SAT practice Test 10

A Short Essay on Volcanoes 

1. A volcano is an opening, in the planet’s surface which allows hot, molten rock, ash and gases to escape from below the surface.
    
2. The name, “volcano” originates from the name Vulcan, a god of fire in Roman mythology. Volcanoes are like giant safety valves that release the pressure that builds up inside the Earth. The Hawaii islands were formed by 5 volcanoes. Classified by the extent of their activity volcanoes are of four types. An ‘active’ volcano is one that erupts regularly. There are about 500 known active volcanoes on Earth, not counting those that lie beneath the sea.
    
3. A ‘dormant’ volcano is one that has not erupted for many years, although there is still some activity deep inside it. An ‘extinct’ volcano is one which has ceased to be active.
    
4. A volcanic eruption occurs when hot rocks and lava burst from a volcano; and geysers and springs are actually just volcanoes that throw boiling water high in the air. They are caused by volcanic heat warming trapped ground water. The liquid rocks inside a volcano are called magma and when it flows out it is called as lava. 
   
   
5. Fresh lava has temperatures from 700 degrees C to 1200’C and glows red-hot to white hot as it flows. The most dangerous volcanic eruption recorded is the eruption of Mount St. Helens in Washington. The tallest volcano in the world is the Ojos del Salado, a volcano in Chile. The world’s largest volcano is the Muano Loa in Hawaii.
   
   
6. Volcanoes are generally concentrated on the edge of continents, along the island chain, or beneath the sea forming long mountain ranges. A major part of the world’s active volcanoes above sea level encircle the Pacific Ocean forming the “Ring of Fire.”
    
7. Volcanoes can have serious affects on the lands and people around them when they erupt. The destruction they leave in their wake accounts for the total annihilation of the surrounding landscape. Around 2, 00,000 people have lost their lives to volcanic eruptions in the past five hundred years.
    
8. Buildings are destroyed, people are rendered homeless, people are killed, plant and animal life are both destroyed and the poisonous gases that emanate from the volcanoes can cause death and diseases like pneumonia in the people who survive it.
    
9. However not everything associated with the volcanoes is negative. The crust of the earth exists due to?the large volumes of magma that did not erupt but instead cooled below the surface. It results in rich soil which is good for cultivation.
    
10. The volcanic ash that blows out of the volcano increases soil fertility by adding nutrients to the soil. Ground water heated by magma can be tapped for geothermal energy. Most of the metallic minerals like copper, gold, silver, lead and zinc are mined from the magmas found deep within the roots of extinct volcanoes.
     
11. With the increasing studies done by scientists on volcanoes it is becoming possible to gauge the activity level of a volcano. With this information although it might not be possible to prevent the erupting of a volcano at least the massive destruction of lives can be avoided by getting people evacuated in time.

Monitoring Volcanic Gases

12.  Scientists have long recognized that gases dissolved in magma provide the driving force of volcanic eruptions, but only recently have new techniques permitted routine measurement of different types of volcanic gases released into the atmosphere. Sulfurous volcanic gas and visible steam are usually the first things people notice when they visit an active volcano, for example Mount St. Helens pictured here. A number of other gases also escape sight unseen into the atmosphere through hot fumaroles, active vents, and porous ground surfaces. The gases escape as magma rises toward the surface, when it erupts, and even as it cools and crystallizes below ground.
     
13. A primary objective in gas monitoring is to determine changes in the release of certain gases from a volcano, chiefly carbon dioxide and sulfur dioxide. Such changes can be used with other monitoring information to provide eruption warnings and to improve our understanding of how volcanoes work. In recent years, we have directed increased attention toward volcanic gas emissions because of the newly appreciated hazards they sometimes pose and their effects on the Earth's atmosphere and climate.
     
14. Gases released by most volcanoes are difficult to sample and measure on a regular basis, especially when a volcano becomes restless. Direct sampling of gas requires that scientists visit a hot fumarole or an active vent, usually high on a volcano's flank or within its summit crater. At some volcanoes, gases discharge directly into crater lakes. The remote location of these sampling sites, intense and often hazardous fumes, frequent bad weather, and the potential for sudden eruptions can make regular gas sampling sometimes impossible and dangerous.
     
15. Measuring gases remotely is possible but requires ideal weather and the availability of suitable aircraft or a network of roads around a volcano. Consistent and favorable wind conditions are needed to carry gases from vents and fissures to where they can be measured. In some cases, automated on-site gas monitoring is feasible. Under corrosive conditions, only a few sensors are available, however, for continuously recording the concentrations of specific gases.
     
16. Scientists face yet another challenge--acid gases, like SO2, easily dissolve in water. Thus, volcanoes with abundant surface or subsurface water can prevent scientists from measuring the emission of acid gases as magma rises toward the surface and even after explosive eruptions. Because CO2 is is less likely to be masked by the presence of water, measuring it when a volcano first becomes restless and between eruptions may be important for determining whether significant magma degassing is occurring.