, tend to erupt explosively because of the silica-based nature of magmas associated with these volcanoes.
Composite volcanoes often form the largest and tallest volcanoes. They are the most explosive and dangerous of the types of volcanoes.
Most of the tall volcanoes, like Mount St. Helens and Mount Rainier in Washington and Mount Fuji in Japan are composite volcanoes. These volcanoes usually have a big explosion when they erupt, and in-between eruptions you might not even be able to tell they are volcanoes, because they are very quiet and look just like other
mountains.
Shape is largely a function of slope angle; at the one
extreme are very shallow slopes that characterize shields, and on the other are the steeper slopes that characterize cones and domes. Among the smaller edifices are cinder cones and domes, which are typically monogenetic (formed from a single eruption episode).
Compared with caldera systems, composite volcanoes erupt smaller volumes more frequently and less explosively, which likely inhibits the long-term extreme differentiation, which typifies caldera-forming magmas.Young stratovolcanoes are typically steep sided and symmetrically cone shaped. There are several active stratovolcanoes in North America. Since 1980 Mount Saint Helens in Washington has become the most familiar.dimension built of alternating layers of lava flow, volcanic ash and cinders.
Famous composite volcanoes include Mount Fuji in Japan, Mount Shasta and Mount Lassen in California, Mount St. Helens and Mount Rainier in
Washington State, Mount Hood in Oregon, and Mount Etna in Italy.
Composite volcanoes will rise as much as 8,000 feet above their base. Most composite volcanoes have a crater at the summit, which contains a central vent or a clustered group of vents.Most volcanoes on Earth are of this type. Stratovolcanoes kill more people than any other type of volcanoes - this is because of their abundance on Earth and their powerful mudflows.
Friday, March 25, 2011
Wednesday, March 23, 2011
Active volcanoes
Active volcanoes are those that are currently erupting or showing signs of unrest, such as unusual earthquake activity or significant new gas emissions.Regularly active volcano ejected lava, ash, smoke and other substances. With a very active volcano this happens almost constantly. In the other between the eruption extended weeks or months.
While there is evidence of volcanic activity in the past, a lot of volcanoes are active today. They’re bubbling with lava, spewing ash and triggering earthquakes as you sit in class.Explosive eruptions can shoot columns of gases and rock fragments tens of miles into the atmosphere, spreading ash hundreds of miles downwind.
While some of the volcanoes are dormant for hundreds of years, others who were believed to be extinct, become active again, as happened 1973rd with Helgafelom (Hajmej, Iceland).
Alaska is home to 41 historically active volcanoes stretching across the entire southern portion of the State from the Wrangell Mountains to the far Western Aleutians. An average of 1-2 eruptions per year occur in Alaska.
Mount Etna, the largest active volcano in Europe, reaching 3,350 m and covering a surface of about 1,260 km2, started its activity at about 600 ka, after the end of Upper Pliocene to Pleistocene subaqueous and subaerial eruptions at the northwestern edge of the Iblean Plateau. Mt.
The New Zealand area is characterised by both a high density of active volcanoes and a high frequency of eruptions.
The largest volcanic eruption of the 20th century occurred at Novarupta Volcano in June 1912. It started by generating an ash cloud that grew to thousands of miles wide during the three-day event.
Some volcanoes expel gas and burning lava in the terrifying outbursts. Others have explosive eruptions and expel clouds of ash and gas.Volcanoes are evidence that the Earth is restless, especially within the crust and upper mantle.
If you live near an active or dormant volcano, you should be prepared to evacuate at a moment’s notice, as eruptions are not always predictable.Volcanoes can be incredibly destructive to buildings and dangerous to your family. In addition to the direct hazards, an eruption can be accompanied by landslides, mudflows, flash floods, earthquakes and tsunamis.
While there is evidence of volcanic activity in the past, a lot of volcanoes are active today. They’re bubbling with lava, spewing ash and triggering earthquakes as you sit in class.Explosive eruptions can shoot columns of gases and rock fragments tens of miles into the atmosphere, spreading ash hundreds of miles downwind.
While some of the volcanoes are dormant for hundreds of years, others who were believed to be extinct, become active again, as happened 1973rd with Helgafelom (Hajmej, Iceland).
