Volcanoes

Volcanoes

                 While most of you are familiar with the word “Volcano” but do you know what a volcano actually is? To put it very simply, a volcano is a rupture in the Earth’s crust where molten (melted) rock, pieces of hot solid rock, and hot gases formed inside the Earth erupt through its surface. The word ‘volcano’ comes from ‘Vulcan’. Vulcan was the Roman god of Fire.

Volcanic activity is the most dramatic and rapid of all the geologic processes that shape the surface of the Earth. While millions of years are needed for natural forces to build mountain ranges and erode canyons, an erupting volcano can build or destroy large, sometimes massive, structures in a matter of minutes or days. For example, on 18 May, 1980, the eruption of Mount St. Helens, in the North-Western United States, destroyed much of the mountain and killed about sixty people. On the other hand, on Nov.15, 1963, an island was born. It happened off the south coast of Iceland, where volcanic activity under the sea created a new island within 24 hours. This was the Island of Surtsey and its birth was the result of constant shifting of the Earth’s crust combined with the pressure of the molten rock. This caused the eruption of the undersea volcano, Sutur.

The formation of volcanoes have contributed to the shaping and configuration of the varied landscapes that make up the planet.

HOW VOLCANOES ARE FORMED?

         The Earth’s interior is very hot, and the heat left over from its formation continually escapes toward the surface. As the heat rises, it warms rock in the Earth’s interior, and this heated rock begins rising slowly toward the surface. Much of this molten rock or magma, gradually cools within the Earth. Sometimes, however magma continues to push upward.

            While heat is what causes magma to rise to the surface, escaping gases provide the driving force for volcanic eruptions. The most volcanic gas is steam. This is formed when water from within the Earth or rainwater soaking into the ground is absorbed by magma and the heated.

             When gas-filled magma rises from the Earth’s interior, it collects in large pools called magma chambers that are several miles below the surface. As the amount of gases increases, the magma becomes lighter, causing it to rise through a system of conduits, or channels. When the magma reaches the surface, it spews out of vents, or openings, at the tops of the magma conduits. Magma that erupts from a vent is known as lava. Lava and other material, such as ash & rock fragments, ultimately build up to form a volcanic cone.

TYPES OF VOLCANOES :-
        Some volcanoes are large mountains with summits, or peaks. Others are small domes of ash or lava. So Scientists recognize three main types of volcanoes:-              
 Stratovolcanoes, Shield Volcanoes and Cinder cone volcanoes.
Stratovolcanoes:-

They are also referred to as Composite volcanoes. They consist of many layers ( strata ) of hardened lava, tephra, pumice and volcanic ash. They generally have steep slopes and are the most common type of volcanoes on Earth. They tend to form at Subduction Zones ( where one tectonic plate is sliding beneath the other ) . Their eruptions are typically explosive and effusive. For example: Krakatoa, Mt. Helen, Mt. Tambora and Vesuvius.

Cinder Cone volcanoes:-

A Cinder Cone volcano is simply a steep conical hill of tephra (volcanic debris) that accumulates around and downwind from a volcano vent. These volcanoes consist almost entirely of loose, grainy cinders consisting typically of basaltic & andesitic material and almost no lava. They are the smallest type of volcano. For example : Paricutin, Sunset Crater and Lava Butte.

Shield Volcano:-

Shield volcanoes, formed when large flows of lava spread rapidly from central vents or rows of vents, are the largest volcanoes. Because the lava moves rapidly and spreads out in a broad area, it does not form a tall, steep cone. Instead,  shield Volcanoes are dome-shaped mountains with broad bases and gentle slopes. For example:- Mauna Loa, Kilauea, Fernandina and Masaya.

          However Scientists use special terms to describe the different kinds of volcanic eruptions. The gentlest eruptions are non-explosive Hawaiian eruptions, named after the volcanoes found in Hawaii. In Hawaiian eruptions, lava erupts relatively quietly from one or more vents, producing quick-moving lava flows & lava fountains. Strambolian eruptions, named after a volcano in Italy, are characterized by many small but relatively weak explosive eruptions. The eruptions occur in fairly short, regular bursts. More explosive than a Strambolian eruption is a Vulcanian eruption, which produces large amounts of ash but few lava flows. It takes its name from the Island of vulcano in Italy. A Peleean eruption, named after Mount Pelee in Martinique, is a violent explosion that is often accompanied by rapidly moving flows of ash, rock fragments and gases. Plinian eruptions are among the most powerful eruptions known named after ‘Pliny the Elder', a famous Roman scholar killed during the eruption of Mount Vesuvius in 79 C.E., This type of eruption hurls plumes of ash tens of miles into the sky.

In addition to the kind of eruption, Scientists classify volcanoes according to how often they erupt. Active volcanoes erupt either constantly or they have erupted sometimes in the last 10,000 years. Dormant volcanoes are ones that have been inactive for long periods of time but may become active again at any time. Extinct volcanoes have been inactive for so long, perhaps tens of thousands of years or more, that they are unlikely to erupt again. In some instances, extinct or dormant volcanoes are so old that erosion has made them unrecognizable as volcanoes.

WHERE VOLCANOES OCCUR?
                Volcanoes have always been a part of the Earth’s long history. Volcanoes or the evidence of volcanoes has been located almost everywhere on the Earth’s surface. Today, however, volcanoes do not occur everywhere, most are located near the edges of continents. The Geologic Theory of Plates Tectonics helps to explain this.

     According to the Theory of Plate Tectonics, the Earth’s crust consists of several huge plates or blocks, that move slowly around the planet. As these crustal plates move, they frequently collide, forcing one plate to slide beneath the other. When this happens, the rocks in the plate are pushed toward the Earth’s interior where they become hot & melt. This melted rock then rises as magma, forming volcanoes near where the plates meet.

      Along the edges of the Pacific Ocean, the huge Pacific Plate is sliding under a number of continental plates. The area along this large arc is called the ‘Ring of Fire’ because many active volcanoes are found along it. Other arcs of active volcanoes run through Italy, Greece, Turkey, Armenia and Indonesia. Volcanoes also are located where plates are spreading apart. Scientists have discovered this type of volcanic activity in the Atlantic Ocean along the Mid-Atlantic Ridge, an undersea mountain range that marks the boundary between huge spreading plates. Iceland’s volcanoes are found along this volcanic ridge.

    While most volcanoes form where crustal plates are colliding or spreading apart, some are located in the middle of plates. The Hawaiian Islands, the most famous mid-plate volcanoes are a good example of this process.

PRODUCTS OF VOLCANOES:-
       An erupting volcano produces a number of volcanic materials, among the most important are lava, rock and heat & gas.

ADVANTAGES & DISADVANTAGES OF VOLCANIC ERUPTION:-

          Advantages:
• It helps to create new islands and land.
• It provides habitat to pioneer species.
• It creates economic mineral deposits.
• It generates tourism.
• It creates beautiful landscapes.
• It provides resources for energy extraction, also called Geo-thermal resources.
• It provides rich soil for farming.

         Disadvantages:
• It destroys old habitat and crops.
• It destroys cities, towns, communities and forests.
• It displaces population.
• It kills people & other animals.
• Disrupts commerce.
• Generate tsunamis.
• It creates many health related problems.