Holmes a volcano is essentially a fissure or vent, communicating with the interior, from which flows of lava, fountains of incandescent spray or explosive bursts of gases and volcanic ashes are casaluma.staging.truecode.pt at the surface. Some scientists have also used the term of vulcanism as synonym to the term of vulcanicity.
It is apparent from the above definitions of volcano and vulcanicity vulcanism that the later vulcanicity is a broader mechanism which is related to both the environments, endogenetic and exogenetic. It is evident that the vulcanicity has two components which operate below the crustal surface and above the crust. The endogenetic mechanism of vulcanicity includes the creation of hot and liquid magmas and gases in the mantle and the crust, their expansion and upward ascent, their intrusion, cooling and essay on volcanoes in hawaii in various forms below the crustal surface e.
Volcanoes of explosive type or central eruption type are associated with the accumulated volcanic materials in the form of cones which are called as volcanic cones or simply volcanic mountains. There is a vent or opening, of circular or nearly circular shape, almost in the centre of the summital part of the cone. This vent is called as volcanic vent or volcanic essay on volcanoes in hawaii which is connected with the interior part of the earth by a narrow pipe, which is called as volcanic pipe.
The enlarged form of the volcanic vent is known as volcanic crater and caldera. Volcanic materials include lavas, volcanic dusts and ashes, fragmental materials etc.
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There is a wide range of variations in the mode of volcanic eruptions and their periodicity. Thus, vocanoes are classified on the basis of: Volcanic eruptions occur mostly in two ways viz.: Thus, on the basis of the nature and intensity of eruptions volcanoes are divided into two types e.
Central eruption type or explosive eruption type of volcanoes occurs through a central pipe and small opening by breaking and blowing off crustal surface due to violent and explosive gases accumulated essay on volcanoes in hawaii within the earth.
The eruption is so rapid and violent that huge quantity of volcanic materials consisting of lavas, volcanic dusts and ashes, fragmental materials etc. These materials after falling down accumulate around the volcanic vent and form volcanic cones of various sorts.
Such volcanoes are very destructive and are disastrous natural hazards. Explosive volcances are further divided into 5 sub-types on the basis of difference in the intensity of eruption, variations in the ejected volcanic essay on volcanoes in hawaii and the period of the action of volcanic events as given below: Such volcanoes erupt quietly due to less viscous lavas and non-violent nature of gases.
Such volcanoes have been named as Hawaiin type because of the fact that such eruptions are of very common occurrence on Hawaii island. The intermittent eruptions continued upto December 21,when the volcano became dormant. It again erupted on January 13, and about million cubic metres of lavas were poured out of one kilometre long fissure.
These materials again fall down in the volcanic craters. The eruptions are almost rhythemic or nearly continuous in nature but sometimes they are interrupted by long intervals. These are named after Vulcano of Lipari island in the Mediterranean Sea. The lavas are so viscous and pasty that these are quickly solidified and hardened between two eruptions and thus they crust over plug the volcanic vents.
These lava crusts obstruct the escape of violent gases during next essay on volcanoes in hawaii. These are the most violent and most explosive type of volcanoes.
The ejected lavas are most viscous and pasty. Obstructive domes of lava are formed above the conduits of the volcanoes. Thus, every successive eruption has to blow off these lava domes. The most disastrous volcanic eruption of Mount Pelee on May 8, destroyed the whole of the town of St. Pierre killing all the 28, inhabitants leaving behind only two survivors to mourn the sad demise of their brethren.
The nuee ardente spread mcg123.000webhostapp.com out of the mountain Mount Pelee with great speed which caused disastrous avalanches on the hillslopes which plunged down the slope at a speed of about kilometres per hour. These are more or less similar to Vulcanian and Strombolian type of volcanoes, the difference lies only in the intensity of expulsion of lavas and gases.
Volcanic materials are thrown up to greater height in the sky. The speed of lava movement depends on the essay on volcanoes in hawaii of magma, volume of magma, slope of ground surface and temperature conditions.
The Laki fissure eruption of in Iceland was so quick and enormous that huge volume of lavas measuring about 15 essay on volcanoes in hawaii kilometers was poured out from a km long fissure. The lava flow was so enormous that it travelled a distance of kilometres. Volcanoes are divided into 3 types on the basis of period of eruption and interval period between two eruptions of a essay on volcanoes in hawaii e.
It is estimated that there are about more than volcanoes in the essay on volcanoes in hawaii. Etna and Stromboli of the Mediterranean Sea are the most significant essays on volcanoes in hawaii of this category. Stromboli Volcano is known as Light House of the Mediterranean because of continuous emission of burning and luminous incandescent gases. Most of the active volcanoes are found along the mid- oceanic ridges representing divergent plate margins constructive plate margins and convergent essay on volcanoes in hawaii margins destructive plate margins represented by eastern and western margins of the Pacific Ocean.
The latest eruption took place from Pinatubo volcano in June in Philippines. Mayon of Philippines re-erupted in Feb. Dormant volcanoes are those which become quiet after their eruptions for some time and there are no indications for future eruptions but suddenly they erupt very violently and cause enormous damage to human health and wealth.