Alaska is home to 41 historically active volcanoes stretching across the entire southern portion of the State from the Wrangell Mountains to the far Western Aleutians. An average of 1-2 eruptions per year occur in Alaska.
Mount Etna, the largest active volcano in Europe, reaching 3,350 m and covering a surface of about 1,260 km2, started its activity at about 600 ka, after the end of Upper Pliocene to Pleistocene subaqueous and subaerial eruptions at the northwestern edge of the Iblean Plateau. Mt.
The New Zealand area is characterised by both a high density of active volcanoes and a high frequency of eruptions.
The largest volcanic eruption of the 20th century occurred at Novarupta Volcano in June 1912. It started by generating an ash cloud that grew to thousands of miles wide during the three-day event.
Some volcanoes expel gas and burning lava in the terrifying outbursts. Others have explosive eruptions and expel clouds of ash and gas.Volcanoes are evidence that the Earth is restless, especially within the crust and upper mantle.
If you live near an active or dormant volcano, you should be prepared to evacuate at a moment’s notice, as eruptions are not always predictable.Volcanoes can be incredibly destructive to buildings and dangerous to your family. In addition to the direct hazards, an eruption can be accompanied by landslides, mudflows, flash floods, earthquakes and tsunamis.
Tuesday, March 22, 2011
Atacama desert facts
Facts about the Atacama are very interesting. The Atacama Desert is between the central Andes and Pacific Ocean in northern Chile. Located in northern Chile and extreme southern Peru, the Atacama Desert is located is perhaps the most unique physiographic location on earth. The Atacama Desert is also known as the Sechura Desert.
It is driest desert in the world. The Atacama Desert lies between two mountain ranges on the west coast of South America, the Coastal Cordillera and the Andean Cordillera. The Coastal Cordillera ranges in elevation from 500 to 3000 meters, and the Andean Cordillera ranges in elevation from 5000 to 6000 meters.Unlike other deserts, such as the Sahara in Africa and the Mojave in California, the Atacama is actually a very cool place with an average daily temperature between 0 ° C and 25 ° C.
Although it seems difficult that there is life in the Atacama, the holes are isolated and small areas of plants that provide a life of some insects and animals. Some plants are very well adapted to this arid environment, the development of long roots that reach to the water below the ground.Since the Andes mountain ranges active volcano, magma pressure of underground water in certain places causing geysers.
The Atacama Desert is probably the oldest desert on earth and has experienced extreme hyperaridity for at least 3 million years and probably 15 million years.The climate of the Atacama Desert is largely controlled by its zonal location between 15° and 30°S in the sub-tropical high-pressure belt where descending stable air produced by the Hadley circulation significantly reduces convection and hence precipitation.
Special attractions are the huge salt lake “Salar de Atacama”, which is almost dried out, and the bizarre landscape formations like the “Valley of the Moon” or the hot springs “Tatio Geysers”.
It is driest desert in the world. The Atacama Desert lies between two mountain ranges on the west coast of South America, the Coastal Cordillera and the Andean Cordillera. The Coastal Cordillera ranges in elevation from 500 to 3000 meters, and the Andean Cordillera ranges in elevation from 5000 to 6000 meters.Unlike other deserts, such as the Sahara in Africa and the Mojave in California, the Atacama is actually a very cool place with an average daily temperature between 0 ° C and 25 ° C.
Although it seems difficult that there is life in the Atacama, the holes are isolated and small areas of plants that provide a life of some insects and animals. Some plants are very well adapted to this arid environment, the development of long roots that reach to the water below the ground.Since the Andes mountain ranges active volcano, magma pressure of underground water in certain places causing geysers.
The Atacama Desert is probably the oldest desert on earth and has experienced extreme hyperaridity for at least 3 million years and probably 15 million years.The climate of the Atacama Desert is largely controlled by its zonal location between 15° and 30°S in the sub-tropical high-pressure belt where descending stable air produced by the Hadley circulation significantly reduces convection and hence precipitation.
Special attractions are the huge salt lake “Salar de Atacama”, which is almost dried out, and the bizarre landscape formations like the “Valley of the Moon” or the hot springs “Tatio Geysers”.
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