a volcano is a landform created by magma from the earth

8/11/2019 A Volcano is a Landform Created by Magma From the Earth

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A volcano is a landform created by magma from the earth'sinterior which penetrates through weaknesses in the Earths surface.Most volcanoes are formed at plate boundaries.A volcano is a mountain that opens downward to a reservoir of molten rockbelow the surface of the earth. Unlike most mountains, which are pushed up

from below, volcanoes are vents through which molten rock escapes to theearths surface. When pressure from gases within the molten rock becomestoo great, an eruption occurs. Eruptions can be quiet or explosive. There maybe lava flows, flattened landscapes, poisonous gases, and flying rock and ashthat can sometimes travel hundreds of miles downwind.

Magma contains a mixture of silicates and dissolved gases.As magma rises closer to the Earths surface the pressuredecreases and the dissolved gases come out of solution to form

bubbles. As the bubbles expand the magma is pushed into thevolcanic vent until it breaks through weaknesses in the Earth'scrust. The explosive potential of the volcano is dependant on theeffervescence of the gases and the viscosity of the magma. Highgas effervescence and low viscosity cause the most explosiveeruptions.

As previously mentioned volcanoes occur at weaknesses inthe Earths surface, these are in one of three tectonic settings:subduction volcanoes, rift volcanoes and hot spot volcanoes.

Subduction volcanoes occur where one tectonic plate is thrust andconsumed by another. This type is the most explosive andcomprises approximately 80% of the worlds active volcanoes. Riftvolcanoes occur where tectonic plates diverge, often on the oceanfloor. These are generally less explosive. Hot spot volcanoes occurin the middle of plate boundaries where magma exits fromweaknesses in the earth's surface. The Hawaiian Islands are anexample of hot spot volcanoes. The most active area of volcanicactivity occurs along the pacific plate boundary which is oftenreferred to as the 'Pacific ring of fire'.

There are about 500 active volcanoes thoughout the world.In an average year approximately 50 of these erupt. Volcanichazards create fewer disasters and deaths compared withearthquakes and severe storms. Many of the deaths associatedwith volcanoes are indirect hazards such as famine due to cropdamage or from secondary hazards such as lahars. Volcanoes arecomposite hazards. There are both primary and secondaryhazards which can be caused by volcanic eruptions. The primaryhazards include pyroclastic flows, air-fall tephra, lava flows andvolcanic gases. The secondary hazards include ground

deformation, lahars (mudflows), landslides and possibly tsunamisin ocean floor volcanic eruptions.


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A volcano is a mountain that opens downward to a reservoir of molten rockbelow the surface of the earth. Unlike most mountains, which are pushed upfrom below, volcanoes are vents through which molten rock escapes to theearths surface. When pressure from gases within the molten rock becomestoo great, an eruption occurs. Eruptions can be quiet or explosive. There may

be lava flows, flattened landscapes, poisonous gases, and flying rock and ashthat can sometimes travel hundreds of miles downwind.

Because of their intense heat, lava flows are great fire hazards. Lava flowsdestroy everything in their path, but most move slowly enough that people canmove out of the way.

Fresh volcanic ash, made of pulverized rock, can be abrasive, acidic, gritty,gassy and odorous. While not immediately dangerous to most adults, theacidic gas and ash can cause lung damage to small infants, to older adults

and to those suffering from severe respiratory illnesses. Volcanic ash also candamage machinery, including engines and electrical equipment. Ashaccumulations mixed with water become heavy and can collapse roofs.Volcanic ash can affect people hundreds of miles away from the cone of avolcano.


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An earthquake is what happens when two blocks of the earth suddenlyslip past one another. The surface where they slip is called the fault orfault plane. The location below the earths surface where theearthquake starts is called the hypocenter, and the location directlyabove it on the surface of the earth is called the epicenter.

Sometimes an earthquake has foreshocks. These are smallerearthquakes that happen in the same place as the larger earthquakethat follows. Scientists cant tell that an earthquake is a foreshock untilthe larger earthquake happens. The largest, main earthquake is calledthe mainshock. Mainshocks always have aftershocks that follow. Theseare smaller earthquakes that occur afterwards in the same place as themainshock. Depending on the size of the mainshock, aftershocks cancontinue for weeks, months, and even years after the mainshock!

What causes earthquakes and where do they

happen?

The earth has four major layers: the inner core, outer core, mantle andcrust. (figure 2) The crust and the top of the mantle make up a thin skin

on the surface of our planet. But this skin is not all in one pieceit ismade up of many pieces like a puzzle covering the surface of the earth.


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(figure 3) Not only that, but these puzzle pieces keep slowly movingaround, sliding past one another and bumping into each other. We callthese puzzle pieces tectonic plates, and the edges of the plates arecalled the plate boundaries. The plate boundaries are made up of manyfaults, and most of the earthquakes around the world occur on thesefaults. Since the edges of the plates are rough, they get stuck while therest of the plate keeps moving. Finally, when the plate has moved farenough, the edges unstick on one of the faults and there is anearthquake.

Why does the earth shake when there is anearthquake?

While the edges of faults are stuck together, and the rest of the block ismoving, the energy that would normally cause the blocks to slide pastone another is being stored up. When the force of the moving blocksfinally overcomes the friction of the jagged edges of the fault and itunsticks, all that stored up energy is released. The energy radiatesoutward from the fault in all directions in the form of seismic waves likeripples on a pond. The seismic waves shake the earth as they move

through it, and when the waves reach the earths surface, they shakethe ground and anything on it, like our houses and us! (see P&S Waveinset)

How are earthquakes recorded?


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Earthquakes are recorded by instruments called seismographs. Therecording they make is called a seismogram. (figure 4) Theseismograph has a base that sets firmly in the ground, and a heavyweight that hangs free. When an earthquake causes the ground toshake, the base of the seismograph shakes too, but the hanging weightdoes not. Instead the spring or string that it is hanging from absorbs allthe movement. The difference in position between the shaking part ofthe seismograph and the motionless part is what is recorded.

a volcano is a landform created by magma from the earth

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