Visuvious volcano is the best example of dormant volcano which erupted first in 79 A. The subsequent eruptions occurred in, kawther-otmani.000webhostapp.com be pointed out that no volcano can be declared permanently dead as no one knows, what is happening below the ground surface.
Mechanisms and Causes of Vulcanism: Theory of plate tectonics now very well explains mp3songs.us mechanism of vulcanism and volcanic eruptions. In fact, volcanic eruptions are very closely associated with the plate boundaries. Most of the active fissure volcanoes are found along the mid-oceanic essays on volcanoes in hawaii which represent splitting zones of divergent plate boundaries fig.
Two plates move in opposite directions from the mid-oceanic ridges due to thermal convective currents which are originated in the mantle below indexgadget.000webhostapp.com crust plates.
This splitting and lateral spreading of plates creates fractures and faults transform faults which cause pressure release and lowering of melting point and thus materials of upper mantle lying below the mid-oceanic ridges are melted and essay on volcanoes in hawaii upward as magmas under the impact of enormous volume of accumulated gases and vapour.
These lavas are cooled and solidified and are added to the trailing ends of divergent plate boundaries and essay on volcanoes in hawaii there is constant creation of new basaltic crust.
It is apparent from the above discussion that the mid-oceanic ridges, representing splitting zones, are associated with active volcanoes wherein the essay on volcanoes in hawaii of lava comes from the upper mantle just below the ridge because of differential melting of the rocks into tholeiitic basalts.
This essay on volcanoes in hawaii has been validated on the basis of the study of the basaltic floor of the Atlantic Ocean and the lavas of several islands. It has been found that the islands nearer to the mid-Atlantic Ridge have younger lavas whereas the islands away from the ridge have older lavas.
For example, the lavas of Azores islands Situated on either side of the mid-Atlantic Ridge are 4- million years old whereas the lavas of Cape Verde Island, located far away from the said ridge, are million years old. Destructive or convergent plate boundaries are associated with explosive type of volcanic eruptions. When two convergent plates collide along Benioff zone subduction zonecomparatively heavier plate margin boundary is subducted beneath comparatively lighter plate boundary.
The subducted plate essay on volcanoes in hawaii, after reaching a depth of km or more in the upper mantle, is melted and thus magma is formed. Such type of volcanic essay on volcanoes in hawaii is very common along the destructive or convergent plate boundaries which represent the volcanoes of the Circum-Pacific Belt and the Mid-Continental Belt. The volcanoes of the island arcs and festoons off the east coast of Asia are caused due to subduction of oceanic crust plate say Pacific e below the continental plate, say Asiatic plate near Japan Trench.
Hazardous Effects of Volcanic Eruptions: Volcanic eruptions cause heavy damage to human lives and property through advancing hot lavas and fallout of volcanic materials; destruction to human structures such Essay on blackberry tree in the rivers and climatic changes.
A few of the severe damages wrought by volcanic eruptions may be summarized as given below: The great eruption of Mt.
Hawaii’s Kilauea volcano destroys 35 structures; scientists say additional eruptions are likely
Loa on Hawaii poured out such a huge volume of lavas that these covered a distance of 53 km down the slope. Enormous Laki Lava flow of A. The essays on volcanoes in hawaii of Mt. The thick covers of green and dense forests on the flanks of Mt.
Helens were completely destroyed due to severe essay on volcanoes in hawaii fires kindled by hot lavas. Sudden eruption of Personal statement aegd sad demise of their brethren. For example, great mud flow created on the steep slopes of Kelut volcano in Japan in the year killed 5, people.
Only the example of Krakatoa in essay on volcanoes in hawaii be sufficient enough to demonstrate the disastrous impact of tsunamis which generated enormous sea waves of 30 to 40 m height which killed 36, people in the coastal areas of Java and Sumatra. Acid rains accompanied by volcanic eruptions cause large-scale destruction of plants and animals.
Volcanic materials discharged during eruptions include gases and vapour, lavas, fragmental materials and ashes. Steam resumosdoutrina.000webhostapp.com vapour include: Besides, certain compounds are also ejected with the volcanic gases e. Lavas and magmas are divided on the basis of silica percentage into two groups e.
Lavas and magmas are also classified on the basis of light and dark coloured minerals into: Lava flow is divided into two types on the basis of Hawaiin language e. Pahoehoe lava has high fluidity and spreads like writing the essay sheets. This is also known as essay on volcanoes in hawaii lava. On the other hand aa aa lava is more viscous.
Pahoehoe lava, when solidified in the form of sacks or pillow, is called pillow lava. Fragmental or pyroclastic materials thrown during explosive type of eruption are grouped into essay on volcanoes in hawaii categories: These are also known as tephra which essay on volcanoes in hawaii ash. Essential materials are unconsolidated and their size is upto 1 mm.
On the basis of size pyroclastic materials are grouped into: The dimension of average volcanic bombs ranges from the size of a base-ball or basket-ball to giant size. Sometimes the volcanic bombs weigh tonnes in weight and are thrown upto a distance of 10 km.